Introduction: It is unclear whether actimetry can be reliably used to measure sleep in severe obstructive sleep apnea (OSA) patients. We compared polysomnography (PSG) with actimetric assessment of sleep on an epoch-by-epoch basis in subjects with and without OSA.
Methods: 21 subjects were recorded with simultaneous overnight standard PSG and actimetry.
Results: 10 subjects with apnea-hypopnea index (AHI) <10 (6.5 +/- 2.8/h) were classified as non-OSA subjects and 11 subjects with AHI >10 (42.0 +/- 27.3/h) were classified as OSA subjects. Overall sensitivity and specificity for actimetry to identify sleep was 94.6% and 40.6%, respectively, with an overall mean sleep/wake simple agreement of 84.6% and kappa of 0.38. There was no difference in agreement between non-OSA and OSA subjects (simple agreement: 83% vs. 86%, p = 0.73; kappa: 0.35 vs. 0.40, p = 0.73). The kappa agreement did not correlate with PSG arousal index (r = -0.21, p = 0.36) but declined with reduced sleep efficiency (r = 0.66, p = 0.001). There was no systematic difference (all p > 0.40) between actimetry and PSG in sleep latency, total sleep time and sleep efficiency, although correlations between the measurements using the two techniques were generally poor. However, while actimetry systematically underestimated wake after sleep onset (WASO) (35.5 +/- 18.8 vs. 59.4 +/- 35.1, p = 0.009), fragmentation index measured by actimetry only underestimated arousal index measured by PSG in OSA patients (23.9 +/- 17.8 vs. 33.1 +/- 18.5, p = 0.04).
Conclusions: Contrary to prior reports, epoch-by-epoch comparison of sleep/wake scoring showed similar fair agreement between actimetry and PSG in subjects with or without OSA. Fragmentation index by actimetry may underestimate arousals caused by respiratory events and offer misleading results in severe OSA patients.