130 AN AMERICAN TENT-BOOK OE PHYSIOLOGY. 



this descent is often steepest in its middle part. Such a peaked curve would 

 indicate, of course, that there is no such thing as the maintenance, daring any 

 large part of the systole of the ventricles, of a varying but high pressure. 

 The experienced observer who is the chief defender of the peaked curve holds 

 the plateau to be a product either of too much friction within the manometer 

 tubes, or of a faulty position of the cannula within the heart, whereby com- 

 munication with the manometer is, for a time, cut off. The able and more 

 numerous adherents of the plateau, on the other hand, attribute the failure 

 to obtain it to the sluggishness of the instrument employed, or to an abnor- 

 mal condition of the heart. Recent comparative tests of elastic manometers, 

 and other studies, would seem to show that the curves obtained by liquid 

 transmission, and which exhibit the plateau, afford a truer picture of the 

 general course of the pressure within the ventricles than the peaked curves 

 written by means of air. 



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 pit -sure within the ventricles; and, in the curve, the very gentle 

 pise 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. 22, 23, 24). 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. 22, 23, 24). 

 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 

 tlnn 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. 

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

 in terms of millimeter- 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 

 or the opening of the semilunar valve, as the case may be. By a converse 

 process, the moment of opening of the cuspid valve, or of closing of the semi- 

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



