INFLUENCE OF RESPIRATION ON THE HEART. 219 



the distention of the pulmonary artery is never so excessive 

 as that of the aorta, either because there is less obstacle to 

 the passage of venous blood -through the lungs than through 

 the general capillaries, or because the injecting force of the 

 right ventricle is less than that of the left, or because less 

 blood is supplied by the capillaries to the veins, and by the 

 veins to the right side of the heart. In either case the prin- 

 cipal accumulation is certainly in the arterial system." ] 



The distention of the heart in asphyxia is therefore due to 

 the fact that unaerated blood cannot circulate in the systemic 

 capillaries. When thus distended, its muscular fibres become 

 paralyzed, like any muscle after a severe strain. 



If respiration be resumed at any time before the heart's 

 action has entirely ceased, the organ in a few moments re- 

 sumes its normal function. We first notice a change from 

 the dusky hue it has assumed to a vivid red, which is owing 

 to the circulation of arterial blood in its capillaries. The 

 distention then becomes gradually relieved, and for a few 

 moments the pulsations are abnormally frequent. If we now 

 open an artery, it will be found to contain red blood. An in- 

 strument applied to an artery will show a diminution of 

 arterial pressure and force of the heart's action, if the arrest 

 of respiration has been carried only far enough to moderately 

 distend the heart ; or an increase in the pressure and force of 

 the heart, if its action has been nearly arrested. A few mo- 

 ments of regular insufflation will cause the pulsations to re- 

 sume their normal character and frequency. 



In the human subject, the effects of temporary or perma- 

 nent arrest of respiration on the heart, are undoubtedly the 

 same as those observed in experiments upon the warm-blood- 

 ed animals. In the same way, also, it is possible to restore 

 the normal action of the organ, if respiration be not too long 

 suspended, by the regular introduction of fresh air into the 

 lungs. The numerous examples of animation restored by 



1 DALTON, Lectures on the Physiology of the Circulation, published in the 

 Buffalo Medical Journal and New York Review, Lecture III., April, 1860. 



