EFFECTS OF LOADING CONDITIONS AND CONTRACTILE STATE (METHOXAMINE AND DOBUTAMINE) ON LEFT-VENTRICULAR EARLY DIASTOLIC FUNCTION IN NORMAL SUBJECTS

The influence of changes in preload, afterload and contractile state on left ventricular (Lv) filling characteristics were examined. Normal subjects underwent echocardiographic determination of the peak release of LV dimension change and wall thinning and their respective timing at rest, after preload augmentation with dextran, during increased afterload with methoxamine and during inotropic stimulation by dobutamine. These 2 peak velocities and their timing in diastole correlated well with each other and responded similarly to interventions. Increased preload resulted in higher peak velocities of dimension change and wall thinning, without changing the time in diastole at which they occur. Both peak velocities moved later into diastole with higher afterload; however, the overall change in magnitude was variable and without statistical significance. Inotropic stimulation resulted in faster rates of peak dimension change and wall thinning, which occurred at an earlier point in diastole. Examination of various means of LV size and function over a wide range of preload and afterload conditions under a constant contractile state revealed a complex set of relations. The ratio of wall thickness-to-dimension at end-diastole showed the most significant relation to the peak rate of dimension change, whereas peak thinning was best correlated with fractional wall thickening. Both velocities were also significantly but more weakly related to other variables of systolic function. The timing of these peak velocities correlated most closely with the end-systolic wall stress and heart rate. LV filling and wall thinning dependent in a complex fashion on leading conditions, heart rate and contractile state. These interactions must be considered when echocardiographic indexes of diastolic function are used in the clinical setting.