HYPOXIC VENTILATORY RESPONSE IN THE NEWBORN MONKEY

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Abstract
Summary: The hypoxic ventilatory response was determined in twelve unanesthetized newborn monkeys, Macaca nemestrina, Measurements of blood gases and ventilation were made during normoxia and hypoxia at the postnatal ages of 2, 7, and 21 days, Data were collected during quiet sleep. The infant monkey demonstrated a definite but transient hyperventilatory response following exposure to a Fi02 of 0.12 or 0.14 on the second day of life. Baseline ventilation increased 15% (Fi02 = 0.14) and 28% (Fi02 0.12) after 1 minute of hypoxia; p. 0.05 in both instanes. Return to baseline ventilation occurred between 3 and 5 minutes after hypoxic stimulus onset. This biphasic response to hypoxia converted to an adult-like, sustained hyperventilation during the ensuing three weeks of postnatal maturation. Episodes of periodic breathing and/or apnea were noted to occur during the induced hypoxemia. These data demonstrate that the infant subhuman primate has a ventilatory response to hypoxia that is similar to that of the human infant and is an excellent model for the study of the maturation of the respiratory control system. Speculation: The mechanisnis involved i n the unique neonatal response to hypoxia have not been elucidated. In light of current evidence, direct suppression of respiratory center output by an inhibitor seems the most likely possibility. However, adverse alterations in pulmonary mechanics brought on by the hypoxia itself or fatigue of the carotid body remain viable alternatives.