INCIDENCE AND MECHANISM OF BRADYCARDIA DURING APNEA IN PRETERM INFANTS

Bradycardia occurred during 363 of 1520 apneas of 10 second''s duration recorded in 28 preterm infants. The incidence increased with increasing duration of apnea (10% of 10-14 seconds, 34% of 15-20 seconds and 75% of > 20 seconds, p < 0.001). This was similar for each type of apnoea.sbd.central mixed, and obstructive. During 133 apneas in five infants the time from the start of the apnea to the onset in the fall in oxygen saturation (mean 6.9 seconds) was significantly related to the onset of the fall in heart rate (mean 9.3 seconds) (r = 0.67, p < 0.001). Recovery in heart rate coincided with resumption of air flow rather than breathing efforts and preceded the recovery in oxygen saturation. These results suggest that bradycardia occurs during apnea as a response to falling oxygen saturation, probably through a peripheral chemoreceptor reflex that is manifest when breathing efforts are absent or ineffective.