BLOOD PRESSURE 



131 



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 

 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- 



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

 cuff is raised by means of the syringe until the pulse can no longer be felt at the wrist. This 

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



tion, in which the procedure is slightly modified. With the stetho- 

 scope 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 

 the auditory systolic index. It will be found to give a systolic pressure 

 a little higher than that obtained by palpation of the artery at the wrist. 

 The sound being now absent, the pressure in the cuff is lowered until 

 the sound reappears, and the point at which this occurs should almost 



