Wakefulness circadian factors

These factors include sleep, continuous hours of wakefulness, circadian rhythms, and sleep disorders. 

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. 

One of us examined the timely use of three factors (melatonin treatment, exposure to light, physical exercise) to hasten the resynchronization of the sleep-wake cycle in a group of elite sports competitors after a transmeridian flight across 12 time zones (Cardinali et al. 2002). Outdoor light exposure and physical exercise were used to cover symmetrically the phase delay and the phase advance portions of the phase-response curve. Melatonin taken at local bedtime helped to resynchronize the circadian oscillator to the new time. Individual actograms taken from sleep log data showed that all subjects became synchronized in their sleep to the local time in 24-48 h, well in advance of what would be expected in the absence of any treatment (Cardinali et al. 2002). More recently, a retrospective analysis of the data obtained from 134 normal volunteers flying the Buenos Aires - Sydney transpolar route in the past 9 years was published this further supports such a role for exogenous melatonin in resynchronization of sleep cycles (Cardinal et al. 2006). 

Existing mathematical models predicting cognitive readiness/performance from sleep/wake history are based on the interaction of three factors. These factors are sleep homeostasis, circadian rhythm, and sleep inertia (12). Three-factor models successfully predict performance effects of acute, total sleep deprivation and... 

The extent to which naps will be beneficial, in terms of improved self-perceived alertness, performance, and objective alertness, is likely to depend on a number of factors. The factors of particular significance that will be addressed in this chapter include (a) sleep inertia, (b) nap duration, (c) nap sleep infrastructure, (d) circadian timing, (e) prior wake time, (f) napping strategies for periods of extended wakefulness, (g) individual differences, and (h) the setting (laboratory vs. applied settings). The discussion will now turn to the first of these factors, sleep inertia. 

The time of falling asleep is determined by three factors, which in normal sleepers occur at bedtime. These are (a) circadian rhythm, i.e. the body s natural clock in the hypothalamus triggers the rest/ sleep part of the sleep-wake cycle, (b) tiredness, i.e. time since last sleep, usually about 16 hours and (c) lowered mental and physical arousal. If one of these processes is disrupted then sleep initiation is difficult, and it is these three factors that are addressed by a standard sleep hygiene program (see below). Early in the course of insomnia rigorous adherence to sleep hygiene principles alone may restore the premorbid sleep pattern but in some patients the circadian process is less stable and they are less susceptible to these measures. 

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