BLOOD PRESSURE 



367 



A very simple sphygmomanometer has been devised by Riva-Rocci. 1 A 

 rubber pouch measuring 5 cm. in width and possessing a length sufficient to 

 encircle the arm, is connected with a mercury reservoir and a pressure bulb. This 

 rubber bag is protected upon its outside by a leather or canvas cuff which is 

 tightened until it fits the arm snugly. The arm is placed in an easy position at 

 the level of the heart, and consequently, no corrections need be made for the 

 hydrostatic effects. If the pouch is now inflated, the pressure in this system 

 rises until the tissues around the brachial artery are compressed in such a degree 

 that the lumen of this blood-vessel is obliterated. This moment is clearly marked 

 by the disappearance of the pulsations in the radial artery, while the pressure 

 necessary to accomplish this end is registered by the manometer of the mercury 

 reservoir. The best procedure to be followed is this: The cuff having been 

 properly adjusted, the fingers of the left hand are placed upon the radial artery at 



FIG. 191. RrvA-Rocci's SPHYGMOMANOMETER. (From Janeway's " Clinical Study of 

 Blood-pressure," D. Appleton and Co., Publishers.) 



the wrist, while the right hand is employed to inflate the rubber pouch. The 

 pressure is read at the very moment when the radial pulse disappears. In quite 

 the same way, the pressure is again noted when the pulse reappears during the 

 gradual deflation of the pouch. The principle involved in this procedure is 

 obvious. When the outside pressure just barely overcomes the intravascular 

 pressure, as is indicated by the loss of the radial pulse, the former may correctly 

 be taken as a measure of the latter. Naturally, this procedure does not permit 

 of definite conclusions being drawn regarding the mean blood pressure, but indi- 

 cates solely the maximum or systolic blood pressure, i.e., the moment when the 

 peaks of the individual pulse waves are just capable of overcoming the outside 

 pressure. 



1 Gaz. med. di. Torino, 1896. 



