PULSE TRACING 91 



with the 3-way tube (T). The latter is connected on the 

 one side with a large bottle, and on the other with a 

 mercury manometer (M). The bottle is also connected 

 with an india-rubber spraying apparatus (P) or a bicycle 

 pump. The observer feels the pulse in the radial artery 

 of the subject, fixes the clamp C and pumps air into the 

 bottle. This causes a gradual rise of pressure in the bag 

 on the arm and in the manometer. At a certain rise of 

 pressure the heart can no longer force blood through 

 the arteries enclosed by the bag, and the pulse at the 

 wrist ceases to be felt. 



The difference in millimetres in the height of the two 

 columns of mercury in the manometer at the moment 

 the pulse ceases to be felt is noted a. 



The clamp C is then slightly relaxed so that the 

 pressure falls slowly ; the difference in the height of the 

 two columns of mercury at the moment the pulse at 

 the wrist is again felt is noted b. 



The mean of a and b is taken as the systolic blood 

 pressure in the arteries of the arm in millimetres of 

 mercury. 



The observations should be repeated several times 

 since it takes practice to determine the exact moment 

 at which the pulse disappears and reappears. 



2. Pulse tracing with two tambours. In taking a 

 pulse tracing the subject rests his arm on a table at 

 about the level of the heart, supporting the wrist on 

 a pad, and bending the hand slightly backwards. The 

 observer feels the pulse at the wrist with the 1st and 

 2nd fingers, makes a mark on the. skin along the line 

 of the radial artery, and a cross mark where the pulse 

 is best felt. 



