Study objectives: To evaluate non-rapid eye movement (NREM) sleep instability, as measured by the cyclic alternating pattern (CAP), in the first months of life in a group of normal healthy infants, in order to obtain more information on the maturation of arousal mechanisms during NREM sleep and to set normative data of CAP parameters in this age range (from 1 to 4 months of life).
Design: Retrospective study.
Setting: Sleep unit of an academic centre.
Participants: Twenty-three healthy newborns and infants with a mean conceptional age (gestational age plus postnatal age) of 47.6 + 3.8 weeks, age range 42 to 55 weeks, 10 boys (43.47%), were studied while they slept in the morning between feedings, by means of a 3-hour video-electroencephalographic (EEG)-polygraphic recording. Sleep was visually scored for sleep architecture and CAP in a blinded fashion, using standard criteria.
Measurements and results: We found 3 different sleep EEG patterns in our infants, according to their age, and we subdivided the entire group into 3 subgroups. Group 1-Tracé alternant mixed with high-voltage slow activity included 9 subjects (3 boys), with a mean conceptional age of 43.9 +/- 1.3 weeks; Group 2 (high-voltage slow activity and rudimentary spindles) included 6 subjects (4 boys), with a mean conceptional age of 49.4 +/- 3.1 weeks; and Group 3 (slow-wave activity and spindles, scored as NREM sleep) included 8 subjects (3 boys), with a mean conceptional age of 50.4 +/- 2.9 weeks. CAP rate was 6.83 +/- 3.58 in infants belonging to Group 2 and increased to 12.91 +/- 2.21 in Group 3. We found a statistically significant higher A1 index in only Group 3. The relative percentages of the A1, A2, and A3 subtypes showed non significant changes with age. The duration of CAP events and the cortical and subcortical arousal indexes were not statistically different between Groups 2 and 3.
Conclusions: With this study, we provide the first data on CAP analysis in infants from 1 to 4 months of life, and we found that there is a transitory period when trace alternant disappears and CAP events begin to occur. Furthermore, we suggest that the more appropriate time of life when CAP analysis can be first performed is related to the appearance of mature stage 2 NREM with spindles and slow delta waves mixed with theta waves, at approximately 3 months of life.