Abstract
AbstractThe relation between contraction frequency and mechanical performance was investigated in isolated perfused heart preparations and in papillary muscles from human fetuses at mid‐gestation. The influence of mepivacaine on the isometric force and the action potential of the papillary muscles and on the contractility of the whole hearts was also studied. Under the experimental conditions used, the isometric force of the papillary muscles increased with frequency within the range 60 to 180 contractions per min. The right intraventricular pressure of the isovolumetrically contracting hearts was influenced only to a minor degree by changes in contraction rate between 60 and 150 contractions per min and decreased at higher frequencies. Mepivacaine (0.625–10 μg/ml) caused a dose‐dependent decrease of the active force and a slight reduction of the duration of the action potential in the papillary muscle. The effects of contraction frequency and of mepivacaine are discussed in relation to the asynchrony of the ventricular contraction.
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