Posted by Heidi/Mermie Delta sleep occurs mostly in the first third of the night and makes up about 10 to 20 percent of total nocturnal sleep in normal young adults, whereas REM sleep takes place predominantly during the last third of the night's sleep. The percentage of delta sleep is affected by age, amount of prior sleep, and various diseases. Delta sleep decreases with age and may be absent in healthy, elderly males. Sleep deprivation increases the rapidity of the onset of delta sleep and its portion of total sleep time. Young children have particularly large proportions of delta sleep, which increases if they are sleep-deprived. This explains why it is frequently difficult to wake children. Elderly people have smaller proportions of delta sleep, which is why they are easily aroused by environmental noise. Medical problems, such as obstructive sleep apnea, periodic leg movements during sleep, and FM may affect the quantity and quality of delta sleep. This in turn probably accounts in some measure for the feeling of fatigue experienced by people suffering from these maladies. Fibromyalgia and Sleep About 20 years ago, researchers in Toronto discovered that patients with FM had NREM stages of sleep "contaminated" by an intercurrent alpha rhythm (like that of wakefulness). But whether the sleep disturbance caused the FM symptoms or was secondary to the disease itself could not be determined. This group of investigators went on to show that healthy subjects selectively deprived of delta sleep by being exposed to noise developed periods of delta sleep mixed with alpha waves. Interestingly, when deprived of delta sleep these people experienced some musculoskeletal discomfort and mood symptoms similar to those of the patients with FM. These data suggested that the stage 4 sleep disturbance caused the appearance of the achiness or pain and mood symptoms. However, it was felt that the effect of delta sleep disturbance on symptoms might be determined by examining the physical and psychological characteristics of the healthy subjects. Their subjects were younger than the patient population with FM and free from illnesses and psychological problems, but they were not particularly physically fit. Yet they had the symptoms of FM when put through the sleep-deprivation process. Their relatively sedentary lifestyle may have been significant, because most reports have pointed to the positive influence of exercise on delta sleep. Sleep disturbances can be triggered in patients by physical or emotional trauma or by a metabolic or other medical problem. Poor sleep can lead to fatigue with resultant diminished exercise causing worsened physical fitness and the establishment of a vicious cycle of inactivity and sleep disturbance with physical and mood-related symptoms. These problems could help lead to the development of FM. Hormones and Sleep An interesting study published in the Journal of Clinical Endocrinology and Metabolism (April 2001) revealed that men seem to become more sensitive to the stimulating effects of corticotropin-releasing hormone (CRH) as they get older. This hormone plays a key role in how your body responds to stress. If you are aroused, you will have higher levels of CRH. In the study, researchers evaluated the sleep habits of twelve middle-aged men and twelve young men over four nights. On one night, the men all received CRH ten minutes after they were asleep. Both groups of men produced higher levels of stress hormones in response to the CRH. While younger men produced higher levels of cortisol (the main stress hormone involved in the "fight or flight" response), middle-aged men stayed awake longer. They also had less slow-wave or deep sleep than did the younger men, showing that middle-aged men may have an increased vulnerability to stress hormones. This, in part, may explain why insomnia increases in middle age as a result of these dysfunctional sleep mechanisms caused by arousal-producing stress hormones. There are also studies showing that people who spend less time in slow-wave sleep are more prone to depression. Because of the effects of estrogen on a woman's sleep pattern, it's more difficult to study women and sleep. Still, for those women who find it difficult to sleep during premenstrual time, you have great company.
on 8/27/2007, 4:33 am
Sleep onset usually is within five to twenty minutes of going to bed. After the start of sleep, there is a cycling though stages 1 to 4 approximately every 45 to 90 minutes with REM sleep punctuating each cycle at about 60 to 90-minute intervals.
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