196 EXDOCARDIAC PRESSURE. [BOOK i. 



Fig. 42 gives a curve of endocardiac pressure of the left 

 ventricle of the dog obtained by this 

 method. The recording surface is 

 travelling quickly, and the movements 

 of the lever are not great. 



12 345 The manometer of Gad differs 



FIG. 42. CURVE OF PRESSURE from that of Hiirthle in the membrane 

 IN THE LEFT VENTRICLE OF being replaced by a thin, elastic disc 

 THE DOG, HURTHLE'S MEM- f mpfal 



BRANE-MANOMETER. 



In the instrument of frey and 



Krehl, which is a modification of one by Tick, the transmission 

 is effected partly by fluid and partly by an air tambour, the 

 button of which presses against a horizontal steel spring. 



A catheter, filled with fluid to prevent clotting and introduced into 

 a cavity of the heart, is connected with a glass cylinder, maintained 

 carefully in a vertical position, the lower half of which is tilled with 

 the same fluid as is the catheter. The upper half of the cylinder, con- 

 taining air only, is connected by a very narrow, in fact a capillary tube, 

 with a small tambour. The changes of pressure within the heart are 

 transmitted through the fluid of the catheter to the air in the cylinder, 

 and so to the air in the tambour, the membrane of which moves 

 accordingly in and out. A button on the membrane presses on a hori- 

 zontal steel spring, and the small movements of the membrane thus 

 transmitted to the spring are recorded by means of a magnifying 

 lever. 



Other instruments have been employed by other observers. 



When we examine the curves which we have given (Figs. 38, 

 39, 42), obtained by three several methods, we find that they agree 

 in the following main features. The curve of pressure in the 

 ventricle, whether right or left, rises at the very beginning of the 

 systole with very great rapidity, very soon reaches its maximum or 

 nearly its maximum, maintains nearly the same height for some 

 time, and then very rapidly descends to the base line (which in 

 these figures indicates the pressure of the atmosphere) or even 

 falls, for a brief space, slightly below it, and remains at or near the 

 base line, until, at the next beat, it repeats the same changes. 

 This means that the contraction of the ventricular walls in the 

 systole acts in such a manner as very suddenly to raise up to a 

 certain height the pressure within the ventricle, which during the 

 diastole was at, or not far removed from that of the atmosphere, 

 that the pressure is maintained without any very great change for 

 a considerable time, and that it then falls back to its original level 

 with great suddenness, almost, if not quite, as suddenly as it was 

 raised. These are the important features of the pressure within 

 the ventricle ; in these features all the three curves agree. We 

 may add that the same features are shewn also in curves of pres- 



