512 



Messrs. M. Flack, L. Hill, and J. McQueen. 



increased tension of the arteries under the armlet and the sound becomes 

 louder. 



The bigger the pulse wave passing to the armlet, the ampler will swing 

 the vessels under the armlet and the less the compression required to 

 increase the force of the pulse wave in the radial artery at the wrist, and 

 produce the dull sounds. We believe these sounds are produced by the 

 impact of the systolic wave vibrating the tense artery and its branches, big 

 and small. Consequently they should be independent of the blood flow. 

 An artery ligated beats up to the point where the ligature is applied. 

 Normally we feel pulses by closing the artery with the ball of the finger or 

 thumb and feeling the impact of the systolic wave on the tip of the finger or 

 thumb. To deform the artery with the finger a lower pressure than the 

 diastolic pressure suffices. The finger deforms it just as the bag of the 

 sphygmometer deforms an artery placed on bone. 



It is possible to arrange an armlet on the upper arm and a second armlet 

 immediately below the tambour at the bend of the elbow. Suppose the 

 pressure is raised in the armlet to 30-40 mm. Hg, sufficient to call forth the 

 dull sounds, and that then the armlet pressure below the bend of the elbow is 

 raised far above the ascertained systolic pressure of the blood. This stops all 

 effective flow in the artery at the bend of the elbow ; the subsidiary branches 

 of the main arterial trunk rapidly fill up, as all exit for the blood is blocked 

 in the distal area by the compressing armlet placed below. Yet the dull 

 sounds persist. Further, these sounds become more audible as the blood flow 

 is stopped. That is exactly what one would expect if the sounds are due to 

 sudden tension. The artery and all its branches become tenser above the 

 block. The whole kinetic energy of the pulse spends itself in striking the 

 tense labile artery and its branches. The whole mass of tissue under the 

 armlet — permeated with blood vessels — is struck by the pulse. 



We find that the phenomenon of an increase in the pulse force in the 

 radial artery at the wrist is often felt best at the first examination of the 

 patient with the sphygmometer. The excitement produced by examination 

 increases the force of the heart, and the high crest of the pulse wave reaching 

 the tissues compressed by the armlet becomes reinforced : an increase in the 

 force of the pulse beat is thus felt easily with a low pressure within the 

 armlet. As the excitement subsides, and the pulse beat becomes normal in 

 its range, the level of pressure at which the increase is felt becomes higher. 



As regards the production of the loud sounds and murmurs heard on 

 passing from diastolic level to systolic level, it is possible to separate the 

 element of sound due to pure tension of the arterial wall and the element of 

 sound which requires a flow of blood. 



