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Length-dependent regulation of left ventricular function in coronary surgery patients
S G De Hert1, T C Gillebert, P W Ten Broecke
1Department of Anesthesiology, University Hospital Antwerp, Edegem, Belgium. sdehert@uia.ac.be
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 microg/kg).
Results:
Leg elevation resulted in a homogeneous increase in end-diastolic volume. The change in stroke volume (SV), stroke work (SW) and dP/dtmax 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/dtmax 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/dtmax 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/dtmax 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.