Observations on venous pressures and their relationship to capillary pressures / by W.M. Bayliss and E.H. Starling.

  • Bayliss, William Maddock, Sir, 1860-1924.
Date:
1894
Catalogue details

Licence: Public Domain Mark

Credit: Observations on venous pressures and their relationship to capillary pressures / by W.M. Bayliss and E.H. Starling. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    In the first place, between capillaries and the arterial pressure is situated the peripheral resistance, i.e. the arterioles, so that, unless we are certain that these arterioles do not alter in size, we cannot say that a rise of general pressure will occasion any corresponding rise in the capillaries beyond the peripheral resistance. If we have to be content with a single determination of pressure, it would be better to take the pressure in the vein coming from the set of capillaries, the condition of which we are investigating. Here there is in most cases no unknown or varying resistance situated between the capillaries and the point at which we are investigating the pressure, so that the venous pressure would give us a better clue to the variations of the capillary pressure than the observations on arterial pressure. As a matter of fact however, neither of these methods suffice in themselves. Since we cannot conveniently measure capillary pressure directly and do not know the rate of fall of pressure in the arterioles, the only method which will give us reliable information as to the variations of capillary pressure, is to take the pressure on both sides of these capillaries, that is to say, to take arterial and venous pressures simultaneously. Even under these circumstances however there is a number of variable factors which must be taken into consideration before we can decide as to the existence or direction of a change in the intracapillary pressure. It will be simpler in the first place to take the case in which the distribution of resistance in the area under consideration undergoes no change, i.e. the arterioles neither contract nor dilate. In this case, if both arterial and venous pressures rise together, or if one pressure rises while the other remains constant, we may say with certainty that the capillary pressure is increased. In the same way if both pressures fall, or if one falls while the other remains constant, the capillary pressure must be diminished. If on the other hand, the pressures vary in different directions, if, for instance, the venous pressure goes up while the arterial pressure sinks, it must be entirely a matter of surmise as to what occurs in the capillaries, and the pressure here may be rising, sinking, or remaining constant. If the arterial pressure rises while the venous sinks, we can in one case assert that the capillary pressure is diminished. This is the case in which the rise in arterial and the fall in venous pressure is due to constriction of the arterioles in the part under observation. In other cases in which there is a change in the calibre of the smaller arteries, the determination of a change in the capillary pressure is a matter of considerable difficulty. We will take for example the splanchnic area. In the diagram a to 6 repre-