365 



The Effect of the Lability [Resilience) of the Arterial Wall on the 

 Blood Pressure and Pulse Curve. — II. 

 By Leonard Hill, F.K.S., and Martin Flack.* 



(Received March 31— Eead April 10, 1913.) 



(From the Physiological Laboratory, London Hospital Medical College, London Hospital 



Eesearch Fund.) 



In a paper published in the ' Proceedings of the Royal Society/ 1913, B, 

 vol. 86, p. 180, Russell Wells and Leonard Hill brought forward evidence to 

 show that the nature of the arterial wall has an important effect in modifying 

 the conduction of the pressure waves from the heart to those arteries where 

 the pulse is usually explored, such, for example, as the radial, where 

 sphygmograms are recorded and readings of arterial pressure taken with the 

 sphygmomanometer. They concluded that the conduction depends on the 

 greater or less " resilience " of the arterial wall, using the term " resilience " 

 to express " the ease with which an elastic tube distends with a rise and 

 recoils with a fall of pressure of the contained fluid " ; thus a rubber tube with a 

 wall of - 2 mm. thick is more " resilient" than one with a wall 0"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 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, also since the degree of contraction and 

 " resilience " may vary locally it is to be expected that the curve of blood- 

 pressure may likewise vary, e.g. in the brachial and in the femoral arteries. 

 We have found this to be the case under certain conditions, namely, in cases 

 of aortic regurgitation.! In such cases the systolic pressure reading for the 

 leg is much higher, 100 mm. or more, than in the arm arteries. Also in normal 

 men a difference in the systolic pressure in the two radial arteries may be 

 observed when the heart is made to beat forcibly by a short period of hard 

 exercise and after one elbow has been placed in hot and the other in cold 

 water. The artery relaxed by heat gives the lower systolic pressure. 



Russell Wells constructed a schema by means of which a known rhythmically 

 changing pressure could be passed (1) through rubber tubes of the same calibre, 

 but varying thickness, e.g. - 8, - 4, - 2 mm., (2) through various lengths of the 



* During tenure of Eliza Ann Alston Eesearch Scholarship. 



t L. Hill, with Martin Flack and W. Holtzmann, ' Heart,' 1909, vol. 1, p. 73 ; L. Hill 

 and R. A. Rowland, ' Heart,' 1912, vol. 3, p. 222. 



VOL. LXXXVI. — B. 2 D 



