Self-report sleepiness measures, objective sleepiness measures and simulated driving performance in controls and patients with obstructive sleep apnea

The ability of self-report and objective measures of sleepiness to predict performance on the York Driving Simulator was evaluated using two experimental protocols. The first study involved one night of prolonged wakefulness in 16 female participants, aged 18 to 19, who were tested at 2300, 0130, 0400 and 0630 hrs. Each test session consisted of the Stanford Sleepiness Scale, Multiple Sleep Latency Test, Repeated Test of Sustained Wakefulness, Alpha Attenuation Test, Four Choice Reaction Time Test, and a 30-minute simulated driving task during which continuous self-appraisals of sleepiness/alertness were made. As wakefulness was prolonged, participants showed signs of increasing sleepiness on each of the sleepiness measures, and progressive impairments in simulated driving performance. The group of objective sleepiness measures and the group of self-report sleepiness were equally effective predictors of simulated driving ability (R2 = 0.59 and R2 = 0.52, respectively). Further exploration of the association between each individual sleepiness measure and simulated driving ability showed that, although the Repeated Test of Sustained Wakefulness was generally the highest ranked predictor of simulated driving ability, its superiority was matched by self-report sleepiness measures (particularly the online self-appraisal of sleepiness/alertness) and the Multiple Sleep Latency Test. The self-awareness of sleepiness appears to be comparable to measures of physiological sleep tendency in predicting impairments in driving ability. The second study consisted of a pre/post treatment design in 18 patients, aged 28 to 78, who were diagnosed with obstructive sleep apnea. Study 2 was carried out in collaboration with Dr. Michael Fitzpatrick of the Sleep Disorders Laboratory at Kingston General Hospital, who was interested in comparing CPAP treatment outcomes when patients were treated with a laboratory-determined fixed pressure level compared with self-adjusted pressure levels. A randomized crossover design was used, consisting of two 5-week treatment limbs (fixed CPAP and self-adjusted CPAP) separated by a 1-week wash-out period. Patients were tested on four occasions, before and after each treatment limb, with each testing day consisting of the Epworth Sleepiness Scale, Stanford Sleepiness Scale, Maintenance of Wakefulness Test, Alpha Attenuation Test, and a 45-minute simulated driving task during which continuous self-appraisals of sleepiness/alertness were made. Treatment outcome (measured by self-reported sleepiness, physiological sleepiness, and simulated driving performance) did not differ significantly between the fixed versus self-adjusted CPAP limbs. The strongest predictors of simulated driving performance were the Maintenance of Wakefulness Test and the self-assessment of sleepiness/alertness while driving. However, there were no significant differences between the predictive ability of the self-report sleepiness measures and the objective sleepiness measures. The findings suggest that (1) self-titrated CPAP can produce treatment outcomes at least as good as those associated with traditional polysomnographic methods, (2) in patients with sleep apnea, simulated driving ability is predicted by both the Maintenance of Wakefulness Test and the self-assessment of sleepiness while driving.