Differentiating Central Sleep Apnea from Obstructive Sleep Apnea
The key differentiator between central sleep apnea (CSA) and obstructive sleep apnea (OSA) is the presence or absence of respiratory effort during apneic episodes: CSA shows absent or reduced respiratory effort (no thoracoabdominal movement), while OSA demonstrates continued or increasing respiratory effort against a closed airway with paradoxical chest-abdominal movements. 1
Primary Distinguishing Features
Respiratory Effort Pattern (The Critical Distinction)
- Central Sleep Apnea: Complete absence of respiratory effort during apneic episodes, with no thoracoabdominal excursions visible on respiratory inductance plethysmography (RIP) belts 1
- Obstructive Sleep Apnea: Continued or progressively increasing respiratory effort throughout the apneic event, often with thoracoabdominal paradox (chest and abdomen moving in opposite directions) 1, 2
Airflow Signal Characteristics on Polysomnography
- CSA: Absence of airflow flattening on nasal pressure waveform, or flattening unchanged from baseline breathing 1
- OSA: Flattening of the inspiratory portion of the nasal pressure waveform, indicating upper airway resistance and flow limitation 1
Associated Clinical Features
- CSA: Often associated with snoring absent during the apneic event itself, no paradoxical thoracoabdominal movement, and typically seen in patients with heart failure, high altitude exposure, or opioid use 1, 3
- OSA: Snoring frequently present (especially during hyperpneic phases), thoracoabdominal paradox visible, and associated with anatomic upper airway narrowing 1
Why the Answer Options Are Misleading
Regarding Option A & B (Reduced Effort/No Respiratory Effort)
This is the correct distinguishing feature. CSA demonstrates reduced or absent respiratory effort during apneic attacks, while OSA shows persistent effort 1, 2. The American Academy of Sleep Medicine guidelines explicitly state that central apneas are characterized by absence of respiratory effort, whereas obstructive events show continued effort despite absent airflow 1.
Regarding Option C (Epworth Sleepiness Score >15)
This is not a differentiator between CSA and OSA. Both conditions can present with excessive daytime sleepiness, though interestingly, patients with CSA more commonly complain of insomnia and depression rather than frank hypersomnolence 4. The Epworth Sleepiness Scale measures symptom severity, not apnea type 1.
Regarding Option D (AHI >35)
This is not a differentiator. The apnea-hypopnea index (AHI) measures severity of sleep-disordered breathing regardless of type 1. Both CSA and OSA can have AHI values >35, indicating severe disease. The AHI does not distinguish mechanism—only the presence of respiratory effort during events determines classification 1.
Clinical Importance of Accurate Differentiation
Distinguishing CSA from OSA is clinically critical because treatments differ fundamentally and inappropriate therapy can cause harm. 1
- Adaptive servo-ventilation for CSA in heart failure patients with reduced ejection fraction causes increased mortality and is contraindicated 1
- CPAP is first-line for OSA but may not adequately treat CSA and can even precipitate treatment-emergent central apnea 1, 5
- The ACC/AHA/HFSA guidelines emphasize that formal sleep assessment must distinguish obstructive from central sleep apnea given different treatment responses 1
Diagnostic Gold Standard
Polysomnography with respiratory effort monitoring (esophageal manometry or dual thoracoabdominal RIP belts) is required for definitive differentiation. 1, 2 Home sleep apnea tests cannot reliably distinguish CSA from OSA because they lack adequate respiratory effort monitoring and CO2 measurement 2.