Apnea Hypopnea Index (AHI)

AHI explained

The apnea hypopnea index records the number of apnea and hypopnea episodes per hour of sleep supervision in order to analyse them and determine the degree of sleep apnea severity the patient suffers from.

An apnea episode is defined as a pause in breathing, for at least 10 seconds, which is associated with a decrease in blood oxygenation. Some subjects experience brief arousal or awaken during an apnea episode.

The AHI determination is often used in polysomnography with oximeters to determine the oxygen desaturation levels or the Respiratory Disturbance Index (RDI). Polysomnography can also evaluate the number of shallow breaths per studied period.

The following table explains the four degrees of severity and their apnea/hyponea associated episodes and the correlated oxygen saturation levels:

Obstructive sleep apnea is diagnosed when AHI or RDI are greater than or equal to 15 events per hour, OR AHI or RDI are greater than or equal to 5 and less than or equal to 14 events per hour with documented symptoms.

Documented symptoms include impaired cognition, insomnia or documented hypertension, ischemic heart disease, or history of stroke.

AHI addresses to adult patients. The pediatric guidelines consider pathologic even the presence of 1 abnormal breathing event during one hour of sleep observation.

Obstructive sleep apnea guidelines

OSA is a serious condition with two main comorbidity risks:

■ Acute myocardial infarction (approx. 70% of MI patients are also diagnosed with OSA and AHI greater than 10).

■ Stroke (approx. 65% of stroke patients are diagnosed with AHI greater than 10).

Obstructive sleep apnea is one of the four SDBs (sleep-disordered breathing) conditions. The other three are: Central sleep apnea (CSA), Nocturnal hypoventilation and Cheyne–Stokes respiration (CS).

OSA risk factors include:

■ Subject age and gender (older males present a higher risk);

■ Decreased muscle tone with increased soft tissue around the airway;

■ Physiologically or pathologically narrowed airways;

■ Genetic factors;

■ Lifestyle factors (sedentarism, smoking, sleep position).

The following table introduces the most common nocturnal symptoms directly related to OSA and other symptoms that are due to poor sleep quality.

Diagnosis consists of evaluation of patient history and sleep analysis through polysomnography. The respiratory conditions that are usually included in differential diagnosis are:

■ Asthma;

■ Narcolepsy;

■ Chronic obstructive pulmonary disease;

■ Gastroesophageal reflux disease;

■ Periodic limb movement disorder.

Mild to moderate cases are recommended lifestyle changes that include loosing weight, changing sleep position, starting an exercise routine.

Some cases may require non invasive therapies such as external or internal nasal dilator strips or sprays.

Moderate to severe cases may require continuous positive airway pressure (CPAP) or if CPAP does not work, surgical treatment to remove or repair the anatomical defect impairing the airflow, for example adenotonsillectomy (removal of tonsils) or Uvulopalatopharyngoplasty (reconstruction of the soft palate).

References

1. Ruehland WR, Rochford PD, O'Donoghue FJ, Pierce RJ, Singh P, Thornton AT. The new AASM criteria for scoring hypopneas: impact on the apnea hypopnea index. Sleep. 2009; 32(2):150-7.

2. Mbata GC, Chukwuka JC. Obstructive Sleep Apnea Hypopnea Syndrome. Ann Med Health Sci Res. 2012; 2(1): 74–77.

3. Shahar E. Apnea-hypopnea index: time to wake up. Nat Sci Sleep. 2014; 6: 51–56.