Increased peripheral chemoreceptor activity may be critical in destabilizing breathing in neonates.

Periodic breathing and apnea are common in neonates, yet the physiological mechanisms involved are not clear. A low arterial PO2 might magnify peripheral chemoreceptor contribution to breathing, with its baseline variability inducing major changes in ventilation, leading to instability of the respiratory control system. We hypothesized that neonates: (1) would depend much more on the peripheral chemoreceptor contribution to breathing than adult subjects and (2) their baseline arterial PO2 would sit on the steep portion of the ventilation/arterial PO2 relationship on the adult nomogram, making breathing prone to oscillate. We analyzed data from previous polygraphic recordings in four groups of subjects: small preterm infants [SPI; postconceptional age (PCA) 33+/-2 weeks; n = 40], large preterm infants (LPI; PCA 36+/-2 weeks; n = 34), term infants (TI; PCA 42+/-1 week; n = 24), and adult subjects (AS; weight 63+/-2 kg; age 29+/-3 years, n = 16). Peripheral chemoreceptor activity was measured by: (1) the immediate decrease in ventilation and (2) apnea time during brief inhalation of 100% O2 (about 1 minute). We found that: (1) the immediate decrease in ventilation with 100% O2 was more pronounced in infants than in adult subjects (38+/-2 versus 6+/-5%), and in infants breathing periodically versus those breathing continuously; (2) the apnea time during 100% O2 was also significantly longer in periodic breathing infants; and (3) the TcPO2 was much lower in infants than in adult subjects (65+/-1 versus 93+/-1 Torr), and also lower in periodic versus continuously breathing infants. It was located significantly to the left of values for the adult subject, on the ventilation/arterial PO2 diagram. The data suggest that: (1) a substantial portion of baseline breathing activity early in life is maintained by increased peripheral chemoreceptor activity; and (2) neonates breathe irregularly with apneas due to the position of their arterial PO2 values on the ventilation/arterial PO2 diagram, in which a change in PO2 produces a more significant change in ventilation than that observed later in life.