Apnea Hypopnea Index – Impact and Measurement

For people who do not know what apnea hypopnea index is, it would be better to begin by explaining what it is. In cases of severe sleep apnea, people wake up numerous times every night due to breathing problems or oxygen deprivation. This leads to poor sleep and excessive fatigue which affects everyday performance and the health of people.

The number of these waking episodes can be measured with an instrument called the “WatchPAT sleep study.” This is also called the apnea hypopnea index (AHI), and can be used at home. It measures the severity of the sleep apnea condition based on the total number of partial obstructions and cessations (i.e. hypopneas and apnea respectively) of the breathing patterns per hour during sleep. The WatchPAT is a diagnostic equipment or device, used to accurately detect sleep apnea and is also FDA approved.

The word “apnea” is a Greek word, which means “without breath.” People suffering of breathing problems can stop breathing for 10 seconds, and sometimes more. In the case of hypopnea, there is a reduced level of airflow through the throat, which leads to the reduced levels of oxygen in the body. It is an abnormally shallow pattern of breathing, which lasts for at least 10 seconds. This can be very dangerous if not handled immediately, because it can sometimes be fatal.

Sometimes it is seen that patients may have 50 or more episodes per hour. Most experts suggest the use of CPAP (continuous positive airway pressure) as a treatment at 10 or more episodes per hour. The CPAP is a device used to solve breathing problems in patients suffering of sleep apnea. It can also be used for other sleep apnea therapies.

Early Death in Stroke Patients

Studies show that obstructive sleep apnea leads to early deaths in stroke patients. Stroke patients suffering of obstructive sleep apnea are seen to die sooner than stroke patients who do not suffer of sleep apnea, or those who have central sleep apnea. The apnea hypopnea index is read with certain figures which determine whether a patient’s condition may be considered normal, mild or moderate.

For example, a research was carried out on 132 stroke patients, out of which 23 had obstructive sleep apnea and 28 patients had central sleep apnea. Those patients having an apnea hypopnea index of 15 or more were 76% more likely to die earlier as compared to the others. Those with a lower index of 10 also had a greater risk of dying early. The findings were particularly fascinating because obstructive sleep apnea is a treatable condition. The results were dependent on the following factors:

  • Age
  • Gender
  • Hypertension
  • Smoking
  • Body-mass index
  • Diabetes
  • Cognitive ability
  • Atrial fibrillation
  • Lifestyles

Other researches conducted using a transcranial Doppler equipment showed that the arterial blood pressure and cerebral blood flow increase during the obstructive sleep apnea condition, and rapidly decrease to lower values when the apnea is cured. This pattern shows that cerebral ischemia (a condition of insufficient flow of blood to the brain) occurs at the time the saturation of oxygen is low. Treating sleep apnea supposedly has the chances of extending the lives of people suffering of stroke.

What’s Considered Good and Bad

Less than 5 episodes of apnea or hypopnea per hour are considered to be normal. 5 and above episodes per hour are considered mild. 15 and more are considered moderate, while 30 and more are considered to be severe.

UARS (upper airway resistance syndrome) or flow limitation is another important form of sleep disordered breathing (SDB). In this, the airflow resistance in the nose or mouth causes the person who is sleeping to wake up. The UARS for respiratory disturbance index (RDI) is more comprehensive as compared to the apnea hypopnea index.

Measurement of Apnea Hypopnea Index

In order to determine the AHI, there is just a simple math procedure to follow. The total number of apnea events or episodes plus the total number of hypopnea events, divided by the total number of sleep time minutes, multiplied by 60 minutes. For example:

Apnea = 200

Hypopnea = 200

Actual sleep time = 7 hours (420 minutes)

Now, Apnea + Hypopnea divided by the actual sleep time, multiplied by 60 will be:

200 + 200/420 x 60 = 57 AHI (severe obstructive sleep apnea)


AHI less than 5 = Normal

AHI of 5 to 15 = Mild

AHI of 15 to 30 = Moderate

AHI greater than 30 = Severe

When the results of apnea hypopnea index values are combined with mild to severe scores, and patients report of excessive sleepiness, it means the results are positive. The next thing a doctor would do is suggest the available treatment options for sleep apnea. A greatly elevated apnea hypopnea index can still be improved by treatment.