A sleep study is conducted during a patient’s through-the-night visit to a sleep laboratory will include monitoring among other things blood oxygen levels, respiration rate, brain-wave activity, leg movements, and most significant, the apnea-hypopnea index, the number of apnea and hypopnea (partial inhalation) incidents the sleeper experiences per hour.
- Your sleep study measures the time spent in each stage, in minutes and as a percentage, and the latencies between the time you fall asleep and the time you enter Stage 4 and REM sleep, respectively.
- Non-REM and REM sleep
- Once you drop off, you should progress through four stages of increasingly deep, dreamless sleep and into a fifth stage during which dreaming--characterised by rapid eye movement--occurs. Over the course of the night, you will cycle repeatedly between Non-REM and REM sleep. The structure of these cycles--poetically known as "sleep architecture"--reveals whether you are getting the restorative sleep you need to feel and be well. Stage 1, the very lightest sleep, should only be 5 percent of the total sleep time, and should only occur at the beginning of the night. The still fairly light Stage 2 sleep should represent about 55 to 60 percent of the TST. Deep sleep--also known as "slow wave" sleep--takes place in Stages 3 and 4, and should account for about 20 percent of the TST. If Deep Sleep is truncated or absent, you will not feel rested the next day.
AROUSALS AND AWAKENINGS
- Arousals--interruptions of sleep lasting 3 to 15 seconds--can occur spontaneously or as a result of sleep-disordered breathing or other sleep disorders. Each arousal sends you back to a lighter stage of sleep. If the arousal last more than 15 seconds, it becomes an awakening. You are usually not aware of arousals, but may be aware of awakenings. The number of arousals and awakenings is registered in the study, and reported as a total number and as a frequency per hour of sleep, which is referred to as an index. The higher the arousal index, the more tired you are likely to feel, though people vary in their tolerance of sleep disruptions. As few as five arousals per hour can make some people feel chronically sleepy. In the worst cases of SDB, the index can be 100 or more.
MECHANICAL MALFUNCTION/ OBSTRUCTION
- The mechanical malfunction occurs when the soft structures in the back of the throat collapse into the airway, reducing the amount of air that makes its way into your lungs and, as a consequence, the amount of oxygen in your bloodstream.
- In an apnea episode, airflow is reduced by at least 80 percent;
- In a hypopnea episode, the range of the reduction is 50 to 80 percent.
EVENTS PER HOUR
- The report indicates the number of times each occurs, as a nighttime total and as an index of EVENTS PER HOUR. This latter number is referred to as either the apnea-hypopnea index or the respiratory disturbance index.
- An index of 5 to 14 indicates a MILD level of breathing--and sleep--disturbance. From 15 to 30 is MODERATE greater than 30 is SEVERE.
- The associated drops in blood oxygen levels, known as DESATURATIONS, are also measured and categorised.
- NORMAL saturation is around 95 percent.
- A MILD desaturation to 86 percent is mild,
- A MODERATE reduction to 80 to 85 percent is moderate,
- A SEVERE reduction to is a 79 percent or less is.
HEART: In addition to the items covered above, the polysomnogram looks at your heart rhythm, and determines if there are any abnormalities.
LIMB MOVEMENT: Another important part of the study is the assessment of limb movement, since leg movement can constitute another sleep disorder.
SNORING: Someone listens your snoring, which is probably the symptom that got you to the lab in the first place.