A textbook of human physiology / translated from [the] 6th German edition by W. Stirling.

  • Landois, Leonard
Date:
1888
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Licence: Public Domain Mark

Credit: A textbook of human physiology / translated from [the] 6th German edition by W. Stirling. Source: Wellcome Collection.

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

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    t blood-pressure may be increased either by the action of the heart or the arterioles. If we divide the vagi the pulse beats more quickly, and in some animals the blood-pressure rises ; in this case, the rise in the two curves occurs together, and if the vagi be stimulated there is a sudden fall of the blood-pressure, due to arrest of the heart's action, so that again the two curves are parallel. If the arterioles contract the blood-pressure rises, but by and by the pulse-rate falls, owing to the cardio-inhibitory action of the vagus ; while, on the other hand, if the arterioles are dilated, the blood-pressure falls, and the heart beats faster. Thus, in both of these cases the pulse-curve and blood-pressure curve i-un in opposite directions. These results only obtain when the vagi are intact (Jirimton).] [The increase in the pulse-rate and blood-pressure following section of the vagi do not run l)arallel. Both sooner or later reach a maximum, but the blood-pressure gradually falls to or below the normal, while the pulse-rate remains above the normal {Miimc/). ] For the effects of the nervous system upon the blood-pressure see § 371. Pathological.—In persons suffering from granular or contracted kidney and sclerosis of the arteries, in lead poisoning, and after the injection of ergotin, which causes contraction of the small arteries, it is found, on employing the method of v. Basch, that the blood-pressure is raised. It is also increased in cases of cardiac hypertrophy Mith dilatation, and by digitalis in cardiac affections, while it falls after the injection of morphia. The blood-pressure falls in fever, a fact also indicated in the sphygmogram (§ 69), and it is low in chlorosis and phthisis. 86. BLOOD-PRESSUREINTHECAPILLARIES,—Methods.—Direct estimation of the capil- lary pressure is not possible on account of the smallness of the capillary tubes. If a glass jilate of known dimensions be })laced on a portion of the skin rich in blood-vessels, and if it be weighted until the capillaries become pale, we obtain approximately the pressure neces- sary to overcome the capillary pressure. N. v. Kries placed a small glass plate (tig. 109) 25-5 S([. mm., on a suitable part of the skin, e.g., the skin at the root of the nail on the terminal phalanx, or on the ear in man, and on the gum in rabbits. Into a scale-pan attached to this, weights were placed until the skin became pale. The pressure in the capillaries of the hand, when the hand is raised, Kries found to be 24 mm. Hg. ; when the hand hangs down, 54 mm. Hg. : in the ear, 20 mm., and in the gum of a rabbit, 32 mm. Roy and Graham Brown compressed from below transparent vascular mem- branes against a glass jdate by means of an elastic bag connected with a manometer, w'hile the variations in the capillaries were observed from above by a microscope. Conditions influencing Capillary Pressure.—The capillary blood-pressure in a given area increases—(1) When the afferent small arteries dilate, so that the blood-pressure within the large arteries is propagated more easily into them. (2) By increasing the pressure in the small afferent arteries. (3) By narrowing the diameter of the veins leading from the capillary area. Closure of the veins may quadruple the pressure. (4) By increasing the ^ tusor^ appara- pressure in the veins (e.(/., by altering the position of a limb). A pressure*!^^ diminution of the capillary pressure is caused by the opposite con- square of glass, ditions. Changes in the diameter of the capillaries influence the internal pres- sure. _ VVe have to consider the movements of the capillary wall itself as well as the pressure, swelling, and consistence of the surrounding tissues. The resistance to the blood-stream is gi-eatest in the capillary area, and it is evident that the blood in a long capillary must exert more pressure at the commencement than at the end of the capillary ; in the iniddle of the capillary area the blood-pressure is just about one-half of the pressure within the large arteries (DoTiders). The capillary pressure must also vary in different regions of the body. Thus, the pressure within the intestinal capillaries, in those constituting the glomeruli of the kidney and in those of lower limbs when the person is in the erect posture, must be greater than in other regions, depending in the former cases partly upon the double resistance caused by two sets of capillaries, and in the latter case partly on purely hydrostatic causes. 87. Blood-Pressure in the Veins.—In the large venous trunks near the heart (innominate, subclavian, jugular) a mean negative pressure ot about-O'l
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