CH. XX.] 



INTRACARDIAC PRESSURE 



243 



second). At D the ventricle relaxes. The flat part of the curve is 

 spoken of as the systolic plateau, and according to the state of the 

 heart and the peripheral resistance may present a gradual ascent or 

 descent ; it occupies about '18 second. Almost immediately after the 



D 



FIG. 252. Curve of intraventricular pressure. (After Hurt/hie.) 



relaxation begins the intraventricular pressure falls below the aortic, 

 so that the aortic valves close near the upper part of the descent at E. 

 The amount of pressure in the heart is measured by a manometer, 

 which is connected to the heart by a tube containing a valve. This 

 was first used by Goltz and Gaule. If the valve permits fluid to go 

 only from the heart, the manometer will indicate the maximum pres- 

 sure ever attained during the cycle. If it is turned the other way, 

 it will indicate the minimum pressure. The following are some of 

 the measurements taken from the dog's heart in terms of millimetres 

 of mercury : 



Left ventricle 

 Right ventricle 

 Right auricle . 



Maximum 

 pressure. 



140 mm. 

 60 mm. 

 20 mm. 



Minimum 

 pressure. 



- 30 to 40 mm. 

 - 15 mm. 



- 7 to 8 mm. 



By a negative ( ) pressure one means that the mercury is sucked up 

 in the limb of the manometer towards the heart. 



Another valuable instrument introduced by Hiirthle is called the differential 

 manometer. In this instrument, two cannulae are brought into connection with 

 tambours (A and B) which work on points of a lever at equal distances from and on 



B A 



FIG. 253. Diagram of Hiirthle's differential Manometer. 



opposite sides of its fulcrum (F). The lever sets in motion a writing style (s). This 

 instrument enables us to determine the relations of the pressure changes in any 

 two cavities. For instance, suppose A is connected to the left ventricle, and B to 

 the aorta ; when the pressure in the ventricle is greater than that in the aorta, the 

 writing style will be raised ; when the pressure in the aorta is greater than that in 

 the ventricle, the style will fall ; when the two pressures are equal, it will be in the 

 zero position. 



