ENDOCARDIAL PRESSURE. 



87 



valves arc closed by the pressure from above, and the difference in 

 time may be 0'05 sec., or even double that time, in which case the 

 second sound appears double (compare p. 94). If the aortic pressure 

 diminishes while that in the pulmonary artery rises, d and e may 

 be so near each other that they are no longer marked as distinct 

 elements in the curve. 



The time, e,f, during which the ventricle relaxes varies somewhat: 

 O'l sec. may be taken as a mean. 



Accelerated Cardiac Action. When the action of the heart is greatly 

 accelerated, the pause is considerably shortened in the first instance (Donders), 

 and to a less extent the time of contraction of the auricles and ventricles. When 

 the pulse-rate is very rapid, the systole of the atria coincides with the closure of 

 the arterial valves of the preceding contraction, as is shown in Fig. 25a, C (dog). 



In registering the cardiac impulse, the apparatus is separated by a greater or 

 less extent of soft parts from the heart itself, so that in all cases the intercostal 

 tissues do not follow exactly the movements of the heart, and thus the curve 

 obtained may not coincide mathematically with the movements of the heart. It 

 is desirable that curves be obtained from persons whose hearts are exposed, i.e., 

 in cases of ectopia cordis. 



Gibson inscribed cardiograms from the heart of a man with cleft sternum. 

 The following were the results obtained : Auricular contraction = O'l 15; ventri- 

 cular contraction (&,c) = 0'28; difference between closure of valves (d, e) = 0'09 

 ventricular diastole (e,f) 0*11 ; pause 0'45 sec. 



Endocardial Pressure. In large mammals, such as the horse, 

 Chauveau and Marey determined 

 the duration of the events that 

 occur within the heart, and also 

 the endocardial pressure, by 

 means of a cardiac sound. Small 

 elastic bags attached to tubes 

 were introduced through the 

 jugular vein into the right auricle 

 and ventricle. Each of these 

 tubes was connected with a regis- 

 tering tambour (Fig. 28), and 

 simultaneous tracings of the varia- Fig. 28. 



tions of pressure within the cavi- Marey 's registering tambour, consisting of 



ties of the heart were obtained 

 by causing the writing-points of 

 the levers of the tambours to 

 write upon a revolving cylinder. 



a metallic capsule, T, with thin india- 

 rubber stretched over it, and bearing 

 an aluminium disc, which acts upon 

 the writing lever, H. By means of a 

 thick-walled caoutchouc tube, it may 

 be connected with any system con- 

 taining air, so as to record variations 

 of pressure. 



Fig. 29, A, gives the result obtained 

 when the elastic bag was placed in 

 the right auricle, introduced through 

 the jugular vein and superior vena cava; B, when it was pushed through the 

 tricuspid valve into the right ventricle ; D, in the root of the aorta, pushed in 



