184 Messrs. S. K Wells and L. Hill. Influence of [Nov. 29, 



Length 



of 

 tube in 



cm. 



Entering pressure. 



Pressure at end of rubber 

 tube. 



Difference between 

 initial and end pressure. 



[Systolic. 



Diastolic. 



Differ- 

 ence. 



Systolic. 



Diastolic. 



Differ- 

 ence. 



Systolic. 



Diastolic. 



15 



30 

 60 



160 

 160 

 117 



40 

 42 

 40 



120 

 118 

 117 



126 

 118 

 108 



60 

 74 

 78 



66 

 44 

 33 



-34 

 -42 

 -49 



+ 20 

 + 32 

 + 38 



The same initial pressure differences were then tried on tubes of the same 

 length and calibre, but with walls of different thicknesses, namely, - 8, - 6, 

 0"4, and - 2 mm., when the same sort of results were obtained, viz., the 

 thinner and consequently the more resilient the tube, the more was the 

 systolic pressure lowered and the diastolic raised by passing through the tube, 

 that is, the nearer the resultant curve approached a straight line. 



It was quite remarkable to observe how with an entering pressure such as 

 160 mm. systolic and 40 mm. diastolic, a curve in the - 8 mm. tube would 

 have all the characters of a low pressure sphygmogram, great amplitude, 

 sharp rise and fall and very well marked dicrotic wave, while with exactly 

 the same entering pressure the curve in the 0'4 mm., and more so in the 

 - 2 mm., took on all the characters of a high pressure sphygmogram, slow 

 rise, fiat top, slow fall, and slightly marked dicrotism. 



L. H. and Martin Flack have since found that the introduction of, say, 

 6 cm. of cat's carotid artery in place of an equal length of pressure tubing 

 alters the characters of the pulse curve from a low to a high pressure curve. 

 The experiments demonstrating this will be published in full later. 



From these experiments conducted by S. E. W. and those of L. H. it seems 

 legitimate to draw these conclusions : the form of curve obtained by a 

 sphygmograph or other instrument recording the pulse is the resultant of two 

 factors, the blood-pressure variations produced by the heart and the resilience 

 of the arterial wall, using the term resilience in the sense defined above. 



Much at times has been made of the supposed influence of reflected waves 

 on the pulse curve. It is the resilience of the wall which we believe to be 

 the important factor in modifying the curve, and not the reflection of waves 

 from the periphery. 



The blood-pressure measured in any artery by the sphygmometer is 

 likewise the resultant of these two factors, and the measurement does not 

 necessarily give us the full systolic pressure produced by the heart ; much 

 of the force is spent in dilating a soft distensile artery. Further, since the 

 character of the flow in an artery largely depends on the resilience of its 



