[Alteration of myocardial contractility during progressive hypoxemia in pigs]

Myocardial contractility independent on the loads of the heart was examined during progressive hypoxemia in nine pigs. left ventricular pressure-volume relation (LVPVR) was analyzed to obtain end-systolic elastance (Ees) and ventriculoarterial coupling (Ea/Ees), concomitantly with the measurements of cardiac output (CO), systemic oxygen delivery (DO2) and other indicators of systemic oxygen metabolism. Hypoxemia was induced by reducing inspired oxygen fraction (FIO2), and the measurement was performed at an FIO2 levels of 0.21, 0.18, 0.15, 0.13, 0.11 and 0.10. During progressive hypoxemia, a maximal increase in CO was observed at FIO2 of 0.11 (P < 0.05, vs FIO2 0.21), while, Ees reached the maximum at FIO2 of 0.13 (P < 0.05, vs FIO2 0.21), then it decreased below FIO2 of 0.11. Ea/Ees showed the best ventriculoarterial coupling at FIO2 of 0.13, and the coupling worsened below FIO2 of 0.11. It is concluded that load-independent myocardial contractility started to decline even when CO was still increasing to compensate the reduction of DO2 during progressive hypoxemia.