Physiological sleepiness

Under some conditions, feelings of sleepiness may be great and protocols that must be run when subjects are extremely sleepy encounter the problem of floor effects. For example, physiological sleepiness may be so great because of a drag effect that sleep latencies are too short to be above statistical noise. In these circumstances, it is difficult to detect subjects with abnormal sleepiness or to detect the effect of any remedial intervention. 

Another potential explanation for differences between the MSLT and the MWT is that the MWT, because of its instructions to remain awake, adds a nonlinear motivational factor that is not present with the MSLT. The MWT often reveals improvement in treated patients who continue to be physiologically sleepy. Thus, the MWT is sometimes considered to be a way of extending the sensitivity range of the MSLT (13). Reasoning that an MWT is simply an MSLT plus a motivational component (even a nonlinear component) falters, however, because it assumes that motivational factors are not present in the MSLT. Such an assumption with respect to the MSLT is not justified. 

Howard and colleagues (31) suggested a reform of residents work and duty hours based on a study that assessed the levels of physiological and subjective sleepiness in 11 anesthesia residents in three conditions (1) during a normal (baseline) work schedule, (2) after an in-hospital 24-hr on-call period, and (3) after a period of extended sleep. MSLT scores were shorter in the baseline (6.7 min) and postcall (4.9 min) conditions, compared with the extended-sleep condition (12 min), and there was no significant difference between the baseline and postcall conditions. Residents daytime sleepiness on the MSLT in both baseline and postcall conditions was near or below levels associated with clinical sleep disorders, and residents were subjectively inaccurate determining EEG-defined sleep onset. 

The Maintenance of Wakefulness Test (MWT) was developed as an alternative, physiologically based test of sleepiness (1). The test was designed for use with patients whose sleepiness during the day might adversely affect performance or safety. Reasoning on the basis of face validity, a person who has little difficulty with falling asleep inappropriately should be able to stay awake in a quiet, sedentary situation such as during MWT trails. Beyond the procedure s face validity, there are other rationales for the use of the MWT, as discussed below. 

RTC Ops demands disrupt sleep and circadian physiology with a variety of consequences. In this section, examples demonstrate how these consequences translate specifically into sleep loss, increased sleepiness, and decreased safety across a variety of representative work settings. 

In a laboratory-based study of sleepiness using the Multiple Sleep Latency Test (MSLT), hospital residents were found to be near the twilight zone following postcall (mean time to sleep of 5.5 min) (46). Perhaps most provocative was that their baseline (not on-call) level of sleepiness was not significantly different at 6.5 min. This demonstrated both the level of chronic sleep deprivation experienced (as reflected in the baseline condition) and the physiological level of sleepiness that can be expressed postcall. When the residents had the opportunity... 

Furthermore, because many of the outcome measures used in these studies are based on self-report, they are also vulnerable to the frequently found discrepancy between self-assessment of sleepiness/alertness level and actual physiological level of sleepiness on the one hand (10,13) and recall bias on the other thus results... 

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