The estimation of contractile element velocity during the isovolumic period: Alterations by cardiac output and contractile state

The relationship between the first derivative of ventricular pressure and developed pressure during the isovolumic period (dP/dt/K.DP) was analysed in anaesthetized dogs using the heart-lung preparation. This relationship has been proposed as a method to obtain V_max and thus to assess contractility in the intact heart. In the present study changes in preload achieved by increases in the cardiac output up to 100% above control did not alter V_max when assessed by this method. When the cardiac output was increased about 200% above control, significant increases in V_max were obtained. The sensitivity of this method in detecting changes in contractility in the intact heart was also analysed. At constant stroke work and heart rate, small decreases in the left ventricular end diastolic pressure (range:-1 to -2mmHg) were produced by calcium infusion. The Vmax estimation with the techniques described herein was not sufficiently sensitive to reflect changes in contractility. Thus, isovolumic dp/dt/P does not provide a consistent correlate with changes in contractility.