Study of heart rate variability in sick newborn infants.

Heart rate variability has been studied in a group of 66 newborn infants for periods of up to 72 hours from birth. Long term variability was reduced in infants suffering from the idiopathic respiratory distress syndrome and this was more marked with severe respiratory distress requiring mechanical ventilation. Persistent reduction in long term variability was associated with increased mortality. Reduction in heart rate variability may be due to high levels of sympathetic activity.