HEART ACTION ON RESPIRATION 403 



column of smoke will be seen to pulsate. These movements may 

 be timed with the pulse. 



If a simultaneous record be obtained of the heart beat and of 

 the movements of the air in the external respiratory passages 

 (e.g. nares), it will be seen that there are three phases of the cardiac 

 cycle in which the influence of the heart on the movements of the 

 air column are manifest : — 



(1) At the beginning of ventricular systole intrapleural pressure 

 is suddenly increased. At this moment the ventricles are closed 

 cavities. 



(2) During ventricular systole intrapleural pressure decreases as 

 systole proceeds. 



(3) During ventricular diastole there is a gradual increase of 

 intrapleural pressure. 



These phases may be seen easily in the smoke-filled tube referred 

 to above, viz. (1) smoke-level suddenly rises when the heart beats ; 

 (2) smoke-level drops ; (3) smoke-level slowly rises. During the 

 period of passive diastole the smoke-level remains steady. 



If a bronchitic patient has a plug of nuicus in a small air passage 

 near the heart, every time air is forced past the plug by the cardio- 

 pneumatic movements the air will be thrown into vibration, and a 

 murnun- will be heard very similar in character to a cardiac 

 nuirmur. 



It is alleged that the movement of air produced in this way by 

 heart action is quite sufficient to keep up the necessary gaseous 

 exchange in hibernating animals. 



^6—3 



