One sleep cycle comprises of four stages and last for about 90-120 minutes. Dreams can occur in any of the four stages of sleep but the most vivid and memorable dreams occur in the last stage of sleep (also commonly referred to as REM sleep). The sleep cycle repeats itself about an average of four to five times per night, but may repeat as many as seven times. Thus, you can see how a person can have several different dreams in one night. Most people, however, only remember dreams that occur closer toward the morning when they are about to get up. But just because you can't remember those dreams does not mean that they never happened. Some people swear on the fact that they simply do not dream when in reality, they just don't remember their dreams.
The Stages Of Sleep
Some text lists four stages of sleep, while others say there are five stages. Some consider the first five-ten minutes when you are falling asleep as a stage in the sleep cycle. We think that it is more of a transitional phase. While the other stages of sleep repeat themselves throughout the night, this phase of sleep does not. For this reason, we have excluded it as part of the sleep cycle.
Stage 1: In this stage of sleep, your eyes move back and forth erratically. Often called REM sleep, this stage occurs at about 90-100 minutes after the onset of sleep. Your blood pressure rises and heart rate and respiration speeds up and becomes erratic. Your voluntary muscle are paralyzed. This stage may also be referred to as delta sleep and is the most restorative part of sleep. This is also where the majority of your dreaming occurs.
Stage 2: You are entering into light sleep. This stage is characterized by Non-rapid eye movements (NREM), muscle relaxation and slowed heart rate. The body is preparing to enter into deep sleep.
Stage 3 and 4: Also characterized by NREM, these two stages involves periods of deep sleep with Stage 4 being more intense than Stage 3. Your body temperature drops and muscles relaxes. You are completely asleep. These stages repeat themselves throughout a night's sleep.
Snoring and the disturbance it causes used to be (and frequently is still) regarded as a joke, about which little could be done. We now know that snoring may be a pointer to abnormalities with breathing at night which may be harmful to the health of the snorer. During sleep all the muscles of the body relax and become more floppy. With relaxation of the muscles which help hold open the throat, a partial collapse and narrowing results. Even in non-snorers this narrowing increases the resistance to the flow of air when breathing in but is usually of no significance. When the narrowing during sleep is greater than normal, the airway behind the tongue may collapse transiently. This gives rise to a fluttering of the throat tissues producing sounds which we recognise as snoring. Should the collapse be complete and longer lasting, no air can be drawn into the lungs and the sufferer is literally without breath - that is experiencing apnoea. Were this situation to persist, the individual would asphyxiate!
We are equipped with a remarkably sensitive
ability to detect impending throat closure. This ability does not seem to be
influenced by the depth of sleep. Had we not got this mechanism the human
race would have choked to death in the night and joined the dinosaurs a long
time ago! So our snorer, sensing impending doom, rouses briefly, avoids
suffocation, takes a few deep breaths and rapidly returns to sleep. This pattern
may be repeated 300 - 500 times during the night without recollection in the
morning! It is the fragmentation of the normal sleep architecture consequent
upon these arousals which is the cause of the daytime symptoms of tiredness and
drowsiness with diminished alertness and performance.
Our understanding of why we sleep is remarkably poor. [Horne J. Why we sleep. Oxford: Oxford University Press, 1988.] The only obvious reason we sleep is to prevent sleepiness! It appears that we need about two hours worth of quality deep sleep to remain alert and function at our best during waking hours. It takes time to drift down into this stage of sleep and we collect it in chunks - a few minutes here and half an hour or so there. As long as the overnight aggregate is about 2 hours we wake refreshed by our sleep. With fragmentation of the sleep pattern due to multiple arousals it becomes impossible to harvest the required two hours of quality sleep. Little wonder that after even more than ten hours of so called sleep, sufferers describe themselves as feeling shattered on waking! It can be conceived of as equivalent to the telephone having rung hundreds of times during the night.
The factors causing sleep apnoea do so by increasing the normal narrowing of the throat during sleep. Anything rendering the throat narrower to start with (for example enlarged tonsils or a set-back lower jaw) makes it more likely that the throat will close off more and obstruct the airway. A partially blocked nose causes lower pressures in the throat during breathing in and this tends to suck the walls of the throat together. Probably the most important factor is being overweight with a consequent thickened neck. We are not yet certain why it is that obesity produces sleep apnoea. It seems most likely that the inertial mass loading of the neck by increased fat deposition overcomes the ability of the throat muscles to keep the airway open when the muscle tone falls off during sleep. Certainly one of the best predictors of this effect is a neck circumference of 17 inches (43 cm) or more. [Stradling JR. et al. Predictors and prevalence of obstructive sleep apnoea and snoring in 1001 middle aged men. Thorax 1991; 46:85-90]
The sort of person we most commonly see with heavy snoring and sleep apnoea is a middle-aged man who is overweight with a big neck, taking a size 17 inch collar or more. Many people with sleep apnoea are not particularly overweight and in some we simply do not understand why they have sleep apnoea. In children the commonest cause is enlarged tonsils. Nowadays sleep apnoea is the commonest reason for recommending that a young child has a tonsillectomy. [Rosenfeld RM et al. Tonsillectomy and adenoidectomy: changing trends. Ann Otol Rhinol Laryngol 1990; 99:187-91]
Sleep apnoea and heavy snoring, severe enough to interfere with sleep quality, is much more common than generally realised. The prevalence of snoring increases with age and is more common in men than women. About 25% of men and 10% of women aged 35 - 65 years snore. Probably more than five in every hundred men have significant sleep apnoea. There is a strong correlation between snoring and daytime sleepiness as a result of the sleep fragmentation caused by snoring alone without obstructive sleep apnoea. In terms of sheer numbers, there are probably more suffers from daytime sleepiness as a result of snoring than as a result of obstructive sleep apnoea. Obstructive sleep apnoea may be associated with greater risk of high blood pressure, stroke, heart attacks, heart failure and thickening of the blood all of which can reduce the quality and duration of life. [Spriggs DA. et al. Historical risk factors for stroke: a case control study. Age, Ageing 1990; 19: 280-7. Telakivi T. et al. Snoring and cardiovascular disease. Compr Ther 1987; 13: 53-7] It is clearly related to an increased risk of road traffic accidents. [Haraldsson PO et al. Sleep apnea syndrome symptoms and automobile driving performance before and after uvulopalatopharyngoplasty. J Otorhinolaryngol Relat Spec 1991; 53: 106-10] [Daily Telegraph. 8th January, 1997.]
Because sleep can be so disrupted by the body having frequently to rouse briefly to reverse the upper airway obstruction, sufferers experience severe daytime sleepiness. To start with this occurs only during potentially boring activities such as reading, watching television or driving on motorways. However when the sleepiness gets worse it begins to interfere with most activities, with the individual falling asleep talking or eating. Poor work performance can lose the sufferer his or her job and of course sleepiness whilst driving can be fatal (sleep apnoea sufferers are about seven times more likely to have car accidents). Snoring will usually have been present for many years and have gone well beyond a joke within the family. There are many other symptoms, as one might expect in someone who is seriously sleep deprived, (irritability for example) but the twin symptoms of snoring and daytime sleepiness are the best pointers to the diagnosis.
The severe morbidity of sleep apnoea coupled with the ready availability of effective treatment means that recognition and diagnosis are important. Already public awareness is increasing following press and television publicity but much remains to be done to increase this awareness. The presence of significant sleep apnoea may be strongly suspected from the symptoms. Snoring, excessive daytime sleepiness, early morning headache and poor concentration should alert patient and doctor alike. These symptoms may be embarrassing or be attributed simply to laziness or ageing. Often the individual's partner has read an article about sleep apnoea and recognises the problem. Often the diagnosis of sleep apnoea can be made on the basis of the history alone. Confirmation of the diagnosis by means of some form of study is important. Unlike most medical problems which can confidently be diagnosed from history and physical examination alone, with sleep apnoea these traditional methods are poor indicators of the severity of the underlying problem. A variety of things can be measured during sleep without having to use any painful needles or devices.
The simplest special test is to make continuous recordings of blood oxygen levels and heart rate during a normal night's sleep and this need not necessarily involve coming into hospital. Analysis of these recordings may provide enough information to exclude the presence of obstructive sleep apnoea without resorting to more complex measures. Even in the presence of normal findings for oxygen levels it may be possible to detect clear evidence of multiple arousals by examining the continuous record of heart rate. [Stradling JR. Handbook of sleep related breathing disorders. Oxford Medical Publications 1993]
The above simple investigation may be supplemented by a continuous overnight video recording (under infrared light) along with audio recording. Processing of the video signal allows movement to be detected and analysed. Computer analysis of these records allows a rapid review of an overnight recording to identify periods of abnormal sleep and the times at which they occur. The corresponding times on the video recording can then be inspected to clarify the diagnosis.
In recent years there has been a move away from the complex multiple measurements known as polysomnography. This involves the application of electrodes over the brain along with sensor devices detecting chest and limb movement along with devices to detect air flow through the nose. These highly expensive and labour intensive techniques are now used only rarely in the UK. Full polysomnography misses snoring induced arousals and is no longer regarded as a good gold standard.
It is essential that treatment is tailored to the patient's needs. Treatment is focused upon correcting the daytime symptoms which result from sleep fragmentation. When the sleep disturbance is not severe simple approaches can help. Losing some weight, not drinking alcohol after 6.00 p.m. (alcohol relaxes the upper airway muscles even more), keeping the nose as clear as possible, and sleeping on one's side or semi-propped up can all help and sometimes be dramatically beneficial. Carefully chosen individuals can be helped by simple dental devices which slightly advance the lower jaw during sleep and help to keep the airway open. In selected cases medication can be very effective. When snoring is very objectionable, with the individual and the partner desperate for a solution, then an operation on the back of the throat may help - but this is a very last resort and should only be done when a sleep study has shown snoring alone with very little, or no, sleep apnoea. Surgery has NOT been shown to be beneficial for people with sleep apnoea and is best avoided for this condition until we learn more about the mechanisms behind it. The worry is that some patients treated surgically for apnoea have been made worse. Also, the permanent alteration of the throat structure denies the individual the benefit of the definitive treatment of nasal CPAP. The only clear indication for surgery is the removal of enlarged tonsils which obstruct the airway.
For individuals with severe sleep related breathing problems and disabling symptoms the highly effective treatment of nasal CPAP can be offered.[Sullivan CE. et al. Reversal of obstructive sleep apnoea by continuous positive airway pressure applied through the nares. Lancet 1981; 1: 862-5] This acronym stands for nasal continuous positive airway pressure. The throat which threatens to narrow is gently held open by blowing air via the nose at slightly increased pressure. A mask is worn during sleep fitting snugly and comfortably over the nose. The mask is connected to a small, quiet pump beside the bed. Breathing is then able to return to normal during sleep with the air gently blowing through the nose and holding open the throat. The response is usually dramatic with greatly improved sleep and disappearance of the daytime sleepiness. Although these devices seem cumbersome to wear and hardly improve appearance, the benefits far outweigh the disadvantages and the vast majority of sufferers happily use their machines every night at home after a one night trial in hospital. The benefit can be dramatic, transforming a previously unmotivated individual into one alive again and determined to lose weight etc.. Research has shown that nasal CPAP improves life expectancy and reverses heart failure.[He J. et al. Mortality and apnea index in obstructive sleep apnea. Experience in 385 male patients. Chest 1988; 94: 9-14.]