Physiology and biochemistry in modern medicine . le, which can be raised or lowered to a specifiedheight, and with a mercury manometer. The displacement of the writingpoint of the spring manometer corresponding to each 10 mm. Hg ofpressure is then written on the tracing. W,0()l> IRKSSIIRK 127 The tracings taken with such a manometer, as shown in Fig. 24, arequite different from those with the mercury manometer. It will be seenthat now the cardiac waves are decidedly the more pronounced, the respira-tory, being comparatively inconspicuous. Instead of there being a fairlysteady pressure in th
Physiology and biochemistry in modern medicine . le, which can be raised or lowered to a specifiedheight, and with a mercury manometer. The displacement of the writingpoint of the spring manometer corresponding to each 10 mm. Hg ofpressure is then written on the tracing. W,0()l> IRKSSIIRK 127 The tracings taken with such a manometer, as shown in Fig. 24, arequite different from those with the mercury manometer. It will be seenthat now the cardiac waves are decidedly the more pronounced, the respira-tory, being comparatively inconspicuous. Instead of there being a fairlysteady pressure in the arteries, this undergoes very considerable altera-tion during each heartbeat.* Examination of this tracing gives us accurate information regardingthe blood pressure both between the heartbeats—diastolic, as it is called—and during them—systolic. It gives us a means of telling what must bethe dead load of the circulation—that is, the pressure that is constantlypresent—as well as the live load that is superadded to this by each heart-. Fig. 25.—Diagram based on experiments on dogs to show the magnitude of the systolic,diastolic and mean blood pressures at different parts of the circulatory system. O is the lineof zero pressure, and the letters below it indicate the parts of the system to which the curvesrefer. (From Brubaker.) beat. This difference is often called the pressure pulse, and in man itamounts to somewhere about 35 mm. Hg. If we take tracings with aspring manometer from different parts of the arterial tree, we shall findthat, as we travel towards the periphery, the pressure pulse becomes lessand less marked, until finally by the time the capillaries are reached ithas almost entirely disappeared. This decline in the pressure pulse canmoreover be seen to be dependent more largely on a fall in systolic thanin diastolic pressure. In other words, the dead load of the circulation—the diastolic pressure—remains practically constant all along the arte-rial tr
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