126 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



being 120 millimeters. In a second dog the figures were 176 and —30 milli- 

 meters for the ventricle, the aortic range being from 158 to 112 millimeters. 1 

 In the right ventricle of the dog such ranges as from 26 to --8 millimeters, 

 from 72 to —25, and various intermediate values, have been noted, both in 

 the unopened and the opened chest. 2 For reasons already stated (p. 103) no 

 trustworthy figures can be given for the pressures in the pulmonary artery ; 

 but they can never fail to be less than the highest pressures within the right 

 ventricle. 



The range of pressure, therefore, within either ventricle is in sharp contrast 

 to that within the artery which it supplies with blood; for the arterial pressure, 

 although it fluctuates, is at all times far above that of the atmosphere, and is 

 able, as we have seen, to maintain the circulation while the semilunar valve is 

 closed and the ventricular muscle is at rest. On the other hand, the pressure 

 within the ventricle, when at its highest, rises decidedly above the highest 

 arterial pressure, and thus the ventricle can overcome this and other opposing 

 forces, open the valve, and expel the blood. These facts have been stated 

 already. In falling, however, the pressure within the ventricle not only sinks 

 below that in the artery, and so permits the semilunar valve to close, but 

 sweeps downward to a point, it may be, below the pressure of the atmosphere, 

 and, in so doing, falls below the pressure in the auricle, and permits the open- 

 ing of the auriculo- ventricular valve and the entrance of blood out of the 

 auricle and the veins. As such a great range of pressure occurs in either 

 ventricle of a heart which is repeating its cycles with entire regularity, it is 

 presumable that at every cycle the pressure not only rises above that in the 

 arteries but may sink below that of the atmosphere. 



Methods of Recording the Course of the Ventricular Pressure. — It 

 now becomes of interest to ascertain, if possible, not only the range, but the 

 exact course, of these swift variations of pressure ; the causes of them, and the 

 effects which accompany them. It is hard to obtain, by the graphic method, a 

 correct curve of the pressure within either ventricle. We have seen that the 

 mercurial manometer is useless for this purpose; and it is very difficult to 

 devise any self-registering manometer which shall truly keep pace with fluctu- 

 ations at once so great and so rapid. The true form of this pressure-curve, 

 therefore, still is partially in doubt, and is the subject of controversies which 

 largely resolve themselves into contests between rival instruments. The 

 following characters are common to the manometers with which the most 

 serious attempts have lately been made to obtain a true and minute record of 

 the fluctuations of pressure, even if great and rapid, within the heart or the 

 vessels (see Fig. 21 |. As in the case of the mercurial manometer, a cannula, 

 open at the end and charged with a fluid which checks the coagulation of the 

 blood, i- tied into a vessel, or. if the heart is under observation, is passed down 

 into it through an opening in a jugular vein or a carotid artery. If the chest 



1 S. de Jager: " Ueber die Saugkraft des Herzens," Pfliiger's Archiv fitr die gesammte Physi- 

 ologic, 18^?,, Bd. xxxi. S. 491. 



-S. de Jager: Loc fit., S. 50fi. 507 ; Goltz and Ciaule: Loc. rit., S. 106. 



