Hypopnea is a form of sleep-disordered breathing characterized by abnormally shallow or slow respiration during sleep. This condition involves a partial reduction of airflow in the upper airway. The reduced breathing causes a measurable drop in the blood oxygen level, leading to fragmented sleep. Hypopnea is a common feature of Obstructive Sleep Apnea-Hypopnea Syndrome, which disrupts the normal breathing cycle many times throughout the night.
Defining Hypopnea and Its Distinction from Apnea
Hypopnea is defined as a respiratory event lasting for a minimum of 10 seconds, during which airflow into the lungs is reduced by 30% or more. This reduction must be associated with a measurable decrease in blood oxygen saturation, typically by 3% to 4%, or an arousal from sleep. This event stems from a partial collapse or narrowing of the upper airway, which limits the volume of air inhaled.
The distinction between hypopnea and apnea lies in the degree of airway obstruction. While a hypopnea is a partial blockage leading to shallow breathing, an apnea represents a complete cessation of airflow, defined as a reduction of at least 90% in breathing for 10 seconds or longer. Both events arise from the muscles in the throat relaxing during sleep, but apnea is the more extreme form of the obstruction. Both conditions are measured together to assess the overall severity of sleep-disordered breathing.
Recognizing Common Symptoms
The symptoms of hypopnea often manifest during both the night and the day. Nocturnal signs commonly include loud and habitual snoring, often interrupted by episodes of gasping, snorting, or choking sounds. This partial airway obstruction frequently causes the person to wake up briefly and repeatedly throughout the night, resulting in restless, fragmented sleep.
During the daytime, consequences include excessive sleepiness and chronic fatigue, which may be mistakenly attributed to other causes. Individuals also experience difficulty with concentration, memory problems, and morning headaches. These symptoms arise because repeated drops in blood oxygen and sleep fragmentation prevent the brain and body from achieving restorative rest.
Diagnostic Procedures and Severity Classification
Hypopnea is confirmed through a sleep study, known as polysomnography (PSG), conducted either in a specialized lab or using a home sleep test. The PSG monitors various physiological functions during sleep, including airflow, brain activity, heart rate, and blood oxygen saturation. These measurements allow clinicians to accurately count and characterize the breathing events occurring throughout the night.
The primary metric used for diagnosis and classification is the Apnea-Hypopnea Index (AHI), which represents the total number of apneas and hypopneas per hour of actual sleep time. An AHI value is considered the standard for determining the severity of sleep-disordered breathing in adults. AHI scores are categorized into specific ranges to guide treatment decisions:
- Fewer than five events per hour is considered normal or minimal.
- Between five and 14 events per hour indicates mild severity.
- Ranging from 15 to 29 events per hour is diagnosed as moderate hypopnea.
- 30 or more events per hour is classified as severe sleep-disordered breathing.
Addressing Underlying Causes and Treatment Options
Obstructive hypopnea is typically caused by physical and lifestyle factors that narrow the upper airway during sleep. Major risk factors include obesity, which increases fat deposits around the neck, and certain anatomical features, such as a smaller jaw or enlarged tonsils. The consumption of alcohol or sedatives before bedtime can also worsen the condition by causing the throat muscles to relax excessively.
Treatment is typically determined by the AHI score and the presence of daytime symptoms. For mild cases, initial management often involves lifestyle modifications like weight loss, avoiding alcohol close to sleep, and positional therapy to prevent sleeping on the back. These changes can reduce the severity of the breathing events by minimizing airway collapse.
For moderate to severe hypopnea, Continuous Positive Airway Pressure (CPAP) therapy is the standard treatment. A CPAP machine delivers pressurized air through a mask worn over the nose or mouth, creating an air splint that prevents the airway from collapsing. Alternative options include oral appliance therapy, which repositions the jaw forward, and, in rare instances, surgical procedures to modify airway structures.