Hypopnea: All You Need To Know

Classified as a sleep disorder, hypopnea is defined as a condition that involves episodes of extremely shallow breathing or an abnormally low rate in which air flows during breathing. The dictionary definition of the disorder mentions that it is a condition with abnormally slow or especially shallow respiration.

What is the difference between sleep apnea and this condition? 

To understand the difference, let us better our understanding of sleep apnea. It is a disorder that is marked by repeated cessations of breathing for about 10 seconds or more. This results in the patient being woken up from sleep. In case the chest wall does not stop moving mechanically during these pauses, the condition is called obstructive sleep apnea.

Hypopnea, on the other hand does not have such a clear identifiable sign. It is more difficult to measure and is less precisely defined. It simply involves reduction in airflow which results in hypoxemia (decrease of partial pressure of oxygen in blood) that leads to arousal. The number of hypopneas in an hour is called the hypopnea index or HI.

Functionally there is hardly any difference between the two episodes. The sum of these incidences per hour is called the apnea-hypopnea index (AHI) which is also referred to as respiratory disturbance index or RDI.

Perhaps the most important point to consider is that during assessment of the severity of obstructive sleep apnea the HI factor plays a key role. For example, when the HI is more than 15, the condition is severe.

Condition that happens both during day and night 

Episodes of shallow breathing may happen both while sleeping or awake. When it happens during sleep, it is part of a sleep disorder that disrupts sleep when the condition is between moderate and severe. Repeated disruptions in breathing result in drop in oxygen levels in the blood which in turn interrupt with different stages of sleep.

Daytime hypopnea is common with people who have impaired breathing muscles as well as during certain neuromuscular ailments. Drop in blood oxygen levels happen also when the HI episodes happen during the day.

What role does it play in the diagnosis and treatment of sleep disorders?  

These episodes are not considered  clinically significant unless there is a 30% or more reduction in airflow lasting for 10 seconds or more. Similarly, the level of oxygen reduction should be 4% or greater.

What exactly happens during and after an episode? 

The carbon dioxide levels increase which is in proportion to the reduction of oxygen levels in the blood is a factor that determines the severity of obstruction in the respiratory tract. Repeated sleep disruption expectedly causes daytime fatigue, focusing problems, irritability and morning headaches.

Hypopnea can be either central or obstructive in terms of origin. When the origin is obstructive, it differs from sleep apnea in the sense that in this case, the airway is partially blocked.

What are the prime causes?

–          Anatomical defects like deviated septum or abnormal narrowness of the nasal passage.

–          Acute tonsillitis and/or adenoiditis

–          Weakened respiratory muscles

–          Use of sleeping pills

–          Alcohol and smoking

–          Ageing

–         Snoring and sleep apnea and factors that cause airway obstruction.

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