152 INFLUENCES OF PRESSURE ON SPHYGMOGRAPHIC TRACINGS. 



action becomes slower and the blood-pressure is raised. Exposure to rarefied air 

 has the opposite effect as the sign of diminished tension in the arterial system; 

 but only when as a result the breathing is enfeebled and the pulse is accelerated. 

 Pathological. In the presence of adhesions between the heart and the large 

 blood-vessels, on the one hand, and the surrounding structures on the other, the 



FIG. 58. Paradoxical Pulse (after Kussmaul). 



pulse may be much diminished in size and otherwise altered during inspiration r 

 or it may even disappear altogether. This phenomenon has been called the 

 paradoxical pulse. It is due to flattening of the subclavian artery in consequence 

 of elevation of the first rib. Varieties of this pulse can be produced also in healthy 

 individuals by voluntary alteration of the breathing during inspiration. 



THE INFLUENCES OF PRESSURE ON THE SHAPE OF SPHYG- 

 MOGRAPHIC TRACINGS. 



The changes induced in the movement of the pulse by increasing the pressure 

 upon it affect both the shape of the sphygmographic curves and their time-rela- 

 tions. Fig. 59 shows at a, b, c, d and e a series of radial curves; a was taken 

 with a minimal pressure and the remainder with a pressure of 100, 200, 250 

 and 450 grams respectively. The curves A and B, on the other hand, show the 

 time-relations of curves taken when the pressure was progressively increased. A 

 study of these curves yields the following results : 



FIG. 59. Variations in the Shape of Sphygmographic Curves Produced by Increasing the Pressure. 



1. With a small load the recoil-elevation is relatively indistinct; the entire 

 curve appears high. 



2. With a moderate load, about from 100 to 200 grams, the recoil-elevation 

 is most distinct; the entire curve appears somewhat smaller. 



3. As the load is increased, the height of the recoil-elevation diminishes. 



4. The smaller elasticity-oscillation immediately preceding the recoil-elevation 

 manifests itself only when the load becomes considerable (from 200 to 300 grams). 



5. The quickness of the pulse varies as the load is increased, the time required 

 for the development of the ascending limb being shortened, and that required for 

 the descending limb prolonged. 



6. The height of the entire curve diminishes as the load increases. 



These points sufficiently emphasize the importance of taking the load of the 

 registering instrument into consideration and the necessity of indicating the actual 



