508 



The Measurement of Arterial Pressure in Man. I. — The 



Auditory Method. 

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



(Received December 3, 1914). 



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

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



In a previous communication* we showed that when an artery, exposed in 

 a living animal, is compressed in a glass compression tube full of water 

 (Ringer's solution), the pulse, distal to the compression, is not obliterated 

 until the pressure of the water is raised just above the systolic pressure of 

 the blood in the artery, whereas when the same artery, placed on bone, wood 

 or glass, is compressed by the bag of Leonard Hill's pocket sphygmometer, 

 or by the armlet of the sphygmometer, so arranged that it does not embrace 

 the surrounding pulsating tissues, the pulse is abolished by pressures under, 

 and even much under, the diastolic pressure of the blood stream. 



These facts are correlated with the manner in which the artery is com- 

 pressed in each case. Enclosed in the compression tube the artery is 

 compressed by the water equally in a circular fashion so that the rise of 

 external pressure, up to the diastolic pressure, has no effect in producing 

 deformation of the artery. Ultimately, when the compression becomes 

 greater than the diastolic pressure, the artery flattens and changes to the 

 oval shape during diastole. It is flattened during systole when the external 

 pressure rises above the systolic pressure. When the carotid artery of the 

 living animal is freed from the surrounding tissues and placed on a watch- 

 glass and compressed by the bag of the pocket sphygmometer, or by the 

 armlet so arranged as not to embrace the pulsing tissues of the neck, the 

 oval deformation sets in at far lower pressures and is complete in relatively 

 thin-walled labile arteries at pressures much under diastolic pressure. 

 Consequently the blood flow is cut down by an external pressure less than 

 diastolic to a mere ineffective trickle of blood, and the pulse is completely 

 damped out. If a branch of the carotid artery distal to the bag were con- 

 nected with a C-spring manometer, the record would show a progressive 

 lowering of both the systolic and the diastolic pressure almost to zero, till 

 with an external pressure much less than the diastolic pressure in the 

 aorta the pulse was damped out and the blood flow became a trickle. 



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



