THE HEART 99 



Work of Heart. During each cycle of the heart there is ejected 

 from the ventricles a quantity of blood known as the contrac- 

 tion or pulse volume. It varies in the same heart at different 

 times, but on an average must be equal for both ventricles, 

 and must also equal the amount that enters the systemic or 

 pulmonary capillaries during the entire cycle. The amount 

 may be roughly measured by introducing a modified stromuhr 

 between the origins of the coronary arteries and of the innomi- 

 nates. It may also be measured by enclosing the heart in 

 a plethysmograph. It has been estimated for man as being 

 from 50 to 100 c.c. If its weight is taken at 100 grams and the 

 blood in an average man weighs about 5300 grams, it is seen 

 that the pulse volume is equal to about one fifty-third of the entire 

 blood, so that all the* blood of a person passes through the heart 

 in less than a minute. Each pulse volume is injected into the 

 arteries against considerable resistance, so that the ventricle 

 performs work. The amount of work may be calculated by 

 multiplying the weight of the pulse volume into the force 

 exerted by the ventricles. The latter is equal to the pressure 

 under which the pulse volume is expelled. This pressure may 

 be measured in animals by introducing a tube through the 

 external jugular into the ventricle, and connecting with a 

 mercury manometer provided with a valve, so that the maxi- 

 mum pressure may be recorded. The left ventricle exerts more 

 than twice as much power as the right. The exact intra ventric- 

 ular pressure in man has not been determined. It has been 

 estimated as being equal to 0.150 meter of Hg on the left 

 side and to 0.06 meter Hg on the right side. Employing the 

 formula w = pr, and making suitable corrections by multiply- 

 ing by 13.6, thus reducing the mercury column to an equivalent 

 column of blood, it follows that the sum of the work performed 

 by both ventricles is equal to 285.6 gramineters. To this 

 must be added the energy represented by the velocity of the 

 mass ejected into the large bloodvessels leaving the heart. 

 Placing this velocity at 0.5 meter for both aorta and pulmonary 

 artery, the energy represented in mechanical work is estimated 



DV" 



from the formula ~ in which p represents the weight of 



the mass moved, y} ^ 'velocity 'cf iVs moVeine-i?:; and g, the 

 accelerating force 1 of : gravity. 1 "' This "* 'gives" 2.'5'6 ' grammeters 



