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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



The Ventricular Pressure-curve and the Auricular Systole. It is 

 striking testimony to the smoothness of working of the cardiac mechanism, 

 that the curve of intra-ventricular pressure rarely gives any clear indication of 

 the beginning or end of the auricular systole. This event may be expected to 

 increase the pressure within the ventricles ; and, in the curve, the very gentle 

 rise which coincides with the latter and longer part of the ventricular diastole 

 passes into the steep ascent of the commencing ventricular systole by a 

 rounded sweep, which indicates a more rapidly heightened pressure within 

 the ventricle during the auricular systole. As a rule, no angle reveals an 

 instantaneous change of rate to show the beginning or end of the injection of 

 blood by the contracting auricle (see Figs. 107, 108, 109). Occasionally, how- 

 ever, a slight " presystolic " fluctuation of the curve may seem to mark the 

 auricular systole. 1 



The Ventricular Pressure-curve and the Valve-play. It is also 

 exceedingly striking that no curve, whether it be pointed or show the sys- 

 tolic plateau, gives a clear indication of the instant of the closing or open- 

 ing of either valve, auriculo-ventricular or arterial (see Figs. 107, 108, 109). 

 These instants, so important for the significance of the curve, can, however, 

 be marked upon it after they have been ascertained indirectly. A method 

 of general application would be as follows : Two elastic manometers are 

 "absolutely graduated " by causing each of them to record a series of pressures 

 already measured by a mercurial manometer. The two elastic manometers can 

 then be made to mark upon the same revolving drum the simultaneous changes 

 of pressure in a ventricle and in its auricle, or in a ventricle and its artery. 



FIG. 110. Diagram of the differential manometer: A, artery: V, ventricle; D, drum of kymograph, 

 revolving in the direction of the arrow, and covered with smoked paper; L, recording lever in contact 

 with the revolving drum ; S, a spring by which the movement of the lever worked by the disks is trans- 

 mitted to the recording lever. (The working details of the instrument are suppressed or altered for the 

 sake of clearness.) 



The pressure indicated by any point of either curve can then be calculated 

 in terms of millimeters of mercury. That point upon the intra-ventricular 

 curve which marks a rising pressure just higher than the simultaneous pressure 

 in the auricle or artery, may be taken to mark the closing of the cuspid valve 



1 von Frey and Krehl : Op. cit., p. 61. 



