A polysomnography, or sleep study, is a non-invasive test used to diagnose sleep disorders. During sleep, it monitors a variety of physiological parameters, such as brain activity, eye movement, heart rate, respiratory effort, blood oxygen levels, and muscle activity.

A sleep study is typically performed in a sleep center or lab, though some studies can be performed at home using portable monitoring equipment. Here's an overview of how a sleep study is performed:

• Preparation: The patient should avoid caffeine and alcohol prior to the study, as these substances can interfere with sleep. They are usually asked to keep a regular sleep schedule and to keep a sleep diary.

• Setup: The patient arrives at the sleep center in the evening on the day of the study. Electrodes and sensors will be attached to the patient's head, face, chest, and limbs by a technician. These sensors are linked to a computer, which records the data all night. The patient will also wear a nasal cannula or an oxygen sensor to measure airflow and oxygen levels. 

• Sleep: At the sleep center, the patient will sleep in a comfortable, private room. A low-light video camera and an intercom system allow the technician to monitor the patient and communicate if necessary.

• Data collection: During the patient's sleep, the monitoring equipment records various parameters such as brain waves (electroencephalogram, or EEG), eye movements (electrooculogram, or EOG), muscle activity (electromyogram, or EMG), heart rate, and blood oxygen levels. This data aids in the identification of sleep stages as well as any abnormalities or disruptions. 

• Data analysis: Following the study, a sleep specialist will review and interpret the data. They will examine the patient's sleep patterns for any irregularities, interruptions, or sleep disorders.

1. Obstructive sleep apnea (OSA): Characterized by pauses in breathing due to airway blockages during sleep, leading to drops in blood oxygen levels and frequent awakenings. 

2. Central sleep apnea (CSA): A less common type of sleep apnea, where the brain fails to send proper signals to the muscles controlling

3. Insomnia: difficulty falling or staying asleep caused by a variety of factors, such as stress, anxiety, medical conditions, or poor sleep hygiene. 

4. Restless legs syndrome (RLS) is a painful sensation in the legs that causes an insatiable desire to move them, disrupting sleep. 

5. Narcolepsy is a neurological disorder that causes excessive daytime sleepiness and unexpected sleep attacks, which are sometimes accompanied by cataplexy (a sudden loss of muscle tone).

6. Periodic limb movement disorder (PLMD) is characterized by involuntary limb movements during sleep that disrupt and fragment sleep.

7. RBD (REM sleep behavior disorder): acting out dreams during REM sleep, such as talking, shouting, or physically moving, which can cause injuries or disrupt sleep. 

Circadian rhythm disorders are caused by a misalignment of the internal biological clock and the external environment, resulting in sleep disturbances. After reviewing the findings, the sleep specialist will make recommendations for appropriate treatment options or lifestyle changes to address the diagnosed sleep disorder(s) or any other identified sleep issues.