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TEXT-BOOK OF PHYSIOLOGY 



of muscle-tissue will carry the wave of excitation from one part to neighboring 

 parts of the ventricle. It is therefore probable that the synchronism is 

 accomplished through muscle connections only. The left ventricle, in 

 keeping with the greater work it has to do, has a greater development than 

 the right, and therefore contracts more energetically. The ratio between 

 the energy of the left and right sides is approximately 3 to i. 



Intra-ventricular Pressure. i. Positive Pressure Ey this term is 

 understood the pressure that arises in the ventricular cavities during the 

 systole. The conditions that give rise to it are the firm closure of the 

 semilunar valves, due to the pressure of the blood in the aorta and pul- 

 monic artery, and the closure of the auriculo-ventricular valves at the 

 beginning of the systole. For a brief period therefore the blood is im- 

 prisoned on all sides. If the semilunar valves are to be opened and the 

 blood discharged, the ventricular walls must exert a pressure on the blood 

 exceeding the existing pressure of the blood in the aorta and the pul- 

 monic artery. So soon as this condition arises, the semi-lunar valves will 

 be pushed open by the excess of pressure in the ventricles and the blood 

 will be discharged. Moreover, as the pressure in the aorta and pulmonic 

 artery rises very considerably as the blood is discharged, the intra-ven- 

 tricular pressure must continue to rise and even to exceed the pressure in 

 the vessels until the blood is discharged and the systole comes to an end. 

 It becomes, therefore, a matter of interest to determine approximately 

 at least, 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 caro- 

 tid artery respectively, and connecting its free extremity with a mercurial 



manometer. By the interposition of a 

 double valve such as represented in Fig. 

 121, it becomes possible, 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 employ- 

 ment of a deyice of this character Goltz 

 found in the left ventricle of the dog a maxi- 

 mal 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 pres- 

 sure, is capable of considerable increase. 



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 resistance to 

 the flow offered by the vessels, as indicated by the arterial pressure. 

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



ma* valve 



to manometer 



mm valve 



'to heart 



FIG. 121. y. 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.) 



