Diagnostics: Polysomnogram (PSG)

What is a polysomnogram?

A polysomnogram (PSG) is a diagnostic test used to evaluate potential sleep disorders. This test records various physiological parameters during sleep, including brain activity, eye movements, muscle activity, heart rate, respiratory effort, and blood oxygen levels.

The polysomnogram takes place in a sleep lab room made to look like a hotel room where the patient is monitored overnight. Electrodes are placed on the scalp to measure brain waves (electroencephalography, EEG), which help determine different sleep stages. Additional electrodes are placed around the eyes to track eye movements (electrooculography, EOG), and sensors are placed on the chin and limbs to record muscle activity (electromyography, EMG).

The respiratory aspects of the test are monitored through belts placed around the chest and abdomen to assess respiratory effort, along with a nasal cannula (tubing that looks like that used for oxygen delivery). Pulse oximetry is used to track blood oxygen level..

The data collected during the PSG are analyzed to identify sleep patterns, detect abnormalities such as obstructive sleep apnea, central sleep apnea, and evaluate other sleep disorders like insomnia or periodic limb movement disorder. The interpreting physician usually produces the report within 10 days or so.

Obtaining insurance approval for financial coverage of a PSG can be challenging for the physician and patient, and if approved may be costly, depending on the insurance deductible. The waiting time between ordering and performing a PSG has historically been weeks to months. A PSG is purely informational (diagnostic) and carries essentially no risk to the patient.

A split night sleep study is combination of a standard PSG in the first part of the night and, if deemed appropriate, using a CPAP or other therapeutic intervention in the second part of the night. This allows for a comparison between the condition (such as obstructive sleep apnea) in the untreated and treated states.

What information is included in a polysomnogram report?

A polysomnogram report provides comprehensive data on various physiological parameters recorded during a sleep study. Key components typically included in the report are:

• Patient Demographics: Basic information about the patient, including age, sex, weight, and relevant medical history.

• Study Overview: Details about the type of polysomnography conducted, the duration of the study, and the indication for the study.

• Sleep Stages: A breakdown of sleep architecture, categorizing the cycles of REM (Rapid Eye Movement) and NREM (Non-Rapid Eye Movement) sleep, along with percentages of total sleep time spent in each stage.

• Respiratory Events: Documentation of apnea (complete cessation of breathing) and hypopnea (partial cessation of breathing), including their frequency and severity, as well as oxygen saturation levels during these events. The number of apneas and hypopnea occurring per hour is the Apnea Hypopnea Index (AHI). The classification based on AHI values is as follows:

  • Normal: AHI of less than 5.

  • Mild Obstructive Sleep Apnea: AHI of 5 to 14.9

  • Moderate Obstructive Sleep Apnea: AHI of 15 to 29.9

  • Severe Obstructive Sleep Apnea: AHI greater than 30

  Of note, the Center for Medicare Services defines apneas and hypopneas more stringently than does the American Society of Sleep Medicine (AASM). Specifically, an apnea or a hypopnea event is counted under AASM criteria when the oxygen saturation level drops by 3% from its baseline or when the patient wakes up from decreased airflow, whereas for Medicare, the oxygen saturation must drop 4% to count. Practically, this means that for Medicare to cover any treatment of obstructive sleep apnea, the scoring of the AHI be done using the more stringent Medicare criteria.

• Movement Artifacts: Observations of body movements during sleep, which can impact sleep quality and may be associated with conditions like restless leg syndrome.

• Heart Rate and Rhythm: Analysis of heart rate variability and any arrhythmia (irregular heart rhythm) observed throughout the study. Apneas and hypopneas that are associated with arrhythmia indicate a more dangerous degree of obstructive sleep apnea.

• Leg Movements: Information on periodic limb movements, including frequency and duration, which may identify restless leg syndrome.

• Patient Events: Any significant occurrences during the study, such as arousals, awakenings, or snoring patterns.

• Overall Impression: A summary of findings with interpretations, including any diagnosed sleep disorders (e.g., obstructive sleep apnea, central sleep apnea, narcolepsy).

• Recommendations: Suggestions for further evaluation or treatment options based on the findings of the polysomnogram.