Time-on-task decrements in "steer clear" performance of patients with sleep apnea and narcolepsy

Loss of attention with time-on-task reflects the increasing instability of the waking state during performance in experimentally induced sleepiness. T o determine whether patients with disorders of excessive sleepiness also di splayed time-on-task decrements indicative of wake state instability, visua l sustained attention performance on "Steer Clear," a computerized simple R T driving simulation task, was compared among 31 patients with untreated sl eep apnea, 16 patients with narcolepsy, and 14 healthy central subjects. Vi gilance decrement functions were generated by analyzing the number of colli sions in each of six four-minute periods of Steer Clear task performance in a mixed-model analysis of variance and linear regression equations. As exp ected, patients had more Steer Clear collisions than control subjects (p=0. 006). However, the inter-subject variability in errors among the narcolepti c patients was four-fold that of the apnea patients, and 100-fold that, of the controls volunteers; the variance in errors among untreated apnea patie nts was 27-times that of controls. The results of transformed collision dat a revealed main effects for group (p=0.006), time-on-task (p=0.001), and a significant interaction (p=0.022). Control subjects showed no clear evidenc e of increasing collision errors with time-on-task (adjusted R2=0.22), whil e apnea patients showed a trend toward vigilance decrement (adjusted R2=0.4 2, p=0.097), and narcolepsy patients evidenced a robust linear vigilance de crement (adjusted R2=0.87, p=0.004). The association of disorders of excess ive somnolence with escalating time-on-task decrements makes it imperative that when assessment of neurobehavioral performance is conducted in patient s, it involves task durations and analyses that will evaluate the underlyin g vulnerability of potentially sleepy patients to decrements over time in t asks that require sustained attention and timely responses, both of which a re key components in safe driving performance.