WORK DONE BY THE HEART 



TABLE LVII 



Output and Mean Aortic Velocity of Blood from the Dog's 



Heart (Lovatt Evans.) 



360 



During a short sprint an athlete may have a pulse rate of 180 per 

 minute with an output of 180 c.c. at each beat and an average 

 arterial pressure of 120 mm. Hg. Then for the systemic heart : 



QR =180 X 0-12 X 13-6 = 294 gram-metres. 



and Qi2 (pulmonary) =180 X 0-025 X 13-6 = 61 gram-metres. 



If the time of outflow is considered as three-eighths of each cardiac 

 cycle, of which there are 180 per minute, then the contents of the 

 ventricle, 180 c.c, are shot into the aorta at the rate of 32-4 litres 

 per minute. If the cross-section of the root of the aorta be taken 

 as 625 sq. mm., then the mean aortic velocity will be 540/625 = 

 0-86 metres per second. Now, as blood is expelled only during a 

 period not greater than about three-eighths of the cardiac cycle, 

 the average velocity of expulsion must be, at least, 8/3 times as 

 much as the mean aortic velocity ; hence 



0-86 X 8/3 = 2-3 metres per second. 



Therefore, wv^l2g = 180 X (2-3)2/2 X 9-8 = 48-8 gram-metres. 



That is, the total work on both sides of the heart will be 



Left side. Right side. Total. 



During rest (81-6 + 0-5) + (16-1 + 0-5) =98-7 gram-metres. 



During work (294 + 48-8) + (61 + 48-8) = 452-6 gram-metres 



per beat. 

 = 81-5 kilogram- 

 metres per minute. 



The main fault to be found with this calculation is that the 

 various quantities required are almost impossible to obtain. For 

 instance, the only methods by which the output of the heart in 

 situ can be determined are indirect. Zuntz, by finding the 



7mv^ 



* Calculated from Lovatt Evans' formula 



8 



B. 



24 



