The effects of beta-adrenergic stimulation on the length-dependent regulation of myocardial function in coronary surgery patients

Increasing cardiac load by leg elevation identifies patients with load-depe ndent impairment of left ventricular (LV) function. This impairment is rela ted to a deficient length-dependent regulation of LV function. We investiga ted the effects of dobutamine on length-dependent regulation of LV function in coronary surgery patients (n = 25). High-fidelity LV pressure tracings were obtained at end-expiration, while hearts were paced at a fixed rate of 90 bpm. Effects of leg elevation on contraction and relaxation were compar ed before and during dobutamine 5 mu g . kg(-1) . min(-1). Effects on contr action were evaluated by analysis of changes in dP/dt(max). Effects on rela xation were assessed by analysis of R (slope of the relation between the ti me constant of isovolumic relaxation and end-systolic pressure). Correlatio ns were calculated with linear regression analysis using Pearson's coeffici ent r. The effects of leg elevation on variables of contraction and relaxat ion were coupled. We found a close relationship between changes in dP/dt(ma x) and individual values of R (r = 0.84; P < 0.001). Dobutamine improved my ocardial function and accelerated LV pressure decrease. Under dobutamine, t he increase in dP/dt(max) with leg elevation was larger (P < 0.001) and loa d dependence of LV relaxation was reduced (P = 0.001). Dobutamine improved the effects of leg elevation on LV function, reflecting improved length-dep endent regulation of LV function. Implications: This study demonstrated tha t beta-adrenoreceptor stimulation with dobutamine improved length-dependent regulation of myocardial function assessed during leg elevation in cardiac surgical patients.