ClIAP. II.] 



RESPIRATION. 



365 



When these undulations of the blood-pressure curve are com- 

 pared carefully with the respiratory movements or with the 

 variations of intra-thoracic pressure, it is seen that while in general 

 the blood-pressure rises during inspiration and falls during expiration 

 neither the rise nor the fall of the former is exactly synchronous 

 with either inspiration or expiration. Fig. 59 shews two tracings 

 from a dog taken at the same time, one, a, being the ordinary 

 blood-pressure curve from the carotid, and the other, 6, representing 

 the condition of the intra-thoracic pressure as obtained by carefully 

 bringing a manometer into connection with the pleural cavity. 

 On comparing the two curves, it is evident that neither the 

 maximum nor the minimum of arterial pressure coincides exactly 

 either with inspiration or with expiration. At the beginning of 

 inspiration (i) the arterial pressure is seen to be falling ; it soon 

 however begins to rise, but does not reach the maximum until 

 some time after expiration (e) has begun ; the fall continues during 

 the remainder of expiration, and passes on into the succeeding 

 inspiration. 



This suggests the idea that, while inspiration tends to increase 

 and expiration to diminish the blood-pressure, there are causes 



EXPIR AT/O/V 



INSPIRATION 



FIG. 60. Influence of respiration on the form of the pulse- wave and the medium 

 blood-pressure. The upper curve gives the radial pulse from a healthy man of 

 27 years of age and with an extra- arterial pressure of 70 mm. mercury. The lower 

 curve gives the movements of the chest wall, the points of the recording levers of 

 both instruments being in the same vertical line. It can be seen that during 

 inspiration the pulse-waves diminish in height and become more dicrotic, while 

 during expiration the height of the pulse-waves is increased and their form tends 

 more towards that of the pulse-wave with a raised arterial pressure. 



