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 z 

 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., 



12=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. 



