OH. xxiv.] RESPIRATION AND BLOOD-PRESSURE. 3 6 5 



the amount passing through the right ventricle, which also exerts 

 a similar suction action, and through the lungs into the left- 

 auricle and .ventricle, and thus into the aorta. This all tends to 

 increase the blood-pressure. The effect of the diminished pressure 

 upon the pulmonary vessels will also help towards the same end, 

 i.e., an increased flow through the lungs, so that, as far as 

 the heart and its veins are concerned, inspiration increases the 

 blood-pressure in the arteries. The effect of inspiration upon the 

 aorta, and its branches within the thorax, would be, however, 

 the contrary ; for as the pressure outside is diminished, the vessels 

 would tend to expand, and thus to diminish the tension of the 



KO- 3 2 7- Comparison of blood-pressure curve with curve of intra-thqracic pressure. (To 

 be read from left to right.) a is the curve of blood-pressure with its respiratory undu- 

 lations, the slower beats on the descent being very marked ; b is the curve of intra- 

 thoracic pressure obtained by connecting one limb of a manometer with the pleura! 

 cavity. Inspiration begins at i and expiration at . The intra-thoracic pressure rises 

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

 air issues from the cheat ; at the beginning of the inspiratory effort the fall becomes 

 more rapid. (M. Foster.) 



blood within them, but inasmuch as the large arteries are capable 

 of little expansion beyond their natural calibre, the diminution of 

 the arterial tension caused by this means would be insufficient to 

 counteract the increase of blood-pressure produced by the effect 

 of inspiration upon the veins of the chest, and the balance of the 

 whole action would be in favour of an increase of blood-pressure 

 during the inspiratory period. But if a blood-pressure tracing 

 be taken at the same time that the respiratory movements are 

 being recorded, it will be found that, although speaking generally 

 the arterial tension is increased during inspiration, the maximum 

 of arterial tension does not correspond with the acme of inspira- 

 tion (fig. 327). In fact, at the beginning of inspiration the 



