WORK 63 • 



work consists in raising the blood from a region of low to a 

 region of high pressure, and in imparting to the same 

 blood a certain velocity. The work performed by the left 

 side of the heart, at each beat, is expressed approximately 

 by the formula — 



W = QR + "^ 



where W is the work, Q the quantity of blood driven out 

 at each beat, R the average arterial resistance, w the mass 

 of blood moved, V its velocity immediately after it has been 

 discharged, and g the acceleration due to gravity. A 

 similar formula gives the work done by the right side, the 

 only factor which is different being R. 



On the basis of this formula, the work done by the resting 

 heart at each beat has been estimated at 100 grammeters 

 per beat, or about 7,200 grammeters per minute. During 

 exercise, this figure is greatly increased owing to the 

 increased output, the increased arterial pressure, and the 

 increased velocity imparted to the blood. 



For measuring the output' of the ventricle at each beat 

 in the intact animal, only indirect methods are available. 

 One of these is Zuntz's Method. 



Two data are necessary — - 



1. The amount of oxygen leaving the lung in a given time. 



2. The difference in the oxygen content of arterial and 

 venous blood. In the case of a horse, it was found that 

 the arterial blood contained 10-33 per cent, more oxygen 

 than venous blood, or in other words that 100 c.c. of blood 

 in passing through the lungs had absorbed 10-33 c.c. of 

 oxygen. Since 2732 c.c. of oxygen was absorbed from the 

 lungs in one minute, the amount of blood which flowed 

 through the lungs in that period was — 



100x2733 ^.,.„,., 

 — ^K^r, — = 26-457 litres. 

 lU-oo 



