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BLOOD PRESSURES IN MAN, NORMAL AND PATHOLOGICAL 323 



poor support like the temporal, where elongation and tortuosity may 

 develop in an apparently healthy vessel. The present writer (89) 

 has shown that the elongation of an artery by internal pressure is 

 enormously great in a relaxed as compared with a tonically contracted; 

 further, as the process of elongation needs time to develop, the con- 

 tinuous (diastolic) pressure is more effective than the transient systolic 

 rises. Abnormal conditions of the arterial wall may of course diminish 

 its resistance to distention. 



2. Apart from such impairment of resistance persistently high pres- 

 sures tend to elongate the artery and to loosen or pull it away from 

 its normal attachments along its normally straight course, as easily 

 recognised in the case of the brachial, especially in a thin arm, where 

 the vessel is felt as a tube running an elongated and devious course in 

 bold curves down the arm — especially prominent a little above the 

 elbow. The absence of such conditions in the presence of high arterial 

 pressure of unknown duration affords presumptive evidence that the 

 high pressure is not of long standing. 



It may be taken as established that high blood pressure readings, 

 when carefully taken, represent approximately correct measurements 

 of the actual intra-arterial pressures as a rule. It is only in a small 

 minority of abnormal cases of thickened arteries with excessive tonic 

 contraction, etc., that serious discrepancy may occur, sclerotic condi- 

 tions without muscular contraction having no important influence. 

 Digital compression for 3 or 4 minutes or massage of the artery are 

 useful in removing abnormal resistance and have the advantage of not 

 causing congestion of the limb which may arise from repeated com- 

 pressions by the armlet — with very disturbing results, especially in 

 some susceptible cases, giving erroneous auscultatory indications or 

 actual changes of arterial pressure, etc. 



The pronounced effects of mental stress, excitement and worry in 

 producing and maintaining high blood pressure emphasise the signifi- 

 cance of the nervous system whether exercised directly through cardio- 

 vascular innervation or more indirectly through endocrine or metabolic 

 alterations. The frequent variation of the pressure from day to day 

 or even at shorter periods opposes the idea of structural causation 

 involving increased peripheral resistance and tells against the presence 

 of permanent chemical agencies acting on the vessels directly. The 

 constancy of a lowered pressure during sleep reported in some high 

 pressure cases points in the same direction (MuUer, Blume, Katsch 

 and Pansdorf). 



