fcATE OF MOVEMENT OF THE BLOOD 213 



55 



quired to absorb 55 c.c. is -- - -1.230 c.c. (1.23L.) or in one minute 



U.4UO X 11, Uo X 1UU 



1.230 



= 3.75 liters. 



0.327 



The methods are admittedly only approximate, but the results are of 

 much interest, mainly because' of the indication they give us as to the 

 amount of blood pumped out by the ventricle with each heartbeat, or 

 during a given period of time. The results have been found to vary 

 considerably ; thus, Krogh and Lindhard 45 give the output of blood per 

 minute as between 2.3 and 8.7 liters, which would correspond, at a 

 pulse rate of 70, to an output per heartbreat of from 40 to 120 c.c. An 

 immediate and very marked increase has been found to occur during 

 muscular work. By comparing the bloodflow through the hand with 

 that through the lungs, an estimate can be formed in a given individual 

 as to the relative magnitude of the peripheral and visceral moieties of 

 blood. Interesting results, which will be referred to later, have been 

 obtained from such measurements. 



The Work of the Heart 



Meanwhile it is of interest to note that we may calculate from the 

 ventricular output of the blood the amount of work that the heart is doing 

 in maintaining the circulation. Of course the calculation is again only 

 approximate, since we have to assume certain figures. If we assume that 

 in a 70-kilogram man the quantity of blood is 4,200 c.c. (see page 85), 

 and that it takes about one minute for all the blood to complete a cir- 

 culation, then the work performed by the left ventricle in one minute 

 will be equal to that done in raising the above quantity of blood to a 

 height corresponding to the mean pressure in the aorta. If we take this 

 pressure as 130 millimeters of mercury, which would correspond to a 

 column of blood 1,755 meters high (13.5x130=1755 mm. blood, or 1.755 

 meter), the work done by the left ventricle would be 1.755x4.2=7.37 

 kilogram-meters in one minute, or in twenty-four hours roughly about 

 10600 kilogram-meters. The work done by the right ventricle is probably 

 about one-third that of the left, this being about the ratio of the pres- 

 sures in the two chambers. The total work of the two ventricles is there- 

 fore about 14000 kilogram-meters. This represents an enormous amount 

 of work; indeed it has been computed that it is sufficient to raise a man 

 of 70 kilograms to about twice the height of the highest skyscraper in 

 New York. The work thus expended in forcing the blood through the 

 capillaries becomes converted by friction in the small blood vessels into 

 heat, the heat equivalent of the above amount of work being roughly 

 about 350 calories (see page 571). 



