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The isometric period of contraction as a determinant of cardiac performance and digitalis action

1960; Elsevier BV; Volume: 6; Issue: 6 Linguagem: Inglês

10.1016/0002-9149(60)90359-3

1879-1913

Mohinder P. Sambhi,

Heart Rate Variability and Autonomic Control

The duration of the isometric period of contraction has been determined from apex cardiograms and arteriograms recorded on thirty subjects. The hypertensive patients showed a significant prolongation of this phase as compared to the normal. This, however, was not related to the height of blood pressure. Digitalization both in normal subjects and patients suffering from cardiac failure produced a uniform and significant increase in the duration of this phase. This increase was unrelated to the cardiac rate. It is suggested that the prolongation, relative or absolute, of the isometric phase is one of the fundamental mechanisms of cardiac performance in response to an increased work load, and acts in conjunction with the mechanisms responsible for adjustment to volume-load (Starling's principle) by altering the gradient of rise of intraventricular pressure and shortening the isometric phase. This gradient of pressure rise is probably the chief determinant of the duration of the isometric phase of contraction. The mechanism whereby digitalis produces compensation in the failing heart also involves a prolongation of the isometric phase.