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BLOOD PRESSURES IN MAN, NORMAL AND PATHOLOGICAL 305 



reduce strong tonic contraction which may sometimes be present in 

 thickened arteries, giving a certain resistance to obliteration and 

 leading to an over-estimation (to some extent) of the actual intra- 

 arterial pressure. But a better method is to close the brachial artery 

 for three minutes by digital pressure upon it, as reconmiended by 

 Mac William and Melvin, instead of constricting the whole limb by the 

 armlet and leading to venous turgescence and the associated tendency 

 to error described above — as especially applicable to a certain (limited) 

 number of subjects. Experiments (unpublished) in this Laboratory 

 show that in some instances at least the trouble is caused mainly by 

 congestion of the limb, not simply by pressure on the brachial artery. 

 Digital compression while removing the abnormal resistance to oblit- 

 eration of the pulse does not induce the auscultatory error referred 

 to above. 



When the auscultatory method is rendered difficult by noisy sur- 

 roundings or by impaired hearing in the observer, the vibratory method 

 of Ehret (38) a modification of the tactile method, can be usefully 

 combined — a finger being applied to the artery on the distal side of the 

 auditory tambour, to detect the vibration associated with the sound 

 at the diastolic level. This method is strongly recommended by 

 Gallavardin (51). It is much simpler than checking by oscillatory 

 methods. But difficulties are present in fat subjects with deep bra- 

 chials, small calibre, and cases (especially aortic regurgitation) where the 

 change in the vibration constituting the diastolic index is less definite 

 than usual. 



As regards the mechanism of the sounds, the subject of various 

 conflicting views (Gittings (55), Erlanger (39), Mac William and 

 Melvin, L. Hill and others) there have been interesting investigations by 

 Gallavardin and Barbier (52), (8) who describe two zones in the curve 

 of sound; 1, in the upper half of the curve with maximum near the 

 systolic index and murmurs caused by whorls in the blood current as 

 it passes through the compressed area of the artery and gets into a 

 region of lower pressure distally to the armlet; 2, in the lower half of 

 the curve with maximum near the diastolic index, the sounds here 

 originating in the vessel wall and related to sympathetic nerve influence 

 on the arterial wall. Attempts to interpret the meanings of the notable 

 variations in the character of the sounds in different subjects, the 

 duration of the phases and the changes induced by armlet compression 

 have been made by Gallavardin with Haour, Barbier (52) and Tixier, 

 and by Tixier (126), B. Smith (116) Sorapure (117) and others, following 



