290 Lieut. -Colonel C. B. Heald and Major W. S. Tucker. 



Yandell Henderson's curve reads from left to right, the record of fig. 3 reads 

 from right to left. 



Theoretical Considerations. 



The maintenance of life depends ultimately upon the efficiency of the 

 circulation. 



Since circulation is maintained by the pumping action of the heart, any 

 measurement of its output gives an effective method of testing the controlling- 

 engine of the body. 



Yandell Henderson used the displacements in the body recoil in an attempt 

 to measure the volume discharged from the heart per unit weight of the body 

 at each contraction. Thus, a body of weight W would suffer a displacement 

 D, corresponding to the propulsion of blood of weight w displacing an amount 

 d at each heart contraction, where 



w = WB/d. 



With accurate measurements of body displacement a figure is thus obtained 

 proportional to the volume of the discharge per systole. It is obvious, 

 however, that the actual work done in producing the movements of the body 

 is not the reaction movement of the left ventricle only, but the algebraic 

 sums of all the movements of blood or body fluids during the period of 

 estimation. 



The difference between our measurements and those of Yandell Henderson 

 can now be clearly indicated. His curves are effective indications of the- 

 potential energy in the body at any moment, and changes in such energy are 

 proportional to systolic discharge. The curves we obtain are indications of 

 the complementary kinetic energy of the body, changes in which are propor- 

 tional to the changes in potential energy. If Yandell Henderson's curves, 

 therefore, measure systolic discharge, the same claim can be made for the 

 curves given by the hot-wire microphone. 



The advantage of obtaining kinetic energy curves rather than those of dis- 

 placement shows itself in one important way. The displacements of the- 

 body produced by causes other than those due to heart action may be consider- 

 able. In the act of breathing, for example, the movements obtained may be 

 many times greater than those clue to propulsion of the blood. For this- 

 reason, Yandell Henderson took special precautions, such as holding the 

 breath or causing the patient to blow steadily through a whistle. In our 

 case, however, we are concerned with velocities rather than displacements, 

 and the velocities in the body resulting from breathing are so small as to be 

 negligible. The same applies also to slow muscular movements in the body r 

 incidental on digestion, etc. Velocities of the air resulting from the- 



