From the Guidelines
Sleep apnea is clinically defined by the apnea-hypopnea index (AHI), which measures the number of breathing pauses (apneas) and partial breathing reductions (hypopneas) per hour of sleep, with a threshold for diagnosis of AHI ≥5 with symptoms or ≥15 with or without symptoms, as stated in the 2021 guideline for the prevention of stroke in patients with stroke and transient ischemic attack 1.
Clinical Metrics for Sleep Apnea
The diagnosis of sleep apnea is based on the following clinical metrics:
- Apnea-hypopnea index (AHI): the hourly sum of apneas and hypopneas per hour of sleep
- Apnea: a complete cessation of airflow for at least 10 seconds
- Hypopnea: a reduction in airflow by at least 30% for 10 seconds or more, accompanied by a 3-4% oxygen desaturation or an arousal from sleep
- Oxygen desaturation index (ODI): the number of times per hour that blood oxygen levels drop by a certain percentage (typically 3-4%)
- Respiratory disturbance index (RDI): includes apneas, hypopneas, and respiratory effort-related arousals
Severity of Sleep Apnea
The severity of sleep apnea can be classified as:
- Mild: AHI between 5-15 events per hour
- Moderate: AHI between 15-30 events per hour
- Severe: AHI more than 30 events per hour
Diagnosis and Assessment
The diagnosis of sleep apnea is typically made using an overnight polysomnography (sleep study), which records sleep stages, body position, limb movements, and cardiac rhythm to provide a comprehensive assessment of sleep-disordered breathing 1. Home sleep apnea testing (HSAT) can also be used to establish the diagnosis among patients with a high pretest probability, with an event index of 15 events per hour or higher indicating moderate to severe sleep apnea 1.
From the Research
Clinical Metrics for Sleep Apnea
The following clinical metrics are used to define sleep apnea:
- Apnea-Hypopnea Index (AHI): the average number of apnea and hypopnea events per hour during sleep 2, 3, 4, 5, 6
- Oxygen Desaturation Index (ODI): the average number of oxygen desaturation events per hour during sleep 2, 3
- Hypoxic burden: a measure of the duration and severity of oxygen desaturation events 3
- Arousal intensity: a measure of the frequency and severity of arousals during sleep 3
- Odds ratio product: a measure of the likelihood of sleep apnea based on various clinical factors 3
- Cardiopulmonary coupling: a measure of the relationship between cardiac and respiratory function during sleep 3
Alternative Metrics
Some studies have proposed alternative metrics for evaluating sleep apnea severity, including:
- Novel parameters that consider the duration and morphology of apnea and hypopnea events 2
- Alternative definitions for apnea and hypopnea events that include respiratory airflow limitations with a temporal span between 5 and 10 seconds 4
- Metrics that assess sleepiness, quality of life, performance, and medical outcomes, such as the Epworth Sleepiness Scale (ESS) 5, 6
Diagnostic Criteria
The American Academy of Sleep Medicine (AASM) recommends the following diagnostic criteria for obstructive sleep apnea/hypopnea syndrome (OSAHS):
- Excessive daytime sleepiness that cannot be better explained by other factors
- Two or more of the following symptoms: choking or gasping during sleep, recurrent awakenings from sleep, un-refreshing sleep, daytime fatigue, and impaired concentration
- More than five obstructed breathing events per hour during sleep 5