Maintenance of wakefulness test as a predictor of driving performance in patients with untreated obstructive sleep apnea

STUDY OBJECTIVE: To determine the ability of Maintenance of Wakefulness Test (MWT) to predict simulated driving performance in patients suffering from sleep apnea syndrome. DESIGN: Study involving one hour of simulated driving, one night of polysomnography (PSG), and a 4 x 40-minute MWT. SETTING: Sleep laboratory. PATIENTS: Thirty male patients with untreated obstructive sleep apnea syndrome (OSAS) (mean age +/- SD] = 51 +/- 8 years, range 34-62; mean body mass index (BMI) +/- SD] = 29 +/- 3, range 24-37; mean apnea/hypopnea index (AHI) +/- SD] = 43 +/- 24, range 14-96). As defined by MWT mean sleep latency, 23.3% of the patients were sleepy (0-19 min), 33.3% were alert (20-33 min), and 43.4% were fully alert (34-40 min). MEASUREMENTS: Nocturnal PSG, mean sleep latency at 4 x 40-minute MWT trials, Epworth Sleepiness Scale (ESS), and standard deviation from the center of the road (SDS) on driving simulator. RESULTS: Mean MWT scores inversely correlated with SDS during the simulated driving session (Pearson's r = -0.513, P < 0.01). We found a significant effect of MWT groups (sleepy, alert, or fully alert) on SDS (ANOVA, F(2, 29) = 5.861, P < 0.01). Post hoc tests revealed that the sleepy group had a higher SDS than the fully alert group (P = 0.006). ESS, AHI, microarousal index, and total sleep time did not predict simulated driving performance. CONCLUSIONS: A pathological MWT mean sleep latency (0-19 min) is associated with simulated driving impairment. Before MWT can be used to predict the driving ability of untreated patients with OSAS, further studies are needed to confirm that pathological MWT scores are associated with real driving impairment.