ENDOCARDIAC PRESSURE 



167 



sistancc which it is desired to give to the movements of the lever, are two holders, G, G', 

 which securely clamp the steel ribbon. 



As the torsion of a steel wire or strip follows Hooke's law, the torsion being proportional 

 to the twisting force, the movements of the lever point are proportional to the force em- 

 ployed to twist the steel strip of ribbon in other words to the pressures which act on the 

 piston, B. To make it possible to record satisfactorily the very varying ventricular and 

 auricular pressures, the resistance to torsion of a steel ribbon adapts itself very conven- 

 iently. 



This resistance can be varied in two ways, ist, by using one or more pieces of steel 

 ribbon or by using strips of different thicknesses; or, 2d, by varying the distance between 

 the holders, G, G', and the central part of the steel ribbon to which the lever is attached. 



Rolleston's conclusions are: That there is no distinct and separate 

 auricular contraction marked in the pressure curves obtained from the right 

 or the left ventricle, the auricular and ventricular rises of pressure being 

 merged into one continuous rise. He concludes that the auriculo-ventricular 



FIG. 166. Hiirthle's Spring Manometer. A, Viewed from the side; B, viewed from the top. 



valves are closed before any great rise of pressure within the ventricle above 

 that which results from the auricular systole, a, figure 165. The closure of 

 the valve "occurs probably in the lower third of the rise AB, figure 165, and 

 does not produce any notch or wave. It is shown that the semilunar valves 

 open at the point in the ventricular systole, situated at C, about or a little 

 above the junction of the middle and upper thirds of the ascending line AB, 

 and the closure about or a little before the shoulder, D. The figures show, 

 finally, that the minimum pressure in the ventricle may fall below that of the 

 atmosphere, but that the amount varies considerably. 



On the whole, the most satisfactory recording instrument for the measure- 

 ment of endocardiac pressures is the membrane manometer devised by 

 Hiirthle. This instrument avoids mechanical errors in a most satisfactory 

 manner. By simultaneous tracings of the pressure in the ventricle and in 

 the aorta by Hurthle's differential manometer, the exact moment of the 



