INFLUENCE OF RESPIRATION ON ACTION OF THE HEART. 51 



possibility of individual peculiarities, when the action of the heart is extra- 

 ordinarily rapid or slow. 



Influence of Respiration upon the Action of the Heart. The relations be- 

 tween the circulation and respiration are very intimate and one process can 

 not go on without the other. If circulation be arrested, the muscles, being 

 no longer supplied with fresh blood, soon lose their contractile power, and 

 respiration ceases. Circulation, also, is impossible if respiration be perma- 

 nently arrested. When respiration is imperfectly performed, the action of 

 the heart is slow and labored. The effects of arrest of respiration are marked 

 in all parts of the circulatory system, arteries, capillaries and veins ; but the 

 disturbances thus produced all react upon the heart. 



If the heart be exposed in a living animal and artificial respiration be 

 kept up, although the pulsations are increased in frequency and diminished 

 in force, after a time they become perfectly regular and continue thus so 

 long as air is adequately supplied to the lungs. Under these conditions, res- 

 piration is entirely under control and the effects of its arrest upon the heart 

 can easily be studied. If respiration be interrupted, the following changes 

 in the action of the heart are observed : For a few seconds pulsations go 

 on as usual, but in about a minute they begin to diminish in frequency. 

 At the same time, the heart becomes engorged with blood and the disten- 

 tion of its cavities rapidly increases. For a time its contractions are com- 

 petent to discharge the entire contents of the left ventricle into the arterial 

 system, and a cardiometer applied to an artery will indicate a great 

 increase in the pressure of blood. A corresponding increase in the move- 

 ments of the mercury will be noted at each contraction of the heart, indi- 

 cating that the organ is acting with abnormal vigor. If respiration be still 

 interrupted, the engorgement becomes intense, the heart at each diastole 

 being distended to its utmost capacity. It now becomes incapable of empty- 

 ing itself, the contractions become very unfrequent, perhaps three or four in 

 a minute, and are progressively enfeebled. The org^an is dark, almost black, 

 owing to the circulation of venous blood in its substance. If respiration be 

 not resumed, this distention continues, the contractions become less frequent 

 and more feeble, and in a few minutes they cease. 



The arrest of the action of the heart, under these conditions, is chiefly 

 mechanical. The unaerated blood passes with difficulty through the capilla- 

 ries of the system, and as the heart is constantly at work, the arteries be- 

 come largely distended. This is shown by the great increase in the arterial 

 pressure while these vessels are full of black blood. If, now, the heart and 

 great vessels be closely examined, the order in which they become distended 

 is readily observed. These phenomena show that in asphyxia the obstruction 

 to the circulation begins, not in the lungs, as is commonly supposed, but in 

 the capillaries of the system, and is propagated backward to the heart 

 through the arteries (Dalton). The distention of the heart in asphyxia is 

 therefore due to the fact that unaerated blood can not circulate freely in the 

 systemic capillaries. When thus distended, the heart becomes paralyzed, like 

 any muscle after a severe strain. 



