INFLUENCE OF PRESSUKE ON THE PULSE-CURVE. 



Midler's Experiment. When the thorax is in the expiratory phase, close the 

 mouth and nose, and take a deep inspiration so as forcibly to expand the chest 

 ( 60). At first the pulse-curves have the characteristic signs of diminished tension, 

 viz., a higher and more distinct dicrotic wave ; then the tension can, by nervous 

 influences, be increased, just as in fig. 93, where C and B, are tracings taken from 



Fig. 93. 



C, curve from the carotid, and R, radial, during Muller's experiment ; C x and R 1? during 

 Valsalva's experiment. Curves written on a vibrating surface. 



the carotid and radial arteries respectively, during Muller's experiment, in which 

 the dicrotic waves, r, r, indicate the diminished tension in the vessels. In C x and 

 Ri, taken from the same person during Valsalva's experiment, the opposite con- 

 dition occurs. 



Compressed Air. On expiring into a vessel resembling a spirometer (see Respiration), 

 (Waldenburg's respiration apparatus), and filled with compressed air, the same result is obtained 

 as in Valsalva's experiment the blood-pressure falls and the pulse-beats increase ; conversely, 

 the inspiration from this apparatus of air under less pressure acts like Muller's experiment, i.e., 

 it increases the effect of the inspiration, and afterwards increases the blood-pressure, which may 

 either remain increased on continuing the experiment, or may fall (Lenzmann). 



The inspiration of compressed air diminishes the mean blood-pressure (Zuntz), and the after- 

 effect continues for some time. The pulse is more frequent both during and after the experi- 

 ment. Expiration in rarefied air increases the blood- pressure. The effects which depend upon 

 the action of the nervous system do not occur to the same extent in all cases. Exposure to 

 compressed air in a pneumatic cabinet lowers the pulse-curve, the elastic vibrations become 

 indistinct, and the dicrotic wave diminishes and may disappear [v. Vivenot). The heart's beat 

 is slowed and the blood -pressure raised {Bert). Exposure to rarefied air causes the opposite 

 result, which is a sign of diminished arterial tension. 



Pulsus Paradoxus. Under pathological conditions, especially when there is union of the 

 heart or its large vessels with the surrounding parts, the pulse during inspiration may be 



Fig. 94. 

 Pulsus paradoxus (after Kussmaul). E, expiration ; J, inspiration. 



extremely small and changed, or may even be absent (fig. 94). This condition has been called 

 pulsus paradoxus (Gricsinger, Kussmaul). It depends upon a diminution of the arterial lumen 

 during the inspiratory movement. Even in health, it is possible by a change of the inspiratory 

 movement to produce the p. paradoxus (Riegel, Sommerbrodt). 



75. INFLUENCE OF PRESSURE ON THE PULSE-CURVE. It is most important to know 

 the actual pressure which is applied to an artery while a sphygmogram is being taken. The 

 changes affect the form of the curve as well as the relation of individual parts thereof. In fig. 

 95, a, b, c, d, e are radial curves ; a was taken with minimal pressure, b with 100, c 200, d 250, 

 and e 450 grams pressure, while A, B, C, D show the relations as to the time of occurrence 

 of the individual phenomena where the weight was successively increased. The study of these 

 curves yields the following results : (1) When the weight is small, the dicrotic wave is 

 relatively less ; the whole curve is high ; (2) with a moderate weight (100 to 200 grams) the 

 dicrotic wave is best marked, the whole curve is somewhat lower ; (3) on increasing the weight 

 the size of the dicrotic wave again diminishes ; (4) the fine elastic vibrations preceding the 

 dicrotic wave appear first when a weight of 220 to 300 grams is used ; (5) the rapidity of the 



