Actigraphic assessment of sleep–wake rhythm during the first 6 months of life

Objectives: To examine the validity of the ‘Gaehwiler’ actigraph (Gaehwiler Electronics, model Z80-32k V1) for the assessment of sleep–wake (S/W) rhythm and sleep structure in infants during the first 6 months of life using an algorithm developed in our laboratory to differentiate sleep and wake states. Methods: A continuous 72 h actigraphic recording was performed in 10 healthy infants at 1, 3 and 6 months of age. The actigraphic data were matched to direct observation of the infantsʹ behavioural states. Using discriminant function analysis a scoring algorithm for automatic identification of S/W states from raw activity data was developed. The chi-square periodogram analysis was performed to estimate periodic components of S/W rhythm. Results: The overall agreement rates between the actigraphic and observer scoring for S/W were between 87 and 95% for the infants after the third month of life, while for the 1-month-old infants they never exceeded 72%. The actigraphic discrimination between active and quiet sleep was the best in 3-month-old infants. The circadian influence on S/W rhythm was already present by the end of the first month of life. Conclusions: Using the ‘Gaehwiler’ actigraph in our study, valid discrimination between sleep and wake states was obtained in infants during 3 and 6 months. The actigraph, however, did not provide valid active vs. quiet sleep state measures. The circadian rhythm of S/W was observed as early as during the first month of life.