Understanding Sleep's Benefits
By Robert J Troell, MD, FACS
Why does a Chiropractor need to know about sleep? All animals require sleep. Sleep restores the body and the mind. Since the purpose of the art of chiropractic medicine is to heal the mind and the body, understanding sleep should be paramount to attaining this goal. Why do human beings sleep? All metabolic processes require restoration of their function, which is achieved through sleep. In 1834, MacNish stated: "Sleep is the intermediate state between wakefulness and death;" wakefulness being regarded as the active state of all the animal and intellectual functions and death as that of their total suspension. Rodents die within about 21 days if completely sleep deprived and it is theorized that humans would die after about 180 days of sleep deprivation.
Sleep Stages: How They are Measured
As Dr. William Dement, the first physician board certified in sleep and founder of the Stanford University Sleep Disorders Center, stated: "The interest in sleep and dreams has existed since the dawn of history and perhaps only ‘love' and ‘human conflict' have received more attention from poets and writers."
There are three distinct physiological states of the human body: awake, non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. The brain waves and the status of the neuromuscular system are different in each of these states. Alterations in the "normal" state of sleep has produced over 160 diagnosis of sleep pathology.
A polysomnogram, or sleep study, is the simultaneous recordings of multiple physiological variables related to sleep, which include electroencephalogram (EEG), recording of eye movements or electro-oculogram (EOG), recording of muscle activity or electromyogram (EMG), cardiac rhythm or electrocardiogram (ECG), nasal and oral air flow, with breathing effort measured by strain gauges known as plethysmographs and oxygen saturation measured by pulse oximetry.
The EEG and EOG assist in determining the stage of sleep of the patient. Non-REM sleep has four levels with different adult normal percentages of each: stage I (2-7%), stage II (45-55%), stage III and stage IV sleep. Stage III and IV are referred to "as slow wave" sleep, also known as delta sleep or deep sleep (10-12%), since the brain waves of each are similar.
REM (20-25%) sleep is an active brain in a paralyzed body.
The normal optimal sleep efficiency (amount time sleeping/total time in bed) is 85%.
The awake state has a predominance of alpha activity as well as low voltage, mixed frequency pattern.
Stage I sleep is the transition from the awake state to stage II sleep, shown by diminished or disappearance of alpha activity and a relatively low voltage, mixed frequency EEG pattern, often in the presence of slow-rolling eye movements. Stage II sleep has K-complexes and sleep spindles with a mixed frequency background. Slow wave sleep reveals high amplitude (>75 microvolts) delta waves with a frequency of 0.5 to 2 Hertz, that is between one-half to two seconds in duration. Delta sleep occurs more commonly in the first one third of the night and decreases with age.
REM sleep is scored having three criteria: First, EEG returns to relatively low voltage, mixed frequency pattern with no K-complexes or sleep spindles. Some patients also reveal a "sawtooth" EEG pattern. Second, chin EMG decreases in amplitude to its lowest levels, and third, EOG reveals rapid eye movements.
REM is more prominent in the last third of the night.
Although one can dream in all stages of sleep, dreams in REM sleep are much more vivid and may have "phasic" body movements associated with them. This is commonly observed when one's dog is dreaming and chasing a feline friend with the extremities moving, the eyes fluttering and the dog barking or panting. REM sleep occurs 90-120 minutes after sleep onset and approximately every 90 minutes thereafter.
Dyssomnias are either intrinsic sleep disorders such as insomnia, narcolepsy, sleep apnea, periodic limb disorder or restless legs syndrome or extrinsic sleep disorders such as inadequate sleep hygiene, insufficient sleep disorder, or drug or alcohol dependent sleep disorder; and circadian rhythm disorders, such as jet lag, shift work sleep disorder, delayed or advanced sleep phase syndrome.
Parasomnias are divided into arousal disorders such as sleepwalking and sleep terrors; sleep-wake transition disorders, such as sleep starts or sleep talking. Parasomnias are usually associated with REM sleep.