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TEXT-BOOK OF PHYSIOLOGY 



ma* valve 



mm valve 



Intra- ventricular Pressure. i. Positive Pressure. It has been stated 

 that during the pause of the heart when its cavities are filling with blood 

 the semilunar valves are kept closed by the pressure of the blood in the 

 pulmonic artery and aorta, a pressure due to the resistance, as will be ex- 

 plained later, offered to the flow of the blood mainly by the smaller arteries 

 and capillaries; that they are opened only when the pressure of the blood 

 within the ventricle exceeds that in the arteries. It is apparent therefore 

 that there must be, during the time of the systole, an intraventricular posi- 

 tive pressure sufficiently high to overcome and even exceed the pressure 

 ordinarily present in the aorta and pulmonic artery. It becomes, there- 

 fore, a matter of interest to determine the extent of this pressure as well 

 as its variations during the course of a cardiac cycle. This can be done 

 by inserting a long catheter into either the right or left ventricle, through 

 the jugular vein, or the carotid artery respectively, and connecting its free 

 to manometer extremity with a mercurial manometer. 

 By the interposition of a double valve such 

 as represented in Fig. 124, it becomes possi- 

 ble, according to the direction in which the 

 blood is permitted to flow, to obtain either 

 the maximal or the minimal pressure that 

 occurs in the heart during a series of 

 cycles. By the employment of a device of 

 this character Goltz found in the left ven- 

 tricle of the dog a maximal pressure of 

 114 to 135 mm. of mercury; in the right 

 ventricle, a maximal pressure of 35 to 62 

 mm. 



The maximal pressure in the ventricles 

 during the systole, though always higher 

 than that in the arteries, is neither a fixed 

 nor an invariable pressure, as it rises and 

 falls with the latter from moment to mo- 

 ment. Within limits the cardiac power, 

 and therefore the intra-ventricular pressure, is capable of considerable in- 

 crease. The function of the heart is to drive the blood through the vessels 

 with a given velocity. This is possible only by first overcoming the resis- 

 tance to the flow offered by the vessels, as indicated by the arterial pres- 

 sure. As this is a variable factor, rising and falling very considerably at 

 times, the heart must meet and exceed each rise, within limits if the circu- 

 lation is to be maintained. This it does by calling on the reserve power 

 with which it is endowed. The power put forth by the heart is propor- 

 tional to the work it has to perform. If the arterial pressure continues 

 higher than the average for any length of time, the heart meets the condition 

 by an hypertrophy of its walls, but in so doing it encroaches on the reserve 

 power proportionally and when the latter has become exhausted the heart 

 may, on some sudden rise of pressure in the aorta, be unequal to the dis- 

 charge of blood from its cavities and hence remain in a state of permanent 

 diastole. 



2. Negative Pressure. It has also been demonstrated by the employ- 

 ment of the minimal valve that there is brief moment in the cycle when the 



'to heart 



FIG. 124. v. FRANK'S VALVE. 

 This is placed in the course of the 

 tube between heart and manometer, 

 so that the latter may be used as a 

 maximum, minimum, or ordinary 

 manometer according to the tap which 

 is left open. (Starling.') 



