Apnea Hypopnea Index (AHI) Calculator

How does this apnea hypopnea index (AHI) calculator work?

This health tool records the number of apnea and hypopnea episodes per hour of sleep supervision and analyses each number in order to estimate the degree of respiratory severity.

This apnea hypopnea index (AHI) calculator uses 4 categories of severity as follows:

■ None/Minimal: AHI 0 – 4 per hour;

■ Mild: AHI 5 – 14 per hour;

■ Moderate: AHI 15 – 29 per hour;

■ Severe: AHI 30 or more per hour.

Apnea episodes are defined as pauses in breathing for at least 10 seconds, usually associated with a decrease in blood oxygenation. During these pauses, the subject either suffers a brief arousal or awakens.

The AHI calculation is used in conjunction with oxygen desaturation levels during polysomnography with oximeters and/or the Respiratory Disturbance Index (RDI) to indicate OSA severity. Polysomnography also evidences the number of shallow breaths per studied period.

The oxygen saturation levels correlated with severity categories is:

■ Normal: 96 – 97% O₂ saturation;

■ Mild: 90 – 95% O₂ saturation;

■ Moderate severity: 80 – 89% O₂ saturation;

■ Severe: <80% O₂ saturation.

AASM diagnostic criteria for OSA includes:

■ AHI or RDI greater than or equal to 15 events per hour, or

■ AHI or RDI greater than or equal to 5 and less than or equal to 14 events per hour with documented symptoms i.e. (EDS), impaired cognition, insomnia or documented hypertension, ischemic heart disease, or history of stroke.

There are two main comorbidity risks associated with obstructive sleep apnea:

■ Acute myocardial infarction/heart attack – with approximately 70% of MI patients being diagnosed with OSA and AHI higher than 10.

■ Stroke – 65% of stroke patients are also diagnosed with sleep disordered breathing and AHI higher than 10.

While AHI is considered an adult tool, for pediatric use, even the presence of 1 abnormal breathing event during one hour of study is considered abnormal.

AHI is higher during the hours when the subject lies on their back and during the REM sleep cycles.

OSA guidelines

There are four sleep related conditions that are known as sleep-disordered breathing SDBs:

■ Obstructive sleep apnea (OSA);

■ Central sleep apnea (CSA);

■ Nocturnal hypoventilation;

■ Cheyne–Stokes respiration (CS).

Some of the main risk factors are old age, male gender, decreased muscle tone with increased soft tissue around the airway, narrowed airways. There is also a genetic factor in the appearance of OSA alongside other lifestyle factors such as smoking, alcohol consumption or sleeping position.

OSA symptoms debut insidiously and patients usually seek help after several years, most common nocturnal signs include:

■ Restless and nonrestorative sleep;

■ Insomnia;

■ Habitual loud snoring;

■ Gasping and choking sensations;

■ Witnessed apneas;

■ Nocturia.

Due to the perceived lack in sleep quality, there are also day symptoms present:

■ Daytime fatigue;

■ Morning headaches;

■ Morning confusion;

■ Sensation of dry or sore throat;

■ Excessive daytime sleepiness (EDS);

■ Hypertension;

■ Gastroesophageal reflux;

■ Depression and/or anxiety;

■ Memory and intellectual impairment;

■ Decreased concentration.

Diagnosis comprises of patient history, sleep analysis through polysomnography and laboratory tests.

Differential diagnosis includes asthmatic episodes, chronic obstructive pulmonary disease, gastroesophageal reflux disease, narcolepsy and periodic limb movement disorder.

The standard treatment is CPAP - continuous positive airway pressure, for moderate to severe cases, which is obtained by wearing a mask that provides a continuous stream of pressurized air in order to maintain optimal oxygen saturation.

Surgical treatment is required in cases where either CPAP methods don’t work or there is an anatomical defect impairing the airflow. One of the common surgical measures are uvulopalatopharyngoplasty with modifications to the soft palate or adenotonsillectomy with the removal of tonsils.

For mild to moderate cases, lifestyle changes (loosing weight, quitting smoking, changing sleep position) or non invasive therapies with over the counter external nasal dilator strips, internal nasal dilators or sprays may help alleviate some of the symptoms.

References

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

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

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

4) TsaraV, Amfilochiou A, Papagrigorakis MJ, Georgopoulos D, Liolios E. (2009) Definition and classification of sleep related breathing disorders in adults. Different types and indications for sleep studies (Part 1) Hippokratia; 13(3): 187–191.