Heart rate pattern during respiratory pauses in normal infants during sleep

We examined the pattern of heart rate during respiratory pauses in 10 normal infants at 1, 2, 3 and 4 months of age during sleep. Ventilation was recorded using barometric plethysmography and heart rate was measured using a precision R-R preprocessor. Typically, during a respiratory pause, the R-R interval increases, reaches a maximum and then returns towards baseline within the period of a respiratory pause or shortly after. The R-R interval starts to increase within 1-3s after the onset of the respiratory pause. The magnitude of increase in R-R interval varies considerably and, in some cases, reaches up to 50% of baseline. More than 73% of respiratory pauses are associated with an increase in R-R interval in quiet sleep but only about 50% in rapid-eye-movement sleep. Screening all the R-R data in each study revealed also spontaneous fluctuations in R-R interval without respiratory pauses. These data suggest that in normal infants in the first 4 months of life a respiratory pause is more likely to be associated with an increase in R-R interval in quiet than in rapid-eye-movement sleep; the increase in R-R interval during a respiratory pause is not related to hypoxaemia and respiratory pauses are not the only events that are associated with an increase in R-R interval during sleep.