What are the characteristics of Obstructive Sleep Apnea (OSA) on a sleep study?

Characteristics of Obstructive Sleep Apnea (OSA) on a Sleep Study

Obstructive Sleep Apnea (OSA) on a sleep study is characterized by repetitive episodes of complete (apnea) or partial (hypopnea) upper airway obstruction during sleep, while respiratory efforts continue, resulting in transient breathing interruptions frequently terminated by arousals or microarousals from sleep. 1

Key Polysomnographic Findings in OSA

Respiratory Events

• Apneas: Complete cessation of airflow for ≥10 seconds despite ongoing respiratory efforts 1
• Hypopneas: Decrease from baseline in the amplitude of breathing during sleep that either:
  • Reaches >50% reduction with an oxygen desaturation of ≥3% or an arousal, OR
  • Shows a 30% reduction with ≥4% desaturation 1, 2
• Respiratory Effort-Related Arousals (RERAs): Episodes of increasing respiratory effort leading to an arousal without meeting criteria for apnea or hypopnea 1

Diagnostic Indices

• Apnea-Hypopnea Index (AHI): Number of apneas and hypopneas per hour of sleep 1, 2
  • Mild OSA: AHI 5-15 events/hour
  • Moderate OSA: AHI 15-30 events/hour
  • Severe OSA: AHI ≥30 events/hour 3
• Respiratory Disturbance Index (RDI): (Number of apneas + hypopneas + RERAs) × 60 / total sleep time in minutes 1
• Oxygen Desaturation Index (ODI): Number of oxygen desaturations per hour of sleep 4

Sleep Architecture Changes

• Increased sleep fragmentation with frequent arousals and microarousals 1
• Reduced sleep quality with disruption of normal sleep architecture 5
• Decreased slow-wave and REM sleep 5

Oxygen Saturation Patterns

• Intermittent hypoxemia with cyclical oxygen desaturations 1
• Characteristic "sawtooth" pattern of oxygen saturation on pulse oximetry 6
• Severity indicated by the nadir of oxygen saturation and time spent below 90% saturation 4

Cardiac Parameters

• Heart rate variability with potential bradycardia during apneas followed by tachycardia during arousal 6
• Blood pressure fluctuations with increases at the terminal portion of apneas 6
• Potential cardiac arrhythmias including atrial fibrillation, bradyarrhythmias, and ventricular arrhythmias 4, 7

Technical Considerations

Sleep Study Types

• Type I: In-laboratory polysomnography (gold standard) with EEG, EOG, EMG, airflow, respiratory effort, oxygen saturation, and cardiac variables 1
• Type II: Comprehensive portable polysomnography 1
• Type III: Limited channel devices (4-7 channels) measuring airflow, respiratory effort, oxygen saturation, and cardiac variables 1
• Type IV: Simplified devices measuring 1-2 parameters (typically oxygen saturation and heart rate) 1

Diagnostic Pitfalls

• Home sleep apnea testing may have higher false-negative rates, particularly for mild-to-moderate OSA 1
• Night-to-night variability can challenge diagnosis both at home and in-laboratory 1
• A single negative home sleep apnea test should be followed by polysomnography if clinical suspicion remains high 1
• Polysomnography is preferred over home sleep apnea testing in patients with significant cardiorespiratory disease, potential respiratory muscle weakness, hypoventilation, chronic opioid use, history of stroke, or severe insomnia 1

Pathophysiological Correlates

• Upper airway obstruction occurs despite continued respiratory efforts, distinguishing OSA from central sleep apnea 5, 2
• Anatomical factors (narrow upper airway, craniofacial abnormalities) and functional traits (airway collapsibility, inadequate muscle response) contribute to obstruction 5
• Marked swings in intrathoracic pressure occur during obstructive events 4
• Sympathetic nerve activity increases constantly during apnea, reaching a peak at the end of apnea and on arousal 6

By recognizing these characteristic polysomnographic findings, clinicians can accurately diagnose OSA and assess its severity, which is crucial for determining appropriate treatment and reducing associated morbidity and mortality.