Left ventricular oxygen and substrate uptake in chronically hypoxemic lambs

Myocardial oxygen demand may be increased in chronically hypoxemic lambs because of their increased heart rate. Therefore, we determined whether left ventricular (LV) oxygen supply, oxygen uptake and oxygen demand were proportionally increased in 6-wk-old lambs, after 4 wk of hypoxemia (n = 15), as compared with control lambs (n = 14). In addition, we determined whether LV glucose, pyruvate, lactate, FFA and ketoacids uptake were altered in hypoxemic lambs, because of alterations in arterial glucose, pyruvate and lactate concentrations, that may occur in hypoxemia. Hypoxemia was induced by the combination of an atrial septal defect and pulmonary stenosis. Arterial oxygen saturation was decreased in hypoxemic lambs (67 +/- 8 versus 91 +/- 3%, p < 0.001), Hb concentration was increased, so that arterial oxygen concentration was similar in both groups of lambs. Myocardial mass (61 +/- 13 versus 44 +/- 9 g, p < 0.001) and total myocardial blood flow (117 +/- 36 versus 62 +/- 27 mL.min-1, p < 0.001) were increased, mainly due to right ventricular hypertrophy. LV oxygen demand, estimated by the rate pressure product (2072 +/- 465 versus 1467 +/- 358 kPa.beat.min-1, p < 0.001), and oxygen uptake (723 +/- 223 versus 556 +/- 184 mumol.min-1 x 100 g-1, p < 0.05) were proportionally increased in hypoxemic lambs. LV oxygen supply increased linearly with oxygen uptake (r = 0.96) in all lambs, by adjustments in LV blood flow, which was increased in hypoxemic lambs (168 +/- 41 versus 134 +/- 45 mL.min-1 x 100g-1, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)