ENDOCARDIAL PRESSURE. 



6 7 



the aorta occurs 0*137 minus '052 = 0*085 second after the beginning of the first sound. The 

 current in the pulmonary artery is interrupted in the depression between d and e. (3) Lastly, 

 the time occupied by the muscular contraction of the ventricle, which begins at b, reaches its 



A B 



Fig. 46. 

 Curves recorded by the ventricle of a rabbit, upon a vibrating plate attached to a tuning-fork 

 (vibration = 0*01613 sec). A, soon after death ; B, from the dying ventricle. 



greatest extent at c, and is completely relaxed at/. The apex of the curve, c, may be higher or 

 lower according to the flexibility of the intercostal space, hence the position of c varies. In 

 hypertrophy with dilatation of the left ventricle, the duration of the ventricular contraction 

 does not greatly exceed the normal. 



The time which elapses between d and e, i.e., between the complete closure of 

 the aortic and pulmonary valves, is greater the more the pressure in the aorta 

 exceeds that in the pulmonary artery, as the valves are closed by the pressure 

 from above, and the difference in time may be 0*05 second, or even double that 

 time, in which case the second sound appears double (compare 54). 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, ef, during which the ventricles relax varies somewhat : 0*1 second 

 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 con- 

 traction 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. 39, C (dog). 



In registering the cardiac impulse, the appara- 

 tus is separated by a greater or less depth 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 ob- 

 tained 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. 



Cleft Sternum. Gibson inscribed cardiograms 

 from the heart of a man with cleft sternum. The 

 following were the results obtained : Auricular 

 contraction = 0*11 5; ventricular contraction (b, d) 

 = 0*28 ; difference between closure of valves (d, e) 

 = 0*09 ; ventricular diastole (e, f) =0*11 ; pause 

 = 0*45 second. 



Endocardial Pressure. In large mam- 

 mals, such as the horse, Chauveau and 

 Marey (1861) 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 at- 

 tached to tubes were introduced through 

 the jugular vein into the right auricle and ventricle. Each of these tubes was 

 connected with a registering tambour (fig. 47), and simultaneous tracings of the 

 variations of pressure within the cavities of the heart were obtained by causing the 

 writing-points of the levers of the tambours to write upon a revolving cylinder. 



Fig. 47. 

 Marey's registering tambour. T, metallic 

 capsule, 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 

 containing ; aii , so as to record variations of 

 pressure. 



