INFLUENCE OF RESPIRATION ON THE, BLOOD-PRESSURE 289 



of the central end of the vagus at a time when no ' spontaneous 

 respiratory movements are going on. This has been observed, for 

 instance, in cats during resuscitation of the brain after a period of 

 anaemia. In man also, in a case of Cheyne- Stokes respiration accom- 

 panied by hiccup, it was seen that the hiccup persisted during the 

 periods of apncea. If the respiratory centre is the centre 'for the 

 hiccup reflex, it can therefore be excited by afferent nervous im- 

 pulses at a time when it is not excited by the normal chemical 

 stimulus (MacKenzie and Cushny). 



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- 



Insp. 



Inso - 



(\ ' A A A 



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 



19 



