216 



PHYSIOLOGY 



CHAP. 



pericardium with a tambour and writing lever, artificial respira- 

 tion being temporarily suspended. 



The plethysmograms obtained by this method give an 

 approximate picture of the quantity of blood with which the 



Fio. 69. Cardiac plethysmograms. (Stefani.) o, b, Descending portion, coinciding with systolic 

 outflow ; b, c, rapidly ascending portion, coinciding with active diastolic influx ; c, a, nlowly 

 ascending portion, coinciding with passive diastolic influx ; d, notches, which nearly always 

 occur on the ascending shoulder. 



heart is charged, or which it discharges at the different periods of 

 its cycle, and consequently of the systolic diminution, and peri- 

 systolic amplitude of the ventricular cavity. 



As appears from the tracings in Fig. 69 we can distinguish : 



(a) A rapidly descending line which coincides with the period 

 of systolic evacuation. 



(ft) A rapidly ascending line (in which there is invariably a 

 notch) corresponding with the period of active diastole. 



(c) A slowly ascending line (sometimes horizontal or even 

 slightly descending as shown in Fig. 70), which corresponds to the 

 time of passive diastole and presystole. 



It is obvious that neither the period of presystole nor the 

 succeeding interval of tension or latent systole, during which the 

 total volume of the heart undergoes no important modification, can 

 be distinctly shown in cardiac plethysmograms. Since in the 



FIG. 70. Cardiac plethysmograms, in which the line :, a of passive refill is descending or 

 almost horizontal. 



third period of the plethysmogram there may be a slight augmenta- 

 tion of cardiac volume, or it may be stationary, or diminish, the 

 deduction of Stefani seems valid, to the effect that " the venous 

 current (in consequence particularly of presystole) must in the 

 first case suffer a simple retardation, in the second an arrest, in 



