Influence of acute hemodynamic changes on the peak velocity of contractile element shortening and maximum velocity obtained by the calibrated apex cardiography in dogs.

The effect of various alterations in preload, afterload and inotropic state of the left ventricle on the noninvasive peak velocity of contractile element shortening (Vpm) and maximum velocity of contractile element shortening (Vmax) was studied in the anesthetized dogs in an attempt to test the methods and clarify some of the determinants of these parameters. Calibrated displacement left apex cardiogram obtained with time constant 3 sec and calibrated first derivative of apex cardiogram were recorded simultaneously with left ventricular pressure and its first derivative, electrocardiogram and phonocardiogram. The values of Vpm obtained from catheterization and calibrated apex cardiography were similar in magnitude and standard deviations under various hemodynamic interventions. A highly significant relation was found between these invasive and noninvasive parameters of myocardial contractility. Both Vpm and Vmax were elevated during the administrations of isoprenaline and strophanthin, where only Vpm showed a decrease after extreme volume or pressure load. In conclusion, the results from this study suggest that Vpm and Vmax of the calibrated apex cardiography are a reliable noninvasive tool for assessing left ventricular function; furthermore, Vpm is relatively load independent, whereas Vmax is virtually unchanged over a broad range of loading conditions.

Influence of acute hemodynamic changes on the negative peak of the first derivative of apex cardiogram during ventricular relaxation in dogs.

The effect of various alterations in the preload, the afterload and the inotropic state of the left ventricle on the first derivative of apex cardiogram (dA/dt) was studied in 9 anesthetized dogs to clarify some of the determinants of the negative peak of dA/dt and isovolumic relaxation time. The first derivative of the apex cardiogram was recorded simultaneously with the left (ventricular pressure, conventional left apex cardiogram, first derivative of left ventricular pressure (dP/dt), electrocardiogram and phonocardiogram. Both dA/dt and dP/dt curves were similar in contour and occurred nearly simultaneously. This close relationship was preserved during various acute haemodynamic changes. The maximum negative dA/dt and the isovolumic relaxation period was closely related to the level of afterload. Large rapid augmentation of mean aortic pressure resulted in a significant increase in the negative dA/dt and shortening of the isovolumetric relaxation time, where reduction of afterload had an opposite effect. Isoprenaline acutely augmented minimum dA/dt. It is concluded that measurement of negative peak dA/dt under some conditions is a reliable noninvasive technique for assessing myocardial relaxation.

Influence of acute hemodynamic changes on the negative peak of the first derivative of apex cardiogram during ventricular relaxation in dogs.

The effect of various alterations in preload, afterload and inotropic state of the left ventricle on the first derivative of apex cardiogram (dA/dt) was studied in the anesthetized dogs, in an attempt to clarify some of the determinants of the negative peak of dA/dt and isovolumetric relaxation time. First derivative of apex cardiogram was recorded simultaneously with left ventricular pressure, conventional left apex cardiogram, first derivative of left ventricular pressure, electrocardiogram and phonocardiogram. Both dA/dt and dP/dt curves represent similarity in contour and were found to occur nearly simultaneously. This close relationship was preserved during various acutely hemodynamic changes. Maximum negative dA/dt and isovolumic relaxation period was closely related to the level of afterload. Large rapid augmentation of mean aortic pressure did results in statistically significant increase of negative dA/dt and shortening of isovolumic relaxation time, where reduction of after load had an opposite effect. Another interventions, which acutely augment min dA/dt was nitroprusside and isoprenalin. It is concluded, that negative peak dA/dt under some conditions provides a reliable noninvasive index for assessing myocardial relaxation.