1008 PHYSIOLOGY 



When exercise is discontinued the pulse-rate and blood pressure rapidly 

 fall to normal, the return being quicker in the case of a trained individual, 

 as is seen in the Table quoted above. 



SECOND WIND. It is a familiar experience that in a running race of 

 any duration the competitors after some time become less distressed than at 

 the commencement of the race. The runner is now said to have got his 



FIG. 473. Curve showing the effect of a sudden rise in the arterial resistance on 

 the output and volume of the ventricles. Systole causes a downward movement 

 of the lever. 



H, heart volume ; BP, arterial blood -pressure ; s, signal showing duration of 

 stimulation of splanchnic nerve ; T, time-marker, 10 sees. 



' second wind,' and can continue running with comparative comfort. There 

 are several factors which may account for this accommodation. In the first 

 place, as a result of the production of metabolites in the contracting muscles, 

 their vessels may be more dilated, so that the flow of blood through them is 

 easier. More important is the change in the heart accompanying the onset 

 of second wind. As Pembrey and Cook have shown, the onset of second 

 wind is always attended with a diminution in the pulse-rate. At the same 

 time there is an alteration in the respiratory quotient. During distress 

 the respiratory quotient is high, i.e. more carbon dioxide is being given out 

 than oxygen taken in. As the distress diminishes, the respiratory quotient 

 also falls. The improved action of the heart may be partly due to the 

 increased coronary circulation, partly to the entry of adrenaline into the 

 circulation. 



