912 PHYSIOLOGY 



The arterial cannula communicates by a T-tube with a mercurial manometer M ' to 

 record the mean arterial pressure, and passes to another T-tube, v, one limb of which 

 projects into a test-tube B. The air in this test-tube will be compressed with a rise 

 of pressure and will serve as a driving force for the blood through the resistance. It 

 thus takes the part of the resilient arterial wall. The other limb of the T-tube passes 

 to the resistance R. This consists of a thin-walled rubber tube (e.g. a rubber finger- 

 stall) which passes through a wide glass tube provided with two lateral tubulures w, w. 

 One of these is connected with a mercurial manometer M 2 and the other with an air 

 reservoir A, into which air can be pumped by the elastic bellows S. When air is in- 

 jected into the outer tube the tube R collapses, and will remain collapsed until the 

 pressure of the blood within it is equal or superior to the pressure in the air surrounding 

 it. It is thus possible to vary at will the resistance to the outflow of the blood from 

 the arterial side. From the peripheral end of R the blood passes at a low pressure 

 and is collected in a vessel N, which is provided with a siphon, and can be made of 

 such dimensions that the blood is siphoned off as soon as 10, 20, or 30 c.c. have collected 

 in the vessel. A lateral branch on the siphon tube leads by a rubber tube to a tambour 

 D. Every time that siphonage occurs there is a change of pressure within the tambour 

 which can be registered by the lever on a blackened surface. THe siphon discharges 

 the blood into a reservoir F, which is kept immersed in a vessel of water maintained 

 at any desired temperature by some source of heat. From the spiral below F, an 

 india-rubber tube leads to a cannula CV, which is placed in the superior vena cava, 

 all the branches of which have been tied. This cannula is provided with a thermometer 

 to show the temperature 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 recording surface we thus have a record of the arterial pressure, 

 of the output of the whole system, as recorded by the tambour, and of the pressure 

 within the right auricle. If desired the simple current measurer described on p. 888 

 can be inserted in the arterial circuit at X, so as to give immediately the output of the 

 left ventricle. 



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 him- 

 self, 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 he 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 

 ^-^-=26,457 c.c. 



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 



