SEC. 7. THE EFFECTS OF RESPIRATION ON THE 

 CIRCULATION. 



We have seen, while treating of the circulation, that the blood- 

 pressure curves are marked by undulations, which, since their 

 rhythm is synchronous with that of the respiratory movements, are 

 evidently in some way connected with respiration. 



_ v\ 



FIG. 59. COMPARISON OF BLOOD-PRESSURE CCRVE WITH CURVE OF INTRA-THORACIC 

 PRESSURE. To be read from left to right. 



a is the blood-pressure curve, with its respiratory undulations, the slower beats 

 on the descent being very marked. 6 is the curve of intra-thoracic pressure 

 obtained by connecting one limb of a manometer with the pleural cavity. In- 

 spiration begins at i, expiration at e. The intra-thoracic pressure rises very 

 rapidly after the cessation of the inspiratory effort, and then slowly falls as the air 

 issues from the chest ; at the beginning of the inspiratory effort the fall becomes 

 more rapid. 



