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



constitutes the mass of the spring and the muscles of the heart the spring 

 itself, but the energy which is imparted to the blood, and therefore to the 

 body as a whole, is immediately absorbed so that the vibrations appear to be 

 dead beat. It is nevertheless true that the resistance variation, though not 

 to be expressed by so simple an equation as that quoted above, can be treated 

 in a similar manner, and for a heart cycle, consisting as it does of a number of 

 vibrations, superimposed or consecutive, between two so-called heart beats, a 

 process of integration can be carried out, and the result will give a quantity 

 from which the periodic terms vanish, and which has a value proportional to 

 a (velocity) 2 , i.e.. to the kinetic energy imparted to the body during the cycle. 



The process of obtaining the kinetic energy of recoil of the body resolves 

 itself, therefore, into the measurement of an area bounded by the heart curve 

 and the zero axis, dividing this by the time, and expressing the result in any 

 desired units of energy, by comparing with a similar area divided by time, 

 given by the vibrating spring of known energy. 



The kinetic energy contained in the spring was found from the relation 

 %M.p 2 d-, where d is the amplitude of the spring and M the effective mass 

 which is maintained in vibration with a periodicity oip' I2ir. This corresponds 

 during calibration to an amplitude in the Einthoven string of a. 



The photographic record shows an amplitude of b, so that the kinetic energy 

 of the spring as recorded is : — 



M.fd 2 bj2a. 



In the case under consideration this quantity works out to 22 x 10 4 ergs 

 and may be measured by the mean ordinate of the spring curve — say Y. 



Dealing now with the heart curve, examination is made over a complete 

 breathing cycle of six heart beats, and the mean ordinate for these is obtained 

 (fig. 3, B). Calling this y, the kinetic energy exhibited in the body corresponds 



to y/Yx 22 x 10 4 ergs 



and this is completely absorbed, the time corresponding to it being t seconds. 

 Hence the kinetic energy produced averages for a breathing cycle 



y/Yt x 22 x 10 4 ergs per sec. 



In this determination y/Y = J and t = 4'23 sees., so that the heart output 

 creates a kinetic energy in the body of 



2 - 6 x 10 4 ergs per sec. 



or CMS gramme-metres per heart cycle. 



The figures obtained do not represent the total kinetic energy of the heart 

 but are, we suggest, proportional to it. They must not, therefore, be compared 

 directly with the work done by the heart, which, as given by Starling (12), is 



