These data allow us to understand the shortness of a morning sleep (4 to 5 hours) observed after a sleepless night. In fact, morning sleep generally starts between 7am and 8am and ends when body central temperature becomes high, generally around 12am.
This situation is found in the case of a westward flight when sleep time is delayed towards physical local night. Sleep duration during the first night can sometimes be longer, as all the environmental factors lend themselves to this, but the sleep will have an abnormal architecture and will be punctuated by awakenings.
6.5.2. NAPPING
6.5.2.1. DEFINITION
A nap corresponds to a period of sleep lasting between 20 minutes and 2 hours.
It plays a fundamental role in reducing sleep dept. It can act as a compensating phenomenon in case of sleep loss and allows fatigue to be overcome.
6.5.2.2. TIME ZONES FAVORABLE FOR NAPS
After a normal night's sleep, drowsiness presents a clear bimodal distribution with a peak in the middle of the afternoon as well as a nocturnal peak.
The nocturnal peak is called the "primary sleep gate" and the one in the middle of the afternoon the "secondary sleep gate".
The zone of least drowsiness located between the secondary and the primary sleep gate is called the forbidden sleep zone.
Napping early in the afternoon is not simply related to a cultural phenomenon, climate or to a good meal. It is a manifestation of the spontaneous two-phase character of sleep inherent to all individuals.
The forbidden sleep zone explains the difficulties that a person can encounter when trying to go to sleep earlier as a preliminary measure for very early rising.
After sleep loss, the bimodal drowsiness structure remains very evident with, however, more marked morning drowsiness related to an immediate shortage phenomenon.
The wakefulness time preceding a nap seems to influence the amplitude of the peaks (higher drowsiness) but not their time of occurrence.
6.5.2.3. ARCHITECTURE
The composition and organization of the various sleep stages during napping both depend on the time of day in which it is located and on its duration for subjects who slept normally during the previous night:
- The morning nap located between 8am and midday has a similar architecture to that of the second half of a nocturnal sleep. It is richer in REM sleep than the afternoon or evening nap (between midday and midnight). REM sleep onset during the morning nap will appear sooner than for normal sleep.
– The architecture of the afternoon or evening nap does not resemble either the first or the second half of nocturnal sleep. It depends more on the length of the nap:
. a nap of thirty minutes does not include REM sleep, 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：Getting to grips with Fatigue & Alertness Management(60)
