PRESSURE CHANGES IN THE HEART DURING ITS ACTIVITY 169 



variations. The requirements for such an instrument are very severe: indeed 

 there occur in the ventricles variations of 130 mm. of Hg. in 0.06 of a second 

 i. e., 2,170 mm. Hg. in a second. The instrument to be used must be capable 

 therefore of righting itself very quickly, and must be at the same time to a 

 high degree aperiodic so that it has no oscillations of its own. The first instru- 

 ment used for this purpose was the writing tambour of Marey. This was con- 

 nected with a sound of peculiar construction (cardiographic sound) passed into 

 the heart chambers. Such a sound (Fig. 55) consists of a tube, the end of 

 which, to be placed in the heart chamber, carries a rubber bulb. The latter is 

 supported by a steel frame (a, v) so that it is not completely compressible. The 



FIG. 56. Intracardial pressure curves of the horse, after Chauveau and Marey. Or. D., right 

 auricle; Vent. D., right ventricle; Vent. G., left ventricle. 



free end of the sound is connected with the writing tambour. With the pressure 

 changes in the heart cavity the air pressure in the bulb changes and the writing 

 tambour records these variations graphically. By suitable means the curves thus 

 obtained can be estimated in absolute terms (millimeters of Hg.). 



B. PRESSURE VARIATIONS IN DIFFERENT CHAMBERS OF THE HEART 



As already observed the auricles contract first. The duration of their 

 systole up to the point of maximum pressure is, in the horse, 0.1 second: that 

 of the ventricles up to the point where the fall in pressure begins is consider- 

 ably longer, namely, 0.4 second (also in the horse). The maximum pressure 

 in the right auricle of the dog is given as 20-22 mm. Hg. (Goltz and Gaule). 



The form of the pressure variations in the heart chambers is variously 

 figured, according to the instruments used in their graphic registration. The 

 difference is due to the fact that not all the different instruments give the 

 rapid variations in pressure with sufficient exactness. 



The most correct form of the intracardial pressure curve appears to cor- 

 respond to the type represented in Fig. 56. If we neglect details which are 

 relatively unimportant, the intracardial pressure runs somewhat as follows: 



