THE HEART 133 



' The first effect of powerful general muscular action 

 is to drive the blood along the veins towards the heart, 

 and the right auricle and ventricle are at once distended. 

 To pass on the blood through the lungs as fast as it 

 arrives, the right heart must act more frequently and 

 powerfully, and the stimulus to this exists in the 

 increased pressure on its inner surface. For a time 

 there is accumulation in the pulmonary circulation, and 

 while this is the case there is dyspnoea and shortness of 

 breath and panting ; but when the individual is vigorous 

 the circulation in the lungs and system becomes equal- 

 ized, and he gets his second wind, as the term is.' * 



All sudden alterations in the general blood-pressure 

 immediately affect the heart through its nervous con- 

 nections. Thus, on standing up the blood-pressure tends 

 to fall, but the heart beats more rapidly to make up for 

 it. The difference in rate between the horizontal and 

 erect postures, indeed, may amount to 8 or 10 beats 

 per minute, or 500 to 600 beats per hour. One can see 

 from this how great rest is afforded to the heart by 

 maintaining the horizontal position. In slow walking a 

 pulse of 60 per minute goes up to about 100, in quick 

 walking to 140, and on running to about 150 (Mac- 

 kenzie). On the other hand, conditions of high blood- 

 pressure are attended by a slowing of the heart which is 

 partly reflex, and partly the result of prolongation of the 

 'compression period' of the systole from the obstacle 

 offered to the expulsion of the ventricular contents. 



Persistent acceleration of the heart from diminution 

 of vagus inhibition seems sometimes to occur as the 

 * Broadbent, * The Pulse,' p, 77. 



