BLOOD PRESSURE 



129 



ably somewhat murnmrish in quality. At a certain pressure this loud 

 character of the sound will suddenly become much less marked, and the 

 murmurish quality if present will suddenly disappear. This point cor- 

 responds to the diastolic pressure, which is now read off from the 

 manometer. 



It must be remembered that below this point, as the pressure in the 

 cuff is further lowered, a sound is still heard in the artery; indeed it 

 does not entirely disappear until the pressure has become quite low. This 

 point of final disappearance is, however, of no significance. The cuff is 



the 



Fig. 26. Apparatus for measuring the arterial blood pressure in man. The pressure in thi 

 :uff is raised by means of the syringe until the pulse can no longer be felt at the wrist. Thi 

 pressure is read off on the mercury manometer (systolic pressure). 



now entirely decompressed, and should be left so for a moment or more, 

 so that the circulation in the part of the arm below it may return to the 

 normal. 



The above readings should then be controlled by a second observa- 

 tion, in which the methods employed are slightly modified. With the 

 stethoscope at the bend of the elbow the pressure in the cuff is run up to 

 a little above the previously determined diastolic pressure, so that the 

 sound is clearly heard. The pressure is then further raised till the 

 sound disappears. This point indicates the systolic pressure; it is called 



