Effects of hyperoxia on neonatal myocardial energy status and response to global ischemia.
BACKGROUND
This study examines the effect of neonatal exposure to clinically relevant hyperoxia levels on both in vivo myocardial metabolism and the subsequent metabolic response to global ischemia.


METHODS
Three-day-old pigs were ventilated to normoxia (80 mm Hg, 2 or 5 hours, n = 11), mild hyperoxia (250 mm Hg, 2 hours, n = 9), or severe hyperoxia (500 mm Hg, 5 hours, n = 14). Ventricular biopsies obtained at the end of the ventilation period, and at early and late ischemia were analyzed for ATP, ADP, AMP, creatine phosphate, glycogen, and lactate.


RESULTS
Hyperoxia did not significantly alter in vivo metabolism. During early ischemia, hearts exposed to severe hyperoxia had better ATP and glycogen preservation (p < 0.003). These hearts exhibited almost complete (92%) creatine phosphate depletion, in contrast to incomplete creatine phosphate use in all other neonatal hearts, even in the face of 30% ATP reductions. However, hearts exposed to severe hyperoxia also had a higher incidence of fibrillation during ischemia, which accelerated ATP and glycogen degradation.


CONCLUSIONS
Although severe hyperoxia provided an energy-sparing effect during early ischemia, it also increased the incidence of ventricular fibrillation, which negated this beneficial effect.
Wittnich
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Institute of Medical Science, University of Toronto and Division of Cardiovascular Surgery, The Hospital For Sick Children, Ontario, Canada. c.wittnich@utoronto.ca
Torrance
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SM
Carlyle
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D000818:Animals; D000831:Animals, Newborn; D004734:Energy Metabolism / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D018496:Hyperoxia / Q000503:physiopathology*; D008297:Male; D015428:Myocardial Reperfusion Injury / Q000503:physiopathology*; D009206:Myocardium / Q000378:metabolism*; D013552:Swine; D014693:Ventricular Fibrillation / Q000503:physiopathology