INFLUENCE OF RESPIRATION ON THE BLOOD-PRESSURE 283 



SECTION VII. THE INFLUENCE OF RESPIRATION ON THE BLOOD- 

 PRESSURE. 



We have already stated, in treating of arterial blood-pressure 

 (p. in), that a normal tracing shows a series of waves corresponding 

 with the respiratory movements. 



The relationship between the respiratory phases and the rise and 

 fall of the blood-pressure is not by any means a simple and invariable 

 one. It depends upon a number of factors, which need not be 

 equally influential under different conditions or in different animals 

 (Lewis). Something depends upon the rate, something upon the 

 relative preponderance of costal and abdominal respiration, and 

 something probably upon the size of the animal. For instance, an 

 inspiratory rise of blood-pressure occurs in man with pure dia- 



Fig. 127. Respiratory Waves in the Blood-Pressure: Simultaneous Tracings of 

 Movements of Respiration and of Radial Pulse in Human. Subject (Lewis). In 

 A the respiration was diaphragmatic; in B, costal. In A the respiratory tracing 

 was taken from the abdominal wall; in B, from the chest. 



phragmatic, and a fall with pure thoracic, breathing (Fig. 127). In 

 cats with fairly fast and not very deep respiration the blood-pressure 

 rises in expiration and sinks in inspiration. With deep and slow 

 respiration the opposite effect may, upon the whole, be seen. In 

 dogs, according to Einbrodt, although the mean blood-pressure is 

 falling for a short time at the beginning of inspiration, it soon reaches 

 its minimum, then begins to rise, and continues rising during the 

 rest of this period. At the commencement of expiration it is still 

 mounting, but soon reaches its maximum, begins to fall, and con- 

 tinues falling through the remainder of the expiratory phase. 



A partial explanation is afforded by a consideration of the mechan- 

 ical changes produced in the thorax by the respiratory movements. 

 Of these, the influence of variations in the intrathoracic pressure 

 on the filling of the heart is of special importance. With deep 

 abdominal breathing the changes of intra-abdominal pressure also 



