128 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



It has been indicated already that the pressure of the blood may be 

 communicated to the disk of an elastic manometer either by means of 

 liquid or of air. A given series of fluctuations of blood-pressure may yield 

 decidedly different curves according to the method of " transmission " employed 

 to obtain them ; and the controversies as to the true form of the endocardiac 

 pressure-trace turn upon the question whether such "transmission by air" or 

 "transmission by liquid " yield the truer curve. The objections to the former 

 method depend upon the readier compressibility of air; the objections to trans- 

 mission by liquid depend upon its greater inertia. 



The General Characters of the Ventricular Pressure-curve. — What- 

 ever kind of elastic manometer and of transmission be used, the curve 



Millimeters of 

 mercury. 



Line of atmospheric 

 pressure. 



Seconds. 



Fig. 22.— Magnified curve of the course of pressure within the right ventricle of the dog, the chest 

 being open ; to be read from left to right. Recorded by the elastic manometer, with transmission by air 

 (von Frey). 



obtained shows certain characters which are recognized by all as properly 

 belonging to the changes of pressure within the ventricle, whether right or 

 left. These general characters, moreover, persist after the opening of the 

 chest. They are as follows (see Figs. 22, 23, 24) : The muscular con- 

 t faction of the systole begins quite suddenly, and produces a swift and ex- 



Liiu of atmospheric 



pressure. 



Fig. 23. — Magnified curve of the course of pressure within the left ventricle and the aorta of the 

 dog, tic chesl being open ; to be read from left t<> right. Recorded simultaneously by two clastic man- 

 rs with transmission by liquid, in both curves tin 1 ordinates having the same numbers have the 

 following meaning: l. the in- taut preceding t lie closing of the mitral valve ; ■_', the opening of the semi- 

 lunar valve; '■'•, the beginning of the "dicrotic wave." regarded as marking the instant of closure of the 

 semilunar valve: I. the instant preceding the opening of the mitral valve (Porter). 



tensive rise of pressure, marked in the curve by a line but slightly inclined 

 from tin; vertical. In the same way the fall of pressure is nearly as sudden 

 and as swift as the rise, and perhaps even more extensive. The systolic rise 

 begins at a pressure a little above that of the atmosphere; the diastolic fall 

 continues, toward its end. perhaps, with diminishing rapidity, till a point is 



