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BLOOD PRESSURES IN MAN, NORMAL AND PATHOLOGICAL 327 



deals with schema results, animal experiments and clinical observations. 

 He concludes that the differential pressure is essentially due to the 

 transference of kinetic energy in a fluid in rapid motion into stress when 

 the flow meets resistance, the relative degrees of slowing thus induced 

 in different vessels and the relative masses of blood concerned being 

 important, while the condition of the arterial wall (suggested by L. 

 Hill) probably plays a part as may also the "breaker formation" 

 of Bramwell and A. V. Hill (20), though not essential. The higher 

 leg pressures are accounted for on these lines, local arterio-sclerotic 

 changes being capable of exaggerating the phenomenon. Larger dif- 

 ferences in arm-leg pressure were found with contracted arterioles — 

 involving greater slowing and greater transformation of kinetic energy. 

 It is suggested that the effects obtained by L. Hill and Rowland (65) 

 with warm baths (equalisation of pressures) are explicable in this way 

 as well as on the hypothesis of altered conditions in the arterial walls. 

 The aortic arm-leg difference is thus regarded as a great exaggeration 

 of the normal carotid-femoral difference described by various observers 

 — essentially the water hammer action of Corrigan's "rushing current" 

 in aortic regurgitation. 



In animal experiments a reversed differential pressure was sometimes 

 seen, i.e., a pressure higher in the upper than in the lower limb, in 

 association with a forcible heart action with regurgitation present and 

 an apparently low peripheral resistance. No evidence seems to be 

 available of the existence of such a condition clinically. 



Capillary pressure. In the attempts to gauge the capillary pressure 

 the various methods and the different criteria applied have produced 

 a discordant and somewhat bewildering assortment of results repre- 

 senting "capillary pressure" as anything between 25 to 50 mm. H2O 

 and 70 mm. Hg. There are at least four modes of observation that 

 have been used. 



1. Blanching methods (skin of finger or hand). Following Von 

 Kries' (75) idea there have been applications by numerous observers, 

 using however different criteria, e.g., the first production of visible 

 paling, used by Easier (11) and by White (132) or complete blanching 

 (v. Basch (10)) or the pressure at which the skin again begins to flush 

 (Recklinghausen (109) and others); much confusion has resulted. Von 

 Basch's figures were 25 to 30 mm. in healthy subjects; he concluded 

 that capillary pressure can vary independently of arterial pressure; 

 Recklinghausen's value was 52,2 mm. Basler with his ochrometer 

 found normal capillary pressures at about 7 mm. Hg, but Landerer 



