SUMMAR Y There have been limited studies of the validation of actigraphy for the determination of sleep and wake in children and in this study we aimed to compare wrist actigraphy with polysomnography (PSG). We studied 45 children (29 M ⁄ 16 F), aged between 1 and 12 years (5.8 ± 2.7 years, mean ± SD). Actigraphic data were collected during standard overnight PSG. Data from the actiwatch were analysed over four separate activity threshold settings (low, medium, high, auto). Actigraphic data were compared epoch-by-epoch with the matching PSG. Sleep time was not different from PSG values for the low or auto activity thresholds, but was significantly less on the medium and high activity thresholds (P < 0.05). In contrast, the low and auto activity thresholds significantly underestimated wake time (P < 0.05), whilst that recorded on the medium and high activity thresholds were not different to PSG values. Agreement rates across the thresholds were all high ranging from 85.1% to 88.6%. Predictive value for sleep and sensitivity were also high with values ranging from 91.6% to 94.9% and 90.1% to 97.7%, respectively. In contrast, predictive value for wake and specificity were low ranging between 46.7-65.6% and 39.4-68.9%, respectively. There was no effect of subject age, OAHI or PSG arousal index on AR for any of the activity thresholds. We conclude that actigraphy is a reliable method for determining sleep in children when compared against PSG. Actigraphy may be a useful tool in paediatric sleep clinics and research.

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SUMMAR Y Obstructive sleep apnoea (OSA) in children is commonly considered to occur predominantly in rapid eye movement (REM) sleep, but clinical experience suggests that this is not universally the case. We hypothesized that there would be a subgroup of children with OSA who have non-REM (NREM) predominance of obstructive events and that these children share certain clinical characteristics. Thus, we aimed to compare the obstructive apnoea-hypopnoea index (OAHI) in REM versus NREM sleep and to assess factors influencing the distribution of events by sleep state. Polysomnography (PSG) recordings of 102 children aged 0-18 years with moderate to severe OSA (OAHI ‡5 h )1 ) were reviewed. OAHI was calculated separately for REM and NREM sleep. A REM predominance index (RPI) was determined using log transformation [RPI = log (REM OAHI + 0.5) ) log (NREM OAHI + 0.5)] and compared with possible influencing factors using multiple linear regression. Analysis showed that obstructive events were more common in REM sleep (median REM OAHI 21.4 h )1 , median NREM OAHI 8.3 h )1 , P < 0.001). Mean RPI was significantly greater than zero (P = 0.003).However, a substantial minority of children (30.4%) had a higher NREM than REM OAHI. The factors that were related significantly to NREM predominance were older age (P = 0.02), higher arousal index (P < 0.001) and higher SpO 2 nadir (P < 0.001). Our findings demonstrate that while OSA is a REM sleep-related problem in the majority of children, there is a significant subset of children with NREM predominance of obstructive events. This finding highlights the importance of considering sleep state distribution of events in studies of the pathophysiology and outcomes of OSA in childhood.

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