Conclusion There was no disparity in sleep quality or KSS scores between CPAP treated OSA patients and healthy controls. Treated OSA patients obtained quality sleep with no elevated day time sleepiness. However, withdrawal of treatment for one night caused sleep quality to deteriorate despite a comparable sleep time; the deterioration in sleep quality could explain the increase in daytime sleepiness. Actigraphy was a sensitive enough measure to record the change in sleep quality and presents an alternative cheaper than PSG for screening studies. OSA patients need to know that even short-term non-compliance with CPAP treatment significantly impairs sleep quality, leading to excessive sleepiness evident during monotonous tasks such as driving. Introduction Actigraphy can reliably assess sleep in healthy adults (Littner et al. 2003) and be used as an indicator of suspected obstructive sleep apnoea (OSA) (Morgenthaler et al. 2007). OSA can be successfully treated with Continuous Positive Air Pressure (CPAP). Polysomnography (PSG) has shown CPAP withdrawal results in the immediate resumption of sleep disordered breathing (Yang et al. 2006). We compared sleep quality for CPAP treated OSA patients and controls, evaluating the impact of stopping CPAP for one night using actigaphy, to see if sleep disturbance can be detected without PSG. CPAP treatment for OSA patients: Effect on sleep quality and quantity as measured by actigraphy A. J. Filtness and L.A. Reyner Sleep Research Centre, Loughborough University, Leicestershire, LE11 3TU, UK Corresponding author: Summary  One nights CPAP withdrawal results in impaired sleep quality of treated OSA patients and increased day time sleepiness.  Actigraphy successfully identifies nights of non-compliance in treated OSA patients.  Actigraphy cannot differentiate between the sleep of CPAP treated OSA patients and healthy controls. Method Participants: 11 CPAP treated OSA male patients (mean age =65.6 y), all compliant CPAP users treated for a mean of 7.8 y, were compared with 11 male controls (mean age = 64.1 y) Protocol: Cambridge Neurotechnology Ltd actiwatches were worn for 1 night by control participants and 2 nights by OSA participants; once while using CPAP and once during CPAP withdrawal. Measures: Sleep quality using the Cambridge Neurotechnology Ltd software. Sleep disturbance index (SDI = number of awake minutes / the assumed minutes asleep). Subsequent daytime sleepiness was recorded between 2pm and 4pm the following day using the Karolinska Sleepiness Scale (KSS). Statistical analysis: Paired t tests (2 tail) compared OSA participants with and without CPAP. Independent t tests (2 tail) compared OSA participants with CPAP and controls. Sleep Length and SDI Figure 1 shows no significant difference in sleep length between OSA participants with and without CPAP, but a significant increase in SDI. For both measures there is no significant difference between controls and treated OSA participants. References Littner, M., Kushida, C.A., McDowell Anderson, W., Bailey, D., Berry, R.B., Davila, D.G. & Hirshkowitz, M. 2003, "Practice parameters for the role of actigraphy in the study of sleep and circadian rhythms: an update for 2002", Sleep, vol. 26, no. 3, pp Morgenthaler, T., Alessi, C., Friedman, L., Owens, J., Kapur, V., Boehlecke, B., Brown, T., Chesson, A.,Jr, Coleman, J., Lee-Chiong, T., Pancer, J. & Swick, T.J. 2007, "Practice parameters for the use of actigraphy in the assessment of sleep and sleep disorders: an update for 2007", Sleep, vol. 30, no. 4, pp Yang, Q., Phillips, C.L., Melehan, K.L., Rogers, N.L., Seale, J.P. & Grunstein, R.R. 2006, "Effects of short-term CPAP withdrawal on neurobehavioral performance in patients with obstructive sleep apnea", Sleep, vol. 29, no. 4, pp Results Actimetry shown no significant differences between OSA participants using CPAP and controls, see table 1. For OSA participants sleep quality was significantly worse during CPAP withdrawal although sleep length remained the same, see table 2. Table 1: Results from paired t test OSA participants following normal sleep and CPAP withdrawal Table 2: Results from independent t test OSA participants following normal sleep and control participants Figure 1: Sleep length and SDI, with standard error Sleep quality and KSS Figure 2 shows sleep efficiency and percent of ‘actual sleep’ (as calculated by the actiwatch software) to be significantly reduced by withdrawal of CPAP. KSS significantly increased without CPAP. There was no significant difference between controls and treated OSA participants. Figure 2: Actual sleep time, sleep efficiency and subsequent KSS, with standard error