Performance of patients with Obstructive Sleep Apnoea (OSA) on a steering simulation after six months treatment with Nasal Continuous Positive Airway Pressure (NCPAP)

The long-term effect of nCPAP on steering performance in OSA has not been assessed. 42 OSA patients (Epworth Sleepiness Score (ESS) ≥ 10, and ≥ 10/hr >4% SaO2 dips) performed three simulator drives each lasting for 30 minutes, and maintenance of wakefulness tests (MWT) at baseline, 1 month and 6 months. Patients were randomised to receive either sub-therapeutic or real nCPAP (Lancet 1999, 352:2100). Patients were retitrated at 1 month to therapeutic nCPAP. Performance was quantified by the standard deviation of steering error across the drive (sd), and reaction time (reactn) to identification of a target digit. Results are median, significance by Wilcoxon test. Median Sub-therapeutic (n = 23) Therapeutic (n = 19) 5/95 MONTH P P MONTH P P centile 0 1 6 0/1 1/6 0 1 6 0/1 1/6 Steer 0.36 0.42 0.23 NS 0.003 0.44 0.20 0.19 0.004 NS Error 0.15 0.14 0.14 0.15 0.13 0.08 (sd) /1.4 /1.2 /0.8 /1.2 /0.7 /0.5 Reactn 2.8 3.2 2.5 NS 0.04 2.7 2.1 2.2 0.001 NS /sec 1.4 1.7 1.3 1.7 1.5 1.2 /5.3 /3.9 /3.6 /5.3 /3.4 /3.2 MWT 20.1 25.7 37.6 NS 0.002 19.5 38.3 40.0 0.001 0.02 /min 7.7 7.1/ 9.5 6.8 15 29 /40 40 /40 /35 /40 /40. Therapeutic NCPAP significantly improves simulated steering performance in OSA. Despite improvement at 6 months the steering performance did not return to that of a group of controls (sd 0.16(0.13/0.31), although reaction time and sleepiness measurements were normal. This differential outcome suggests factors other than sleepiness may contribute to the impaired steering simulation performance in OSA, which persists after treatment.