Are you superhuman?

So what is sleep? The definition remains elusive. However, sleep has two principle features. The first is that sleep erects a barrier between the conscious mind and the outside world. If a sound is loud enough - like thunder overhead, then the sleeper can be woken. The second feature of normal sleep is that it is readily reversible. If intense or persistent stimulation does not wake the sleeper, then they are either unconscious or dead. Furthermore, we know that sleep occurs naturally, unlike a coma, and it occurs daily in humans. Importantly we all need good quality sleep.

Assessing Sleep
We can assess sleep by measuring the electrical activity of the brain. When we first snuggle up in bed, we gently drift off into very light sleep (Stage 1). This shows characteristic changes in brain-wave activity and generally occurs for a very short period of time. There follows slightly deeper sleep (Stage 2), which also has very characteristic brain-wave activity. Over a whole night of say 8 hours, most of the night will be in Stage 2. After Stage 2, the deep and importantly recuperative sleep (Stages 3 and 4 - Slow-Wave Sleep) occurs. This is essential for the body to be able to recover before the next day starts. About 20 to 25% of the night is spent in Stages 3 and 4 in a normal sleep pattern. As the night progresses towards morning, less Stage 3 and 4 sleep occurs. This is replaced by increasing periods of dreaming (REM) sleep, which cycles every 90 to 120 minutes throughout the night. Each sleep period becomes longer, but it is very difficult to remember your dreams unless you wake up in them, which often occurs early in the morning. Irritatingly, if you wake up in a dream your enjoying it is very difficult to get back into the same dream! By monitoring the brain waves throughout the night, we can assess the stage of sleep and determine the amount of each type of sleep stage - wake, stages 1 - 4 and REM.

Sleep Deprivation
The study carried out by our three volunteers clearly demonstrates the effects of sleep deprivation. Their ability to carry out simple tasks such as driving, to concentrate on tasks, to be sociable all showed changes characteristic of sleep deprivation. Despite not sleeping properly for about 60 hours, their bodies rapidly recovered following a single night's sleep. This clearly demonstrates that the body can adapt and readily recover over short periods of sleep disruption.

This may also be the case for some of the many sleep disorders that are now recognized by sleep specialists. Some patients appear to have difficulty in getting to sleep and when they do, actually remaining asleep (Insomnia). Others will suddenly fall asleep sometimes without warning or have muscle weakness or excessive daytime sleepiness (Narcolepsy). Patients with breathing problems during sleep may stop breathing for short periods throughout the night (Sleep Apnoea). This disrupts the sleep pattern and results in excessive daytime sleepiness. When the patients are treated their sleep pattern returns to close to normal and their daytime sleepiness decreases. People often associate and confuse sleep apnoea with snoring. They both have the problem of noise and disturb other people. However sleep apnoea is more of a medical problem than snoring is, and patients need to be assessed correctly before any treatment.

Whatever the cause of disrupted sleep, it can have a knock-on effect. Sleep is needed by the body to recover at the end of each day. Lack of sleep, which may be due to life-style rather than a sleep disorder, may result in poor performance at work, increased risk of road traffic accidents, with about one-third of traffic accidents due to drivers falling asleep at the wheel, increased risk of accidents in the home or at work and changes in behaviour and mood. Excessive sleepiness and sleep disruption is not good for the individual or for those around them.

Dr. Adrian Kendrick, The Bristol Royal Infirmary