Criteria of Obstructive Sleep Apnoea

Sleep apnoea occurs during sleep when a cessation of airflow occurs for at least 10 seconds
(usually 20-30 s but rarely >2 min). 

The term “Sleep Apnoea” describes 2 major sleep-related clinical problems:

(1) obstructive sleep apnoea (OSA), and

(2) central sleep apnoea.

OSA is caused by upper airway (UA) obstruction at the level of the pharynx and is the most common form of sleep apnoea. Central apnoea is the result of impairment in respiratory control of breathing.

Sleep apnoea syndrome encompasses a spectrum of sleep-related breathing disorders -  ranging from simple snoring to severe sleep apnoea with associated Neuro cognitive deficits, residual daytime sleepiness, pauses in breathing, and cardiovascular consequences such as hypertension and stroke.

Sleep apnoea is defined in adults as a temporary absence or cessation of breathing during sleep for 10 or more seconds.  According to the International Classification of Sleep Disorders: Diagnostic and Coding Manual, the description of OSA includes:

1. repetitive episodes of UA obstruction during sleep,
2. arterial oxygen desaturation in association with apnoeas,
3. daytime hypersomnolence, and
4. snoring.

• In obstructive apnoea, ventilatory effort is present but airflow ceases due to closure of the UA.
• In central apnoea, ventilatory effort is absent and, therefore, airflow ceases. In mixed apnoea, ventilatory effort is not observed initially (central apnoea component) but ventilatory effort follows (obstructive apnoea component).
• Partial reductions in inspiratory airflow (hypopneas) also have been identified in patients with SDB.
• A hypopnea is a decrease in inspiratory flow to 50% of baseline and is associated with desaturation.

The apnoea index (AI), which is the total number of apnoeas during sleep divided by the total number of hours of sleep, is a relative measure of apnoea severity.

Traditionally, an AI of 5 or more has been used to define the presence of OSA. Many laboratories are reporting the apnoea-hypopnea index, also known as the respiratory disturbance index (RDI).

Back to Top