246 



PHYSIOLOGY OF THE HEART 



[CH. XX. 



A 



Grehant and Quinquand, and Zuntz adopted an indirect method based on the 

 comparison of the amount of oxygen absorbed in the lungs with the amount added 

 to the blood in its passage through the pulmonary circulation. 



G. N. Stewart has introduced an ingenious method, the principle of which is 

 the following : A solution of an innocuous substance, which can be easily recog- 

 nised and estimated, is allowed to flow for a definite time and at a uniform rate into 



the heart ; the substance selected was 

 sodium chloride. This mingles with the 

 blood and passes into the circulation. 

 At a convenient point of the vascular 

 system, a sample of blood is drawn off 

 just before the injection, and an equal 

 amount during the passage of the salt ; 

 the quantity of the sodium chloride 

 solution which must be added to the 

 first sample in order that it may contain 

 as much as the second sample is deter- 

 mined. This determination gives the 

 extent to which the salt solution has 

 been mixed with the blood in the heart, 

 and knowing the quantity of the solu- 

 tion which has run into the heart, the 

 output in a given time can be calculated. 

 All these experiments have been on 

 animals. The results obtained neces- 

 sarily vary with the size of the animal 

 used, and with the rate at which the 

 heart is beating. If the same relation- 

 ship holds for man as for animals, 

 Stewart calculates that in a man weigh- 

 ing 70 kilos, the output of each ventricle 

 per second is less than 0*002 of the body 

 weight, i.e., about 105 grammes of 

 blood per second, or 87 grammes (about 

 80 c.c.) per heart beat with a pulse rate 

 of 72. Zuntz obtained rather smaller 

 numbers by his method. 



An instrument called the cardio- 

 meter was invented by Roy for regis- 

 tering the output of the heart. His 

 instrument was made of metal, and oil 

 was used as the transmitting medium 

 in its interior. A simple modification 

 of this applicable to the heart of a small 

 mammal like a cat has been devised by 

 Barnard. It consists of an indiarubber 

 tennis ball with a circular orifice cut in 

 one side of it large enough to admit the 

 heart ; a glass tube is securely fixed into 

 a small opening on the opposite side 

 of the ball. The animal is anaesthetised, 

 and its thorax opened. The animal is 

 kept alive by artificial respiration. 



The pericardium is then opened by a crucial incision, the heart is slipped into the 

 ball ; the pericardium overlaps the outside of the ball, and the apparatus is 

 rendered air-tight by smearing the edges of the hole with vaseline. The four 

 corners of the pericardium are then tightly tied by ligatures round the glass tube 

 just mentioned. This tube is connected by a stout indiarubber tube to a Marey's 

 tambour or a piston-recorder, the writing-point of which is applied to a moving 

 blackened cylinder. When the heart contracts, air will be withdrawn from the 



FIG. 254. Stolnikow's apparatus. A and B are 

 two cylinders fitted with floats provided with 

 writing-points at their upper ends. The tube 

 from the lower end of each bifurcates into 

 two, a and v from A ; a' and v' from B. a and 

 a, are united together and enter the right 

 carotid artery ; v and v' unite and are inserted 

 into the superior vena cava. The remaining 

 branches of the aorta and the inferior vena 

 cava are tied. B is first filled with defibrin- 

 ated blood, which passes down v' into the 

 right auricle, thence to the right ventricle, 

 lungs (where it is oxygenated), and then 

 enters the left side of the heart ; the left 

 ventricle expels it by the tube a into A, so 

 that the float in A rises while that in B falls. 

 As soon as B is empty the tubes v and a' 

 which were previously clamped are released, 

 and t/ and a are clamped instead. The left 

 ventricle now expels its blood by the tube a' 

 into the cylinder B ; simultaneously A empties 

 itself through v into the right side of the 

 heart. Zigzag lines are thus traced by the 

 writing-points on the top of the floats, and 

 their frequency enables one to estimate the 

 output of the left ventricle in a given time. 

 (After Starling.) 



