Scientific research that applies known physiological principles to the demands and practices of the transportation industry has dramatically grown in the past several years. Researchers have been gathering data on the physiological and psychological effects of fatigue on human performance for decades. More recently, these established principles have been used to examine specifically the effects of fatigue in transportation and the development of countermeasures to maximize performance and alertness during operations.
Background
`Fatigue' is a generic term used to encompass a range of experiences described as anything from `sleepy,' `tired,' or `exhausted' to `beat.' There are two major physiological phenomena that have clearly been demonstrated to create `fatigue:' sleep loss and circadian rhythm disruption. This directory contains references to the scientific literature describing the many and varied topics related to sleep and circadian rhythms. Some basic information is provided here as background and to provide a minimal foundation for the symposium and this directory.
Sleep is a vital physiological function. Like food and water, sleep is necessary for survival. Sleepiness results when sleep loss occurs. Sleepiness is the brain's signal, analogous to hunger or thirst, that sleep is needed. Sleep loss, as the term implies, describes the phenomenon of getting less sleep than is needed for maximal waking performance and alertness. If an individual normally needs 8 hr of sleep to feel completely alert, and gets only 6 hr of sleep, 2 hr of sleep loss has been incurred. Sleep loss over successive days accumulates into a sleep debt. If the individual needing 8 hr of sleep gets only 6 hr a night for 4 nights in a row, an 8-hr sleep debt has been accumulated. The negative effects of one night of sleep loss are compounded by subsequent sleep loss. Sleep loss and the resultant sleepiness can degrade most aspects of human performance. In the laboratory, it has been demonstrated that losing as little as 2 hr of sleep can negatively affect alertness and performance. Performance effects can include: degraded judgment, decision-making, and memory; slowed reaction time; lack of concentration; fixation; and worsened mood. The brain is programmed for two periods of maximal sleepiness every 24 hr: (about) 3-5 am and 3-5 p.m..
Circadian rhythms are physiological and behavioral processes (e.g., sleep/wake, digestion, hormone secretion, and activity) that oscillate on a 24-hour basis. Each rhythm has a peak and a low point (nadir) during every 24-hr period. Time cues, called zeitgebers, keep the circadian/body clock "set" to the appropriate time of day. Common zeitgebers include bright light (e.g., sunlight) and work/rest schedules. If the circadian clock is moved to a different schedule, for example when crossing time zones or changing from a day- to a night-shift, the clock requires a certain amount of time to adjust to the new schedule. This amount of time depends on many variables; for example, the number of hours the schedule is shifted. During this transition, the circadian rhythm disruption can produce effects similar to those of sleep loss. When circadian disruption and sleep loss occur together, they can interact to compound their adverse effects.
When extreme, fatigue can cause uncontrolled and involuntary shutdown of the brain. That is, regardless of motivation, professionalism, training, or pay, an individual who is extremely sleepy can lapse into sleep at any time, despite the potential consequences of inattention. Transportation incidents and accidents involving fatigue provide dramatic examples of this fact.