On the capacity of the central bloodvessels in rabbits 1

By

H. Hemmingson and B. P. Sdfverskiold

(From the roentgen dept. of the Serafimerlasarettet, and the pharmacological dept.of the Karolinska Institutet)

(With 2 figures in the text)

It has been previously pointed out that the large central vessels,including the heart, might be of great importance as bloodstores, and thatbecause of their contractility they are able to play an important partin compensating for decrease of the body's absolute or circulating quan­tity of blood (Silfverskiold 1938).

As these experiments were made for the most part on mice, andas it may seem both surprising and improbable that the large vessels inbigger animals should really be able to hold nearly 1/3 of the quantityof blood which was found in the above-mentioned investigation, thisparticular study was carried out in order to measure the. capacity ofthe central vessels in living rabbits.

MethodThe rabbits were anesthetized with 20% urethane, injected intra­

venously (7 co/kg body weight) I hour or more before the beginning ofthe experiment. About 12 cc of thorotrast and 1-2 CC 5% heparine(Jorpes 1935) were injected intravenously in the first 3 animals about10 minutes before the examination, in the 4th 30 minutes before, andin the last ones, more than I hour previous to the examination. Theanimals did not seem to be unfavourably affected by this treatment,but gave the impression of being in very good condition. Next, theanimal was fixed on a table on its back and a roentgenphoto was taken,immediately afterwards the animal was turned over for a sidepicture.

The rabbit was then put to death by means of ether, and when ithad ceased breathing, the thoracic cavity was opened by cutting throughthe sternum, after which new side and front pictures were taken.

1 Received 21 September 1939

OX THE CAPACITY OF TIlE CENTRAL BLOODVESSELS IN RABBITS 163

One, or if that was not found to be enough, two Spencer-Wellswere placed in such a way that the vena cava and the aorta were clampedoff immediately above the diaphragm. The abdominal wall was cut alongthe edge of the rib, so that it might be ascertained that it was not pos­sible for the blood to flow this way from or to the thoracic cavity. Arubber tube was tightly attached to the animal's neck just below thehead. As it had been made sure that there was only a slight quantityof blood in the more distal parts of the forelegs, these were not tied.Having made certain that there was no fluid in the pleural cavity, thelarge vessels of the thoracic cavity were intersected. The blood whichthen flowed into this cavity was absorbed and measured with a graduatedsyringe.

Table I

Nr. Weightkg I

, Cc blood in the central I Per cent of totalvessels inc!. the heart amount of blood *)

2·72.62·72·32·3

I.

2.

3·4·5·

2824282626

26·4

*) Total amount of blood calculated as 6 per cent of the rabbit's bodyweight(v. Fleischer-Hansen 1928).

From table I it is evident that the central vessels, including theheart, in the rabbit contain 1/4 of the body's total mass of blood.

Roentgen examination

The purpose of the roentgen examination was to study the relativecapacity in vivo and post mortem of the rabbit's heart and large vessels.This capacity can be roentgenologically studied after intravascular in­jection of thorotrast, a colloidal solution of thorium dioxide, whichmixes with blood homogenously, and does not leave the blood streamfor several hours, when it becomes stored in the reticuloendothelialsystem. Due to the contrast, the blood can be seen in the heart and thelarge trunk vessels, which with a short time-exposure show distinctoutlines. A time-exposure of 0.04 seconds with 70 Kw. and 300 Ma.was used. The focus film distance was 170 em. In the side picture, theheart has an elliptical shape, and its transversal surface can thus be cal­culated according to the formula of the ellipse, which was verified byusing a graph chart cross-ruled in millimeters, Even in the frontal pic-

164 H. HEMMINGSO:-;f A:-;fD B. P. SILFVERSKIOLD

ture with the animal lying on its back, the heart has an elliptical shapeand therefore its volume can be calculated according to the formula forthe ellipsoid. The animal, however, often lies in a slanting positionbecause of its narrow back and its large, heavy abdomen. Therefore itproved to be very difficult to obtain straight front views, i. e. with afrontal heart projection, in the roentgen picture perpendicular to thetransversal heart projection in the side picture. We have therefore givenup determining the exact heart volume by roentgen photograph, andinstead have used its transversal surface as a relative measure of theheart volume. Because of the great focus film distance and the near­ness of the object to the film, any possible enlargement of the heartin the roentgen picture need not be taken into consideration.

In the roentgenogram, the aorta also appears as well as the pul­monary artery, and the posterior vena cava. The aorta can be tracedfrom where it leaves the left ventricle a long way down into the ab­domen. Its diameter lessens perceptible after the branching off of theinnominate artery and the left subclavian artery on the aorta arch.Therefore the diameter was measured in the ascending as well as inthe descending part of the aorta. The pulmonary artery leaves the rightventricle on the front side of the heart base, but it is difficult here todistinguish its lower contour from the outline of the heart. Thus onlythe right and left pulmonary arteries are clearly outlined and measurable.Their transversal diameters were measured immediately after division ofthe pulmonary artery. The posterior vena cava is of uniform size alongits intrathoracic course. The anterior vena cava, the jugular veins, thecarotid arteries, and also the axillary arteries and veins have a lesserdiameter in comparison with the above-mentioned trunk vessels, buttogether probably have a rather large volume. However, they are dif­ficult to identify in roentgenograms, especially in the side pictureswhere they are often projected on top of each other.

In the 5 rabbits examined, the following figures were obtained ofthe transversal surface of the heart, and also of the diameters of theascending and descending parts of the aorta, the right and left pulmonaryarteries, and the posterior vena cava.

Furthermore, one rabbit was examined as previously mentioned. Thisanimal was kept lying down for about 2 1/ 2 hours after the contrast in­jection had been given. This examination was made in the same manneras that of the other animals in the series, and gave about the sameresults as those noted in the first five animals. However, by then, thecontrast had become so diluted, that exact measurements could not beobtained.

ON THE CAPACITY OF THE CENTRAL BLOODVESSELS IN RABBITS 165

Table II

Transv. sur- Augrnen- Diam. of Diam. of a. Diam.ofv,

Nr.face of heart tation of aorta *) pulm. dx. et sin. cava post.

in I post heart's in post in I post in postvivo mort. surface vivo mort. vivo mort. vivo mort.

em' em' mm mm mm mm mm mm1. 9.8 10.2 4% 7.5-6.5 4.0-3.0 4·5 3.0 6.0 6.02, 7,2 7.6 6% 7.0-4.5 3.5-3.0 3·5 2.0 5.0 4·53· 7·9 8.2 4% 6·5-4·5 2.0-2.0 4.0 2.0 5·5 4·54· 7·7 8.2 6% 8.0-5·5 4.0-2.0 3·5 notrnea- 4·5 5·5

Isurable

5· 7·4 8·4 14% 7.0-5.0 3.0-2.5 3.0 2.0 5.0 6.0

*) First figure in each column refers to aorta ascend. Second figure in eachcolumn refers to aorta descend. thoracal.

As table II makes clear, the heart is increased in volume after death,which corresponds at autopsy to a relaxed heart. The increase in volumeis however moderate and in the first 4 cases at the most 6% as regardsthe heart's transversal surface. In the last case, the same surface in­creases 14% in size. As to the intrathoracic blood quantity in livingand dead animals, the postmortal increase in volume of the heart seemsto be at least partially compensated for by the substantial decrease involume of the aorta and the pulmonary arteries, which constantly showa considerably smaller diameter postmortally. On the other hand, theposterior vena cava shows no obvious or constant difference in diameterbefore and after death. It seems as if the anterior vena cava, and alsothe veins of the neck and of the forelegs must behave likewise.

The roentgen photographs (fig. I and 2) show side pictures of ani­malL in the series. Figure I shows the living animal; figure II thesame after death.

The roentgen examination therefore seems to indicate that evenif the heart increases somewhat in volume post mortem, the arteries,on the other hand, decrease very considerably in diameter, while theveins seem to have the same capacity before and after death.

Discussion

It appears from comparing the roentgen pictures, that no im­portant differences in the blood quantity of the vessels examined, werelikely to have arisen from anesthetization to death. It is evident that inthese rabbits anesthetized with urethane, the anterior central vessels,including the heart, contain a very large part of the body's blood.

The purpose of the present examination was to ascertain whetheran equivalent could be found in rabbits, which would correspond in

166 H. HEMMINGSON AND B. P. SILFVERSKIOLD

Figure I

Figure 2

ON THE CAPACITY OF TilE CENTRAL BLOODVESSELS IN RABBITS 167

importance to the role played by the central blood vessels in blooddistribution in mice, a fact already established by one of the presentauthors. In this previous experiment the result was obtained throughthe use of a special "clamping off" technique, combined with the ex­traction of the colouring matter of the blood, in the parts isolated. Inthe same investigation, a study was also made of the blood quantityin the large vessels in rabbits put to death by anesthetization. Highfigures were obtained for the blood quantity of the vessels in question,in the animals examined at that time. The new feature of the presentexperiment is that it proves that in living rabbits also, the centralvessels can have a great capacity.

The objection might be made that in this case very great quantitiesof fluid were injected into the blood stream before the examination,and that it is possible that the large capacity of the central vessels arosefrom the fact that they were dilated by the increased quantity of blood.An investigation was consequently made of the dilution of the blood,by means of a "Sicca" hemometer. A blood sample was taken from therabbit's auricular vein just before the injection of urethane and thoro­trast, and another sample 45 minutes after the injection. The blood inthe 2 animals examined did not appear to be diluted after this intervalof time, a condition to be expected, in as much as fluid can disappearquickly into the tissues and through the kidneys.

It must then be considered as rather probable that the large vesselsin the type of animals examined, contain significant quantities of blood.One must note in addition, that the vessel region examined does includea great part of the large central vessels, but not all, as the large abdominalvessels are not counted in. As may be seen in the pictures, the nearestpart of the vena cava lying below the diaphragm, has great volume.The capacity of the abdominal vena cava, however, is difficult to deter­mine. One can count on the fact that the central vessels hold a veryconsiderable part of the body's blood.

In the above-mentioned investigation of Silfverski6ld, it was shownin mice and rabbits that these vessels, on loss of blood, contract verydecidedly in compensation. In the great number of shock conditionswhich nowadays are ascribed to loss of blood (see Blalock 1934), it isprobable that these vessels act as blood reservoirs.

SummaryAn examination was made to determine the capacity in rabbits of

the anterior central vessels, including the heart.By X-ray examination was made probable that the total capacity

of these vessels was about the same in the living rabbits as in those;anesthetizated to death.

168 H. HEMMINGSON AND B. P. SILFVERSKIOLD, ON THE CAPACITY ETC.

It was shown that that vessel area may have a very large capacity(about 1/4of the total blood quantity). It is conceivable that it has animportance as a blood reservoir, corresponding to that which wasearlier demonstrated for mice by Silfverskiold.

References

Blalock, A., Surg, Gynec. Obst. 1934, 58, 551.Fleischer-Hansen, C. C., Studier over Bloduolumen, Kopenhagen FJ28.

Jorpes, E., Biocbem : ], 1935,29,1817.SilfverskiOld, B. P., This Archiv 1938, 79, Suppl. 14.