Interrelationships Between Nocturnal Sleep, Daytime Alertness, and Sleepiness: Two Types of Alertness Proposed

The authors studied daytime sleepiness and alertness (based on the Multiple Sleep Latency Test [MSLT] and Maintenance of Wakefulness Test [MWT]) and nocturnal sleep in 22 patients with depression/anxiety and in 47 nondepressed patients with sleep apnea. The patients underwent two overnight sleep studies followed by daytime tests. In depressed patients, MWT scores correlated negatively with total sleep time and stage 3. MSLT scores correlated negatively with total sleep time and with sleep efficiency. Apneic patients showed a negative correlation between MWT results and amount of stage 1 sleep. MSLT results correlated positively with sleep onset latency on the preceding overnight sleep study. Thus, in depressed patients, there is a paradox that with more disturbed sleep there is greater daytime alertness. In contrast, the more disturbed the sleep is in sleep apnea patients, the more difficult it is to maintain daytime alertness.