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 rates 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 measures 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. Thus, LV filling and wall thinning depend in a complex fashion on loading conditions, heart rate and contractile state.(ABSTRACT TRUNCATED AT 250 WORDS)