1014 



PHYSIOLOGY 



being gradually filled with blood flowing in from the great veins and 

 arteries. 



The period of outflow of blood, which lasts over the whole of the 

 plateau and during the latter part of the ascending portion of the 

 curve, represents the period during which the aortic valves are open 

 and the pressure in the ventricle is slightly higher than that in the 

 artery. 



The maximum pressure in the left ventricle of the dog may amount 

 to 200 mm. Hg, but is more usually about 130 to 140 mm. Hg. On 



*s v s 



FIG. 397. Curve of pressure in left ventricle of cat. (STRATJB.) 

 AS, auricular systole ; vs, ventricular systole. 



the right side the maximum pressure is probably much less 25 

 to 35 mm. Hg. The general course of events is, however, approximately 

 identical on the two sides of the heart. 



Straub has lately investigated the course of the pressure changes in the 

 auricles and ventricles of the cat. In order to avoid friction he used the method 

 devised by Rolleston of plunging a cannula through the heart wall directly into 

 the cavity under investigation. Directly connected with this cannula was a 

 manometer consisting of a membrane, the movements of which were recorded 

 photographically, as in Frank's manometer. A curve obtained in this way 

 is shown in Fig. 397. It is interesting that no trace is to be seen in these curves 

 of the systolic plateau or of any secondary waves, though they are not unlike 

 the systolic part of the aortic pressure curve as recorded by Frank with his 

 improved methods. The first heart sound is also shown in the originals of these 

 tracings as fine vibrations just before the systolic rise. No trace is seen of the 

 second heart sound, which would fall on the rapidly descending part of the 

 curve. 



