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pulse may pass through the arterioles and reach the capillaries when the arterioles are dilated or when the capillaries are only filled at each systole, as may be seen in the See also:

PINK

pink of the See also:

NAIL (O. Eng. naegal, cf. Dutch, Ger., Swed. nagel; the word is also related to Lat. unguis, Gr. ovu, Sans. nakhas)

nail when the See also:

ARM (a common Teutonic word; the Indo-European root is ar, to join or fit; cf. the Lat. armus, shoulder, and the plural word arma, weapons, Gr. apphs, joint, and the reduplicated apapilKSV, to join)

arm is held above the See also:

head, and in cases of aortic regurgitation. A venous pulse may be recorded in the jugular vein; it exhibits oscillations synchronous with auricular and ventricular systole, and affords us important See also:

INFORMATION (from Lat. informare, to give shape or form to, to represent, describe)

information in certain cases of See also:

heart disease. The normal See also:

AVERAGE

average pulse See also:

RATE

rate is 72 per See also:

minute, in woman about 80; but individual See also:

variations from 40–100 have been observed consistent with See also:

HEALTH

health.

In the newborn the pulse beats on the average 130–140 times a minute; in a one-See also:

YEAR

year-old See also:

child 120–130; three years too; ten years 90; fifteen years 70-95. Active See also:

MUSCULAR

muscular exercise may increase the pulse rate to 130. See also:

NERVOUS

Nervous excitement, extreme debility and rise of See also:

BODY

body temperature also increase it markedly. The pulse is more frequent when one stands than when one sits, or lies down, and this is especially so in states of debility. The taking of See also:

food, especially hot food, increases it. By placing tambours on, say, the See also:

CAROTID

carotid and radial See also:

ARTERIES (Gr. ap-rnpia, probably from a"spew, to raise, but popularly connected by the ancients with ai7P, air)

arteries and recording the two pulses synchronously, it has been found that the pulse occurs later, the further the seat of observation is from the heart. The velocity with which the pulse wave travels down the arteries has been determined thus. It is about 7–8 metres per second. The wave length of the pulse is obtained by multiplying the duration of the inflow of blood into the aorta by the velocity of the pulse wave. It is about 3 metres. As the return of venous blood and pulmonary circulation is favoured during See also:

INSPIRATION (Lat. inspirare, breathe upon or into)

inspiration so that the output of the See also:

LEFT

left ventricle during the first See also:

PART

part of inspiration is lessened and subsequently increased, From See also:

Young and See also:

Robinson, See also:

Cunningham's See also:

TEXT (Lat. textum, woven fabric, from texere, to weave)

Text-See also:

BOOK

Book of See also:

Anatomy. From Young and Robinson, Cunningham's Text-Book of Anatomy.

the sphygmograph reveals See also:

RESPIRATORY

respiratory oscillations; the whole See also:

LINE

line of the tracing falls during the first part of inspiration and rises subsequently. The circulation in the capillaries may be studied by placing under the See also:

MICROSCOPE (Gr. µucp6s, small, asenreiv, to %view)

microscope a transparent membrane such as the See also:

WEB (a word common to Teutonic languages, cf. Du. webbe, Dan. vaev, Ger. Gewebe, all from the Teutonic wabh—to weave)

web of the The See also:

FROG

frog's See also:

FOOT

foot, tail of See also:

TADPOLE

tadpole, wing of See also:

bat, &c. By a See also:

SPECIAL

special capillary See also:

ILLUMINATION

illumination one may see the See also:

SHADOW (0. Eng. Schadewe, sceadu; a form of " shade "; connected with Gr. 6-Ore's, darkness)

shadow of the blood See also:

cor- cacula- puscles moving through the retinal vessels of one's own See also:

eye, See also:

don. and even calculate the velocity of flow. The See also:

DIAMETER (from the Cr. &a, through, µErpov, measure)

diameter of the smaller capillaries is such as to permit the passage of the red blood corpuscles in single See also:

FILE

file only; their length is about nth of an See also:

INCH (O. Eng. ynce from Lat. uncia, a twelfthpart; cf. " ounce," and see As)

inch. The endothelial cells confine the blood from See also:

DIRECT

direct contact with the See also:

TISSUE (Fr. tissu, tissue, participle of tisser, Lat. texere, to weave)

tissue See also:

LYMPH

lymph and so prevent its coagulation, but allow and regulate the See also:

EXCHANGE

exchange of material between the blood and lymph. This exchange is regulated by the vital activity of the cells, and does not follow such See also:

LAWS

laws as pertain to filtration and See also:

DIFFUSION (from the Lat. diffundere; dis-, asunder, and fundere, to pour out)

diffusion through dead membranes. There is See also:

EVIDENCE (Lat. evidentia, evideri, to appear clearly)

evidence to show that the cells of the hepatic capillaries are capable of protoplasmic See also:

MOVEMENT

movement and of See also:

PHAGOCYTOSIS (Gr. 0ayeiv, to eat, devour, and KtTOS, cell)

phagocytosis. The pressure in the capillaries stands in closer relationship to that in the See also:

VEINS

veins than to that in the arteries; for example, a rise of pressure in the venae cavae, other things remaining the same, raises the pressure in the hepatic capillaries to a like amount, while a rise of pressure in the aorta does not, for most of the arterial pressure is spent in overcoming the peripheral resistance. The filling of the capillaries in the skin varies greatly with temperature, posture, &c. When the See also:

hand is See also:

COLD (in O. Eng. cald and ceald, a word coming ultimately from a root cognate with the Lat. gelu, gelidus, and common in the Teutonic languages, which usually have two distinct forms for the substantive and the adjective, cf. Ger. Kolte, kalt, Dutch koude

cold the arterioles are so constricted that blood only passes through the wider and more direct capillaries. As the skin becomes warm it flushes, the arterioles dilating and all the capillary networks becoming filled with blood. Muscular movements See also:

EXPRESS (through the French from the past participle of the Lat. exprimere, to press out, by transference used of representing objects in painting or sculpture, or of thoughts, &c. in words)

express the blood out of the capillaries, as may be seen by the blanching of the skin which occurs on clenching the hand.

Raising the hand blanches, and lowering it congests the capillaries. The pressure and velocity in the capillaries thus constantly vary, owing to alterations in hydrostatic pressure, the pressure of the body against See also:

EXTERNAL

external See also:

OBJECTS

objects, the contraction of the muscles, and the contraction of the arterioles. It is not possible therefore to set any definite figure to the capillary pressure or velocity. In the frog's web, with the foot confined and at See also:

REST (O. Eng. rest, reste, bed, cognate with other Teutonic forms, e.g. Ger. Rast, Riiste, rest, and probably Gothic Rasta, league, i.e. resting or stopping place)

rest, the velocity is about t mm. per second. We continually make slight movements to counteract the hydrostatic effect and prevent the congestion of blood in the capillaries of See also:

LOWER

lower parts of the body. It is this tendency to congestion which makes it so difficult to stand absolutely See also:

motion-less for any length of See also:

time. The red corpuscles, being the heavier, occupy the See also:

AXIS (Lat. for " axle ")

axis, and the See also:

white corpuscles the peripheral layer of the capillary stream. If an irritant is placed on the membrane it will be observed that the capillaries become wider and crowded with corpuscles, the flow slackening and finally becoming arrested owing to the passing out of the plasma through the damaged capillary See also:

wall. The white corpuscles creep out between the endothelial cells into the tissues. Such are the first phenomena of inflammation. After obstruction of an artery See also:

COLLATERAL (from Med. Lat. collateralis,—cum, with, and latus, lateris, side,—side by side, hence parallel or additional)

collateral pathways are in most parts rapidly formed, for the anastomatic capillaries, stimulated by the increased blood flow, develop into arterioles and arteries. Numerous anastomoses exist between the veins, so that if the flow of blood be obstructed in one direction it readily finds a passage The flow in another.

Muscular movement, alterations of posture and la the respiratory movements particularly forward the venous veins. circulation. The See also:

BARBER (from Lat. barba, beard)

barber's See also:

pole of the barber surgeon was grasped to increase the flow in the old blood-letting days. The valves in the veins allow the blood to be forced only towards the heart. The pressure in the veins varies according to the hydrostatic pressure of the blood See also:

COLUMN (Lat. columna)

column above the point of measurement. In the See also:

HORIZONTAL

horizontal position, when this See also:

FACTOR (from Lat. facere, to make or do)

factor is almost eliminated, the pressure in the large veins is about equal to 5–Jo mm. of See also:

mercury, and even may become negative on taking a deep inspiration. There thus arises the danger of See also:

air being sucked into a wounded jugular vein. If air does thus gain entry it may fatally obstruct the circulation. The venous circulation is impeded by (i) a lessening of heart See also:

POWER [WILLIAM GRATTAN] TYRONE (1797-1841)

power, (2) valvular defects, such as incompetence or narrowing of the orifice which they guard, (3) obstruction to the filling of the heart, as in cases of pericardial effusion, (4) obstruction of the pulmonary circulation as in coughing, by pleuritic effusion, &c. The results of venous congestion are a less efficient arterial circulation, a dusky See also:

APPEARANCE (from Lat. apparere, to appear)

appearance of the skin, a fall of cutaneous temperature, and an effusion of fluid into the tissue spaces producing oedema and See also:

DROPSY (contracted from the old word hydropisy, derived from the Gr. 154w¢; i Swp, water, and appearance)

dropsy. This last effect is not due to increased capillary pressure producing increased transudation as has been supposed, for no such increase in venous and capillary pressure persists under the conditions. It is due to the altered See also:

NUTRITION

nutrition of the capillary endothelium and the tissues, which results front the deficient circulation. If for any See also:

REASON (Lat. ratio, through French raison)

reason the left ventricle fail to maintain its full systolic output, it ceases to receive the full auricular input, and in consequence the pulmonary vessels congest.

This tells back on the right heart, and the right ventricle is unable to empty itself into the congested pulmonary vessels, and this in its turn leads to venous congestion. The final result of any obstruction thus is a pooling of the blood in the venous cistern. Dyspnoea results from cardiac insufficiency. It is excited by the increased venosity of the blood acting on the respiratory centre. Both excess of See also:

CARBON (symbol C, atomic weight 12)

carbon dioxide and deficiency of See also:

OXYGEN (symbol 0, atomic weight 16)

oxygen excite this centre. The increased respiratory movements aid the circulation. The venous See also:

side of the vascular See also:

SYSTEM

system, owing to the See also:

GREAT

great See also:

SIZE

size of the veins, has a large potential capacity, while many of the capillaries in each See also:

ORGAN

organ are empty and collapsed, except at those periods of vaso-See also:

DILATATION (from Lat. dis-, distributive, and lotus, wide)

dilatation and hyperaemia which accompany extreme activity of See also:

FUNCTION

function. The vascular system cannot be regarded as a closed system, for the blood-plasma, ,whenever the capillary pressure is increased, transudes through the capillary wall into the tissue-spaces and enters the lymphatics. Thus, if fluid be transfused into the circulatory system, it not only collects in the capacious reservoirs of the veins and capillaries—especially in the lungs, See also:

LIVER (O. Eng. lifer; cf. cognate forms, Dutch lever, Ger. Leber, Swed. lefver, &c.; the O. H. Ger. forms are libara, lipora, &c.; the Teut. word has been connected with Gr. i'prap and Lat. jecur)

liver and abdominal organs–but leaks into the tissue-spaces. Hence the pressure in the vascular system cannot be raised above the normal for any length of time by the injection of even enormous quantities of fluid. The lymphatics of tissue-spaces must be regarded as part of the vascular system. There is a See also:

CONSTANT, BENJAMIN (1845-1902)

constant give and take between the blood-plasma and the tissue lymph.

If the fluid part of the blood be increased, then the capillary transudation becomes greater, and the excess of fluid is excreted from the kidneys and glands of the alimentary See also:

canal. If the fluid part of the blood diminish, then fluid passes from the tissue-spaces into the yaemor- blood, and the sensation of thirst arises, and more drink is rh~e and taken. The circulation may be greatly aided by the trans-. See also:

FUSION

fusion of See also:

salt See also:

SOLUTION (from Lat. solvere, to loosen, dissolve)

solution (0.8 %) or blood after severe hemor- See also:

SION [Ger. Sitten]

sion. rhage, or in states of surgical See also:

SHOCK, or COLLAPSE

shock. Only the blood of See also:

man must be used. The direct giving of blood by connecting the radial artery of a relation to the median vein of a patient has been used as a means of effecting restoration. Blood may be withdrawn from the system slowly to the extent of 4 %, rapidly to the extent of 2 % of the bodyweight, without lowering the arterial pressure, owing to the compensatory contraction of the arterioles and the rapid absorption of fluid from the tissues into the blood. The withdrawal of the tissue-lymph excites extreme thirst and the great need for See also:

WATER

water which occurs after severe hemorrhage. About 75 % by See also:

WEIGHT

weight of the tissues, excluding See also:

FAT (O.E. fdett; the word is common to Teutonic languages, cf. Dutch vet, Ger. Fett, &c., and may be ultimately related to Greek Irian, and =apos, and Sanskrit pivan)

fat and See also:

bone, consists of water. The quantity of blood in the body is about Q~th of the body weight. That of tissue-lymph is unknown, but it must be considerable, probably greater than that of the blood; The lymphatics drain off the excess of fluid which transudes from the capillaries, and finally return it to the vascular system. The interchange between tissue, blood and lymph depehds on the forces of the living cells, which are as yet far from See also:

COMPLETE

complete elucidation.

We may define the velocity of the blood at any point in a See also:

VESSEL (O. Fr. vaissel, from a rare Lat. vascellum, dim. of vas, vase, urn)

vessel as the length of the column of blood flowing by that point in' second. In the See also:

case of a See also:

TUBE (Lat. tuba)

tube, supplied by a constant head of pressure, we can See also:

DIVIDE

divide the tube and measure velocity the outflow per second; knowing the See also:

VOLUME

volume of this, oTf blood and the See also:

CROSS

cross See also:

AREA

area of the artery, we can determine the length of the column. This See also:

KIND (O. E. ge-cynde, from the same root as is seen in " kin," supra)

kind of experiment flow. cannot be done on the living See also:

animal, because the opening of the vessel alters the resistance to flow, and the loss of blood also changes the physiological conditions. To determine the velocity other means must be devised. See also:

Ludwig invented an instrument called the stromuhr, consisting of two bulbs mounted on a rotating See also:

PLATFORM (Fr. plateforme, i.e. ground plan)

platform pierced with two holes. One bulb is filled with oil—the other with blood. The bulbs are connected together by a tube at their upper end, and the lower end of the one full of oil is brought over the hole in the platform. The central end of the artery is connected to the same hole and the peripheral end to the other, over which stands the bulb full of blood. The blood being allowed to flow displaces the oil out of the one bulb into the other; directly this happens, the bulbs are rotated and the one full of oil is again brought over the central end of the artery. The number of rotations per minute is counted, and the volume of the bulb being known we obtain the volume of blood that passes through the instrument per a - minute. In another instrument, the haemo- c dromograph of Chauveau, there is inserted FIG. 25.-Ludwig', into the artery al tube in which hangs a small Stromuhr. pendulum; the See also:

STEM (O. Eng. staefn, stemn, cf. Du. stain, Ger. Stamm, &c., probably related to " staff ")

stem of the pendulum passing through a See also:

RUBBER, INDIARUBBER

rubber See also:

dam which closes the See also:

VERTICAL (from Lat. vertex, highest point)

vertical See also:

LIMB

limb of the tube.

The pendulum is deflected by the flow, and the greater the velocity the greater the deflection. The deflection can be recorded by connecting the See also:

FREE

free end of the pendulum to a See also:

TAMBOUR (Fr. for " drum " )

tambour arrangement. This instrument allows us to See also:

RECORD (Lat. recordari, to recall to mind, from cor, heart or mind)

record and measure the variations of velocity during systole and diastole of the heart, but it can only be used in the vessels of large animals. Still other methods have been employed by Cybuleki and See also:

Stewart. The See also:

general relations of the velocity of the blood in the arteries, capillaries and veins is expressed by the See also:

CURVE (Lat. curvus, bent)

curve shown in fig. 26. The velocity in the large arteries may reach 50o mm. per second in systole and fall to 15o mm. in diastole. The smaller the artery I The introduction of rubber tubing for the connexions made the the less is this difference and the more See also:

UNIFORM

uniform the rate of flow, method. of inquiry comparatively See also:

SIMPLE

simple. The tubing connecting the arterial cannula and the See also:

MANOMETER (Gr. µavos, thin or loose; µerpov, a measure)

manometer was filled with a suitable fluid to prevent coagulation of the blood; also to prevent more than a trace of blood entering the connexions. A saturated solution of See also:

SODIUM [symbol Na, from Lat. natrium; atomic weight 23.00 (0=16)]

sodium sulphate, or a i % solution of sodium citrate, may be employed for this purpose. Ludwig (1847) added a See also:

FLOAT (in O. Eng. floc and flota, in the verbal form f eotan; the Teutonic root is flut-, another form of flu-, seen in " flow," cf. " fleet "; the root is seen in Gr. a-M e, to sail, Lat. pluere, to rain; the Lat, fluere and fluctus, wave, is not connect

float provided 1; ; 1 with a See also:

writing See also:

style to the See also:

MERCURIAL

mercurial manometer, and brought the style to write on a See also:

DRUM (early forms drome or dromme, a word common to many Teut. languages, cf. Dan. tromme, Ger. Trommel: the word is ultimately the same as " trumpet," and is probably onomatopoeic in origin; it appears late in Eng. about the middle of the 16th century)

drum covered with smoked See also:

paper and driven slowly See also:

ROUND (O. Fr. rond, Lat. rotundus, the Fr. is the source also of Du. rond; Ger., Swed., Dan. and Nor. rond)

round by clockwork—a kymograph By this means tracings of the arterial blood pressure are obtained, and the See also:

INFLUENCE (Late Lat. influentia, from influere, to flow in)

influence upon the blood pressure of various agents recorded and studied. For the veins a manometer filled with salt solution is used, as mercury is too heavy a fluid to record the far slighter changes of venous pressure.

The manometer may be connected with a recording n Je`~> tambour. The arterial blood-pressure record obtained with the mercurial manometer exhibits cardiac and respiratory oscillations as shown ' lreiha in fig. 18. The method gives us a fairly accu- • rate record of the mean pressure, but the See also:

mass of the mercury causes such inertia that the instrument is quite unable to faithfully record the systolic and diastolic variations of pressure. To effect this record, delicate See also:

SPRING (from " to spring," " to leap or jump up," " burst out," O. Eng., springau, a common Teut. word, cf. Ger. springer, possibly allied to Gr. QnrFpxecOac, to move rapidly)

spring manometers of rapid See also:

ACTION

action and small inertia have been in-vented. A mercury manometer provided with maximum and minimum valves has also been employed to indicate the maximal systolic and minimal diastolic pressure. To determine the blood pressure in man, an instrument called the sphygmometer is used. The writer's sphygmometer consists of a rubber bag covered with d See also:

SILK

silk which is filled with air, and See also:

con- nected by a See also:

SHORT, FRANCIS JOB (1857– )

short length of tube to a manometer. This manometer con- sists of a graduated See also:

glass tube, open at one end. A small hole is in the side of the tube near this end. A r,.r may meniscus of water is introduced up to the side hole—the zero See also:

mark on the scale—by placing the open end of the i tube in water. The bag is now con- nected 1 to the See also:

GAUGE, or GAGE (Med. Lat. gauja, jaugia, Fr. jauge, perhaps connected with Fr. jale, a bowl, galon, gallon)

gauge so that the side hole is closed by the rubber tube.

Covering the rubber bag with the hand and pressing it on the radial artery until the pulse (See also:

FELT (cognate with Ger. Filz, Du. vilt, Swed. and Dan. fill; the root is unknown; the word has given Med. Lat. filtrum, " filter ")

felt beyond) is obliter- ated, one reads the height to which i the meniscus rises in the manometer, and this gives us the systolic pressure in the artery. The air above the meniscus acts as a spring, converting the instrument into a spring manometer. It is empirically graduated in mm. Hg. r It is very necessary to remember that the blood pressures, taken in different vessels and postures, vary with the hydrostatic pressure of the column of blood above the point of measure- ment. (t, Thus in the See also:

STANDING

standing posture the arterial pressure in the arteries of the See also:

leg is higher than in the arm by the height of the column of blood that separates the two points of measure- ment. In the horizontal posture the pressure is practically the same in all the big arteries. The pressure in the ascending aorta is kept about the same in all postures, while that of the leg arteries varies widely. The effect of gravity is compensated there by active changes in heart force, splanchnic dilatation, &c. (L. See also:

Hill). The systolic pressure of young men, taken in the radial artery with the arm at the same level as the heart, may be taken to be about See also:

ITO, HIROBUMI, PRINCE (1841-1909)

Ito mm. of Hg. In men of 4o-6o years the systolic pressure is often about 140 mm., but in some robust men it is no higher than in youth.

The venous pressure in man may be measured by finding the pressure just required to prevent a cutaneous vein refilling after it has been emptied beyond a See also:

VALVE (Lat. valva, a leaf of a double or folding door, allied to volvere, to roll, as of a door on its hinges)

valve. There is no accurate method The time necessary for a See also:

section of the system. Thus the greatest velocity is where the See also:

TOTAL

total See also:

bed is narrowest, and slowest where the bed widens to the dimensions of a See also:

lake. The blood in leaving the heart may take a short See also:

CIRCUIT (Lat. circuitus, from circum, round, and ire, to go)

circuit through the coronary system of the heart and so back to the right heart, or it may take a See also:

long an devious course tothe toes and back, or through the intestinal capillaries, portal system and hepatic capillaries. It is obvious, then, that the time any two particles of blood take to complete the circuit may be widely different. Experiments have been made to determine how rapidly any substance, like a See also:

POISON

poison, which enters the blood ma be distributed over the body. A salt such as See also:

POTASSIUM [symbol K (from kalium), atomic weight 39.114 0=16)]

potassium ferrocyanide is injected into the jugular vein, and the blood collected• in successive samples at seconds of time from the opposite jugular vein. These samples are tested for the presence of the salt, or a strong solution of methylene See also:

BLUE (common in different forms to most European languages)

blue is injected into the jugular vein, and the moment determined with a stop-See also:

WATCH (in O. Eng. wcecce, a keeping guard or watching, from wacian, to guard, watch, wacan, to wake)

watch when the blue See also:

COLOUR (Lat. color, connected with celare, to hide, the root meaning, therefore, being that of a covering)

colour appears in the carotid artery. The velocity of flow also can be determined in any organ by injecting salt solution into an artery, and observing, with the aid of a See also:

WHEATSTONE, SIR CHARLES (1802–1875)

Wheatstone's See also:

BRIDGE

bridge arrangement, the galvanometric See also:

CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

change in See also:

electrical resistance which occurs in the corresponding vein when the salt solution reaches it. The moment of injection and that of the alteration in resistance are observed with a stop-watch (Stewart). It has been determined that the blood travelling fastest can complete the circuit in about the time occupied by 25 to 30 heart-beats, say in 20 to 30 seconds; a result which shows how rapidly methods must be taken to prevent the absorption of poisons—for example, snake-poison. The blood travelling fastest in the pulmonary circuit occupies only about one-fifth of the time spent by that in the systemic circuit.

That some of the blood takes a very long time to return to the heart is shown by the long time it takes to See also:

WASH, THE

wash the vascular system free of blood by the injection of salt solution. That the blood is under different pressure in the various parts of the The system has long been known. From a divided artery the pressure blood flows out in forcible spurts, while from a vein it relation flows out continuously and with little force. It takes in the very little pressure of the fingers to blanch the capillaries vascular of the skin, but an appreciable amount to obliterate the system. radial artery. Flo. 28.—Hill's Sphyg- Capillaries .. From Allchin's Manual of Medicine, by permission of Macmillan & Co. Ltd. , complete circula- tion. Arteries the Blood in the Arteries, Capillaries and Veins. The flow in the large veins is approximately equal to that in the large arteries. In the jugular vein of a See also:

dog the mean velocity was found to be 225 mm. and in the carotid 260 mm. per second.

The velocity in the capillaries has been measured by direct observation with the microscope. It is very small, e.g. o .5-I mm. per second. The variation of velocity in different parts of the vascular system is explained by the difference in width of bed through which the stream flows. The vascular system may be compared to a stream which on entering a See also:

field is led into a multitude of See also:

IRRIGATION (Lat. in, and rigare, to water or wet)

irrigation channels, the sum of the cross sections of all the channels being far greater than that of the stream. The channels unite together again and leave the field as one stream. If the flow proceeds uniformly for any given unit of time, the same volume must flow through any cross See also:

Stephen See also:

Hales (1733) was the first to measure the blood pressure. He inserted a See also:

brass tube into the femoral vein of a See also:

HORSE (a word common to Teutonic languages in such forms as hors, hros, ros; cf. the Ger. ross)

horse and connected it to a long glass tube held vertically, using the trachea of a See also:

goose as a flexible tube, and found the blood See also:

rose to the height of 8 ft., oscillated there with each heart-See also:

BEAT (a word common in various forms to the Teutonic languages; it is connected with the similar Romanic words derived from the Late Lat. battere)

beat, and rose and See also:

fell some-what with inspiration and expiration. In the vein he found the pressure to be only about 12 in. Poiseuille (1828) adapted to the same purpose the mercurial manometer, a U-shaped tube containing mercury, which, being 13.5 times heavier than blood, allowed the manometer to be brought to a convenient height. mometer. From See also:

HOWELL, JAMES (c. 1594-1666)

Howell's Text-Book of See also:

PHYSIOLOGY (from Gr. 4 i s, nature, and koyos, discourse)

Physiology, by permission of W . B.

Saunders Co. and Diastolic Pressure. Systolic or nl xtmuof ro i mm zoo mm Mean `WA~. _- WAIL Diastolic or minimum 8omm See also:

BASE

Base line -6o mm -4o mm -somm it is difficult to determine whether a rise of pressure in the pulmonary artery is induced really by constriction of the pulmonary system, or by changes in the output of the heart; hence different observers have reached conflicting conclusions. In the case of lungs which have been supplied with an artificial circulation and a constant head of pressure to eliminate the action of the heart, no diminution in outflow has been observed in exciting the branches of the vagus or sympathetic nerves which See also:

SUPPLY (through Fr. from Lat. supplere, to fill up)

supply the lungs, or by the injection of adrenalin (See also:

Sir See also:

Benjamin C. See also:

Brodie (1783–1862), and See also:

Dixon, See also:

Burton-Spitz). The portal circulation is See also:

PECULIAR

peculiar in that the blood passes through two sets of capillaries. Arterial blood is conveyed to the capillary networks of the See also:

STOMACH (Gr. vrbsaxos from arbga, a mouth)

stomach, See also:

SPLEEN (Gr. o-1rXilv)

spleen, See also:

PANCREAS (Gr. rag, all; 1cpks, flesh)

pancreas and intestines The by branches of the abdominal aorta The portal vein is of measuring the capillary pressure. It and the venous pressure constantly vary from nothing to a See also:

POSITIVE (or PORTABLE) ORGAN

positive amount with rest or movement of muscles, change of posture, &c. The arterial pressure is raised during exertion by the more forcible beat of the heart—e.g. pressures of 140–190 mm. Hg have been observed immediately after a 3-mile See also:

RACE

race. It rapidly sinks to a lower level than usual after the exertion is over, e.g.

90 mm. Hg, owing to the quieter action of the heart and the persistence of the cutaneous dilatation of the blood vessels which is evoked by the rise of body temperature. The writer has observed in athletes rectal temperatures of 102–105° F. after long races. After meals there is an increase in cardiac force to maintain the flow through the dilated splanchnic vessels. See also:

MENTAL

Mental excitement raises the pressure—e.g. the writer's pressure may be to mm. before and 125 mm. Hg after giving a lecture. The origin of the blood pressure in the arteries is the See also:

ENERGY (from the Gr. ivipyela; iv, in, ipyov, work)

energy of the heart. The pressure gradient depends on the peripheral resistance. In the arterials the pressure is spent, and little of it reaches the capillaries. The return of the capillary blood to the veins and the pressure in the veins is due partly to the See also:

REMAINDER, REVERSION

remainder of the cardiac force, but more largely to the contraction of the skeletal muscles and the viscera, to the action of gravity in changes of posture and to the respiratory See also:

PUMP

pump. The pulmonary artery, carrying venous blood, divides and sub- divides, and the smallest branches end in a plexus of capillaries The pul- on the walls of the air-cells of the See also:

LUNG

lung. From this plexus the blood is drained by the radicles of the four pulmonary monary veins which open into the left See also:

AURICLE (from Lat. diminutive of auris, ear)

auricle.

The pressure in c/rcu/a- the pulmonary artery is less than one-third the aortic uO°' pressure, and the blood takes only one-third of the time to complete the pulmonary circuit that it takes to make the systemic. The four See also:

CHIEF (from Fr. chef, head, Lat. caput)

chief factors which influence the pulmonary circulation are: (1) the force and output of the right ventricle; (2) the diastolic filling action of the left auricle and ventricle; (3) the diameter of the pulmonary capillaries, which varies with the respiratory expansion of the lungs; (4) the intrathoracic pressure. In inspiration the lungs are distended in consequence of the greater positive pressure on the inner surfaces being greater than the negative pressure on their See also:

OUTER

outer pleural surfaces. The negative pressure in the intrathoracic cavity results from the enlargement of the See also:

THORAX (Gr. BWpaE, breastplate, also the part of the body covered by it)

thorax by the inspiratory muscles. When the elastic lungs are distended by a full inspiration they exert an elastic See also:

TRACTION (Lat. trahere, to draw)

traction amounting to about 15 mm. Hg. The heart and vessels within the thorax are submitted to this traction—that is, to the pressure of the See also:

ATMOSPHERE (Gr. fir µ6r, vapour; orkaipa, a sphere)

atmosphere minus 15 mm. Hg—while the vascular system of the rest of the body bears the full atmospheric pressure. The thin-walled auricles and veins yield more to this elastic traction than the thick-walled ventricles and arteries. Thus inspiration exerts a suction action, which furthers the filling of the veins and auricles. This action is assisted by the positive pressure exerted by the descending See also:

DIAPHRAGM (Gr. Scat/pay,aa, a partition)

diaphragm on the contents of the See also:

ABDOMEN (a Latin word, either from abdere, to hide, or from a form adipomen, from adeps, fat)

abdomen. Blood is thus both pushed and sucked into the heart in increased amount during inspiration.

Experiment has shown that the blood vessels of the lungs when distended are wider than those of collapsed lungs. Suppose an elastic bag having minute tubes in its walls be dilated by blowing into it, the lumina of the tubes will be lessened, and the same occurs in the lungs if they are artificially inflated with air; but if the bag be placed In a glass See also:

BOTTLE (Fr. bouteille, from a diminutive of the Lat. butta, a flask; cf. Eng. " butt ")

bottle, and the pressure on its outer See also:

SURFACE

surface be diminished by removing air from the space between the bag and the side of the bottle, the bag will distend and the lumina of the tubes be increased. Thus it is evident that inspiration, by increasing the calibre of the pulmonary vessels, draws blood into the lungs, and the movements of the lungs become an effective force in carrying on the pulmonary circulation. It has been estimated that there is about one-twelfth of the whole blood quantum in the lungs during inspiration, and one-fifteenth during expiration. The great degree of distensibility of the pulmonary vessels allows of frequent adjustments being made, so that within wide limits,as much blood in a given time will pass through the pulmonary as through the systemic system. The limits of their See also:

ADJUSTMENT (from late Lat. ad juxtare, derived from juxta, near, but early confounded with a supposed derivation from justus, right)

adjustment may, however, be exceeded during violent muscular exertion. The compressive action of the skeletal muscles returns the blood to the venous cistern, and if more arrives than can be transmitted through the lungs in a given time, the right heart becomes engorged, breathlessness occurs, and. signs of venous congestion appear in the flushed See also:

FACE (from Lat. fades, derived either from facere, to make, or from a root fa-, meaning " appear "; cf. Gr. cbatvstv)

face and turgid veins. The weaker the musculature of the heart the more likely is this to occur; hence the breathlessness on exertion which characterizes cardiac affections. The training of an See also:

ATHLETE (Gr. aOX177'7r; Lat. athleta)

athlete consists largely in developing and adjusting his heart to meet this See also:

STRAIN (through O. Fr. straindre, estraindre, mod. i treindre, from Lat. stringere, to draw tight, related to stress, stretch, string, &c.)

strain. Similarly the weak heart may be trained and improved by carefully adjusted exercise. Rhythmic See also:

COMPRESSION

compression of the thorax is the proper method of resuscitation from suffocation, for this not only aerates the lungs, but produces a circulation of blood. By compressing the abdomen to fill the heart, and then compressing the thorax to empty it, the valves meanwhile directing the flow, a pressure of blood can be maintained in the aorta even when the heart has ceased to beat, and this if patiently continued may See also:

lead to renewal of the heart-beat.

There is no certain evidence that the pulmonary arteries are controlled by vaso-motor nerves. In the intact animalformed by the confluence of the mesenteric veins with the Portal splenic vein, which together drain these capillaries. The ctionrcala- portal blood breaks up into a second plexus of capillaries . within the substance of the liver. The hepatic veins carry the blood from this plexus into the inferior vena cava. Ligation of the portal vein causes intense congestion of the abdominal vessels, and so distensile are these that they can hold nearly all the blood in the body: thus the arterial pressure quickly falls, and the animal See also:

DIES, CHRISTOPH ALBERT (1755-1822)

dies just as if it had been bled to See also:

DEATH

death. The portal circulation is largely maintained by the action of the respiratory pump, the peristaltic movements of the See also:

INTESTINE (Lat. intestinus, internal, usually in neuter plural intestina. from intus, within)

intestine and the rhythmic contractions of the spleen; these agencies help to drive the blood through the second set of capillaries in the liver. The systole of the heart may tell back on the liver and cause it to swell, for there are no valves between it and the inferior vena cava. Obstruction in the right heart or pulmonary circulation at once tells back on the liver. The increased respiration which results from muscular exercise greatly furthers the hepatic circulation, while it increases the See also:

CONSUMPTION (Lat. consumere)

consumption of food material. Thus exercise relieves the over-fed man. The liver is so vascular and extensile that it may hold one-See also:

QUARTER (through Fr. from Lat. quartarius, fourth part)

quarter of the blood in the body. The circulation of the See also:

BRAIN (A.S. braegen)

brain is somewhat peculiar, since this organ is enclosed in a rigid bony covering.

The limbs, glands and viscera can expand considerably when the blood pressure rises, but the expansion of the brain is confined. By the The expression of venous blood from the veins and sinuses the cerebra! brain can receive a larger supply of arterial blood at c/rcu/a- each pulse. Increase in arterial pressure increases the tlon. velocity of flow through the brain, the whole cerebral vascular system behaving like a system of rigid tubes' when the limits of expansion have been reached. For as the pressure transmitted directly through the arteries to the capillary veins must always be greater than that transmitted through the elastic wall of the arteries to the brain tissue, the expansion of the arteries can-not obliterate the lumina of the veins. The pressure of the brain against, the See also:

SKULL

skull wall is circulatory in origin: in the See also:

INFANT (in early forms enfaunt, enfant, through the Fr. enfant, from Lat. infans, in, not, and fans, the present participle of fari, to speak)

infant's fontanelle the brain can be felt to pulse with each heart-beat and to expand with expiration. The expiratory impediment to the venous flow produces this expansion. A blood See also:

CLOT, ANTOINE

clot on the brain or depressed piece of bone raise the brain pressure by obliterating the capillaries in the compressed area and raising the pressure therein to the arterial pressure. The arterial supply to the brain by the two carotid and two vertebral arteries is so abundant, and so assured by the See also:

ANASTOMOSIS (a Greek word in which the second o is long, from avaaroµovv, to furnish with a mouth or outlet)

anastomosis of these vessels in the circle of See also:

Willis, that at least two of the arteries in the See also:

MONKEY

monkey can be tied without See also:

GRAVE

grave effect. Sudden compression of both carotids may render a man unconscious, but will not destroy See also:

LIFE

life, for the centres of respiration, &c., are supplied by the vertebral arteries. The vertebral arteries in their passage to the brain are protected from compression by the cervical vertebrae. Whether the muscular coat of the cerebral arteries is supplied with vaso-motor nerves is uncertain.

Hurthle and others observed a rise of pressure in the peripheral end of the carotid artery on stimulating the cervical sympathetic See also:

NERVE (Lat. nervus, Gr. vevpov, a bowstring)

nerve. The writer found this to be so only when the cervical sympathetic nerve was excited on the same side as the carotid pressure was recorded. If the circle of Willis was constricted, excitation of either nerve ought to have the effect; it is possible that the effect was produced by the vasoconstriction of the extra-See also:

CRANIAL

cranial branches of the carotid. After establishing an artificial circulation of the brain Wiggins found that 'adding adrenalin to the nutritive fluid reduced the outflow, and it is supposed that adrenalin acts by stimulating the ends of the vasomotor nerves, rather than by stimulating the muscular coats of the arteries. The veins of the pia and dura mater have no See also:

MIDDLE

middle muscular coat and no valves. The venous blood emerges from the skull in man mainly through the opening of the lateral sinuses into the See also:

INTERNAL

internal jugular vein; there are communications between the cavernous sinuses and the ophthalmic veins of. the facial system, and with the venous plexuses of the See also:

SPINAL

spinal See also:

CORD (derived through the Fr. corde, from the Lat. chorda, Gr. xop(5rt, the string of a musical instrument)

cord. The points of emergence of the veins are well protected from See also:

CLOSURE (Fr. clooture)

closure by compression. The brain can regulate its own blood supply by means of the cardiac and vaso-motor centres. Deficient supply to these centres excites increased frequency of the heart and constriction of the arteries, especially those of the great splanchnic area. Cerebral excitement has the same effect, so that the active brain is assured of a greater blood supply (Bayliss and L. Hill). In each unit of time the same quantity of blood must, on the average, flow through the lesser and greater circuit, for otherwise the The a circulation would not continue.

Likewise, the average The Non velocity at any part of the vascular system must be incul during versely proportional to the total cross-section at that part. muscular In other words, where the bed is wider, the stream is slower; actin #y. the total sectional area of the capillaries is roughly estimated to be 700 times greater than that of the aorta or venae cavae. Any general change in velocity at any section of this circuit tells both backwards and forwards on the velocity in all other sections, for the average velocity in the arteries, veins and capillaries, these vessels being taken respectively as a whole, depends always on the relative areas of their total cross-sections. The vascular system is especially constructed so that considerable changes of pressure may be brought about in the arterial section, without any (or scarcely any) alteration of the pressures in the venous or pulmonary sections of' the circulatory system: A' high-pressure See also:

main (the arteries) runs to all the See also:

ORGANS

organs, and this is supplied with taps; for by means of the vaso-motor nerves which See also:

CONTROL (Fr. contrdle, older form contre rolle, from Med. Lat. contra-rotulus, a counter roll or copy of a document used to check the original; there is no instance in English of the use of " control " in this, its literal, meaning)

control the diameter of the arterioles, the stream can be turned on here or there, and any part flushed with the blood, while the supply to the remaining parts is kept under control. Normally, the sum of the resistances which at any moment opposes the outflow through the capillaries is maintained at the same value, for the vascular system is so co-ordinated by the nervous system that dilatation of the arterioles in any one organ is compensated for by constriction in another. Thus the arterial pressure remains constant, except at times of great activity. The great splanchnic area of arterioles acts as " the resistance See also:

box " of the arterial system. By the constriction of these arterioles during mental or muscular activity the blood current is switched off the abdominal organs on to the brain and muscles, while by dilating during rest and digestion they produce the'contrary effect. The constriction of the splanchnic vessels does not sensibly diminish the capacity of the total vascular system, for the veins possess little See also:

ELASTICITY

elasticity. Thus variations of arterial pressure, brought about by constriction or dilatation of the arterial system, produce little or no effect on the pressure in the great veins or pulmonary circuit. The contraction of the abdominal muscles, on the other hand, greatly influences the diastolic or filling pressure of the heart. It is obviously of the utmost importance that the heart should not be over-dilated by an increased filling pressure during the See also:

period of diastole.

When a man strains to lift a heavy weight he closes the glottis, and by contracting the muscles which are attached to the thorax raises the intrathoracic pressure. The rise of intrathoracic pressure See also:

AIDS

aids the pericardium in supporting the heart, and prevents over-dilatation by resisting the increase in venous blood pressure. This increase results from the powerful and sustained contraction of the abdominal and other skeletal muscles. In the See also:

DIAGRAM

diagram already given it is clear that the contraction of T will counteract the contraction of A. At the same time the rise of intrathoracic pressure supports the lungs, and prevents the blood, driven out from the veins, from congesting within the pulmonary vessels. Over-dilatation both of the heart and lungs being thus prevented, the blood expressed from the abdomen is driven through the lungs into the left ventricle, and so into the arteries. So long as the general and intense muscular spasms continue, there is increased resistance to the outflow of the blood through the capillaries both of the abdominal viscera and the limbs. The arterial pressure rises, therefore, and the flow of blood to the central nervous system is increased. The rise of the intrathoracic and See also:

INTRA

intra-abdominal pressures, and the sustained contraction of the skeletal muscles, alike hinder the return of venous blood from the capillaries to the heart, and, owing to this, the face and limbs become congested until the veins stand out as knotted cords. It is obvious that at this See also:

STAGE (Fr. 6/age; from Lat. stare, to stand)

stage the total capacity of the vascular system is greatly diminished, and the pressure in all parts of the system is raised. It is during such a muscular effort that a degenerated vessel in the brain is prone to rupture and occasion See also:

APOPLEXY (Gr. arov n i.a, from aroaMvvew, to strike down, to stun)

apoplexy. The venous obstruction quickly leads to diminished diastolic filling of the heart, and to such a decreased velocity of blood flow that the effort is terminated by the lack of oxygen in the brain.

During any violent exercise, such as See also:

RUNNING

running, the skeletal muscles alternately See also:

contract and expand, and the full See also:

flood of the circulation flows through the locomotor organs. The stroke of the heart is then both more energetic and more frequent, and the blood circulates with in-creased velocity. Under these conditions the filling of the heart is maintained by the pumping action of the skeletal and respiratory muscles. The abdominal wall is tonically contracted, and the reserve of blood is driven from the splanchnic vessels to fill the dilated vessels of the locomotor organs. The thorax is tonically elevated and the thoracic cavity enlarged, so that the pulmonary vessels are dilated. At each respiration the pressure within the thoracic cavity becomes less than that of the atmosphere, and the blood is aspirated from the veins into the right side of the heart and lungs; conversely, at each expiration the thoracic pressure increases, and the blood is expressed from the lungs into the left side of the heart. While the respiratory pump at all times renders important aid to the circulation of the blood, its action becomes of supreme importance during such an exercise as running. The runner pants for breath, and this not only increases the intake of oxygen, butmaintains the diastolic filling of the heart. It is of the utmost importance that man should grasp the fact that the circulation of the blood depends not only on the heart, but on the vigour of the respiration and the activity of the skeletal muscles. Muscular exercise is for this reason a sine quit non for the See also:

MAINTENANCE (Fr. maintenance, from maintenir, to maintain, support, Lat. manu tenere, to hold in the hand)

maintenance of vigorous mental and bodily health. Under the influence of the muscular system comes not only the blood but the lymph. The lymphatics form a subsidiary system of small valved vessels, and drain the tissues of the excess of lymph, which transudes from the capillaries of the organs during functional activity, or in con-sequence of venous obstruction.

The larger lymphatics open into the veins at the See also:

root of the See also:

NECK (O. Eng. hnecca; the word appears in many Teutonic languages; cf. Dutch ride, Ger. Nacken; in O. E. the common word was heals; cf. Ger. Hals)

neck. It is chiefly by the compressive action of the skeletal and visceral muscles, and the aspirating action of the respiratory pump, that the lymph is propelled onwards. It must be See also:

BORNE, KARL LUDWIG (1786–1837)

borne in mind that the descent of the diaphragm during inspiration compresses the abdominal organs, and thus aids the aspirating action of the thorax in furthering the return to the heart both of venous blood and of lymph. The circulation remains efficient not only in the horizontal but also in the erect position, and just as much so when a man, like a gymnast, is ceaselessly shifting the position of his body. Influence Yet in a man standing six feet the hydrostatic pressure of of poa a column of blood reaching from the vertex to the soles of tore on the feet is equal to 14 cm. of mercury. The blood, owing the d, to its weight, continually presses downwards, and under the culation. influence of gravity would sink if the veins and capillaries of the lower parts were sufficiently extensile to contain it. Such is actually the case in the snake or See also:

eel, for the heart empties so soon as one of these animals is immobilized in the vertical posture. This does not occur in an eel or snake immersed in water, for the hydrostatic pressure of the column of water outside balances that of the blood within, During the See also:

EVOLUTION

evolution of man there have been See also:

DEVELOPED

developed special mechanisms by which the determination of the blood to the lower parts is prevented, and the See also:

ASSUMPTION, FEAST OF

assumption of the erect posture rendered possible. The pericardium is suspended above by the deep cervical See also:

FASCIA (Latin for a bandage or fillet)

fascia, while below it is attached to the central tendon of the diaphragm. Almost all displacement of the heart is thus prevented. The pericardium supports the right heart when the weight of a long column of venous blood suddenly bears upon it, as, for example, when a man stands on his head. The abdominal viscera are slung upwards to the spine, while below they are sup-ported by the pelvic See also:

basin and the wall of the abdomen, the muscles of which are arranged so as to See also:

ACT (Lat. actus, actum)

act as a natural See also:

WAIST

waist-See also:

BAND

band.

In tame hutch rabbits, with large patulous abdomens, death may result in from 15 to 30 minutes if the animals are suspended and immobilized in the erect posture, for the circulation through the brain ceases and the heart soon becomes emptied of blood. If, however, the capacious veins of the abdomen be confined by an abdominal bandage, no such result occurs. Man is naturally provided with an efficient abdominal See also:

belt, although this in many is rendered toneless by neglect of exercise and See also:

GROSS

gross or indolent living. The splanchnic arterioles are maintained in tonic con-traction by the vaso-motor centre, and thus the flow of blood to the abdominal viscera is confined within due limits. The veins of the limbs are broken into short segments by valves, and these support the weight of the blood in the erect posture. The brain is confined within the rigid wall of the skull, and by this wall are the cerebral vessels supported and confined when the pressure is increased by the head-down posture. Every contraction of the skeletal muscles compresses the veins of the body and limbs, for these are confined beneath the taut and elastic skin. The pressure of the body against external objects has a like result. Guided by the valves of the veins, the blood is by such means continually driven upwards into the venae cavae. If the reader hangs one arm motionless, until the veins at the back of the hand become con• Bested, and then either elevates the limb or forcibly clenches the fist, he will recognize the enormous influence which muscular exercise, and continual change of posture, has on the return of blood to the heart. It becomes wearisome and soon impossible for a man to stand motionless. When a man is crucified—that is to say, immobilized in the erect posture—the blood slowly sinks to the most dependent parts, oedema and thirst result, and finally death from cerebral See also:

ANAEMIA (from Gr. ay-, privative, and aiµa, blood)

anaemia ensues.

In man, standing erect, the heart is situated above its chief reservoir—the abdominal veins. The blood is raised by the action of the respiratory movements, which act both as a suction and as a force pump, for the blood is not only aspirated into the right ventricle by the expansion of the thoracic cavity, but is expressed from the abdomen by the descent of the diaphragm. When a man faints from fear, his muscular system is relaxed and respiration inhibited. The blood in consequence sinks into the abdomen, the face blanches and the heart fails to fill. He is resuscitated either by compression of the abdomen, or by being placed in the head-down posture. To prevent faintness and drive the blood-stream to his brain and muscles, a soldier tightens his belt before entering into action., Similarly, men and See also:

WOMEN

women with lax abdominal wall and toneless muscles take See also:

REFUGE

refuge in the wearing of abdominal belts, and find comfort in prolonged See also:

IMMERSION (Lat. immersio, dipping),

immersion in See also:

BATHS

baths. It would be more rational if they practised rope-hauling, and, like fishermen, hardened their abdominal muscles. In the mature foetus the fluid brought from the See also:

PLACENTA (Lat. for a cake)

placenta by the umbilical vein is partly conveyed at once to the vena cava ascendens Foetal by means of the ductus venosus and partly flows through two trunks that unite with the portal vein, returning the blood from the intestines into the substance of the liver, thence to be carried back to the vena cava by the hepatic vein. Having thus been transmitted through the placenta and the liver, the blood that enters the vena cava is purely arterial in See also:

CHARACTER (Gr. xapareri7p, from xap&crew, to scratch)

character; but, being mixed in the vessels with the venous blood returned from the See also:

TRUNK (Fr. tronc, Lat. truncus, cut off, maimed)

trunk and lower extremities, it loses this character in some degree by the time that it reaches the heart. In the right auricle, which it then enters, it would also be mixed with the venous blood brought down from the head and upper extremities by the descending vena cava were it not that a See also:

PROVISION (Lat. provisio)

provision exists to impede (if it does not entirely prevent) any further admixture. This consists in the arrangement of the Eustachian valve, which directs the arterial current (that flows upwards through the ascending vena cava) into the left side of the heart, through the foramen ovale—an opening in the septum between the auricles—whilst it directs the venous current (that is being returned by the See also:

SUPERIOR

superior vena cava) into the right ventricle. When the ventricles contract, the arterial blood contained in the left is propelled into the ascending aorta, and supplies the branches that proceed to the head and upper extremities before it undergoes any further admixture, whilst the venous blood contained in the right ventricle is forced into the pulmonary artery, and thence through the ductus arteriosus—branching off from the pulmonary artery before it passes to the two lungs—into the descending aorta, mingling with the arterial currents which that vessel previously conveyed, and thus supplying the trunk and lower extremities with a mixed fluid.

A portion of this is conveyed by the umbilical arteries to the placenta, in which it undergoes the renovating influence of the maternal blood, and from which it is returned in a See also:

state of purity. In consequence of this arrangement the head and upper extremities are supplied with pure blood returning from the placenta, whilst the rest of the body receives blood which is partly venous. This is probably the explanation of the fact that the head and upper extremities are most developed, and from their weight occupy the inferior position in the uterus. At See also:

BIRTH (a word common in various forms to Teutonic languages from the root of the verb " to bear ")

birth the course of the circulation undergoes changes. As soon as the lungs are distended by the first inspiration, a portion of the blood of the pulmonary artery is diverted into them and undergoes aeration; and, as this portion increases with the full activity of the lungs, the ductus arteriosus gradually shrinks, and its cavity finally becomes obliterated.' At the same time the foramen ovale is closed by a valvular See also:

FOLD

fold, and thus the direct communication between the two auricles is cut off. When these changes have been accomplished, the circulation, which was before carried on upon the See also:

plan of that of the higher See also:

REPTILES (Lat. Reptilia, creeping things, from reptilis; ref ere, to creep; Gr. Ep7rety, whence the term " herpetology," for the science dealing with them)

reptiles, becomes that of the complete warm-blooded animal, all the blood which has been returned in a venous state to the right side of the heart being transmitted through the lungs before it can reach the left side or be propelled from its arterial trunks". After birth the umbilical arteries shrink and See also:

close up and become the lateral ligaments of the See also:

BLADDER (from A.S. blaeddre, connected with bl¢wan, to blow, cf. Ger. blase)

bladder, while their upper parts remain as the superior vesical arteries. The umbilical vein becomes the ligamentum teres. The ductus venosus also shrinks and finally is closed. The foramen ovale is also closed, and the ductus arteriosus shrivels and becomes the ligamentum arteriosum. The blood vessels are supplied with constrictor and dilator nerve See also:

fibres which regulate the size of the vascular bed and the See also:

DISTRIBUTION (Lat. distribuere, to deal out)

distribution The vaso- of the blood to the various organs. The arteries may be motor compared to a high pressure main supplying a See also:

TOWN

town.

By m means of the vaso-motor nerves the arterioles (the See also:

house nerves. taps) can be opened or closed and the current switched on to or off any organ according to its functional needs. If all the arterioles be dilated at one and the same time, the aortic pressure falls, and the blood taking the pathways of least resistance, gravitates to the most dependent parts of the vascular system, just as if all the taps in a town were opened at once the pressure in the main would fail, and only the taps in the lower parts of the town would receive a supply. The See also:

DISCOVERY

discovery of the vaso-motor nerves is due to See also:

CLAUDE, JEAN (1619-1687)

Claude See also:

Bernard (1850. He discovered that by section of the cervical sympathetic nerve he could make the See also:

EAR (common Teut.; O.E. are, Ger. Ohr, Du. oor, akin to Lat. auris, Gr. ovs)

ear of a See also:

RABBIT

rabbit flush, while by stimulation of this nerve he could make it blanch. Claude Bernard had the See also:

GOOD, JOHN MASON (1764-1827)

good See also:

FORTUNE, ROBERT (1813-188o)

fortune to make the further discovery that stimulation of certain nerves, such as the chorda tympani supplying the salivary gland, produces an active dilatation of the blood vessels. The vaso-constrictor fibres issue in the anterior spinal roots, from the second thoracic to the second lumbar root, and pass to the sympathetic See also:

CHAIN (through the O. Fr. citable, chcene, &c., from Lat. catena)

chain of ganglia. The fibres are of small diameter, and probably arise from cells situated in the lateral, See also:

horn of the See also:

grey See also:

MATTER

matter of the spinal cord. They each have a See also:

CELL (from Lat. cella, probably from an Indo-European kal —seen in Lat. celare, to hide; another suggestion connects the word with Lat. cera, wax, taking the original meaning to refer to the honeycomb)

cell station in one other ganglion and proceed as post-ganglionic fibres to the cervical sympathetic, to the mesenteric nerves and to the nerves of the limbs. See also:

NICOTINE, C10H

Nicotine paralyses ganglion cells, and by applying this test to the various ganglia the cell stations of the vaso-constrictor fibres sup-plying each organ have been mapped out. The vaso-dilator fibres have not so restricted an origin, for they issue in the efferent roots in all parts of the neural axis. The two kinds of See also:

net'ves, although antagonistic in action, end in the same terminal plexus which'surrounds. the vessels. The presence of vaso-dilator fibres in the See also:

COMMON

common nerve trunks is masked, on excitation, by the overpowering action of the vaso-constrictor nerves.

The latter are, however, more rapidly fatigued than the former, and by this and other means the presence of vaso-dilator fibres can be demonstrated in almost all parts of the body. The nervi-erigentes to the penis and the chorda tympani supplying the salivary glands are the most striking examples of vaso-dilator nerves. The vaso-dilator nerves for the limbs issue in the posterior spinal roots (Bayliss). The posterior roots contain the afferent nerves (See also:

TOUCH (derived through Fr. toucher from a common Teutonic and Indo-Germanic root, cf. " tug," " tuck," O. H. Ger. zucchen, to twitch or draw)

touch, See also:

pain, &c.). Excitation of these fibres causes reflexly a rise of blood pressure directly, a vaso-dilatation of the part the nerves supply. Thus it is assured that the irritated or injured• part receives immediately a greater supply of blood. The vaso-motor ,centre exerts. a tonic influence over the calibre of the arterial and portal systems. Much labour has been done. since to determine the origin and exact distribution of the vaso-motor nerves to the various organs, and the reflex conditions under which they come normally into action, and, as the See also:

FRUIT (through the French from the Lat. fructus; frui, to enjoy)

fruit, our knowledge of these inquiries has come to a See also:

CONDITION (Lat. condicio, from condicere, to agree upon, arrange; not connected with conditio, from condere, conditum, to put together)

condition of considerable exactness. This knowledge is of great See also:

PRACTICAL

practical importance to the physician, and it is See also:

worth noting that it has been obtained entirely by experiment on living but anaesthetized animals. No dissections of the dead animal could have informed us of the vaso-motor nerves. Vaso-motor effects can be studied by (I) inspection of the See also:

flushing or blanching of an organ; (2) measuring the venous outflow; (3) recording the pressure in the artery going to and the vein leaving the organ; (4) observations on the volume of an organ. To make these observations, the organ is enclosed in a suitable air-tight box or plethysmograph, an opening being contrived for the vessels of the organ to pass through so that the circulation may continue.

The box is filled with air or water and is connected with a recording tambour (see fig. i8). The chief effects of vaso-constriction are an increased resistance and lessened flow through the organ, diminished volume and tension of the organ, the venous blood issues from it darker in colour. and the pressure rises in the artery and falls in the vein of the organ, and its temperature sinks. Lastly, if a large area be constricted the general arterial pressure rises. The centre is situated in the spinal bulb beneath the middle of the See also:

FLOOR (from O. Eng. flor, a word common to many Teutonic languages, cf. Dutch vloer, and Ger. Flur, a field, in the feminine, and a floor, masculine)

floor of the See also:

FOURTH

fourth ventricle. The See also:

TONE, THEOBALD WOLFE (1763-1798)

tone of the vascular system is not disturbed when the great brain and See also:

mid brain is destroyed as far as the region of the pons Varolii, but as soon as the spinal `bulb is injured or destroyed the arterial pressure falls very greatly, and the animal passes into the condition of surgical shock if kept alive by artificial respiration. See also:

PAINTING

Painting the floor of the fourth ventricle with a See also:

LOCAL

local anaesthetic, e.g. See also:

COCAINE, C17H21NO4

cocaine, has the same lowering effect on the blood pressure. See also:

DIVISION (from Lat. dividere, to break up into parts, separate)

Division of the cervical spinal cord or of the splanchric nerves lowers the blood pressure greatly. The one See also:

LESION (through Fr. from Lat. laesio, injury, laedere, to hurt)

lesion cuts off the whole body, the other the abdominal organs from the tonic influence of the centre. The fall of pressure is due almost entirely to the pooling of the blood in the portal veins and vena cava inferior. On the other hand, electrical excitation of the lower end of the divided cord or splanchnic nerves raises the pressure by restoring the vascular tone. If an animal be kept alive after division of the spinal cord in the lower cervical region, as it may be, for the phrenics, the chief motor nerves of respiration, 'come off above this region, it is found that the vascular tone after a time becomes restored and the condition of shock passes away. By no second section of the spinal cord can the general condition of shock be reproduced, but a total obstruction of the cord once more causes a general loss of the vascular tone.

From the experimental result, so obtained, it is argued that subsidiary vaso-motor centres exist in the spinal cord, and there is evidence to show that these centres may be excited reflexly. After the lumbar cord has been destroyed the tone of the vessels of the lower limbs is recovered in the course of a few days. In this case the recovery is attributed to the ganglionic and nervous structures which are intercalated between the spinal cord and the muscular walls of the blood vessels. There are thus three mechanisms of control, the bulbar centre influenced particularly by the visual, auditory and vestibular nerves, the spinal centres and the peripheral ganglionic structures. The vaso-motor centre is reflexly excited by the afferent nerves, and its ever-varying tonic action is made up of the See also:

BALANCE (derived through the Fr. from the Late Lat. bilantia, an apparatus for weighing, from bi, two, and lanx, a dish or scale)

balance of the " pressor " and `° depressor influences which thus reach it, and from the quality of the blood which circulates through it. Pressor effects, i.e. those causing increased constriction and rise of arterial pressure, may be produced by stimulating the central end of almost any afferent nerve, and especially that of a cutaneous nerve. Depressor effects are always obtained by stimulating the depressor nerve, and may be obtained by stimulating the afferent nerves under special conditions. That these reflex vaso-motor effects frequently occur is shown by the blush of shame, the blanching of the face by fear,, the blanching of the skin by exposure to cold and the flushing which is produced by See also:

HEAT (0. E. haktu, which like " hot," Old Eng. hat, is from the Teutonic type haita, hit, to be hot; cf. Ger. hitze, heiss; Dutch, hitte, heet, &c.)

heat. The rabbit's ear blanches if its feet are put into cold water. The vaso-motor mechanism is one of the most important of those mechanisms which control the body heat. , Stimulation of the nasal mucous membrane causes flushing of the vessels of the head, constriction elsewhere and a rise of arterial pressure. Food' in the mouth,. or even the sight or 944 See also:

SMELL (connected etymologically with " smoulder " and " smoke ")

smell of food, cause dilatation of the vessels of the salivary gland.

The mucous membrane of the air passages flush and secrete more actively when a See also:

DRAUGHT (from the common Teutonic word " to draw "; cf. Ger. 7'racht, load; the pronunciation led to the variant form " draft," now confined to certain specific meanings)

draught of cold air strikes the skin. See also:

ICE (a word common to Teutonic languages; cf. Ger. Eis)

Ice placed on the abdomen constricts not only the vessels in the skin but those in the See also:

KIDNEY

kidney. Many other examples might be given of the control which the vaso-motor system exerts, but the above are sufficient to suggest the influence which the physician can bring to See also:

bear on the blood supply of the various organs. Discussion has taken See also:

PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place as to whether depressor reflexes are brought about by lessening of the vaso-constrictor tone or by ex-See also:

CITATION (Lat. citare, to cite)

citation of vaso-dilator nerves. See also:

PROOF (in M. Eng. preove, proeve, preve, &°c., from O. Fr . prueve, proeve, &c., mod. preuve, Late. Lat. proba, probate, to prove, to test the goodness of anything, probus, good)

Proof of an undoubtable character seems to have been produced that after division of the vaso-constrictor nerves dilatation of a limb can be brought about reflexly by stimulating the depressor nerve, and in this case the effect must be produced by active excitation of the vaso-dilator nerves. Under certain unusual conditions, e.g. deficient supply of oxygen, the vaso-motor centre exhibits rhythmical variations in tonicity which make themselves visible as rhythmical rises and falls of arterial pressure of slow tempo. A waxing and waning of respiration (See also:

CHEYNE, THOMAS KELLY (1841— )

Cheyne-See also:

Stokes breathing) frequently accompanies these waves. Such are observed in See also:

SLEEP (0. Eng. slcepan; Ger. schlafen; cf. Lat. labi, to glide, and " slip ")

sleep, especially in See also:

CHILDREN, LAW RELATING TO

children and in hibernating animals. IV. See also:

PATHOLOGY (from Gr. raBos, suffering)

PATHOLOGY OF THE VASCULAR SYSTEM On See also:

account of its intimate relations with every part of the body, the circulation is prone to disturbances arising from a great See also:

SERIES (a Latin word from serere, to join)

series of causes. Some of these produce effects which may be regarded as functional—mere changes in See also:

METABOLISM (from Gr. ,uera(3oXh, change)

metabolism, whose disturbances react upon the rest of the body; others give rise to definite structural alterations. In considering the pathology of the circulation, it is useful to divide it into that of the heart, that of the blood vessels and that of the blood.

The heart is liable to changes in the pericardium, malformations, changes in the myocardium, changes in the The heart. endocardium, valvular lesions and functional disorders. he (1) The pericardium may become the seat of morbid changes in various cardiac enlargements, it may become stretched or distended; but the most common and important of the changes is an inflammatory one, i.e. pericarditis. This may arise by way of the blood stream, as in See also:

RHEUMATISM (from Gr. /56µa, flux)

rheumatism, scarlatina and other infective diseases, or by way of the lymph stream. The micro-organisms chiefly responsible for the See also:

PRODUCTION (Lat. productionem, from producere, to pro-duce)

production of pericarditis are the pneumococcus, the different varieties of streptococci and staphylococci, the bacillus See also:

TUBERCULOSIS

tuberculosis, the bacillus coli, and sometimes the gonococcus. In the acute form of the disease the shining serous membrane becomes first dull and lustreless, the blood vessels engorged and an exudation of serum takes place; then See also:

FIBRIN, or FIBRINE

fibrin is deposited both on the visceral and parietal layers. When the fluid is insufficient to keep the surfaces apart, the separation at each diastole gives rise to the well-known " See also:

FRICTION (from Lat. fricare, to rub)

friction rub." Sometimes the amount of exudation pent up in the pericardial See also:

sac is so great as to necessitate its being See also:

DRAWN

drawn off. The fluid may be serous or sero-fibrinous, or may be haemorrhagic, or have undergone a putrefactive change. An effusion of serous fluid into the pericardial sac causes considerable embarrassment to the course of the blood, by rendering the negative pressure, normally See also:

PRESENT

present in the sac, positive. The reason for the interference with the circulation brought about by this alteration of pressure is that the auricles are by compression rendered incapable of accommodating the blood-return from the veins. Analogous effects are produced by pressure upon the heart from without, whether by See also:

ANEURYSM, or ANEURISM (from Gr. avebpuvµa, a dilatation)

aneurysm or See also:

TUMOUR (Lat. tumor, a swelling)

tumour, and pleural effusion or pneumothorax, affecting the viscera from without. In pericarditis it has further to be remembered that the effect of the See also:

PROCESS

process itself upon the muscle fibres lying beneath the membrane is to cause a softening of texture and weakening of function, whereby the See also:

DRIVING (from " to drive," i.e. generally to propel, force along or in, a word common in various forms to the Teutonic languages)

driving power of the heart is diminished. In obliteration of the pericardium, again, the presence of the adhesions between these two layers leads to interference with the contraction of the myocardium, whereby its functions are interfered with.

Acute ventricular dilatation may be associated with pericarditis particularly when the latter is of rheumatic origin and is the result of the myocardial softeningreferred to. Pericardial effusions usually undergo absorption, but various adhesions, and thickenings known as " white spots," may remain. Effusions other than inflammatory are found in the pericardium, i.e. hydropericardium, a dropsical See also:

ACCUMULATION (from Lat. accumulare, to heap up)

accumulation, may be mistaken for an inflammatory one. It occurs in scarlatina, See also:

Bright's disease, as part of a general dropsy, or occasionally from some See also:

MECHANICAL

mechanical difficulty interfering with the local circulation. When the fluid is abundant, it may produce the effects noticed under the inflammatory effusion, and the pericardium may become soddened and its endothelium degenerated. Haemopericardium, or blood in the pericardium, may occur apart from the amount that may be mixed with inflammatory effusions. It is associated with See also:

FOREIGN

foreign bodies penetrating from the See also:

OESOPHAGUS (Gr. o'lvca=I will carry, and r/)ayeiv, to eat)

oesophagus, rupture of an aneurysm, or occasionally associated with See also:

SCURVY (Scorbutus)

scurvy and See also:

PURPURA

purpura. See also:

Gas and air may sometimes distend the pericardium. It is also liable to new growths, which are usually secondary in character, and tuberculosis and hydatids are sometimes found. (2) Malformations.—We are ignorant of the causes which lead to imperfect development of the heart. Many of its malformations are of purely pathological See also:

INTEREST

interest, but others, such as deficiencies of the intraventricular septum, non-closure of the foramen ovale, patency of the ductus arteriosus, or malformations of the valves, See also:

pro-duce a series of secondary effects resultant on the deficient aeration of the blood and sluggishness of the circulation and of venous congestion. The See also:

TRAIN (M. Eng. trayn or trayne, derived through Fr. from Late Lat. trahinare, to drag, draw, Lat. trahere, cf. trail, trace, ultimately from the same source)

train of symptoms is similar to those mentioned below under acquired valvular lesions, but dropsy is very rare.

(3) The Myocardium.—The coverings of the heart muscle can-not long be diseased without affecting the contractile substance itself. Any morbid changes in the lung tissues which impede the circulation through them, and more particularly See also:

EMPHYSEMA (Gr. Eµ / vuav to inflate)

emphysema, lead to change in the substance of the right ventricle, while morbid changes in the systemic arteries lead to changes in the left ventricle. In See also:

HYPERTROPHY (Gr. inrEp, over, and rpo(A, nourishment)

hypertrophy we have an increase of substance. Tangl found by direct measurement that the muscle cells are increased in diameter. The hypertrophy may be due to increased See also:

WORK

work thrown upon the muscle, as in athletics (idiopathic hypertrophy), or may be compensatory, when the muscle is trying to overcome a circulatory defect, as in valvular stenosis or regurgitation. Hyper-See also:

TROPHY (Gr. Tpo7rauov, from TpE7rw, put to flight; Lat. tropaeum)

trophy, when within physiological limits, is to be considered as a means of See also:

ADAPTATION (from Lat. adaptare. to fit to)

adaptation. When occurring in pathological circumstances, it must be regarded as a method. of See also:

COMPENSATION (from Lat. compensare, to weigh one thing against another)

compensation. Every structure and every function in a healthy body has greater or lesser reserve of energy. In healthy conditions the See also:

ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary demands made upon various organs are far below their possible responses, and if these be excessive in extent or duration, the organs adapt themselves to the conditions imposed on them. In abnormal circumstances the process of hypertrophy is brought about by the power which the structures have of responding to the demands made upon them; and so long as the process is adequate, all disturbances may be averted. As an example of such readjustment may be cited the fact that in chronic renal cirrhosis, with increased thickness of the middle See also:

TUNIC (0. Eng. tunice, tunical, taken, before the Norman con-quest, directly from Lat. tunica, of which the origin is unknown)

tunic of the arteries, there is hypertrophy of the left ventricle. Dilatation of the heart is due to the inability of the heart muscle to expel the contents of its cavities.

It may occur from temporary overstress or in the failing 'compensation of valvular disease, or may accompany pathological changes in the muscle such as myocarditis or one of the degenerations. From the presence of toxic substances in the blood (whether introduced from without or arising within the body) the cells of the cardiac muscle fibres are See also:

apt to undergo what is termed cloudy swelling—the simplest form of degenerative process. The cells become larger and duller, with a granular appearance, and the nuclei are less distinct. As a result of interference with nutrition, whether by simple diminution or perverted processes, fatty de-See also:

GENERATION (from Lat. generare, to beget, procreate; genus, stock, race)

generation ensues. It may be associated, but is not necessarily connected, with adipose accumulation and encroachment commonly termed infiltration. In true fatty degeneration the muscle cells have part of their See also:

PROTOPLASM

protoplasm converted into adipose tissue. The fibres become granular, and the cells lose their See also:

DEFINITION (Lat. definitio, from de-finire, to set limits to, describe)

definition, while the nuclei are obscure. The myocardium undergoes both acute and chronic reaction changes. In the former there is enlargement of the nuclei, with proliferation but without karyokinesis. The muscle cells become swollen and lose their striation, while they are softer in texture and altered in outline. The intermuscular tissues are swollen, and may be invaded by leucocytes; this may end in See also:

ABSCESS (from Lat. abscedere, to separate)

abscess formation or in the production of newly formed fibrous tissue. Chronic processes affecting the myocardium give rise to a large amount of fibrosis, and the newly formed fibrous tissue separates and compresses the areas of muscle fibres, giving rise to what is commonly known as chronic interstitial myocarditis.

Restitution or recovery may occur to a varying extent in almost all of the disease-processes which have been considered, but it has to be kept in view that in certain of the degenerative affections there is little if any possibility of getting rid of the results of the process, which in the reactive changes terminating in the formation of much fibrous tissue, or its See also:

CONVERSION (Lat. conversio, from convertere, to turn or ,change)

conversion into adipose or calcareous material, the same holds true. Many of the changes, which are no doubt in their essence conservative, lead to far-reaching con-sequences, by their interference with nutritive possibilities. Diseased conditions of the myocardium are frequently associated with atheromatous degenerations of the coronary arteries, and angina pectoris is said to depend upon such state of malnutrition. The causes which operate by means of the myocardium are almost invariably of a secondary character. The various degenerations already detailed, and the different forms of myocarditis, as well as simple debility of the muscle, are all examples of changes due to general or local disturbance. All • processes which directly or indirectly interfere with the energy of the walls of the heart produce twofold effects, by diminishing the aspiratory or suction-pump action daring diastole, and by lessening its expulsive or force-pump action during systole. The immediate result upon the heart itself of such disturbances is dilatation of that cavity immediately affected. This may occur under perfectly healthy conditions. In these, however, the dilatation is evanescent, while in the circumstances now under See also:

CONSIDERATION (from Lat. considerare, to look at closely, examine, generally taken to be from con-, and the base seen in sidus, sideris, a star, the word being supposed to be originally an astrological or astronomical term)

consideration it is permanent, and, although compensated, it leads to persistent dilatation. Upon the blood vessels the result, whether on account of diminished aspiratory or propulsive energy, is that the amount of blood in the arterial system is decreased, while it is increased in the venous. It is not a necessary consequence that because there is less blood in the arteries the arterial pressure will be diminished, or the venous pressure increased because the veins contain more than their normal amount of blood, seeing that the blood pressure depends upon many different factors. It is a fact, nevertheless, that in consequence of the alteration in the relative amount of blood in the arteries and veins there is a considerable disturbance of blood pressure.

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