914 PHYSIOLOGY 



experiment lasted twenty-eight seconds. The amount of blood passing through the 

 lungs per minute was therefore 4-2 litres. This figure represents the output from the 

 right ventricle during one minute, and if the pulse rate is 70 per minute, the output 



per beat will be c ' c ' = 60 c.c. per beat. The figure arrived at in this way for the 



average output of each ventricle in man during rest, thus agrees with the figure obtained 

 by Zuntz. The output of both ventricles is, of course, the same. 



According to Krogh, the ventricular output per minute in man may vary from 2-8 

 litres to 21 litres of blood per minute. The latter is an extreme figure and was obtained 

 in a powerful athelete doing hard work. In the case of Krogh himself, the maximum 

 output was about 12 litres per minute. It is interesting to note that the same perform- 

 ance may be obtained from a dog's heart in the heart-lung preparation, allowing for 

 the difference in size between the hearts of the dog and man respectively. 



CARDIOMETRIC METHOD. Of the various methods which have been devised for 

 recording plethysmographically the changes in the volume of the heart at each beat (as 

 first carried out by Roy), the simplest is that devised by Henderson. The chest and 

 pericardium being opened, a glass cardiometer, of the shape shown in Fig. 407, is slipped 



FIG. 407. Henderson's glass cardiometer. 



over the heart. This cardiometer consists of a glass sphere with a wide opening. To 

 the margin of the opening is tied a rubber diaphragm with a hole in it which accurately 

 fits the heart as it lies in the auriculo-ventricular groove. The tube of the cardiometer is 

 connected with some form of piston recorder or a tambour with a slack membrane. 

 The disadvantage of this method is that the graphic record of rapid and ample changes 

 in volume is one of the most difficult problems in experimental physiology, the inertia 

 and friction of the moving piston tending to deform the shape of the curve obtained. 

 Straub has therefore used a soap bubble as the volume measurer, photographing its 

 edge and using the record as an index to the change in volume. It is possible, how- 

 ever, to obtain a pistol recorder moving sufficiently freely to give a fairly correct re- 

 production of the volume changes of the heart, provided that these do not occur with 

 too great rapidity. It has been suggested by Piper to convert the volume changes 

 into small pressure changes, and to record these latter by one of the methods described 

 above. 



The factors which determine the output of the left ventricle are best 

 studied in the heart lung preparation. In this it can be shown that, pro- 

 vided the venous inflow remains constant, the output is also constant and 

 is unaffected by considerable alterations of arterial resistance and of the 

 rate of the heart. Thus with a moderate venous inflow the output remains 

 constant whether we maintain the average arterial pressure at 60 mm. Hg. 

 or at 160 mm. Hg. It is also unaffected by altering the rate of the heart 

 from 80 beats per minute up to 160, or even 200, beats per minute. On 



