Sweet Dreams
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To understand the relationship between sleep, overall health and how obesity and age play roles in disrupting sleep, the biology of sleep itself bears a closer look.

Essentially, sleep has five stages: Stage one is called the introduction to sleep, lasting only a few minutes. We often experience sleep starts during this stage, a jolt or falling sensation that wakes us up. At this point, the brain is disconnecting from the outside environment.

Stage two is often referred to as the beginning of real sleep. Typically, the body begins to enter deep sleep at this point. The heart rate should slow down. Body temperature should decrease.

Stages three and four are deep sleep phases, known as slow-wave or delta sleep. The waves refer to brain activity. At this point, brain activity is slowing down, and the body is preparing to enter the fifth stage, rapid eye movement (REM) sleep.

Each stage prior to REM lasts about five to 15 minutes with all four stages of the non-REM sleep taking about 90 to 120 minutes in total. Upon reaching stage four, the brain will then revert back to stage 3 and then stage 2 before entering REM sleep, which lasts for about 90 minutes.

Dr. Eleni Giannouli, Medical Director of the Sleep Disorder Centre, says completing the cycle about every 24 hours or so is essential to good health. Sleep regulates growth of bones, muscles and organs. It allows the body to repair itself and helps regulate body temperature. Sleep also is important to our immune system and helps cleanse the body of toxins that build up while we are awake. The REM stage is particularly important, says Giannouli, because it plays a large role in promoting neural plasticity, allowing the brain to restore pathways needed to promote learning and consolidate memories. People who cannot complete the sleep cycle rarely achieve the deeper stages of sleep, including REM sleep - otherwise known as the dream state.

How important is a full cycle of sleep? Giannouli says a 1993-study by the National Institutes of Health in the U.S. found that rats deprived of sleep for weeks developed sepsis and eventually died. No evidence exists that a person has died from sleep deprivation, but cumulative sleep deprivation not only exasperates already existing illnesses, it also causes neurological impairment leading to depression, reduced libido, irritability, memory loss and anxiety.

To feel normal, most adults need about six to nine hours of sleep per night, though exceptions do exist. "Some people are short sleepers," Giannouli says. "So for them, sleeping five hours is not a problem because they do not have signs and symptoms of sleep deprivation." Other people may need more than nine hours. But once we start missing those needed hours of sleep, either by purposely staying up or because of a sleep disorder, a deficit builds up.

There are six major sleep disorders, including insomnia, sleep-related movement disorders (restless leg disorder, periodic leg movement disorder), hyper-somnolence (narcolepsy), parasomnia-related (sleep walking, night terrors and REM Behaviour Disorder) and circadian rhythm disorders, where the body's internal clock causes unusual sleeping hours.

In terms of sheer numbers, however, sleep-disordered breathing, or sleep apnea, is the most common sleep disorder. Apnea (the word means pause in airflow) can be broken down into two types - obstructive and central. The latter is often associated with Cheyne-Stokes breathing (CSB), and happens when the brain periodically fails to send a message to the muscles that control breathing. "This is periodic breathing, a waxing and waning pattern of breathing that is commonly seen in patients with heart failure," Giannouli says. CSB is seen in normal, developing newborns and in people suffering from heart failure or neurological diseases.

Obstructive apnea - where the airway is blocked and impedes airflow - is much more common than central apnea, Giannouli says. A person with obstructive sleep apnea will usually have breathing pauses of up to 30 seconds while sleeping. Although brief, these pauses result in lower
oxygen levels, and ultimately disrupt sleep. Once airflow has stopped, the sufferers choke and are briefly roused from sleep - even though they may not remember it. This process often repeats itself hundreds of times throughout the night, fracturing sleep patterns and interfering with the body's ability to reach deeper stages of sleep.

A major risk factor for obstructive sleep apnea is obesity. Experts say people who are overweight may have fat deposits around the upper airways that restrict breathing. A short, thick neck can also be a risk factor for the same reason. "When they (people who are overweight) fall asleep, their muscles relax and the effect of the weight doesn't allow enough muscle power to breathe properly," says Wayne Thompson, Chief Technologist at the Sleep Disorder Centre.

In addition to upper airway dysfunction, morbidly obese individuals may also experience hypo-ventilation (inadequate breathing) in their sleep. The inability to draw in enough air means carbon dioxide levels in the blood rise while the oxygen levels decrease.

In addition to leaving people fatigued and prone to nodding off at inopportune times, such as at work or when driving a car, sleep apnea and other forms of sleep-disordered breathing are significant because they will exacerbate other health conditions and may even be at the root of illnesses for some patients, says Giannouli.

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Wave is published six times a year by the Winnipeg Regional Health Authority in cooperation with the Winnipeg Free Press. It is available at newsstands, hospitals and clinics throughout Winnipeg, as well as McNally Robinson Books.