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

  • Landois, Leonard
Date:
1888
Catalogue details

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.

    112/980 page 60
    on the upper limb the valve is acted on only at each systole of the heart, blood is driven beyond it, but (larin<,' diastole it closes and no blood can I'eturn. This goes on until the pressure beyond the valve in the mercury manometer is the same as in the heart. If the valve be reversed, it is converted into a minimum manometei .] 49. PATHOLOGICAL CARDIAC ACTION.—Cardiac Hypertrophy.—All resistance.'? to the movement of the blood through the various chambers of the heart, and through the vessels com- municating with it, cause a greater amount of work to be thrown upon the x^ortion of the heart specially related to this part of the circulatory system ; consequently, there is produced an increase in the thickness of the muscular walls and dilatation of the heart. If the resistance or obstacle does not act upon one part of the heart alone, but on parts lying in the oniuard direc- tion of the blood-stream, these parts al.so subsequently undergo hypertrophy. If in addition to the muscular thickening of a ]iart of the heart, the cavity is simultaneou-slj' dilated, it is spoken of as eccentric hypertrophy or hypertrophy with dilatation. The obstacles most likely to occur in the blood-vessels, are narrowing of the lumen or want of elasticity in their walls; in the heart, narrowing of the arterial or venous orifices or insufficiency or incompetency of the valves. Incompetency of the valves forms an obstruction to the movement of the blood, by allowing part of the blood to flow back or regurgitate, thus throwing extra work upon the heart. Thus arise—(1) Hypertrophy of the left ventricle, owing to resistance in the area of the systemic circulation, especiallj' in the arteries and capillaries—not in the veins. Amongst the causes are—constriction of the orifice or other parts of the aorta, calcification, atheroma, and want of elasticity of the large arteries and iriegular dilatations or aneurisms in their course ; insufficiency of the aortic valves, in which case the same pressure always obtains within the ventricle and in the aorta ; and, lastly, cirrhosis of the kidneys, whereby the excretion of water by these organs is diminished. Even in mitral insufficiency, compensatory hypertrophy of the left ventricle must occur, owing to the hypertrophy of the left atrium in consequence of the increased blood-pressui'c in the pulmonary circuit. (2) Hypertrophy of the left auricle occurs in stenosis or constriction of the left auriculo-ven- tricular orifice, or in insufficiency of the mitral valve, and it occurs also as a result of aortic insufficiencj', because the auricle has to overcome the continual aortic pressure within the ventricle. (3) Hypertrophy of the right ventricle occurs («) when there is resistance to the blood- stream through the pulmonary circiiit. The resistance may be due to (o) obliteration of large vascular areas in consequence of destruction, shrinking or compression of the lungs, and the disappearance of numerous capillaries in emphysematous lungs ; (/3) overfilling of the pulmonary circuit with blood in consequence of stenosis of the left auriculo-ventricular orifice, or mitral insufficiency—consequent upon hypertrophy of the left auricle resulting from aortic insufficiency, {h) When the valves of the pulmonary artery are insufficient, thus permitting the blood to flow back into the ventricle, so that the pressure within the pulmonary artery prevails within the right ventricle (very rare). (4) Hypertrophy of the right auricle occurs in consequence of the last-named condition, and also from stenosis of the tricuspid orifice, or insufficiency of the tricuspid valve (rare). Artificial Injury to the Valves.—If the aortic valves are perforated, with or without simultaneous injury to the mitral or tricusjnd valves, the heart does more work; thus the physical defect is overcome for a time, so that the blood-pressure does not fall. The heart seems to have a store of reserve energy which is called into play. Soon, however, dilatation takes place, on account of the regurgitation of the blood into the heart. Hypertrophy then occurs, but the compensation meanwhile must be obtained through the reserve energy of the heart {0. Rosenbaclb). Impeded Diastole.—Among causes which hinder the diastole of the heart are—copious effusion into the pericardium, or the pressure of tumours upon the heart. The systole is greatly inter- fered with when the heart is united to the pericardium and to the connective-tissue in the mediastinum. As a consequence the connective-tissue, and even the thoracic wall, are drawn in (luring contraction of the heart, so that there is a retraction of the region of the apex-beat during .systole, and a protrusion of this part during the diastole. [Palpitation is a symptom indicating generally very rapid and quick action of the heart, the l)ul.sations often being unequal in time and intensity, while the person is generally conscious of the irregularity of the cardiac action. It may be due to some organic condition of the heart Itself, especially where the cardiac muscles are weak, in cases of dilatation and hypertrophy of the left ventricle, where the heart is gradually becoming unable to overcome the resistances offered to its work, and especially during exertion when the heart is taxed above its strength It may also occur where the blood-pressure is low, as in anremia, so that the heart contracts quickly there being little resistance opposed to its action. The excitability of the cardiac muscle may be increased as in fatty heart, when very slight exertion may excite it often in a paroxysmal way. In other cases, it is ncrmxis in its origin, being either direct or reflex. In very emotional and excitable people (especially in women) it is easily set up, and in some people it may be
    digitised image 1
    digitised image 2
    digitised image 3