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The Influence of the Resilience of the Arterial Wall on Blood- 

 Pressure and on the Pulse Curve. 

 By S. Russell Wells and Leonard Hill, F.E.S. 

 (Eeceived November 29, 1912,— Eead February 6, 1913.) 



This communication is the result of two independent but converging lines 

 of research. It is well known that when a fluid is driven with a rhythmically 

 varying pressure through a sufficient length of a distensile elastic tube, the 

 pressure at the exit loses its rhythm and becomes constant and the flow 

 continuous, whereas if the tube is rigid, the pressure at the outlet varies 

 as that at the inlet (less the change due to friction) and the outflow is 

 intermittent. 



Since the arteries are distensile elastic tubes and the blood is rhythmically 

 forced into them by the heart, it follows that the curve of blood-pressure 

 must be altered to a greater or lesser degree by the distensibility and 

 elasticity of the arterial wall. 



We use the term resilience in this paper to express the ease with which an 

 elastic tube distends with a rise and recoils with a fall in pressure of the 

 contained fluid ; thus, a rubber tube with a wall 02 mm. thick is more 

 resilient than one with a wall - 4 mm. thick, the thinner, more resilient 

 tube yields with the rise and recoils with the fall of pressure more than 

 the " harder," thicker walled, less resilient tube. A glass tube in this sense 

 has no resilience, and the same may be said of rubber pressure tubing. 



As the arterial wall contains muscle its resilience will be altered by a more 

 or less contracted state ; as the degree of contraction and resilience may vary 

 locally it is to be expected that the curve of blood-pressure may also vary, 

 e.g. in the brachial and femoral arteries. Further, as the peripheral resistance 

 in any area may alter the tension of the arterial wall, its resilience may vary 

 without any change in the muscular state of the arterial wall. 



Observations made by one of us (L. H.) with W. Holtzman and Martin 

 Flack, and later with E. A. Eowlands,* on cases of aortic regurgitation placed 

 in the horizontal position, have shown that the systolic pressure is much 

 higher in the leg than in the arm, e.g. 100-150 mm. of mercury higher, 

 and so characteristic is this difference that it is a diagnostic sign of the 

 condition. Thomas Lewis found that the same held good in the case of a 

 dog in which he had experimentally rendered the aortic valves incompetent 

 one month previous to taking the observations.f His measurements were 



* ' Heart,' 1909, vol. 1, p. 73 ; and 1912, vol. 3, p. 219. 

 t ' Heart,' 1912, vol. 3, p. 222. 



