The blood-pressure and its variations in the arterioles, capillaries and smaller veins / by Charles S. Roy and J. Graham Brown.

  • Roy Charles S. (Charles Smart)
Date:
[1878?]
Catalogue details

Licence: Public Domain Mark

Credit: The blood-pressure and its variations in the arterioles, capillaries and smaller veins / by Charles S. Roy and J. Graham Brown. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    of tlie compressed, as compared with the surrounding skin. The plates he used were of various sizes, varying from 2'56 to 4'56 sq. mm. Given the area of the plate made use of and the weight employed to press it against the skin, it is of course easy to calculate the equivalent water or mercury pressure. In making his experiments he assumed that the pressure which sufficed to cause an evident change in the colour of the small area of skin lying under the glass plate, was equal to the pres- sure of the blood in the capillaries lying nearest the surface, being led to suppose from theoretical considerations that the more superficially situated vessels would be fully exposed to the influence of pressure, such as he used, applied to the surface of the skin, while the more deeply seated capillaries would be protected in some measure by the elasticity of the tissues; and taking it further for granted, that the first distinct change in colour, produced by gradually increasing the pressure on the spot of skin, was to be looked upon as indicating a collapse of the upper layer of capillaries. That, with small plates such as those employed by v. Kries, the deeper lying capillaries would be less pressed upon than those lying under the epidermis, is probable enough. At the same time, the degree to which the elastic resilience of the tissue lying between the plate and the bone would lessen the true extravascular pressure as compared with that applied, must necessarily vary greatly with the area of the glass plate employed. We cannot assume, moreover, that the elasticity of the compressed tissue would not also protect to some extent the superficial capillaries from pressure applied to the surface of the skin. How far this would be the case, could not, of course, be learned for any given measurement. That the first distinct whitening of the skin, px-oduced on gradually increasing the weights used to press the glass plate on the portion of skin, could be taken as evidence of collapse of the upper layer of capillaries, is, we believe, only permissible on the assumption, firstly, that the walls of these capillaries, as well as of those lying deeper, and which assist in giving a reddish colour to the skin, are practically inelastic, and secondly, that the extra-capillary pressure which will cause collapse of the capillaries of a given plexus, will be the same for all of its component vessels. According to our own observations neither of these suppositions is correct, as we hope to shew further on. It would be unfair, however, to criticize v. Kries’ method as one which was supposed to give absolute values; it was only upon the relative values obtained under varied conditions that weight was laid by the author referred to, and against these there cannot be much objection.