6.6.3.1. PREVENTION FACTORS
6.6.3.1.1. Short layovers
During short layovers, biological rhythms do not have time to adjust to the new time zone. This type of layover requires specific management of rest-activity rhythms. One has to force one's self to keep bedtimes and meal times synchronized with home or base times, even if in opposition to local social rhythms.
Results obtained from our work with long-haul aircraft pilots show that those who attempted to synchronize with local time were either affected by a degradation in sleep quality (Case N° 1) characterized by high sleep latency and frequent awakenings, or by a reduction in sleep time (Case N° 2).
In Case N° 3, pilots maintained bedtimes synchronized with home or base times as put forward in the recommendations. It can be seen that sleep is indeed longer and of better quality.
6.6.3.1.2. Long Layovers
Biological clock inertia is the primary cause of disorders related to changing sleep-wake cycle times.
To prevent disorders of this type, the biological clock must be adjusted to the new sleep-wake cycle times. You must therefore harmonize the biological clock phase with that of the sleep period in as short a time as possible.
Natural factors should be used to favor this adjustment:
– exposure to light,
– social contacts (meals, leisure activities, etc.),
– moderate physical exercise.
Exposure to light represents, as will be seen, the most powerful factor in adjusting the biological clock to new time zones.
6.6.3.2. EFFECTS OF LIGHT
6.6.3.2.1. Basic information
Daily and seasonal changes in the length of day (photoperiod) are transmitted to the biological clock by means of melatonin, a hormone secreted by the pineal gland.
This hormone has a clearly marked circadian rhythm with total absence of secretion during daylight hours, production occurring during night-time only.
The longer are the nights, the longer the secretion of melatonin and vice versa.
The period of least efficiency (OFF) coincides with maximum melatonin secretion.
Whenever going through a time zone change, the aim should be to induce a shift in the biological clock phase that is of the same amplitude and in the same direction as the normal sleep period.
This would be accomplished by means of light, the result of its action on the biological clock being the movement of melatonin production towards the new sleep period.
This shift is accompanied by a similar shift in OFF period.
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