Performance of the Chronically Hypoxic Young Rabbit Heart

Hearts isolated from 30 rabbits, raised from birth to ~5 weeks of age under either hypoxic (FIO₂, 0.10) or normoxic (FIO₂, 0.21) conditions, underwent retrograde aortic perfusion using a nonrecirculating, well-oxygenated crystalloid solution. The left ventricular end diastolic pressure was initially set at ~5 mmHg. Aerobic performance was studied by measuring peak systolic pressure (PSP), coronary flow, glucose oxidation, and oxygen consumption. Anaerobic function was assessed by determining time for the onset of contracture (TOC) in the presence of zero coronary flow. Hypoxic vs normoxic hearts (mean ± SEM): heart rate, 197 ± 6 vs 190 ± 5 beats per minute; PSP, 136 ± 4* vs 108 ± 4 mmHg; (+) dP/dt _max, 2294 ± 125* vs 1549 ± 144 mmHg/sec; relaxation time constant (Tau), 26.9 ± 1.1* vs 41.6 ± 4.8 msec; (−) dP/dt _max, 1422 ± 43* vs 1001 ± 63 mmHg/sec; coronary flow, 86.3 ± 4.2* vs 59.9 ± 2.9 ml/min/g_dry; glucose oxidation, 3511 ± 118* vs 2979 ± 233 nmol/min/g_dry; oxygen consumption, 28.2 ± 1.4* vs 22.7 ± 1.4 µmol/min/g_dry; and TOC, 11.8 ± 1.2* vs 22.9 ± 2.2 min (*p < 0.05). Hearts isolated from young rabbits, exposed to hypoxia from birth, exhibited enhanced ventricular systolic and diastolic mechanical function, elevated coronary flow, retained capacity for aerobic metabolism, and a shorter TOC compared to their normoxic counterparts.