What is Central Sleep Apnea?
Central sleep apnea (CSA) is a sleep-related breathing disorder characterized by recurrent cessations or reductions in airflow during sleep caused by a temporary failure or withdrawal of the brain's respiratory drive, resulting in absent or markedly reduced contraction of the inspiratory thoracic and diaphragmatic muscles—fundamentally different from obstructive sleep apnea where breathing effort continues despite airway obstruction. 1, 2
Core Pathophysiology
The neurophysiological basis involves a temporary failure in the pontomedullary pacemaker that generates breathing rhythm 1. The fundamental hallmark is ventilatory control instability 3. Two critical mechanisms drive this:
The apnea threshold concept: When PaCO₂ falls below a certain threshold level, breathing cessations occur. This happens when drive is excessive (robust chemosensitivity) or when hyperventilation occurs (such as following arousal) 2
Loss of wakefulness drive to breathe: At sleep onset, some rise in PaCO₂ naturally occurs. In patients with already low central drive, this further loss can lead to marked hypercapnia 2
Clinical Classification
CSA manifests in two distinct patterns based on ventilatory state 3, 2:
Excessive Drive (Eucapnic/Hypocapnic CSA)
- Cheyne-Stokes breathing (most common in heart failure patients)
- High altitude-induced periodic breathing
- Post-hyperventilation central apneas
Inadequate Drive (Hypercapnic CSA)
- Sleep hypoventilation syndrome
- Narcotic-induced central apnea
- Idiopathic CSA
- Post-hypoventilation central apneas
Common Etiologies and Risk Factors
The most common causes in adults are congestive heart failure and chronic opioid use 1. Additional risk factors include:
- Elderly age
- Cardiac disease (systolic/diastolic dysfunction, atrial fibrillation, coronary artery disease)
- Neurological disease (stroke, carotid artery stenosis)
- Certain cardiac medications
- Obesity hypoventilation syndrome 4, 5, 6
Clinical Presentation
Patients may present with 4:
- Insomnia or frequent arousals
- Excessive daytime sleepiness
- Gasping for breath during the night
- Irritability and forgetfulness
- Recurrent headaches
- Fatigue
Critical caveat: Patients with CSA and cardiovascular disease are often less symptomatic than those without CVD, despite having the condition 7. This can lead to underdiagnosis.
Diagnostic Severity
Severity is measured by polysomnography using the apnea-hypopnea index (AHI) 6:
- Mild: AHI 5-14/hour with no or mild symptoms
- Moderate: AHI 15-30/hour with occasional daytime sleepiness
- Severe: AHI >30/hour with frequent daytime sleepiness interfering with daily activities
Cardiovascular Consequences
CSA significantly impacts cardiovascular health through 6:
- Recurrent hypoxemia and hypercarbia
- Increased sympathetic/decreased parasympathetic activity
- Oxidative stress and endothelial dysfunction
- Cardiac remodeling
These mechanisms increase risk of coronary artery disease, heart failure, stroke, and cardiac dysrhythmias, with dose-dependent relationships between nocturnal desaturation and mortality 8.
Clinical Significance
Unlike central apneas that occur normally at sleep onset (not clinically significant), pathological CSA results in important comorbidity and increased risk of adverse cardiovascular outcomes 1, 5. CSA may serve as a clinical marker of underlying medical disorders with resultant significant morbidity and mortality 4.
Major clinical pitfall: CSA is currently underdiagnosed and undertreated due to challenges in prediction and detection, lack of well-defined optimal treatment guidelines, and the fact that many patients—particularly those with cardiovascular disease—may be relatively asymptomatic despite significant disease 6, 7.