516 



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



7. Clinicians know that the pulse in the radial artery hecomes more 

 forcible when they begin to compress the arm. At the beginning of com- 

 pression of the arm, the armlet, by obstructing the venous outflow and 

 making tenser the arteries in diastole, improves the conduction of the 

 systolic wave. The pulse in the radial artery, therefore, becomes reinforced. 

 The dull sound and the reinforcement of the pulse are due to the same 

 cause. 



8. Evidence has been obtained then, by experiments on man, of the effect 

 of increased tension of the arterial wall (lessened lability) on the conduction 

 of the crest of the systolic wave. 



The peripheral conditions affect the lability and the pressure readings. 



The Measurement of Arterial Pressure in Man. II. — A Schematic 



Investigation. 



By Martin Flack, Leonard Hill, F.R.S., and James McQueen. 



(Received December 3, 1914.) 



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

 Research Fund), and the Pathological Laboratory, Aberdeen University.) 



MacWilliam and Melvin* have demonstrated in the case of the excised 

 artery — compressed in their schema — that a compressing force which was not 

 sufficient to obliterate the pulse caused a great fall in the manometer, which 

 they placed distally to the compression tube. To cite an example, the 

 entering pressures in the proximal manometers were : systolic 178 mm. Hg, 

 diastolic 118 mm. Hg. A compressing force of 140 mm. Hg caused a great fall 

 in the distal manometers — systolic became 42 mm. Hg, diastolic 22 mm. Hg. 

 We find that the artery, under these conditions, is flattened during diastole, 

 and the inflow during systole is not of sufficient duration to maintain the 

 distal pressure, supposing the resistance to outflow is unchanged. If the 

 resistance to outflow is increased, no such distal fall of pressure occurs. 



Their schema differs in essential points from the conditions which pertain 

 to an artery embedded in living tissues and encircled by an armlet. The 

 pressure within the armlet at first does not deform the artery, but expresses 

 blood from, and increases the peripheral resistance in, the mass of tissue it 



* ' Heart,' vol. 5, p. 153 (1914). 



