From 2-3 weeks of age, all infants (i.e., full-term and premature) in a warm environment respond tohypoxemiawith atransient increase in ventilation followed by sustained ventilatory depression, however in infants born at 32 to 37 weeks, hyperpnea does not occur in a cool environment.
By contrast,when pure oxygen is administered, ventilation initially decreases, followed by sustained hyperventilation.
Thisbiphasic response is thought to be due to central depression(as opposed to peripheral chemoreceptors), althoughanimal studies suggest that the biphasic response to hypoxemia is due to either thoracic stiffness or airway obstruction. Premature infants may show a biphasic response up to 25 days after birth.
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