The sleep process is smoothened out in hypnogram results unlike it occurs naturally. The restrictions of measuring sleep at short 30-second epochs limits the ability to record events shorter than 30 seconds hence, the macrostructure of sleep can be evaluated while the microstructure is not. Hypnograms are rarely used to provide quantitative data, however it has been suggested that statistical evaluation can be carried out using multistate survival analysis and log-linear models to provide numerical significance. The main use of a hypnogram is as a qualitative method to visualise the time period of each stage of sleep, as well as the number of transitions between stages. For example, the anticonvulsant Phenytoin (PHT) can be seen to disrupt sleep by increasing the duration of NREM stage 1 and decreasing the duration of SWS whereas the drug Gabapentin is seen to revive sleep by increasing the duration of SWS. The effects of certain medications on sleep architecture can be visualised on a hypnogram. Disruptions or irregularities to the normal sleep cycle or sleep stage transitions can be detected for example a hypnogram can show that in obstructive sleep apnea (OSA) the stability of transition between REM and NREM stages is disrupted. Sleep architecture can be evaluated using hypnograms, demonstrating irregular sleeping patterns associated with sleep disorders. Hypnograms for healthy persons vary slightly according to age, emotional state, and environmental factors. The stage that occurs before waking is normally REM sleep. The second half of the sleeping period contains most REM sleep and little or no SWS and may contain brief periods of wakefulness which can be recorded but are not usually perceived. Most SWS occurs in the first one or two cycles this is the deepest period of sleep. On a hypnogram, a sleep cycle is usually around 90 minutes and there are four to six cycles of REM/NREM stages that occur during a major period of sleep. During rest following a sleep-deprived state, there is a period of rebound sleep which has longer and deeper episodes of SWS to make up for the lack of sleep. The number of hours of sleep is variable, however the proportion of sleep spent in a particular stage remains mostly consistent healthy adults normally spend 20–25% of their sleep in REM sleep. A normal healthy adult requires 7–9 hours of sleep per night. Output Normal sleep Ĭycles of REM and non-REM stages make up sleep. Prior to this the Rechtschaffen and Kales (RK) rules were used to classify sleep stages. There is a protocol defined by the American Academy of Sleep Medicine (AASM) for sleep scoring, whereby the sleep or wake state is recorded in 30-second epochs. Certain frequencies displayed by EEGs, EOGs and EMGs are characteristic and determine what stage of sleep or wake the subject is in. The output from these three sources is recorded simultaneously on a graph by a monitor or computer as a hypnogram. Hypnograms are usually obtained by visually scoring the recordings from electroencephalogram (EEGs), electrooculography (EOGs) and electromyography (EMGs). Method A hypnogram (top) with other readings below The previously considered 4th stage of NREM sleep has been included within stage 3 this stage is also called slow wave sleep (SWS) and is the deepest stage of sleep. NREM sleep can be further classified into NREM stage 1, 2 and 3. It allows the different stages of sleep: rapid eye movement sleep (REM) and non-rapid eye movement sleep (NREM) to be identified during the sleep cycle. It was developed as an easy way to present the recordings of the brain wave activity from an electroencephalogram (EEG) during a period of sleep. Here, both stage 3 and stage 4 are shown these are often combined as stage 3.Ī hypnogram is a form of polysomnography it is a graph that represents the stages of sleep as a function of time. Graph of a person's sleep Example hypnogram of a normal, healthy adult
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