250 PHYSIOLOGY. 



Anatomical differences, then, in the heart musculature permit the 

 conclusion that the left heart, the walls of which are thicker, has more 

 force than the right heart. It is reasonable to state from these 

 premises that where the ventricular walls are three times thicker in 

 one-half of the heart than they are in the other, that one must have a 

 thrice greater systolic force than the other half. 



The work of the heart is usually expressed in kilogrammeters. A 

 kilogrammeter is equal to 7.24 foot-pounds. To estimate the work of 

 the heart according to Dr. Leonard Hill, the mean pressure and 

 velocity in the aorta and the volume of blood ejected by the ventricle 

 must be obtained. 



If W be the work done during systole of the left ventricle in gram 

 centimeters ; Q, the volume of the output in cubic centimeters ; M, the 

 mass of the output in grams; P, the specific gravity of the blood 

 (.-. M = PQ); V, the mean velocity in the aorta; H, the mean 

 aortic pressure in grams per centimeter; g, the acceleration due to 

 gravity =--981 centimeters per second, then 



MV 2 

 W=.QH + - 



= QH 



The mean aortic pressure may be put down as 12 centimeters of 

 mercury (specific gravity of mercury = 13.5). The volume of the 

 systolic output is about 110 cubic centimeters. Substituting these 

 data in the above equation one obtains : 



1.05 X HO X 32 2 



W = 110 + 12 + 13.5 H - = 17.880 gram cen- 



2 X 981 



timeters. 



If in the case of the right ventricle the mean pressure in the 

 pulmonary artery be taken to be 4 centimeters of the mercury, the 

 work of that ventricle will be one-third of that of the left ventricle. 

 Thus, the total work of each systole of the heart will be 17,880 X % 

 23,640 gram .centimeters, and the total work of the heart will be 

 per day about 24,000 kilogrammeters, or 1,000 kilogrammeters per 

 hour, or the equivalent of about %o of the whole amount of heat pro- 

 duced in the body. 



