EFFECT OF RESPIRATION ON THE CIRCULATION 



323 



Apparent recuperation with the re-establishment of both normal and 

 respiratory activity may occur, yet later stoppage will come about. Prolonged 

 asphyxiation leaves the body and tissues so clogged with carbon dioxide 

 and other waste products, that the renewal of the vital activity of the nervous 

 centers is under a weakened condition. In such cases it is highly necessary 

 to prolong artificial respiration. Even after asphyxiation of short duration 

 it may be some hours or even days before the body is brought back to its 

 normal level of functional efficiency. 



THE EFFECT OF RESPIRATION ON THE CIRCULATION. 



As the heart, the aorta, and pulmonary vessels are situated in the air- 

 tight thorax, they are exposed to a certain alteration of pressure when the 

 capacity of the latter is varied during respiration. The disturbance of pres- 

 sure which occurs during inspiration causes, first, a .decrease in the intra- 



FIG. 242. Diagram of an Apparatus Illustrating the Effect of Inspiration upon the 

 Heart and Great Vessels within the Thorax. I, The thorax at rest; II, during inspiration; 

 D represents the diaphragm when relaxed; D', when contracted (it must be remembered 

 that this position is a mere diagram), i. e., when the capacity of the thorax is enlarged; H, 

 the heart; V, the veins entering it, and A, the aorta; Rl,Ll, the right and left lung; T, the 

 trachea; M, mercurial manometer in connection with pleura. The increase in the capacity 

 of the box representing the thorax is seen to dilate the heart as well as the lungs, and so to 

 pump in blood through V, whereas the valve prevents reflux through A. The position of 

 the mercury in M shows also the suction which is taking place. (Landois.) 



thoracic pressure, a decrease which affects all the organs of the thorax the 

 lungs, the great blood-vessels, the heart. The expansion of the elastic lungs 

 counterbalances this change in pressure in part, but it never does so entirely, 

 since part of the pressure within the lungs is expended in overcoming their 

 elasticity. The amount thus used up increases as the lungs become more 

 and more stretched, so that the intrathoracic pressure during inspiration, as 



