1912.] Resilience of Arterial Wall on Blood-Pressure. 183 



It was found when the same resilient tube was used, but the diastolic 

 pressure of the entering fluid varied, keeping the interval between the 

 systolic and diastolic pressures as far as possible the same, that the higher 

 the pressure and consequently the more the resilience of the tube was 

 brought into action by stretching, the nearer together were the diastolic and 

 systolic pressures at the end of the resilient tube. In other words the 

 smaller was the amplitude of the pressure waves, and the more closely did 

 the pressure approach to a continuous one. As an instance, the following 

 experimental results may be cited, working with 30 cm. of a rubber tube, 

 the walls of which were 0*8 mm. thick and recording the pressures in milli- 

 metres of Hg. 



Entering pressure. 



Pressure at end of rubber 

 tube. 



Difference between 

 initial and end pressure. 



Systolic. 



Diastolic. 



Difference. 



Systolic. 



Diastolic. 



Difference. 



Systolic. 



Diastolic. 



145 

 184 

 220 



50 

 86 

 125 



95 

 98 

 95 



120 

 152 

 188 



60 

 104 



148 



60 

 48 

 40 



-25 

 -32 

 -32 



+ 10 

 + 18 



+ 23 



The same general results followed, no matter what the thickness of the 

 wall of the tube experimented on might be, and no matter what its length, 

 but the difference in the case of the thinner walled tubes was even more 

 striking. 



Working with a rubber tube 30 cm. long, and with walls 0*2 mm. thick, 

 with an entering pressure of 78 mm. of Hg diastolic and a 148 mm. systolic, 

 an almost continuous pressure of 104 mm. diastolic and 107 mm. systolic 

 was obtained at the end of the resilient tube. 



With raised pressure not only was the curve of less amplitude, but its 

 form also was altered, the top becoming flattened and the dicrotic wave less 

 marked, indeed it took on the characters which have frequently been 

 described as occurring in the sphygmograms of cases of high blood pressure. 



In order to test the correctness of the supposition that as the general level 

 of pressure was raised the resilience of the wall was increasingly brought 

 into play, a series of experiments was carried out, using the same initial 

 pressures and the same thickness of tube wall, but varying lengths of tube. 

 It was found that lengthening the tube had the same effect of approximating 

 the systolic and the diastolic pressures and making the curve take on the 

 characters of a " high pressure " sphygmogram. For instance, using a tube 

 with walls 0*8 mm. thick, the following results were obtained : — 



