About Sleep

Introduction

Sleep accounts for a third of our lives, and a growing number of doctors believe that it should receive more attention from the medical community. Diet and exercise have been the focus of health professionals for many years now, but sleep has started attracting more attention. Doctors have now linked sleep-related illnesses to hypertension, stroke, congestive heart failure, depression, and an overall decreased quality of life.

Many physicians want to add information about sleep to the standard medical history taken during doctor visits. Not that long ago the family physician didn't ask questions about your physical activity, but now you can expect questions about the type, frequency, and duration of exercise you enjoy. You can also expect questions about your diet. Hopefully, in the not too distant future, your family physician will ask about your sleep:

• Do you sleep well?
• Do you wake refreshed?
• Are you sleepy during the day?
• Do you snore? (Though this question will be directed at a partner if possible)
• Do you wake with headaches?

Answers to simple questions like these can help a physician decide whether further discussion or testing is necessary. For most patients, the answer to their sleep problems is simple—better sleep hygiene. For others, medical intervention may be necessary. Determining the need for medical intervention has always been difficult because our knowledge about sleep and our ability to diagnose sleep problems have been inadequate.

Sleep Architecture

In 1935, scientists first recognized the separate and distinct brain wave patterns of sleeping individuals. Then in the 1950s, scientists identified the presence of rapid eye movements (REM) as a characteristic of dream sleep. The term REM sleep is still used to describe the phase of sleep in which we dream. Prior to these research milestones, scientists believed that sleep was a state of passive rest and uniform inactivity. But sleep is far more complex. In the 1960s, more medical researchers began performing sleep studies. By 1970, the first sleep research center opened at Stanford University, and sleep science began to evolve into its own discipline. One of the first great discoveries was that sleep has an architecture, different stages that last different lengths of time and occur in different orders.

The two basic types of sleep, REM and Non-REM (NREM), include a total of five stages that we move into and out of as we sleep. The duration and quality of these stages can vary greatly, depending on age, health, sleep hygiene, and the individual. The table below provides a brief explanation of NREM and REM sleep and their relative sleep stages, as well as alternate terms for the stages where applicable.

TYPE OF SLEEP	STAGE OF SLEEP
NREM Sleep NREM sleep contributes to physical rest and may bolster the immune system. Researchers often group NREM stages 3 and 4 together, calling them delta sleep.	Stage 1 (Light Sleep): A transitional stage between waking and sleeping, usually lasting 5 or 10 minutes. Breathing becomes slow and regular, the heart rate decreases, and the eyes exhibit slow rolling movements.
	Stage 2 (True Sleep): A deeper stage of sleep where fragmented thoughts and images pass through the mind. Eye movements usually disappear, muscles relax, and there is very little body movement.
	Stage 3 (Deep Sleep): A further deepening of sleep with additional slowing of heart and breathing rates.
	Stage 4 (Deep Sleep): This is the deepest stage of sleep, in which arousal is the most difficult. Typically, sleep walking and bed wetting occur in this stage.
REM Sleep REM sleep contributes to psychological rest and long-term emotional well-being. It may also bolster memory.	REM Stage (Dream Sleep): A dramatic decrease in muscle tone and an essential paralysis characterize this stage of sleep. Other characteristics are irregular breathing, increased heart rate, and rapid eye movements. The brain uses more oxygen, and the body stops regulating temperature. In this stage, people experience vivid, active dreams with complex symbols.

Sleep and Age

Age affects our sleep more than any other factor. Our sleep architecture (patterns) actually change as we age. The table below gives an example of how sleep patterns change for the average person. Notice that far more variation exists in elderly than in young sleepers.

Type of Sleep	Infant	Child	Young Adult	Elderly Adult
Stage 1	< 5%	< 5%	< 5%	8-15%
Stage 2	25-30%	40-45%	45-55%	70-80%
Delta Sleep	20%	25-30%	13-23%	0-5%
REM Sleep	50%	25-30%	20-25%	20%

Many people think that we sleep less as we age, but research doesn't support this notion. Studies that have looked at elderly sleep patterns have found that while elderly people sleep for shorter periods at night, they tend to take more naps during the day. The actual number of hours we sleep each day does not change much from early to late adulthood.

Circadian Rhythms

A circadian rhythm is like an internal clock. It's a cycle of about 24 hours (circa means "about" and dian means "day"). Each of us has a sleep-wake schedule that follows circadian rhythm. There are other circadian rhythms that control things like the release of growth hormones. Our circadian rhythms for sleep make us more alert at certain times of the day and less alert at others. This is probably why there are "morning people" and "night people." Our circadian rhythms actually affect our energy, concentration, and creativity.

Many people experience an afternoon lull around 2pm. Contrary to popular belief, afternoon sleepiness does not result from consuming a large meal, though that may add to the effect. Afternoon lulls are merely part of our circadian rhythms. For this reason, most sleep specialists agree that a short nap in the early afternoon is perfectly healthy. However, most specialists would also discourage late afternoon or evening naps especially if they make it more difficult to sleep at night.

As with our sleep architecture, our circadian rhythms change as we age. Teenagers tend to have circadian rhythms that encourage them to sleep later in the morning and stay up later at night. Teenagers and children also require more sleep than adults. They also spend more time in deep sleep (probably because their bodies are growing and maturing rapidly).

One curious aspect of circadian rhythms is that they seem to be slightly longer than 24 hours, so most people experience the urge to sleep later than their consistent wake-up time. Researchers don't know why circadian rhythms are slightly longer than a day, but they say that people should expect a little tiredness when they wake and resist the temptation to sleep until they can sleep no more, called "sleeping out." If you "sleep out" too many days in a row, your circadian rhythm may begin to shift. When catching up on sleep, you should go to bed early and wake at your usual time.

Healthy Sleep

Good health requires healthy sleep, but it also requires a consistent schedule. Sleep research shows that a consistent schedule can be more important than the number of hours one sleeps. A National Sleep Foundation poll revealed that 65% of Americans do not get at least eight hours of sleep per night. When the National Sleep Foundation asked the people who said they did not get eight hours of sleep about the quality of their sleep, they discovered this:

• 70% of those who did not maintain a regular schedule reported having sleep problems
• 58% of those who kept a regular schedule reported having sleep problems.

In other words, people who maintained a schedule reported having better quality sleep on average. The National Sleep Foundation poll suggests that a regular schedule can help protect us from the effects of insufficient sleep.

In our work of 24-hour activity, our sleep patterns often suffer. Our internal clocks operate with environmental cues, primarily light. When light fades, the eyes send a message to a part of the brain. That part of the brain communicates with two other parts of the brain. One part stops production of chemicals that keep us awake; the other part starts production of melatonin, a hormone that causes sleepiness. This system probably worked perfectly when we had no artificial lighting, but we have created a world of electric lights, televisions, and computers. We insulate ourselves from the signals that once kept our bodies on schedule.

Many people find themselves up too late because of television or the computer, and the following day can be a sleepy one. However, maintaining a good schedule does more than keep us alert while working or going to school. A good sleep schedule keeps our bodies running properly. In addition to our sleep-wake schedule, we have other circadian rhythms that regulate other bodily functions, some of which are tied to our sleep-wake cycle. Hormones, such as growth hormone, depend on circadian rhythms. Metabolism also depends on a circadian rhythm. Disturbing our sleep-wake schedule can have a ripple effect that alters other body functions and leads to subtle changes in our body chemistry.

Sleep Hygiene

If you have difficulty falling asleep or don't sleep well, try the following suggestions.

• Wake at the same time every day, regardless of when you went to sleep
• Maintain a consistent bed time
• Exercise regularly, but not within two to four hours of bedtime
• Perform relaxing activities before bed
• Keep your bedroom quiet and cool
• Don't have anything with caffeine for at least six hours prior to bedtime
• Don't have nicotine for at least six hours prior to bedtime
• Don't drink alcohol for at least four hours prior to bedtime
• Don't watch television for at least an hour before bedtime
• If you nap, only nap early in the day, not in the late afternoon or evening

Sleep hygiene doesn't have to be the center of our lives, but it's especially important for those having trouble with sleep. We all need to pay attention to our individual needs. While some people need only four hours of sleep per night, others need ten or twelve, so getting eight will not suit everyone.

Sleep Deprivation

More and more Americans report feeling sleep deprived. Americans surveyed by the National Sleep Foundation report receiving an average of only 6.5 hours of sleep per night—that's 1.5 hours below the average person's needs. The National Sleep Foundation also reports that every year at least 100,000 automobile accidents occur because a sleepy driver gets behind the wheel. Approximately 71,000 injuries and 1,500 deaths result from these easily avoided accidents.

Two recent studies indicate that drivers with untreated obstructive sleep apnea (OSA) have a much greater chance of being involved in a traffic accident. One study found an increased risk of six times, another fifteen times.

These numbers provide a dramatic illustration of the importance of sleep. Some activists have even begun to compare driving sleepy to driving drunk. Studies show that reaction times of sleepy drivers are as bad as or worse than drivers with blood alcohol levels of 0.08%, which is the legal limit in some states. Most people won't drive drunk, but they don't think twice about driving when sleepy.

For sleepy drivers, even more so than drunk drivers, there is a sense that "it can't happen to me." Unfortunately, it can. It happens because our bodies begin to take "microsleeps" when we deprive them of rest for too long. You may have already taken a few microsleeps at the wheel without knowing it. In the early stages of sleep deprivation, they last only a few seconds, but that's long enough to cause an accident.

Copyright © ResMed 2005, Used with Permission