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-dependent impairment of left ventricular (LV) function. This impairment is related to a deficient length-dependent regulation of LV function. We investigated 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 compared before and during dobutamine 5 microg x kg(-1) x min(-1). Effects on contraction were evaluated by analysis of changes in dP/dtmax. Effects on relaxation were assessed by analysis of R (slope of the relation between the time constant of isovolumic relaxation and end-systolic pressure). Correlations were calculated with linear regression analysis using Pearson's coefficient r. The effects of leg elevation on variables of contraction and relaxation were coupled. We found a close relationship between changes in dP/dtmax and individual values of R (r = 0.84; P < 0.001). Dobutamine improved myocardial function and accelerated LV pressure decrease. Under dobutamine, the increase in dP/dtmax with leg elevation was larger (P < 0.001) and load dependence of LV relaxation was reduced (P = 0.001). Dobutamine improved the effects of leg elevation on LV function, reflecting improved length-dependent regulation of LV function.


CONCLUSIONS
This study demonstrated that beta-adrenoreceptor stimulation with dobutamine improved length-dependent regulation of myocardial function assessed during leg elevation in cardiac surgical patients.
De Hert
S G
SG
Department of Anesthesiology, University Hospital Antwerp, Belgium. sdehert@uia.ac.be
Van der Linden
P J
PJ
Broecke
P W
PW
Rodrigus
I E
IE
Sermeus
L A
LA
Moulijn
A C
AC
Gillebert
T C
TC
D000318:Adrenergic beta-Agonists / Q000008:administration & dosage / Q000627:therapeutic use*; D000368:Aged; D002302:Cardiac Output / Q000187:drug effects; D002304:Cardiac Pacing, Artificial; D002306:Cardiac Volume / Q000187:drug effects; D002316:Cardiotonic Agents / Q000008:administration & dosage / Q000627:therapeutic use; D001026:Coronary Artery Bypass; D004280:Dobutamine / Q000008:administration & dosage / Q000627:therapeutic use*; D017558:Elective Surgical Procedures; D005260:Female; D006339:Heart Rate; D006801:Humans; D007866:Leg / Q000502:physiology; D016014:Linear Models; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D011187:Posture; D013318:Stroke Volume / Q000187:drug effects; D016277:Ventricular Function, Left / Q000187:drug effects*; D017725:Ventricular Pressure / Q000187:drug effects
D000318:Adrenergic beta-Agonists; D002316:Cardiotonic Agents; D004280:Dobutamine