Length-dependent regulation of left ventricular function in coronary surgery patients

Background: Load-dependent impairment of left ventricular (LV) function was observed after leg elevation in a subgroup of coronary surgery patients. The present study investigated underlying mechanisms by comparing hemodynamic effects of an increase in LV systolic pressures with leg elevation to effects of a similar increase In systolic pressures with phenylephrine. Methods: The study was performed in patients undergoing elective coronary surgery prior to cardiopulmonary bypass. High-fidelity LV pressure tracings (n = 25) and conductance LV volume data (n = 10) were obtained consecutively during leg elevation and after phenylephrine administration (5 mu g/kg). Results: Leg elevation resulted in a homogeneous increase in end-diastolic volume. The change in stroke volume (SV), stroke work (SW) and dP/dt(max) was variable, with an increase In some patients but no change or a decrease in other patients. For a matched increase in systolic pressures, phenylephrine increased SW and dP/dt(max) in all patients with no change in SV. Load dependence of relaxation (slope R of the tau-end-systolic pressure relation) was inversely related for changes in SV, SW, and dP/dt(max) with leg elevation but not with phenylephrine. Conclusions: The different effects of leg elevation and phenylephrine suggest that the observed decrease in SV, SW, and dP/dt(max) with leg elevation in some patients could not be attributed to an impaired contractile response to increased systolic LV pressures. Instead, load-dependent impairment of LV function after leg elevation appeared related to a deficient length-dependent regulation of myocardial function.