WORK OF HEART 



281 



where W (gram-metres) is the work done at each stroke, w is the 

 weight in grams and Q the quantity of fluid in c.c. expelled at 

 each stroke ; R is the average resistance of the circuit, v (metres 

 per sec.) is the velocity of expulsion, and g is the acceleration 

 due to gravity=9-8 metres per sec. per sec. That is, QR repre- 



wv 



sents the resistance pressure (r in Fig. 60) and - - (v in Fig. 60) 



& 



the velocity pressure while is the energy expended in overcoming 

 the resistance to outflow at the orifice of the pump. 



FIG. 61. Diagram of a simple force pump (outer circuit.) to compare with diagram 

 of circulation from left side of heart (inner circuit). 



If we take average figures for the left heart as follows : 

 Q=60 c.c., 

 ,R=100 mm. Hg pressure in aorta 



=0-1 X13-6 gram-metres (1 c.c. of Hg weighs 

 13-6 grams), 



the expression QR may be evaluated as 



60 xO-1 m. x 13-6 =81 -6 gram-metres. 



