Abstract
These experiments were designed to measure the effects of graded hypoxia on cerebral phosphorus containing compounds (ATP; phosphocreatine, PCr; inorganic phosphate, Pi) and cerebral pH in newborn lambs. The phosphate potential (PCr/Pi) has emerged as a measure of bioenergetic reserve. In tissues of mature animals, resting PCr/Pi is > 7 and levels < 1.0 are associated with lactic acidosis and cellular injury. We measured cerebral pH and phosphate potential with surface coil 31-PNMR spectroscopy in paralyzed, ventilated newborn lambs (<7 D). PCr and Pi were measured from spectral heights; pH was calculated from the spectral shift of Pi relative to PCr. In control lambs (PaO2 > 75 mmHg), cerebral PCr/Pi was 1.7, pH 7.1. Moderate hypoxia (PaO2 35-43 mmHg) did not alter the cerebral phosphate potential or pH. Severe hypoxia (PaO2 13-20 mmHg) caused a rapid decline in PCr/Pi which stabilized after 5 min at 1.0; pH did not fall as fast, but did not plateau. PCr/Pi recovered to resting levels in 2.5 min and preceded pH changes. Extreme hypoxia (PaO2 < 12 mmHg) caused a precipitous drop in PCr/Pi to 0.7 and the recovery time increased to 4.5 min. When PCr/Pi fell below 0.7, MABP began to fall; if hypoxia was reversed, the recovery time increased to 12.5 min; if hypoxia was not reversed, the lamb promptly expired. These studies demonstrate that newborn lambs develop lactic acidosis at a PCr/Pi 1.0 and have a “critical” PCr/Pi of 0.7 at which the recovery time is prolonged as much as 5-fold and beyond which the lamb dies, probably from cardiogenic shock.
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Younkin, D., Wagerle, L., Delivoria-Papadopoulos, M. et al. EFFECTS OF GRADED HYPOXIA ON CEREBRAL PHOSPHATE POTENTIAL IN NEWBORN LAMBS: A CRITICAL BIOENERGETIC LEVEL. Pediatr Res 18 (Suppl 4), 303 (1984). https://doi.org/10.1203/00006450-198404001-01260
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DOI: https://doi.org/10.1203/00006450-198404001-01260