Increased oxygen cost of contractility in the endotoxemic porcine left ventricle.
OBJECTIVE
Myocardial oxygen consumption (MVO) in the septic myocardium is comparatively high in relation to the sepsis-induced reduction in ventricular work. Our previous studies indicate that this energetic inefficiency is due to increased energy consumption in excitation-contraction (EC) coupling, i.e. myocardial calcium handling.


METHODS
To further confirm this observation, we assessed the oxygen cost of contractility in anesthetized pigs before and 2 h after induction of endotoxemia (1 microg/kg endotoxin infusion over 1 h, Escherichia coli toxin, n=6). Baroreceptor reflexes were blocked by hexamethonium. Contractility was increased by stepwise dopamine infusions at baseline and 2 h after induction of endotoxemia. Oxygen cost of contractility was assessed as the relationship between myocardial contractility (E or elastance) and non-mechanical oxygen consumption (unloaded MVO), a measure of energy consumption in EC coupling or calcium handling.


RESULTS
Non-mechanical oxygen consumption (unloaded MVO) was higher after endotoxin infusions than at baseline (0.641 +/- 0.05 vs 0.383 +/- 0.07 J/beat/100 g, p < 0.05). The relationship between unloaded MVO and E, constructed by the dopamine response, was highly linear both at baseline and endotoxemia (r2 =0.76-0.99). However, endotoxin increased oxygen cost of contractility by approximately 45% (baseline 0.06 +/- 0.03 vs endotoxin 0.09 +/- 0.04 J ml/mmHg/beat/100 g).


CONCLUSIONS
Acute endotoxemia increases oxygen cost of contractility, a measure of energy consumed in EC coupling or myocardial calcium handling.
Aghajani
Ebrahim
E
Department of Digestive Surgery, University Hospital North Norway, Tromsø, Norway. ebrahim.aghajani@fagmed.uit.no
Korvald
Christian
C
Nordhaug
Dag
D
Revhaug
Arthur
A
Myrmel
Truls
T
D032761:Animal Experimentation; D000818:Animals; D019446:Endotoxemia / Q000503:physiopathology*; D006352:Heart Ventricles / Q000503:physiopathology*; D006439:Hemodynamics / Q000502:physiology; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology*; D013552:Swine