[Circadian and ultradian rhythms of the heart rate in the neonate]

Abstract

Few papers deal with the chronobiologic characteristics of heart rate in neonates. A better knowledge of this topic could be useful under both clinical and therapeutical point of view. We studied the circadian and ultradian rhythms of heart rate in 10 healthy neonates (5 males and 5 females). Six of them (60%) show a well defined circadian rhythm of heart rate such as adult subjects even if with an obviously higher mesor and with acrophases dispersed throughout the 24 hours. We also demonstrated one or more ultradian rhythms of heart rate for each neonate. The most frequent have a period between 4 hours and 6 minutes and 4 hours and 36 minutes. These rhythms are out of phase with the world outside which is the best evidence that they are not imposed by some undetected external factors.