REM sleep latency and its relation to sleep efficiency and sleep quality

Introduction

REM or rapid eye movement sleep is one of four stages of sleep characterized by bursts of rapid eye movement, desynchronized brain wave activity, strong dreams, and muscle paralysis. The other stages of sleep include wake, N1, N2, and N3. Collectively, N1, N2, and N3 are termed non-rapid eye movement sleep or non-REM sleep. Non-REM sleep is also said to be ‘quiet sleep’ in which the body’s heartbeat, breathing rate, eye movement, and brain activity waves lower down in a gradual manner. However, REM sleep is known as ‘deep sleep’. These stages of sleep run across the night in the form of cycles ,i.e. wake followed by N1, N2, N3, REM sleep, and repeat. It is pertinent to mention here that cycles in the earlier part of the night have a major proportion of deep sleep, and cycles in the later part of the night tend to have a major portion as REM sleep. Close to awakening, the body chooses REM sleep and almost entirely skips the deep sleep. In this article, the main focus is to understand REM latency and the different types of disorders linked to it.

Difference between sleep latency and REM sleep latency

Sleep Latency or sleep onset latency is the time taken by an individual to fall asleep after going to bed. It is very important to realize that going to bed does not refer to tucking yourself in and turning off the lights. It’s important to stop all attention-seeking activities like reading a book, scrolling on your phone, or even talking to your partner. The average sleep latency in healthy human beings is between 10-20 minutes. However, sleep latency of fewer than 8 minutes indicates sleep hunger in the body.[2].

The definition of REM sleep latency is the time taken by a person to enter the REM phase during the first cycle of sleep. The average REM sleep latency is between 70 to 110 minutes, while the average REM sleep cycles between every 90 to 120 minutes. Decreased REM latency is linked with certain psychiatric conditions including depression, schizophrenia [3], personality disorder, narcolepsy, eating disorder(Anorexia nervosa, Bulimia nervosa), obsessive-compulsive disorder, etc.

Sleep Debt

Sleep debt is an important concept when dealing with sleep hygiene. Sleep debt is basically sleep that that person endures over multiple nights. It is an indirect measure of how tired a person is with respect to sleep deprivation. For example, if a person sleeps 8 hours a day and remains active throughout the day, and some days he gets 3 hours of sleep, the sleep debt would be 5 hours. This lack of sleep would manifest itself as physical, behavioral, and mental problems. Multiple studies have suggested that rising trends of sleepless nights and increasing sleep debt lead to negative impacts on metabolic and hormonal/endocrine functions and physiological rhythms [4], increasing obesity{5} and depression [6].

Sleep Efficiency and Sleep Quality

Sleep efficiency and sleep quality are two interrelated terms. Sleep efficiency is the duration of time spent sleeping compared to the total time spent in bed. This parameter is very significant because the more time you spend sleeping in bed, the better your sleep is. It’s represented by a ratio calculated as the total time spent sleeping divided by the total time spent in bed. Normally 80-85% sleep efficiency is considered good.

As far as sleep quality goes, there are no specific criteria to define sleep quality. Everyone has their own insight and understanding of the quality of sleep. However, the average standard of quality sleep would be to wake up refreshed without feeling tired, in a good mood and with enough energy to continue day to day activities. There are numerous factors that affect the quality of sleep including; Regular sleeping routine, a quiet and dark environment in the sleeping room, and avoiding nocturnal/at-night consumption of caffeine or alcohol. All these factors can be worked upon and managed by a person to improve their quality of sleep. However, there are other factors that affect the quality of sleep and need to be consulted with a doctor to get proper quality sleep. These conditions include;

1. Breathing disorders like asthma [7], COPD [8], cardiovascular diseases [9], etc.
2. Drugs such as Diuretics can make you wake up mid-sleep and disturb the quality of sleep. Similarly, Sleeping pills can make you oversleep during the daytime and disturb your night sleep.
3. Snoring in Obstructive sleep apnea [10], hypertrophied adenoids [11], etc.
4. Sleep Disorders include insomnia, nightmares, narcolepsy, etc.
5. Other Psychiatric Disorders include depression, anxiety, schizophrenia, etc.

Epidemiology

A medical study was undertaken from 2008-2010 all across the US to estimate the prevalence and incidence of narcolepsy, with and without cataplexy(the sudden loss of muscle strength triggered by intense emotion) with respect to age, gender, and ethnicity. Participants were under 66 years old with enrollment in the program from 2008 to 2010. The results obtained were as under:

The incidence of narcolepsy without cataplexy was higher than narcolepsy with cataplexy. The age group from 21-30 had more prevalence and incidence was higher in early 20’s and late teens. The North Central United States had the highest prevalence of narcolepsy[12].

In a study conducted in the United States in 2009, researchers examined the prevalence and effects of sleep disorders and sleep habits of the general population. The findings revealed that sleep apnea was the most common sleep disorder, affecting 4.2% of the population. Insomnia had a prevalence rate of 1.2%, while Restless Leg Syndrome affected 0.4% of the population. These three sleep disorders were found to have the greatest impact on concentration and memory.

The study also looked into sleep habits and related difficulties. It found that Hispanics had longer sleep durations compared to Blacks, with a difference of 24 to 30 minutes. The most prevalent sleep habit reported was snoring during sleep, affecting 48% of participants. Feeling unrested during the day, an indicator of poor sleep quality, was reported by 26.5% of participants. Additionally, 26% of participants reported experiencing sleep debt, leading to poor sleep.

The study identified the main sleep-related difficulties in the sample population as difficulty concentrating(reported by 25% of participants) and memory issues(reported by 18% of participants)[13].

The purpose of highlighting these research/medical studies is to convey the importance of REM latency, normal REM latency and decreased REM latency. REM latency definition and sleep latency definition tell us that there is a slight difference between the two. Sleep latency is the time taken by a person to fall asleep. However, REM latency refers to the time period from falling asleep to reaching the REM stage of the first sleep cycle. Both sleep latency and REM latency are affected by certain sleep disorders. Increased or decreased REM sleep latency is attributed to multiple sleep disorders. The most common one being insomnia. Other sleep disorders include:

1. Narcolepsy
2. Idiopathic hypersomnia
3. Circadian rhythm sleep disorders
4. Restless leg syndrome
5. Sleepwalking, sleep terrors
6. Nightmares disorder
7. REM sleep behavior disorder
8. Sleep related Epilepsy

How to measure Sleep Latency

There are roughly five ways to measure sleep latency which include:

1. Self-Report
2. Multiple sleep latency test (MSLT)
3. Maintenance of wakefulness test (MWT)
4. Actigraphy
5. Polysomnography

Now, we’ll discuss these diagnostic procedures, and their uses in multiple sleep disorders.

1. Self-Report

Self-report simply involves asking the concerned individual about their sleep. It involves asking questions like how long does it take you to fall asleep. Self-assessment can lead to error because while a person can accurately report when they went to bed, it is hard for them to tell exactly when they fell asleep. This inability to accurately report the time of falling asleep makes this method unreliable.

2. Multiple Sleep Latency Test (MSLT)

Multiple Sleep latency test (MSLT) [13] is the gold standard to objectively assess daytime sleepiness. During the Multiple Sleep Latency Test, individuals are evaluated by taking 4-5 naps in daytime. If the person falls asleep, their brain activity is recorded on an EEG for the first 15 minutes, focusing on if they enter the REM stage. In the case of narcolepsy, sleep latency is around 8 minutes or less. Additionally, individuals with narcolepsy often experience Sleep Onset REM periods(SOREMPs) in at least 2 out of 4-5 daytime naps. SOREMPs refer to abnormal episodes of entering REM sleep within the first 15 minutes of falling asleep.

It is worth noting that having a sleep latency of fewer than 5 minutes is considered problematic and indicative of severe sleepiness.

3. Maintenance of wakefulness test (MWT)

The Maintenance of Wakefulness test is a variation of MSLT where the sleeper is tested for their ability to stay awake in cases of sleep disorders associated with excessive daytime sleepiness. This test is advised by doctors in cases where it is suspected the patient has sleep apnea or narcolepsy. An EEG recorder monitors the brain waves and researchers analyze different aspects of sleep including total sleep time, sleep latency and sleep stages. In a 20 minute nap, a normal MSL is 18 minutes. Maintenance of wakefulness tests with results between 11 - 18 minutes needs to be reviewed again. Test results of less than 11 minutes are indicative of excessive sleepiness.

4. Actigraphy

Actigraphy is a non-invasive test that involves wearing a device similar to a wristwatch that monitors your movement. This device does not measure sleep directly, instead it measures sleep latency by calculating the time between laying down for sleep until the first extended period of immobility. Actigraphy is used in conjunction with certain tests to evaluate the efficacy of treatment in certain sleep disorders. These disorders include:

1. Insomnia
2. Sleep-related breathing disorders
3. Circadian rhythm sleep-wake disorders
4. Insufficient sleep syndrome
5. Excessive daytime sleepiness

5. Polysomnography

Polysomnography is a sleep test that measures sleep parameters through EEG, Electromyography(EMG), Electro-oculography(EOG), Electrocardiography(ECG), airflow, leg movements and monitoring oxygen saturation to assess one’s sleep. Usually, this test is conducted one night before a multiple sleep latency test. ECG and respiratory evaluation allow the physicians beforehand to have an idea of possible cardiovascular and respiratory issues that may be causing sleep difficulties. Polysomnography includes the recording of sleep latency. This involves a technician who turns off the lights, and then all the above-mentioned measurements are stopped when the sleeper’s brain waves in EEG indicate sleep.

What the Doctor may offer if you have a sleep disorder?

Different treatments of a wide spectrum of sleep disorders have been developed after extensive research on individual disorders. Next, we’ll briefly review the treatment options for two extremes of sleep disorders, Insomnia and Narcolepsy.

Treatment Options for Insomnia:

Lifestyle and Behavioral modifications

1. Go to bed and wake up at the same time everyday
2. Don’t lie down unnecessarily. Only go to bed if you are tired
3. Don’t watch television or use your smartphone before going to bed
4. Don’t eat heavy meals 2 hours prior to bedtime
5. Don’t over hydrate yourself before sleep
6. Limit using caffeine products like coffee and tea at least 4 hours before sleep
7. Don’t use alcohol as an aid to help you sleep
8. Start practicing natural relaxation techniques(e.g. Deep breathing)
9. Create a sleep friendly environment using dim lights and quiet surroundings
10. Workout regularly
11. Don’t smoke
12. Avoid overthinking about anxiety inducing topics

Drugs

Hypnotics are used mainly to address insomnia. The drug classification for the treatment of Insomnia is as follows:‍

Treatment Options for Narcolepsy:

Certain CNS stimulants are used for treatment as alerting agents in narcolepsy. Symptoms of cataplexy are managed with REM suppressants.

Sleep is one of the most important determinants of good health and well-being, but so many are deprived of good quality sleep. In this connection, knowing about sleep, REM latency meaning, REM sleep latency, normal REM latency, and decreased REM latency, along with diagnostic tests and when to contact a doctor, is vital.

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