956 PHYSIOLOGY 



have been tied. This cannula is provided with a thermometer to show the temper- 

 ature of the blood supplied to the heart. A tube placed in the inferior vena cava and 

 connected with a water manometer shows the pressure in the right auricle. On the record- 

 ing surface we thus have a record of the arterial pressure, and of the pressure within the 

 right auricle. The output of the whole system can be measured at any time by opening 

 the tube X, clamping F, and allowing the blood to flow for a given number of seconds 

 into a graduated cylinder. 



This method, although of considerable importance in giving information as to the 

 conditions which determine the output of the left ventricle and the maximum capacity 

 of the heart as a pump, tells us nothing as to the output of the left ventricle under 

 normal conditions in the intact animal. For this purpose some indirect means must 

 be adopted which can be used on the intact animal and if possible on man himself, 

 so that the output can be measured under different conditions of rest and activity. 

 Moreover the output as measured on the other side of the artificial arterial resistance 

 represents the ventricular output minus the blood flow through the coronary arteries. 

 It is possible however to insert a cannula into the coronary sinus, and so to measure 

 the blood flow through the heart muscle. The coronary circulation must be added 

 to the flow through the arterial resistance in order to arrive at the correct total output 

 of the left ventricle. The two chief methods for the determination of the ventricular 

 output in the intact animal are those of Zuntz and of Krogh. 



ZUNTZ 'S METHOD. This is based on a comparison of the differences in gases 

 contained in the arterial and venous blood and the actual amount of oxygen taken 

 from the air in the lungs. Thus in one case he found that in a horse weighing 360 

 kilos. 2733 c.c. of oxygen were taken up in the lungs per minute, while the arterial 

 blood contained 10-33 per cent, more oxygen than the venous blood. Since therefore 

 every 100 c.c. of blood that passed through the lungs had taken up 10-33 c.c. of oxygen, 

 and 2733 c.c. had been taken up in the course of a minute, it is evident that 



100 X 2733 

 10-33 



of blood must have passed through the lungs in the time. This therefore was the output 

 of blood by the right ventricle in a minute and was equivalent to -00122 of the body 

 weight per second. 



In a similar experiment on a dog the output per second of the right ventricle was 

 found to be -00157 of the body weight. In order to get the output at each beat it will 

 be necessary to divide the output per minute by the number of heart beats in the same 

 time. From the results of determinations made in this way Zuntz concluded that the 

 output of the right ventricle in man at each beat varies between 50 and 100 c.c. and 

 may be taken on an average at 60 c.c. 



KROGH 'S METHOD. In Krogh's method an endeavour is made to determine 

 the volume of blood flowing through the lungs in a given time by finding out how 

 miifli nitrous oxide is taken up from a mixture of nitrous oxide and air, with which 

 t he lungs arc filled. Nitrous oxide is chosen because it can be breathed in considerable 

 proportions without injury, and is itself very soluble in water or in the blood. The 

 estimation is canied out in fho following way. A small recording spirometer is filled 

 with about 11 litres o f a gas mixture containing 10 to 25 per cent. N 2 O and 20 to 25 

 l> i rent, oxygen. The subject, seated in a chair or on a bicycle ergometer, expires to 

 the greatest possible extent, and then takes a deep inspiration from the spirometer. 

 He holds his breath for live to fifteen seconds, breathes out sharply into the spirometer, 

 expiring at least one litre. At the end of this sharp expiration, a sample of his alveolar 

 air is taken by connecting the tube from his face-piece wiih an evacuated glass bull), 

 as in Haldane's method of determining alveolar air. The breath is now held for a 

 period varying between six and twenty-five seconds. He then makes a final sharp 

 ample expiration into the spirometer, a sample of his alveolar air being taken at the 

 end of t his expiration. The excursions of t he spirometer indicate exactly what volume 

 of air he has breathed in and breathed out at each part of the experiment. These are 



