406 PHYSIOLOGICAL, REGULATIONS 



At simultaneous points rate of cardiac output is correlated with 

 heart frequency ("W, fig. 185). The points during exercise (in- 

 creasing loads) and the points after exercise (decreasing loads) 

 fall upon a single line W. The changes in rate of cardiac output 

 (V) and in heart frequency (T) therefore form similar halves of 

 two net equilibration diagrams. Both in transitional and in re- 

 covery states the initial changes are the fastest. 



When cardiac output is correlated with oxygen consumption 

 (X), the points fall along a very narrow loop. The shape of the 

 loop is an indication of the great deceleration of oxygen consump- 

 tion at the beginning of recovery (curve U). Again the initial 

 changes of state are the fastest. 



The similarities among the three components are much greater 

 than anyone would anticipate in figure 176. Not only the loads in 

 relation to time, but the loads in relation to one another and in 

 relation to their rates of change are of one pattern. But the mag- 

 nitudes are very different when computed, as all of them are, in 

 per cent of the rate or frequency in the control state. Possibly 

 relative scales that would make the magnitudes equal are justified; 

 further utility in such an equalization would be found if it turned 

 out that in a variety of kinds and intensities of exercise and of other 

 circumstances, uniform proportions prevailed among the three 

 components. 



Figure 185 shows that cardiac output changes 3.9 times as much 

 as heart frequency. Or, for each 1.0 per cent of increment in heart 

 beat 3.9 per cent of additional blood circulates. This is the slope 

 of line W. Similarly the slope of line X is such that cardiac output 

 changes 0.44 times as much oxygen consumption. And, oxygen 

 consumption augments 8.9 times as much as heart frequency. 



The three components are, indeed, commonly recognized to be 

 related to one another by the fact that their ratios have names: 

 (a) oxygen consumption/cardiac output = arterio-venous oxygen 

 difference; (b) oxygen consumption/heart frequency ^= oxygen 

 pulse; (c) cardiac output/heart frequency = stroke volume. Each 

 of these ratios of absolute units varies somewhat during the exer- 

 cise, since none of the three regressions is exactly linear and 

 through the origin. 



The acceleration in exchange of the three components are simi- 

 lar, within about 15 per cent, for uniform fractions of the loadings ; 

 that is, the three dash lines of figure 185 are superimposable if 



