The strength of the force of myocardial contraction is dependent on direct autonomic control affecting preload and afterload but also on the contractility of the myocardium. Contractility is a measure’ of the intrinsic ability of the myoto contract to produce a peak tension from a given resting fibre length. This property is independent of loading conditions. It should not be confused with the force of contraction, which is directly affected by preload and afterload. The degree of contractility is also known as the inotropic state. A positive inoresponse is an increase in contractility. Myocardial contractility can be increased directly by sympathetic stimulation, to some extent by a decrease in parasympathetic tone and indirectly by an increase in heart rate.
When contractility is reduced, for example as a result of myocardial disease, stroke volume will fall. This will result in a reflex increase in heart rate and an adjustment in the tone of the peripheral cardiovascular system to ensure that blood pressure is maintained. In the long-term, changes in sodium and water retention will occur, and a high level of catecholamines will be present until an equilibrium is met. To some extent, this will improve contractility via beta receptor mechanisms. Factors which affect contractility are summarised in
The strength of the force of myocardial contraction is dependent on direct autonomic control affecting preload and afterload but also on the contractility of the myocardium. Contractility is a measure’ of the intrinsic ability of the myoto contract to produce a peak tension from a given resting fibre length. This property is independent of loading conditions. It should not be confused with the force of contraction, which is directly affected by preload and afterload. The degree of contractility is also known as the inotropic state. A positive inoresponse is an increase in contractility. Myocardial contractility can be increased directly by sympathetic stimulation, to some extent by a decrease in parasympathetic tone and indirectly by an increase in heart rate.When contractility is reduced, for example as a result of myocardial disease, stroke volume will fall. This will result in a reflex increase in heart rate and an adjustment in the tone of the peripheral cardiovascular system to ensure that blood pressure is maintained. In the long-term, changes in sodium and water retention will occur, and a high level of catecholamines will be present until an equilibrium is met. To some extent, this will improve contractility via beta receptor mechanisms. Factors which affect contractility are summarised in
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