54 CIECULATION OF THE BLOOD. 



cases which present considerable febrile movement, the patient is generally in the recum- 

 bent posture. The variations induced by violent exercise are easily recognized, while 

 those dependent upon temperature, the condition of the digestive system, etc., are so 

 slight that they may practically be disregarded. It is necessary to bear in mind, how- 

 ever, 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 extraor- 

 dinarily rapid or slow. 



Influence of Respiration upon the Action of the Heart. The relations between the 

 functions of circulation and respiration are very intimate, and 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 circulation 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 interest and importance. 



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 circumstances, we have the respiration entirely at our com- 

 mand 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, and 

 the distention 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 movements of the mercury will be noted at each 

 action of the heart, indicating that the organ is acting with abnormal vigor. If respira- 

 tion be still discontinued, the engorgement becomes intense, the heart at each diastole 

 being distended to its utmost capacity. It now becomes incapable of emptying itself, 

 the contractions become very unfrequent, perhaps three or four in a minute, and are 

 progressively enfeebled. The organ 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 en- 

 tirely cease. 



The arrest of the action of the heart, under these circumstances, is chiefly mechani- 

 cal. The unaerated blood passes with difficulty through the capillaries of the system, 

 and, as the heart is constantly at work, the arteries become immensely distended. This 

 is proven by the great increase in the arterial pressure while these vessels are full of 

 black blood. If we now closely examine the heart and great vessels, we are able to 

 note distinctly the order in which they become distended. These phenomena were par- 

 ticularly noticed and described by Prof. Dalton, and they demonstrate conclusively that, 

 in asphyxia, the obstruction to the circulation commences, not in the lungs, as is com- 

 monly supposed, but in the capillaries of the system, and is propagated backward to 

 the heart through the arteries. 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, the muscular fibres of the heart 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 



