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Case 2a and 2b of BBS2051, biorhythms in homeostasis
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Case of 13 pages for the course BBS2051 Biorhythms In Homeostasis at UM (Case 2a and b)
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Case 2a, Circadian misalignmentProblem statement
How can the circadian rhythm be disrupted? With focus on jet lag.
Learning goals
1. What is jet lag and what are the symptoms?
2. Difference between flying west or east
3. What can you do to overcome the jet lag?
Sources
https://www.sciencedirect.com/science/article/pii/S1477893909000064
https://www.sciencedirect.com/science/article/pii/S0140673607605297#tbl2
https://www.frontiersin.org/articles/10.3389/fphys.2019.00927/
full#F2
1. What is jet lag and what are the symptoms?
Definition jet lag
Jet Lag Disorder (JLD): is a consequence of circadian misalignment that occurs after
crossing time zones too rapidly for the circadian system to keep pace. The diagnostic criteria
for Jet Lag Disorder are straightforward:
There is a complaint of insomnia or excessive daytime sleepiness associated with trans
meridian jet travel across at least two time zones;
There is an associated impairment of daytime function, general malaise, or somatic
symptoms such as gastrointestinal disturbance within one or two days after travel;
The sleep disturbance is not better explained by another current sleep disorder, medical or
neurological disorder, mental disorder, medication use, or substance of disorder.
Factors influencing the intensity and duration of a jetlag
The intensity and duration of the jet lag symptoms are related to a number of factors: (1) the
number of time zones crossed, (2) the direction of travel, (3) the ability to sleep while
traveling, (4) the availability and intensity of local circadian time cues upon arrival, and (5)
individual differences in tolerance to circadian misalignment.
Pathological mechanism of Jet Lag Disorder
JLD shares the pathophysiologic mechanism of all circadian rhythm sleeping disorders;
namely, a mismatch between endogenous circadian rhythm (generated by the circadian clock
in the SCN) with the desired (or required) schedule for sleep and wake.
Homeostatic sleep drive refers to the process in which sleep tendency increased with the
duration of prior wake; thus, homeostatic sleep drive begins to accumulate immediately upon
awakening and gradually accumulates as the day progresses. However (according to the
opponent process model) this accumulating sleep drive is not manifested as overt sleepiness
because, during the day, the circadian system generates an alerting signal that counteracts
(opposes) the expression of sleep drive. Then at the end of the day, an hour or two before
habitual bedtime, the circadian alerting signal subsides and the balance between the opponent
processes shifts, and a person begins to feel sleepy. With the onset of sleep, the accumulated
homeostatic sleep drive begins to dissipate, and with a full night of sleep, will be gone by
morning. For normally entrained individuals living according to a regular, conventional
schedule, the homeostatic and circadian systems are synchronized with each other and with
the 24-h solar day-night cycle.
, In JLD, the homeostatic and circadian processes are out of alignment. This results in an
inappropriately timed circadian alerting signal that shortens sleep duration and reduces sleep
quality. Furthermore, the effects of
circadian misalignment are compounded
by travel-related interruptions to sleep that
increase sleep debt. Homeostatic sleep
drive can accumulate over several days if
jet lag insomnia persists. Moreover, with
circadian misalignment, the circadian
alerting signal is reduced or is absent
during the day; thus, during the waking
hours, homeostatic sleep drive may be
unopposed, and sleepiness may emerge
even when an individual has obtained
what would seem to be a sufficient amount
of sleep.
According to this model, an individual’s
level of alertness (relative sleepiness) is a
vector sum derived from the opposing forces of sleep drive that accumulates in proportion to
the duration of prior wakefulness, and an alerting process, generated by the circadian
pacemaker in the SCN. (1) During the day, sleep drive accumulates, but is counteracted by an
opposing alerting signal. In the early evening, the circadian alerting signal peaks and, even
though sleep drive is strong, initiating sleep may be difficult. (2) Prior to bedtime, the alerting
signal recedes, sleepiness emerges, sleep commences, and sleep drive dissipates. At the time
of final awakening, sleep drive is at a minimum. After sleep inertia has receded, the daytime
level of alertness is restored to a normal zone. The lower pane illustrates the consequences of
circadian misalignment upon arrival after eastward flight across nine time zones. Because
clock resetting has yet to occur, the circadian alerting process remains anchored to the time
zone of departure. (3) The conventional time for sleep at the new location coincides with an
elevated alerting signal and sleep is thereby shortened and non-restorative. (4) The
conventional time for work (or sightseeing) at the new location is coincident with a recession
of the circadian alerting signal; consequently, accumulated sleep drive is unopposed by the
circadian alerting process, and intense daytime sleepiness is to be expected.
Symptoms of Jet lag
- Poor sleep during the new night-time, including delayed sleep onset (after eastward
flights), early awakening (after westward flights), and fractionated sleep (after flights
in either direction).
- Poor performance during the new daytime at both physical and mental tasks
- Negative subjective changes. These include increased fatigue, frequency of headaches
and irritability, and decreased ability to concentrate.
- Gastrointestinal disturbances (indigestion, the frequency of defecation, and the
consistency of the stools) and decreased interest in, and enjoyment of, meals.
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