We studied nine healthy preterm infants during the first 35 days of life to define the relationship between periodic breathing, apnea, and hypoxia. For this purpose we compared ventilation/apnea (V/A), minute ventilation, and alveolar and capillary blood gases during periodic breathing induced by hypoxia and during spontancous periodic breathing in room air. We induced periodic breathing by giving the baby in sequence 21, 19, 17, and 15% O2 to breathe for 5 minutes each, and also by giving 21, 15, and 21% O2. We measured ventilation with a nosepiece and a screen flowmeter. With a decrease in arterial oxygen tension, preterm infants (1) hypoventilated, (2) breathed periodically more frequently, and (3) showed a decrease in V/A due to an increase in the apneic interval. In one baby this led to apnea lasting 30 seconds.
These findings support our hypothesis that preterm infants breathing periodically hypoventilate and suggest that hypoxia may be a primary event leading to periodic breathing and apnea.