392 PRACTICAL PHYSIOLOGY 



M = the mass of the output in grammes = Q multiplied by the 

 specific gravity of the blood. 



Close the clip on the arteriole tube and start the pump. Note the 

 mean pressure H indicated by the manometer M. 



To obtain V inject into the artery, at 1 metre from the capillary 

 tube, 1 c.c. of sat. sol. methylene blue. A side tube is provided 

 for the purpose of making this injection. Note with a stop-watch, 

 or by an electric signal and drum, the time between the injection 

 and the appearance of the blue at the beginning of the capillary 

 tube. 



Having obtained V, the output can be reckoned if the sectional area 

 (a) of the aorta be obtained and the time (t) of a cardiac cycle. 

 Measure the diameter of the artery. Half this and obtain the 

 radius. 



a = irr 2 . * 



Count the number of pulses per minute, and by dividing the number 

 found by 60 obtain t. Then Q = avt. 



Now calculate the work of the pump from the data obtained. The 

 work spent in maintaining velocity is almost negligible in comparison 

 with that spent in overcoming resistance. 



In man the output may be taken as 110 grms., the average aortic 

 pressure as 120 mm. Hg, the velocity of flow in the aorta as 320 mm. 

 per sec. Mercury 13'5 times heavier than blood. 



The right heart is considered as doing one-third of the work of the left 

 heart. 



The total work of the human heart is estimated to be about 24,000 

 kilogramme-metres per day, or 1000 kg.m. per hour. This equals 

 56*6 kilo-calories (425 kg.m. = 1 kilo-calorie). 



In the dog the output can be obtained by estimating the amount of 

 oxygen taken up by the blood from the inspired air in one minute. 

 This can be obtained by Fredericqs' or Zuntz's method (see p. 147). 

 At the same time samples of arterial and venous blood are obtained, 

 and the oxygen difference between the two samples estimated by the 

 blood pump or Haldane's ferricyanide method (see p. 398). The number 

 of heart beats per minute is also counted. Suppose 100 c.c. of oxygen 

 are taken up per minute, the arterial blood contains 5 c.c. per cent. 

 more oxygen than the venous blood, and the heart beats 80 times per 

 minute. Then, as every 100 c.c. of blood carries away 5 c.c. 2 , 2000 



