Sleep loss caffeine

The Walter Reed Army Institute of Research s Department of Behavioral Biology has developed a field-deployable version of a commercial Psychomotor Vigilance Task (PVT) that has been widely used in sleep research. The software runs on handheld PDAs running the Palm Operating System (Palm OS). It is modeled after the simple reaction time task of Wilkinson and Houghton,57 as modified by Dinges and Powell.58 The Palm OS version incorporates additional stimulus, feedback, control, and data options developed by Dr. Thome. In laboratory studies, performance on the PDA task has been shown to be sensitive to time-on-task fatigue effects, sleep deprivation, and circadian variation.18 Field studies have utilized the PVT to measure the efficacy of caffeine gum as a sleep loss countermeasure. 

Interventions such as naps and caffeine to counteract the neurobehavioral effects of sleep loss and sleepiness in healthy adults have been found to improve PVT performance (73-77). The PVT has been successfully used to track the effects of napping in laboratory (77) and operational (31) settings. The use of naps in the laboratory to augment the performance of sleep-deprived subjects is illustrated in the control condition of Figure 3, which shows that PVT errors of omission and commission during 88 hr of sleep deprivation are substantially reduced by 2-hour naps taken every 12 hr. 

There is evidence of performance benefits from combining naps and caffeine consumption during sleep loss (79,80). Although these studies did not use... 

The Effect of Naps and Caffeine On Alertness during Sleep Loss and Nocturnal Work Periods... 

MSLT observations (proportion of prestudy baseline latency to Stage 2 sleep) for nap and caffeine groiq)s during sleep loss. The presence of brackets indicates overall statistically significant differences between groups at that time point Data points within brackets indicate nonsignificant differences From Bonnet et al (1995). Copyright 1995 by 5/eep journal Reprinted with permission. 

In summary, these studies have demonstrated the beneficial effect of obtaining additional sleep prior to periods of sleep loss and the additive benefits of caffeine use. Subjects for the studies were healthy young adults who did not report significant daily caffeine use and who were not sleep deprived prior to the beginning of each study. In the real world, of course, it is common that shift workers will suffer fiom both chronic sleep loss and tolerance to caffeine. Such limitations could reduce the beneficial impact of both prophylactic naps and caffeine in applied settings. On the other hand, knowledge of the ability of naps and caffeine to produce baseline levels of alertness across nocturnal work periods when used correctly should allow planners to develop improved sustained work schedules. 

So what is the big deal Although there is still plenty of debate about caffeine and its effects on the body, empirical evidence has shown that large quantities can cause significant health and behavioral problems. For instance, too much caffeine can result in nervousness and insomnia. The insomnia causes fatigue, leading to more caffeine consumption, more insomnia, more lack of sleep, irritability, and so on. Additionally, increased caffeine consumption appears to correlate with an inaease in bone loss and occasionally, abnormal heart rhythms. Addiction to caffeine is possible, with unpleasant symptoms resulting upon cessation of use. 

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