Chapter

Clinical physiology of the normal heart

David E.L. Wilcken

in Oxford Textbook of Medicine

Fifth edition

Published on behalf of Oxford University Press

Published in print May 2010 | ISBN: 9780199204854
Published online May 2011 | e-ISBN: 9780199570973 | DOI: http://dx.doi.org/10.1093/med/9780199204854.003.160103_update_001

Series: Oxford Textbooks

Clinical physiology of the normal heart

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The function of the heart is to provide the tissues of the body with sufficient oxygenated blood and metabolites to meet the moment-to-moment needs as dictated by physical activity and postural and emotional changes.

The energy requirements of the heart during rest and exertion are influenced by ventricular volume, outflow resistance (blood pressure), venous return, and the activity of the autonomic nervous system. An increase in ventricular volume increases wall tension during contraction, and an augmented myocardial oxygen supply is then required to maintain the same systemic blood pressure and stroke volume.

The normal integration of the venous return, heart rate, stroke volume, and arterial blood pressure ensures that there is an adequate supply of oxygen and nutrients to the tissues. The activities of the sympathetic and parasympathetic nervous systems contribute to the adjustment of cardiac performance to immediate needs—the former by increasing heart rate and myocardial contractility during exertion and emotion, the latter by maintaining a relatively slow heart rate at rest. Vagal fibres in the heart are distributed mainly to the sinoatrial node and the atria; sympathetic innervation is to both the atria and the ventricles. There is a normal diurnal variation in autonomic function, with an increased sympathetic outflow in the mornings, soon after wakening.

Coronary flow occurs largely in diastole. It is finely adjusted to meet metabolic requirements and may increase five- or sixfold during strenuous exercise. The inner layers of the ventricular muscle normally receive a slightly greater blood flow than the outer layers. Haemodynamic and ventilatory responses during exercise take 2 to 3 min to equilibrate and adjust to an increased workload and reach a new steady state. Regular exercise to least 60% of maximal heart rate about three times a week improves effort tolerance. Measurement of the cardiovascular response to exercise provides an objective assessment of cardiac function.

Chapter.  8187 words.  Illustrated.

Subjects: Cardiovascular Medicine

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