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TEXT-BOOK OF PHYSIOLOGY. 



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from the auricle during the diastole. At o the pressure suddenly 

 rises passes quickly to its maximum value, (2), which is maintained 

 with' slight variations for some time, and then suddenly (3) begins 

 to fall and, rapidly reaches the line of atmospheric pressure, or even 

 passes below it, becoming negative in fact for a short period. The 

 curve may also be taken as a record of the ventricular contraction, 

 for there are reasons to believe that the two closely coincide through- 

 out their entire course. A characteristic feature of this curve is the 

 more or less horizontal portion comprised between the points 2 and 3, 

 marked by several elevations and depressions, which has been termed 

 the systolic plateau. 



With other forms of elastic manometers, especially those in which 

 the transmission of the intra-ventricular pressure is effected by air 

 or by a combination of air and liquid, this portion of the curve is 



represented by a single peak, which 

 is taken as an indication that the 

 maximum pressure once reached is 

 not maintained, but immediately 

 begins to fall to its original level, 

 notwithstanding the continued con- 

 traction of the ventricle. Those 

 who adhere to this view attribute 

 the plateau to the closure of the 

 orifice of the catheter by the con- 

 tracting and approximating walls 

 of the ventricle. There are reasons 

 for believing, however, that the 

 former curve is the more correct 

 representation of the course of the 

 intra-ventricular pressure. Bayliss 

 and Starling photographed on a 

 moving surface the oscillations of a fluid, a solution of sodium sul- 

 phate, in a capillary glass tube one end of which was closed, the 

 other end placed in connection with an intracardiac catheter, the 

 oscillations representing the variations in pressure. The photogram 

 thus obtained resembles the curve obtained by Hiirthle's membrane 

 manometer. 



The Relation of the Intra-ventricular Pressure Curve to the 

 Intra-cardiac Mechanisms. By itself the curve of the intra- 

 ventricular pressure affords no indication as to events occurring 

 within the heart: i. e., as to the times during the systole, of the 

 closure of the auriculo-ventricular valves and the opening of the 

 semilunar valves, or the times during the diastole, of the closure of the 

 semilunar valves and the opening of the auriculo-ventricular valves. 

 By registering the curve of pressure in the aorta simultaneously 



FIG. 123. V. Curve of the pressure 

 in the ventricle of the dog. 

 (Hiirthle.) A. Curve of the pres- 

 sure in the aorta. The curves 

 were taken simultaneously. s. 

 Tuning-fork vibrations, too per 

 second. 



