The health of the blood-vessels / by David Fraser Harris.

  • David Fraser Fraser-Harris
Date:
1900
Catalogue details

Licence: In copyright

Credit: The health of the blood-vessels / by David Fraser Harris. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    tbe arterial wall at each ])oint throughout the arterial system— that is, in doing work against its elastic force, and hence, as it travels to the periphery, its dilating force gets spent. The phe- nomenon of the pulse depends on the degree of elasticity of the arterial wall; if the wall has become inelastic from thickening or rigid from atheroma, gouty conditions, calcareous infiltrations as in old age, then the arterial pulse is less perceptible, but a pulse instead may appear in the capillaries, since it has not been able to expend itself on the inelastic arterial wall. If the arterial blood-pressure be considerably reduced, as happens when the peripheral resistance is greatly diminished, owing, for instance, to dilatation of the arterioles over the whole skin, e.g. in a warm bath, then the pulse-wave does not spend so much of its force as before against the arterial wall, and thus, not being exhausted on arrival at the capillaries, may pass over not only into them, but into the veins, giving rise to the venous pulse. It will therefore be apparent that unless arteries were always a little over-full you could have no pulse-wave, for if they were flabby and half empty, their walls would not be stretched by the blood thrown out of the heart. In the veins, the blood-pressure is still less than in the capil- laries, and in connection with this it may be noted that the walls of veins are very thin; as they have no great pressures to with- stand, they need not be thick. IsTature is usually economical. Quite close to the heart the pressure in the veins becomes what is called negative —that is, it is less than the pressure of the atmosphere, so that if such a vein be opened, air is liable to be sucked in, carried to the heart, and thence to the lungs, where it blocks up some of the capillaries. Venous blood returns to the heart because of aspiration of heart and chest in their movement, and also through muscular contraction coupled with the jiresence of valves in veins. Arterial blood-pressure may vary within the limits of health; a persistently high arterial pressure (tension) may be the sign of a more or less serious condition; it may indicate ple- thora, certain forms of kidney disease and gouty tendencies. A high blood-pressure, especially if associated with degenerated arterial wall (fatty, calcareous or atheromatous), may result in the vessel bursting: when this happens in the brain it is known as apoplexy. The blood-pressure must be of a certain