Circadian rhythms are regular fluctuations in both mental and physical states that happen in approximately 24-hour cycles when there are no external timing cues. A circadian pacemaker in the suprachiasmatic nuclei (SCN) is responsible for generating these circadian rhythms. When light hits the photoreceptors of the retina, it causes signals that move along the optic nerve to the SCN and then pineal gland which switches off the production of melatonin.
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Abnormalities in the circadian rhythm
Circadian rhythm disorders are a completely different class of sleep disorders. These disorders are the result of changes in the external environment or in the circadian timing system. Other factors that affect how severe the disorders are include:
They are often present as complaints in hypersomnia and insomnia.
Most biobehavioral functions happen in a rhythmic pattern, leading to major diurnal changes in a person’s performance abilities. A disruption to this rhythm has been tied to many physical and mental problems and could affect productivity, performance, and safety no matter whether the factors are involuntary (advanced age, illness) or voluntary (shift work, jet lag).
Regulation of the sleep-wake cycle
There is a complex interaction between the homeostatic and endogenous circadian processes that help produce and regulate the human sleep-wake cycle. However, it’s important to note that environmental factors also play a role. The key role of the circadian rhythm is to promote wakefulness by day and sleepiness at night.
The sleep homeostatic drive increases during wakefulness, hitting its maximum in the late hours of the evening (close to bedtime). The ability to sleep fluctuates with the circadian process, which keeps us awake by day and helps us sleep at night by counterbalancing the progressive accumulation of the sleep load.
The Multiple Sleep Latency Test (MSLT) looks at and assesses the temporal changes in physiological sleep tendencies and shows two phases of the circadian rhythm of alertness.
People will experience a drop in alertness and productivity around 2 to 4p.m. that follows a rise in alertness that lasts to mid evening hours. Interestingly, maximal alertness happens during the time when the drive for sleep is also the highest. Alertness drops to its lowest between 4 and 6a.m.
The sleep homeostatic process also affects how much and how deep sleep a person gets. The process builds up just before waking up. The only surefire way to decrease the sleep drive after being awake longer than one should is to sleep. It’s important to align the sleep-wake behaviors and circadian timing to get the best possible sleep and ensure productivity.
The 3 parts of the circadian rhythm model
- Input pathway – ties the internal cycle to the external light/dark cycles via photic or nonphotic signal transduction pathways. It’s not known what the input pathway is, but it’s thought to be a conduit for the clock to synchronize to.
- Self-sustained oscillator – is an autonomous pacemaker that produces circadian fluctuations.
- Output pathway – changes the circadian rhythmicity into obvious behavioral and physiological rhythms. It’s coordinated with the 24-hour day by light information that the retina in the eye sends to the SCN in the hypothalamus.
Circadian rhythm sleep disorders
Disruptions to the circadian rhythm are the result of incompatibility in the sleep/wake pattern as stipulated in a person’s environment and sleep/wake pattern which causes insomnia or hypersomnia. People who have this disturbance could also have other impairments that interfere with their occupational, social, and other life functions. It can cause them to feel tremendously stressed.
Circadian rhythm sleep disorders are caused by two key factors:
- changes in the external environment that affects the internal circadian timing system such as jet lag or shift work
- changes in the endogenous circadian system (recognized by a change in the timing of the consolidated sleep period with delayed or advanced sleep patterns compared to conventional sleep-wake times. This correlates to delayed sleep phase disorder and advanced sleep phase disorder.).
It’s usually an amalgamation of environmental, behavioral, and physiological factors that causes the majority of circadian rhythm sleep disorders.
Free running circadian rhythm sleep disorder
This is an extremely rare disorder denoted by steady drifting of the sleep period by one to two hours every day. People who try to maintain normal sleep-wake times report problems with early morning wake times, hypersomnia, and insomnia.
The symptoms take hold when the nonentrained circadian clock is out of sync with the typical sleep-wake times. When this happens, a person may feel socially impaired – unable to function in their job, at home, etc. However, when the endogenous circadian rhythm is aligned with traditional sleep times, the person may sleep normally and soundly.
Some people will change their sleep patterns to delay their sleep times by an hour or two every day to avoid misalignment.
Most sufferers from this disorder are blind and do not have the photic entrainment. About 50% of blind people have this with 70% of them reporting chronic sleep disruptions. The free running circadian rhythm sleep disorder is hardly seen in people with sight and the cause of this condition in them is still unclear. This suggests that lack of photic entrainment is the primary cause of the free running circadian rhythm of sleep and wake times in blind people.
Does this mean that all blind people suffer from the free running circadian rhythm sleep disorder? No, but it may be that they have gotten cues from work and social schedules. Plus, some blind people with a circadian pacemaker can respond to bright light even without visual perception of light.
For a diagnosis of this disorder to be made there should be at least a two-month established pattern where no other sleep or mental disorder can explain the problem. Keeping a two- to four-week sleep diary will help to recognize the disorderly pattern and show a progressive drift in the sleep/wake times. It could denote lack of stable entrainment of the sleep/wake cycle during the 24-hour physical environment.
Irregular sleep-wake circadian rhythm sleep disorder
This disorder occurs when there is no sleep/wake circadian rhythm. People with irregular sleep-wake circadian rhythm sleep disorder may have either hypersomnia or insomnia, which depends on the timing of their sleep-wake experience. While the total amount of sleep is normal, they may have at least three sleep episodes each night that vary in duration and length. It’s not uncommon for these sufferers to want to nap in the day.
People with this type of disorder should rule out the possibility of a voluntary irregular sleep schedule and poor sleep hygiene. It’s not known how prevalent this disorder is, but it’s thought to be rare.
The absence of a sleep-wake circadian rhythm is often the result of a disruption in its timing system and a decreased exposure to light and activity. The disorder has also been tied to brain injury, dementia, and childhood mental retardation.
Advanced sleep phase circadian rhythm sleep disorder (ASPS)
The ASPS is noted by going to bed and waking up several hours earlier than conventional and/or desired times. People with this condition wake up very early and suffer from insomnia or hypersomnia during the late afternoon/early evening. Sufferers will go to sleep between 6 and 9p.m. and wake up between 2 and 5a.m.
The sleep-wake patterns in ASPS are often tied to age, and ASPS not related to age is thought to be rare. About one percent of middle-aged adults have this disorder. And while age does increase the chances of developing this sleep disorder, the jury is still out on whether this is the same entity as ASPS in younger individuals.
Delayed sleep phase circadian rhythm sleep disorder (DSPS)
DSPS is recognized by bedtimes and wake times that take place up to six hours later than desired sleep-wake times. People with insomnia typically experience it between 2 and 6a.m. and will wake up earlier than 10a.m. and 1p.m. They may also have problems going to sleep when they want to, but once they do, they tend to sleep just fine.
DSPS sufferers report feeling very tired in the morning, but are more alert in the late evening hours. Due to this evening alertness trying to fall asleep early for these individuals is nearly impossible. If they don’t have anywhere to be the next day at a weekend or on vacation, they may sleep late into the morning, leading to late bedtimes.
To find out if a person has delayed sleep phase disorder, doctors may ask their patients to keep a sleep diary for two weeks.
Of all primary circadian rhythm sleep disorders DSPS is the most common with five to 10% of sufferers facing chronic insomnia. Up to 16% of teenagers and young adults have the condition, and a positive family history is present in about 40% of people who have DSPS.
DSPS sufferers often look for treatments because attempts to stick to traditional sleep-wake times result in excessive sleepiness, insomnia, functional impairments, etc. And these problems are usually present in the morning hours.
Shift work circadian rhythm sleep disorder
If your job involves shift work, it can upset the sleep-wake cycle by changing sleep to times when the societal cues and internal clock are not in sync. Roughly 25% of people who work nights have this disorder.
Night shift workers in the transport industry are highly vulnerable to the consequences of this disorder. How much impairment the shift work causes depends on each person, and it’s not uncommon for some shift workers not to have the problem at all.
There are a number of internal and external factors that play a role in a person’s ability to function in shift work, including but not limited to:
- commuting times
- home responsibilities
- work schedule
- diurnal preferences
- another sleep disorder (narcolepsy or sleep apnea).
People with the shift work circadian rhythm sleep disorder tend to display signs of hypersomnia or transient insomnia, which is tied to their work schedules. Hypersomnia needs to be separated from other types of sleep disorders such as sleep apnea and narcolepsy. The relationship between the shift work schedule and sleep disruption is often noted in the person’s history.
People are advised to keep a two- to four-week sleep diary, note their work history, and even wear an actigraphy (wrist device to record movements while sleeping). This information can be used to determine how disruptive their sleep actually is. A work diary is also recommended for people who have irregular schedules as it can help figure out the relationship between sleep and work.
All this information can be used to come up with an effective treatment plan.
People who have shift work circadian rhythm sleep disorder often claim that they don’t feel rejuvenated when they wake up. And the feeling lingers even if they improve their sleep environment and promote good sleep hygiene. They tend to feel sleepier because they must stay awake when the circadian propensity for sleep is high.
Jet lag circadian rhythm sleep disorder
Jet lag sleep disorder is usually temporary, as it happens when a person travels from one time zone to another. The aftereffects, though short lived, can be disruptive and include stomach upset, excessive daytime sleepiness, problems with sleeping, decreased productivity, etc.
How severe the symptoms are and the ability to get a handle on them all depend on two things:
- the number of time zones crossed (from Eastern U.S. to Western U.S. there are four time zones)
- direction of travel (slower adaptation when going east).
When traveling east, it’s usually harder to get to sleep. When traveling west, it’s usually harder to stay asleep. Remember, not everybody is the same and suffers the same level of jet lag. The differences result from individual variations that could be similar to those noted in shift work.
How to improve your sleep/wake cycle
It’s imperative that you get a comprehensive treatment plan for your sleep/wake disorder. Many of your sleep problems are easily treatable by making simple changes to your sleep routine and hygiene. For example, increasing your exposure to daylight and bright light in the waking times can reset your circadian clock. This can improve the amount and quality of sleep you get.
What other things can you do?
- Maintain strict sleep-wake times to reset the clock
- reserve the bedroom for just sleeping and intimacy
- exercise regularly, but not within several hours of bedtime
- create a relaxing atmosphere in the bedroom – cool, comfortable, quiet
- partake in relaxing nighttime activities such as reading
- not drink alcohol or consume caffeine several hours before bedtime
- not take naps in the late afternoon (if any at all)
- take sleep medications or over-the-counter sleep remedies at the lowest effective doses.
Conventional stimulants – modafinil and methylphenidate – have helped shift workers improve their alertness, especially if they don’t get enough sleep which hinders their productivity and safety (for them and others). Modafinil is the only drug the U.S. Food and Drug Administration has approved for this use.
What you should remember…
People who suffer from circadian rhythm sleep disorders tend to suffer from hypersomnia and insomnia, complaining that they cannot sleep when they want to. The most common reason for these disorders is that the endogenous circadian rhythm system is not aligned with the external environment. Also causing grief and adding to the problems are behavioral and social factors, which must be dealt with along with implementing techniques and treatments that can improve the sleep/wake cycle of the sufferer.