Definition and Overview
Obstructive sleep apnea (OSA) is a sleep-disordered breathing condition in which the upper airway is repeatedly partially or completely obstructed during sleep, causing recurrent apnea and hypopnea episodes that result in oxygen desaturation, sleep fragmentation, and excessive daytime sleepiness.
The prevalence in adults is approximately 24% in men and 9% in women, making it one of the most common sleep disorders [1]. It is distinguished from central sleep apnea; OSA is characterized by airway obstruction occurring despite continued respiratory effort.
Causes and Pathophysiology
Anatomical Factors
Anatomical factors that predispose to upper airway collapse include periairway fat deposition (obesity), tonsillar and adenoid hypertrophy, micrognathia, retrognathia, and increased neck circumference.
Sleep-Related Muscle Tone Reduction
During sleep, upper airway muscle tone (particularly the genioglossus) decreases, narrowing or occluding the airway. Muscle tone is lowest during REM sleep, tending to worsen apnea episodes.
Autonomic and Cardiovascular Mechanisms
Repeated apneic episodes cause hypoxia and hypercapnia, stimulating chemoreceptors and triggering sympathetic overactivation. This leads to increased heart rate, vasoconstriction, and elevated blood pressure. Reduced heart rate variability (HRV) and a nocturnal non-dipping blood pressure pattern are characteristically observed [2].
Symptoms
Nocturnal Symptoms
- Loud snoring (usually reported by bed partner)
- Witnessed apnea during sleep (bed partner report)
- Awakening with a choking or gasping sensation
- Nocturia
- Sleep fragmentation and insomnia
Daytime Symptoms
- Excessive daytime sleepiness (drowsiness while driving, at work)
- Morning headache
- Dry mouth and sore throat (morning)
- Poor concentration and memory impairment
- Irritability and mood changes
Diagnosis
Apnea-Hypopnea Index (AHI)
The AHI is the combined number of apneas and hypopneas per hour of sleep:
- Normal: AHI < 5
- Mild: AHI 5-14
- Moderate: AHI 15-29
- Severe: AHI >= 30
Overnight Polysomnography (PSG)
PSG is the standard test that simultaneously measures electroencephalography (EEG), electrooculography (EOG), electromyography (EMG), respiratory effort, airflow, oxygen saturation, electrocardiography, and limb movements [4]. It analyzes respiratory patterns and arousal responses across sleep stages.
Home Sleep Apnea Testing (HSAT)
In adults without significant comorbidities where moderate or greater OSA is suspected, home sleep apnea testing may serve as a first-line screening tool. It is simpler than PSG but has limitations in sleep staging analysis.
Epworth Sleepiness Scale
A self-reported scale rating daytime sleepiness in 8 situations from 0-3, where a score of 10 or above suggests clinically significant daytime sleepiness.
Treatment
CPAP Therapy
Continuous positive airway pressure (CPAP) is the first-line standard treatment for moderate or greater OSA. It provides continuous positive pressure through a nasal or oronasal mask to prevent upper airway collapse during sleep.
Clinical studies report that CPAP therapy reduces blood pressure by an average of approximately 2.5 mmHg and significantly improves daytime sleepiness [3]. Risks of atrial fibrillation, nocturnal hypertension, and drowsiness-related motor vehicle accidents are also reduced.
Oral Appliance (MAD)
A mandibular advancement device (MAD) moves the mandible forward during sleep to widen the upper airway. It is an alternative for patients with mild to moderate OSA or those unable to tolerate CPAP.
Surgical Treatment
Surgical options including uvulopalatopharyngoplasty (UPPP), maxillomandibular advancement, and tongue base reduction may be selectively performed [4]. Surgery is effective when clear anatomical abnormalities (such as tonsillar hypertrophy) are present.
Lifestyle Modification
Weight loss in obese patients (10% weight reduction decreases AHI by approximately 25%) is effective for improving OSA. Avoidance of supine sleep position, limiting alcohol and sedative use, and smoking cessation are recommended.