Sleep apnea (SA) is a common sleep-related breathing disorder characterized by repeated pauses in breathing during sleep. These interruptions can last from a few seconds to minutes and occur many times each hour, preventing the body from receiving adequate oxygen. The disorder disrupts sleep quality and is linked to numerous long-term health concerns.
Defining Sleep Apnea and Its Primary Types
Sleep apnea is defined by episodes of apnea (complete cessation of airflow) or hypopnea (significant reduction in airflow), both lasting ten seconds or longer. These respiratory events result in poor ventilation and are followed by brief awakenings that fragment the sleep cycle. The condition is categorized into two main forms based on the underlying cause of the breathing interruption.
Obstructive Sleep Apnea (OSA) is the more common type, accounting for the majority of cases. OSA occurs when the muscles and soft tissues in the back of the throat relax during sleep, causing the upper airway to collapse and physically block airflow. Despite the blockage, the person’s chest and diaphragm continue to try and breathe, which distinguishes this type.
Central Sleep Apnea (CSA) does not involve a physical obstruction in the airway. Instead, it is a failure of the brain’s respiratory control center to send the correct signals to the breathing muscles. The body makes no effort to inhale because the brain temporarily stops issuing the command to breathe. This form is often associated with other medical conditions, such as heart failure or neurological issues.
Medical Classification and Distinctions
Sleep apnea is medically categorized as a sleep-related breathing disorder, distinguishing it from a primary pulmonary disease. Primary pulmonary diseases, such as chronic obstructive pulmonary disease (COPD) or asthma, involve structural damage or chronic inflammation within the lung parenchyma. This damage directly impairs the lungs’ ability to exchange oxygen and carbon dioxide.
Sleep apnea originates in the upper airway or the neurological control system, not in the lung tissue. OSA is a mechanical problem of the upper airway, while CSA is a neurological signaling issue. The lungs themselves are generally healthy and capable of function if air can reach them or if the brain signals them to work.
This distinction is important for diagnosis and treatment. Primary pulmonary diseases require management focused on the lower airways and lung tissue. Since SA’s primary pathology is external to the lungs, it is classified as a disorder of sleep and breathing control, not a primary pulmonary disease.
Secondary Effects on Lung Function
Untreated sleep apnea has secondary consequences on the pulmonary and cardiovascular systems. The repeated pauses in breathing cause cyclical oxygen desaturation (hypoxia) and a buildup of carbon dioxide (hypercapnia). These chemical changes trigger a stress response in the body.
Chronic intermittent hypoxia causes the small blood vessels in the lungs to constrict, a process called pulmonary vasoconstriction. This narrowing increases resistance to blood flow through the lungs, elevating blood pressure in the pulmonary arteries. This condition is known as pulmonary hypertension.
The right side of the heart must work harder against this elevated pressure. Over time, this increased workload can cause the right ventricle to enlarge and weaken, leading to cor pulmonale. Up to one-third of individuals with severe OSA may develop pulmonary hypertension. The strain on the heart and chronic low oxygen levels increase the risk for cardiovascular events, including heart attack, stroke, and heart failure.
Diagnosis and Treatment Approaches
The definitive diagnosis of sleep apnea relies on an overnight sleep study called polysomnography. This test monitors multiple physiological parameters during sleep, recording brain activity, eye movements, heart rate, oxygen saturation levels, breathing effort, and airflow. The data gathered allows clinicians to calculate the Apnea-Hypopnea Index (AHI), which measures the number of breathing events per hour to determine severity.
For Obstructive Sleep Apnea, the common treatment is Continuous Positive Airway Pressure (CPAP) therapy. A CPAP machine delivers a steady stream of pressurized air through a mask, acting as a pneumatic splint to hold the upper airway open and prevent collapse. Alternative treatments for mild to moderate OSA include oral appliances that reposition the jaw and tongue, or lifestyle modifications like weight loss.
Central Sleep Apnea treatment first involves addressing any underlying medical condition, such as heart failure. Specific device therapies, such as Adaptive Servo-Ventilation (ASV), are often used for CSA. Unlike CPAP, the ASV device monitors the patient’s breathing pattern and provides support breaths, adjusting pressure to stabilize respiration and normalize the breathing rhythm.