A text-book of physiology for medical students and physicians . threenegative waves. Of the three positive waves, the a wave marks, *See Mackenzie, The Study of the Pulse, 1902; also Lewis, in Hills Further Advances in Physiology, New York, 1909. THE PULSE. 521 undoubtedly, the contraction of the auricle, but in order tolocate this wave or, indeed, to interpret at all the complicatedvenous pulse, it is necessary to have a simultaneous tracing ofthe arterial pulse, preferably the carotid, or of the apex beat ofthe heart. Either of these latter tracings enables one to markupon the venous pulse t
A text-book of physiology for medical students and physicians . threenegative waves. Of the three positive waves, the a wave marks, *See Mackenzie, The Study of the Pulse, 1902; also Lewis, in Hills Further Advances in Physiology, New York, 1909. THE PULSE. 521 undoubtedly, the contraction of the auricle, but in order tolocate this wave or, indeed, to interpret at all the complicatedvenous pulse, it is necessary to have a simultaneous tracing ofthe arterial pulse, preferably the carotid, or of the apex beat ofthe heart. Either of these latter tracings enables one to markupon the venous pulse the point at which the ventricular systolebegins, and the wave immediately preceding this point mustbe due to the auricular contraction, the a wave (Figs. 217 and218). Following the rise of the a wave there is a fall, the firstnegative wave, which is clue to the auricular relaxation. Theinterpretation of the other two positive and negative waveshas been the subject of much discussion. Mackenzie, one ofwhose tracings is reproduced in Fig. 218, believed that the. Fig. 217.—Simultaneous tracings of the carotid and venous pulses. In the venoustracing (internal jugular) a indicates the auricular wave due to the contraction of the auri-cle; c is the carotid wave due (Mackenzie) to an impulse from the neighboring carotidartery; v is the ventricular wave due to the checking or stagnation of the flow into theauricle as this chamber fills during the period of closure of the auriculoventricular valves;x, dilatation due to auricular relaxation; y, the period of ventricular diastole. (Mackenzie.) c wave is due simply to the pulse in the neighboring carotidartery, and that, therefore, it has no significance in regard tochanges within the heart itself. Careful records made by otherobservers show, however, that this explanation is c wave begins in the jugular before the arterial pulse wavereaches the carotid, hence this wave cannot be due wholly tothe carotid pulse. As is sho
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