INFLUENCE OF THE RESPIRATORY MOVEMENTS. 151 



the recoil-elevation particularly being distinctly less pronounced. If, 

 however, the forced pressure is maintained, the sphygmographic curves 

 begin to exhibit signs of diminished tension. This is due to the influ- 

 ence of the vasomotor center, acting reflexly through the pulmonary 

 nerves. It must be assumed that forced pressure such as is produced 

 in Valsalva's experiment when continued, exerts a depressing effect 

 on the vasomotor center. Coughing, singing, and reciting act in a 

 manner similar to Valsalva's experiment; the pulse-frequency being 

 at the same time increased. On the conclusion of Valsalva's experi- 

 ment the blood-pressure rises until it exceeds the normal by almost as 

 much as it had before been diminished, to return again to the normal 

 after a few minutes. 



Conversely, when the circulation is more completely emptied by 

 means of J. Miilier's experiment, the sphygmographic curve at first 

 exhibits the characteristic signs of diminished pulse-tension, particularly 

 a higher and more distinct recoil-elevation. After a time, however, 



FIG. 57. The Effect of Marked Expiratory and Insoiratory Pressure on Sphygmographic Curves: C and R, 

 tracings made from the carotid (C) and the radial (R) during Miilier's experiment; Q and Rj, similar tracings 

 made during Valsalva's experiment. The curves were recorded on a tablet attached to a vibrating tuning- 



fork. 



likewise owing to nervous influences, increased tension may manifest 

 itself. In Fig. 57, C and R represent carotid and radial curves recorded 

 during Miilier's experiment, in which the great recoil-elevation clearly 

 shows the diminished tension in the vessels; C l and Rj represent curves 

 taken from the same individual during Valsalva's experiment and clearly 

 show the opposite condition. 



Expiration into a vessel like a spirometer (Waldenburg's respiratory apparatus, 

 for example) filled with compressed air has the same effect as Valsalva s experi- 

 ment, causing after a time a slight lowering of the blood-pressure and a simulta- 

 neous increase in the frequency of the pulse. Conversely, inspiration of rarefied 

 air from the same apparatus acts like Muller's experiment, heightening the effect 

 of inspiration, and it may after a time increase the blood-pressure, which, as the 

 experiment is continued, may remain high or fall again. 



Inspiration of compressed air lowers the mean blood-pressure, and the after- 

 effect is maintained. The pulse during and after the experiment is increased in 

 frequency. Expiration into rarefied air increases the blood-pressure. 



These last-mentioned alterations emanate from the nervous system; they are 

 not produced as readily and are not equally marked in all individuals. 



Exposure to compressed air (in the pneumatic chamber) lowers the pulse- 

 curve: the elasticity-oscillations become correspondingly more distinct, as the 

 recoil-elevation diminishes and finally disappears. At the same time the heart's 



