The Measurement of Arterial Pressure in Man. 



535 



Not only the tissue schema of the first but that of the second schema has 

 then to be expanded and rendered tense before the pulse of the second 

 schema becomes restored. 



Our experiments demonstrate, then, the important influence which the 

 tissue vessels have on the conservation of the pulse in the main arteries. 



Let us now return for a moment to an experiment we published in a 

 previous paper.* On fomenting with hot water the lower arm, and icing 

 the upper arm, we found the radial pulse was obliterated by a pressure which 

 was less when the armlet was applied to the upper arm than when it was 

 applied to the lower arm. In the cooled upper arm the tissue vessels and 

 veins were constricted and emptied. In the warm lower arm they were 

 flushed and filled. The compression applied to the latter at once raised the 

 diastolic pressure in the arteries, and by increasing their tension, i.e. lessen- 

 ing their lability, improved the conduction of the crest of the systolic wave. 

 This was not so in the case of the cold upper arm. The pulse was not so 

 well conserved by the action of the tissue vessels there, and the brachial 

 artery was thus deformed at a lower pressure. We see then how potently 

 the condition of the peripheral circulation may influence the reading of 

 systolic pressure. 



There is an experiment published by Mac William, Kesson. and Melvin,f 

 which, it is claimed, refutes all the proofs we have brought forward as to 

 the effect of the lability of arteries on the conduction of the pulse wave. 

 These authors figure two lengths of tubing, one rigid tube, the other artery, 

 connected by a T-piece to the aorta of a cat. They connect first one and 

 then the other of these tubes to the manometer, and find the pulse records 

 are the same. Therefore, say they, the artery is no more labile than the 

 rigid tube. 



We would point out that under their conditions the pulse, as recorded, is 

 affected by the lability of the artery whichever tube is connected to the 

 manometer. To make their experiment adequate they must clip off the 

 artery while recording the pulse from the rigid tube. The lability of the 

 artery comes no less into play when it is connected by one end to the rigid 

 tube, as we showed in our previous communication 4 



Conclusion. 



1. The simple schema, hitherto used for studying the compression of 

 excised arteries, does not reproduce the conditions which pertain when the 

 arm is compressed. 



* ' Eoy. Soc. Proc.,' B, vol. 87, p. 344 (1914). 

 t 1 Heart,' vol. 4, p. 393, Experiment 7 (1913). 

 1 'Eoy. Soc. Proc.,' B, vol. 86, p. 365 (1913). 



