Sleep Apnea: Obstructive and Central

Sleep apnea is a disorder characterized by repeated interruptions to breathing during sleep, with measurable consequences for cardiovascular health, metabolic function, and daytime cognitive performance. Two primary forms — obstructive sleep apnea (OSA) and central sleep apnea (CSA) — share the surface symptom of disrupted sleep but differ fundamentally in mechanism and clinical management. Understanding that distinction is essential for accurate diagnosis and treatment selection, particularly given the role of federal agencies such as the Centers for Medicare & Medicaid Services (CMS) in defining coverage criteria for diagnostic testing and devices.

Definition and Scope

Sleep apnea is formally classified by the American Academy of Sleep Medicine (AASM) according to the number of breathing events per hour of sleep, quantified as the Apnea-Hypopnea Index (AHI). An AHI of 5–14 events per hour meets the threshold for mild sleep apnea; 15–29 events per hour constitutes moderate disease; and 30 or more events per hour defines severe sleep apnea (AASM, International Classification of Sleep Disorders, 3rd ed.).

The prevalence of OSA among adults in the United States is estimated by the National Heart, Lung, and Blood Institute (NHLBI) to affect roughly 1 in 5 adults in some measurable form, with severe disease affecting a smaller but clinically significant subset (NHLBI Sleep Apnea overview). OSA accounts for the large majority of diagnosed cases; CSA represents a minority of presentations and is frequently associated with underlying neurological or cardiac conditions.

Both variants are covered under the broader pulmonary and sleep medicine landscape outlined across pulmonaryauthority.com, where related conditions such as snoring and daytime sleepiness are discussed in symptom-level detail.

How It Works

Obstructive Sleep Apnea

In OSA, the airway physically collapses or narrows during sleep when muscle tone in the throat decreases. The tongue, soft palate, and surrounding pharyngeal tissues relax and partially or fully block airflow. The brain continues to send respiratory drive signals, but airflow is mechanically obstructed. Each episode typically ends when the oxygen desaturation triggers a brief arousal — often too short to be consciously remembered — that restores muscle tone and reopens the airway.

The physiological cascade from repetitive OSA events includes:

1. Intermittent hypoxia — cyclic drops in arterial oxygen saturation
2. Sympathetic nervous system activation — repeated surges in heart rate and blood pressure
3. Sleep fragmentation — loss of restorative slow-wave and REM sleep stages
4. Systemic inflammation — elevated markers such as C-reactive protein associated with chronic intermittent hypoxia

Central Sleep Apnea

In CSA, the upper airway remains patent. The failure originates in the central nervous system: the brainstem's respiratory control centers do not send adequate or appropriately timed signals to the diaphragm and breathing muscles. No respiratory effort is made during the apneic interval, which distinguishes CSA from OSA on polysomnographic tracings.

CSA is subdivided by etiology. Cheyne-Stokes respiration — a crescendo-decrescendo breathing pattern followed by apnea — is the variant most commonly associated with heart failure and stroke. Treatment-emergent central apnea (also called complex sleep apnea) can develop after positive airway pressure therapy is initiated for OSA, a phenomenon that resolves in many patients within weeks to months.

Diagnostic confirmation for both types relies on sleep studies performed in accredited laboratory settings or, when appropriate, validated home sleep apnea testing devices.

Common Scenarios

Certain clinical presentations are strongly associated with each type:

OSA presentations:
- Middle-aged or older adult with obesity (body mass index ≥ 30 kg/m²), observed apneas reported by a bed partner, loud snoring, and morning headaches
- Postmenopausal women, in whom hormonal changes increase pharyngeal collapsibility
- Children with tonsillar or adenoidal hypertrophy, where pediatric pulmonology and ENT evaluation often overlap
- Commercial vehicle operators subject to Federal Motor Carrier Safety Administration (FMCSA) guidance, which addresses OSA screening for safety-sensitive positions (FMCSA Medical Examiner Handbook)

CSA presentations:
- Patients with systolic heart failure (ejection fraction below 45%) exhibiting Cheyne-Stokes respiration
- Individuals using long-term opioid medications, which suppress central respiratory drive
- Patients at high altitude, where hypocapnia from hyperventilation destabilizes respiratory rhythm
- Patients who develop emergent centrals after CPAP titration for previously diagnosed OSA

The regulatory context for pulmonary medicine is particularly relevant to sleep apnea in occupational and transportation sectors, where undiagnosed or untreated OSA carries documented safety risks.

Decision Boundaries

Distinguishing OSA from CSA, and from mixed apnea (events that begin as central and terminate as obstructive), requires scored polysomnography rather than clinical history alone. The AASM scoring rules define:

• Obstructive apnea: cessation of airflow ≥ 10 seconds with continued respiratory effort
• Central apnea: cessation of airflow ≥ 10 seconds with absent respiratory effort
• Mixed apnea: absent effort at event onset, effort resuming before airflow returns
• Hypopnea: ≥ 30% reduction in airflow for ≥ 10 seconds, associated with ≥ 3% oxygen desaturation or arousal

Treatment decisions diverge sharply by type. OSA is primarily managed with CPAP/BiPAP therapy, with alternative options including mandibular advancement devices and surgical intervention depending on anatomical factors. CSA treatment targets the underlying cause — optimization of heart failure management, opioid dose reduction where feasible, or adaptive servoventilation (ASV) in selected cases, though CMS coverage criteria for ASV in heart failure patients with low ejection fraction have been restricted following the SERVE-HF trial findings (referenced by CMS Decision Memo CAG-00405N).

Patients whose primary complaint is shortness of breath should also be evaluated for cardiac and other pulmonary contributors, as OSA frequently coexists with conditions such as pulmonary hypertension and COPD in a pattern termed overlap syndrome.

References

• American Academy of Sleep Medicine (AASM) — International Classification of Sleep Disorders, 3rd Edition
• National Heart, Lung, and Blood Institute (NHLBI) — Sleep Apnea
• Federal Motor Carrier Safety Administration (FMCSA) — Medical Examiner Handbook
• Centers for Medicare & Medicaid Services (CMS) — National Coverage Analysis Decision Memo CAG-00405N (Adaptive Servoventilation)
• AASM — Sleep Apnea Scoring Rules and Definitions

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