Pulse Wave and the Measurement of Arterial Pressure. 345 



Eussell "Wells* on rubber tubing made with a thickness of wall corre- 

 sponding to an artery. While the lability effect has been shown by us in 

 exposed arteries, in the body the main arteries are surrounded with tissues 

 permeated with small arteries into which the blood pulsates. As the 

 arterial wall is supported by the pulsing tissues the lability effects obtained 

 on the exposed arteries cannot be directly ascribed to the same arteries 

 in situ. Further investigation must be made on these. 



Now J. McQueen, Ingram, and Leonard Hilly have shown that there is 

 an extraordinary difference in the pressure required to damp down the 

 pulse wave in arteries such as the aberrant radial and the dorsalis pedis, 

 where these run superficially and lie upon bone, as compared with the same 

 or other arteries lying in the midst of pulsating " resonating " tissues. 

 They suggest that the pulse wave is supported on its way to the periphery 

 by the pulsing tissues, and that the higher leg readings obtained in cases of 

 aortic regurgitation may be due in part to the better conduction of waves 

 which have a high crest through the pulsating mass of the abdomen and 

 thigh. The reading of pressure in the case of the aberrant radial or dorsalis 

 is taken with the Leonard Hill pocket sphygmometer. The small bag of 

 this instrument when pressed on the radial artery (embedded in the tissues 

 of the forearm) gives the same readings as the armlet method. "When 

 pressed on the aberrant radial or on the dorsalis pedis a far lower reading is 

 obtained, e.g., in a youth 35 mm. Hg against 110 mm. Hg. 



We have constructed a wooden C-shaped box in which the arm can be 

 suspended freely by a sling. If the armlet be placed round this box so that 

 it presses on the front of the forearm, the obliteration of the pulse in the 

 radial is obtained by the same pressure as is required if the armlet be used 

 in the ordinary way. If the forearm be put in the box with the radial 

 border uppermost, and the aberrant radial be pressed upon by the armlet, 

 then the pulse is obliterated by a pressure of 35 mm. Hg. Using the armlet 

 in the usual way the pulse is obliterated in this artery by 110 mm. Hg. 

 In the one case the artery lying on bone is deformed by the armlet just as 

 it is deformed by the bag. In the other case the pulse in the aberrant radial 

 is not obliterated until the systolic pressure in the tissues of the forearm is 

 overcome. 



"We have recently investigated several cases of " high blood-pressure " and 

 find the following divergence between the readings of the leg and arm 

 arteries, using the armlet and the dorsalis pedis, the patients being in the 

 horizontal posture : — 



* Eussell "Wells and Leonard Hill, ' Roy. Soc. Proc.,' B, vol. 86, p. 180. 



t J. McQueen, Ingram, and Leonard Hill, ' Roy. Soc. Proc.,' B, vol. 87, p. 255 (1913). 



