INFLUENCE OF RESPIRATION ON THE HEART. 217 



It is necessary to bear in mind, however, the variations which 

 exist in the sexes, and at different periods of life, as well as 

 the possibility of individual peculiarities, when the action of 

 the heart may be extraordinarily rapid or slow. 



Influence of Respiration upon the Action of the Heart. 

 The relations between the functions of circulation and respi- 

 ration are very intimate. One function cannot 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. We shall also find that circu- 

 lation is impossible if respiration be permanently arrested. 

 When respiration is imperfectly performed, the action of the 

 heart is slow and labored. All physicians are familiar with 

 the slow, full pulse, indicating labored action of the heart, 

 which occurs in profound coma. The effects of arrest of 

 respiration are marked in all parts of the circulatory system, 

 arteries, capillaries, and veins ; but the disturbances thus pro- 

 duced all react upon the heart, and the modifications which 

 take place in the action of this organ are of the greatest in- 

 terest and importance. 



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

 respiration be kept up, though the pulsations are increased in 

 frequency and diminished in force, after a time they become 

 perfectly regular, and continue thus as long as air is ade- 

 quately supplied to the lungs. Under these circumstances 

 we have the respiration entirely at our command, and can 

 study the effects of its arrest upon the heart with the greatest 

 facility. If we arrest respiration, we observe the following 

 changes in the action of the heart : 



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, a condition 

 which rapidly increases. For a time its contractions are 

 competent to discharge the entire contents of the left ventri- 

 cle into the arterial system, and a cardiometer applied to an 



