Sleep debt

Eliminating Cumulative Sleep Debt and Sleep Satiation.555... 

IV. The Concepts and Definitions of Sleep Need, Sleep Debt, and Extra Sleep. 559... 

V. Potential Benefits of Sleep Debt Reduction and the Way We Feel. 562... 

Van Dongen HPA, Rogers NL, Dinges DF. Understanding sleep debt theoretical and empirical issues. Sleep Biolo Rhythms 2003 1 4—12. 

Spiegel K, Leproult R, Van Cauter E. Impace of sleep debt on metabolic and endocrine function. Lancet 1999 354 1435-1439. 

Sleep can be disrupted in two ways acutely or through a cumulative sleep debt. Acute sleep loss will typically refer to the total amount of sleep an individual obtains in the 24-hr period prior to work. A work-related cumulative sleep debt can be calculated by adding the sleep loss acquired over days. This calculation should begin after an identified recovery period when an individual would have an opportunity to zero out any existing sleep debt. Sleep is a core physiological factor that affects waking alertness, safety, and performance and, as will be apparent, RTC Ops can affect sleep acutely and over time through a cumulative sleep debt. 

RTC Ops can affect all of these physiological factors acute sleep loss and cumulative sleep debt, hours of continuous wakefulness, circadian/time-of-day, and sleep disorders. Diverse work requirements lead inevitably to physiological disruptions and subsequent effects on waking alertness, safety, and performance. 

Inherent in RTC Ops is the associated sleep and circadian disruption that makes the opportunities for recovery sleep very important. Therefore, time off is an important scheduling issue to zero out any accumulated sleep debt and potentially stabilize any circadian disruption. It is critical that these recovery opportunities are both predictable and protected. Individuals working RTC Ops can plan for recovery sleep if the opportunity can be anticipated. Therefore, protecting the recovery opportunity from interruptions, whether work- or home-... 

Predictability provides an individual with the opportunity to plan, whether for work, recovery requirements, or home activities. When possible, schedule stability provides more consistent circadian cues and the opportunity to create individual patterns and habits that minimize the physiological disruptions. Modem work demands, especially 24/7 requirements, are often associated with overtime, which may be elective or on occasions required. Extending work has the potential to increase the continuous hours awake, be affected by circadian factors by working through a window of circadian low, and contribute to both acute sleep loss and a cumulative sleep debt. The timing and amount of overtime and whether it is elective or required, can all affect the level of physiological disruption. 

One clear outcome of the operational factors discussed thus far is that individuals lose sleep and can build a cumulative sleep debt. Examples of sleep loss experienced in transportation, health care, and public safety demonstrate how these actual operational demands can result in physiological disruption. 

In summary, across all of these examples, any type of nonday or nonstandard work schedule can result in an average total sleep time that is significantly below comparative baselines and demonstrates both the acute and cumulative sleep debt that results from RTC Ops. 

Figure 1 Relationship between the sleep debt in the 24 hr before the interview and the duration of driving.

In aviation much consideration has been given to the maximum duration of duty periods. In Europe the amendment A5-0263/2002, which has recently been passed by the European Parliament, determines a maximum duty period of 14 hr for pilots. Therefore, the European Cockpit Association has argued that this maximum allowable period together with the mandated rest times may constitute a recipe for cumulative sleep debt. This suspicion is supported by the work of Hamelin, who found that accident risk doubles when duty periods exceed 11 hr. Thus, this new EU regulation is weaker in its potential to prevent pilot fatigue than the old UK regulation. 

Melatonin is not currently recommended for enhancing sleep or adjusting to shift work because the factors (dose, timing, level of extant sleep debt) governing melatonin s effects have yet to be clearly elucidated—and, until then, a simplified doctrine applicable for military use is not possible. Although it has... 

Endurance and time to exhaustion are also important components of athletic performance. Decreases in either measure were observed in several studies (19,21,38 12). Holland (38) noted a 10% reduction in work performed during all-out cycle ergometer exercise after 24 hr of sleep deprivation. Brodan and Kuhn (39) evaluated subjects (n = 7, sleep debt = 120 hr) with the Harvard step test (reflects cardiorespiratory endurance and recovery) and revealed adaptation during the test but impaired recovery. Martin (41) utilized treadmill testing at 80% V02 max and found decreased time to exhaustion, increased perceived exertion, and increased minute ventilation (n = 8, sleep debt = 36 hr). Martin and Chen (42) revealed a 20% reduction in time to exhaustion after 50 hr of sleep deprivation. Decreased time to exhaustion after 30 hr of sleep deprivation has been demonstrated even when subjects were allowed caffeine intake (21). 

Although potential drawbacks are associated with pharmacological interventions, the problems attributable to untreated fatigue seem more immediate and severe, especially when there are few alternatives other than to accomplish the task at hand with a high degree of skill regardless of the extent of sleep debt. A case in point is the fact that several military mishaps have been attributed to fatigue, but none have thus far been attributed to stimulants (i.e., amphetamines)... 

Two similar experiments carried out 30 years apart dramatically confirm the concept that human beings can unknowingly carry a large sleep debt. Neither experiment was designed by the researchers primarily to study sleep. In both experiments, brain waves were continuously recorded as one of many measurements of the effects of the experimental protocol on the volunteers. 

The interpretation of these results is that the subjects entered the protocol carrying sizable individual sleep debts, defined as the accumulated loss of sleep. Of course, neither the subjects nor the researchers were aware of such a possibility. The baseline period probably did little to reduce the subjects sleep debts and may even have resulted in a small increase. As in the Navy Hospital experiment, when the opportunity to sleep was greatly increased, the subjects large sleep debts caused a very large increase in total daily sleep time. As the subjects sleep debts decreased, total sleep time per day declined proportionally. 

If we assume that the steady state value in the last week of the 10-hr-pho-toperiod (14 hr in bed) schedule represented the real daily sleep need for this group of subjects, we may conclude that all amounts of sleep above these values represented extra or makeup sleep. Accordingly, the mean payback of sleep debt for the group averaged about 30 hr. For purposes of comparison, individuals who were not at all sleep-deprived would have to spend more than 3 consecutive days with no sleep at all to accumulate a sleep debt of similar magnitude. 

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