Apnea | What Happens When You Stop Breathing in Your Sleep?

Apnea is clinically defined as the temporary cessation of respiratory airflow. For an event to be classified as an apnea, the pause in breathing must last for a minimum of 10 seconds. This condition is primarily categorized into three types based on its underlying cause. The most common form is Obstructive Sleep Apnea (OSA), which occurs when the airway becomes physically blocked despite persistent respiratory effort. This blockage is typically caused by the collapse of soft tissues in the back of the throat, such as the soft palate and uvula. The second type is Central Sleep Apnea (CSA), where the cessation of breathing occurs because the brain fails to send the necessary signals to the muscles that control respiration. In CSA, both airflow and respiratory effort are absent. The third category, Complex or Mixed Sleep Apnea, is a combination of both obstructive and central events. Understanding the specific type of apnea is critical for determining the appropriate therapeutic intervention.

During an apneic event, the lack of airflow leads to a rapid decline in blood oxygen levels, a condition known as hypoxemia, and an increase in carbon dioxide levels, or hypercapnia. Specialized sensory neurons called chemoreceptors detect these chemical changes and transmit urgent signals to the brainstem. In response, the brain triggers a brief arousal from sleep, often manifesting as a gasp, snort, or body jerk. This arousal, termed a 'micro-arousal', tightens the upper airway muscles and restores normal breathing. While this is a protective reflex, repeated occurrences throughout the night fragment the sleep cycle. This prevents the individual from reaching and sustaining the deep, restorative stages of sleep (NREM Stage 3 and REM sleep) necessary for physical and cognitive recovery.

For Obstructive Sleep Apnea (OSA), the leading risk factor is excess body weight, as fatty deposits in the neck can narrow the airway. Anatomical features such as a large neck circumference, a naturally narrow throat, or enlarged tonsils also increase susceptibility. OSA is more prevalent in males and its incidence increases with age. Other contributing factors include alcohol or sedative use, which relax throat muscles, and smoking, which causes inflammation and fluid retention in the upper airway. For Central Sleep Apnea (CSA), the risk factors are often related to neurological or cardiovascular conditions, such as congestive heart failure, stroke, or high-altitude exposure. The use of opioid medications can also suppress the brain's respiratory drive, leading to CSA.

The most prominent daytime symptom resulting from sleep fragmentation is excessive daytime sleepiness (hypersomnia). Individuals may feel overwhelmingly tired despite having spent an adequate number of hours in bed. Cognitive functions are also significantly impaired, leading to difficulties with concentration, attention, and memory. Morning headaches are another common complaint, caused by elevated carbon dioxide levels in the blood overnight. Chronic sleep deprivation also affects mood regulation, often resulting in irritability, anxiety, or symptoms of depression. These symptoms collectively degrade overall quality of life and can impair performance in daily activities, including work and driving.

Chronic, untreated sleep apnea imposes significant stress on the cardiovascular system. The recurrent episodes of hypoxemia and the stress response from frequent arousals elevate blood pressure, leading to a high risk of developing persistent hypertension. This sustained strain on the heart and blood vessels significantly increases the likelihood of major adverse cardiovascular events, including heart attack (myocardial infarction), stroke, and cardiac arrhythmias such as atrial fibrillation. Beyond cardiovascular disease, sleep apnea is strongly linked to metabolic dysfunction. It can exacerbate insulin resistance, increasing the risk for type 2 diabetes, and is associated with non-alcoholic fatty liver disease. The systemic inflammation and oxidative stress generated by apnea can also impair immune function and accelerate cognitive decline over the long term.