Central vs obstructive sleep apnea

Obstructive apnea is a blocked airway that the chest is still trying to inflate. Central apnea is a pause in the respiratory drive: the chest and abdomen stop making the effort. Those two events can share an AHI number and still need different tests and different machines. A home sleep apnea test, which often lacks EEG and sometimes lacks decent effort belts, can miss or under-count central events. Treating the wrong physiology with the other condition’s device is not a small paperwork error.

What is the actual difference in the body?

In obstructive sleep apnea, the upper airway narrows or closes. Respiratory effort continues. The rib cage and abdomen pull against a plugged pharynx. Airflow drops or stops. Oxygen may fall. Sleep may fragment. That is a plumbing and muscle-tone problem in the throat, which is why continuous positive airway pressure, an oral appliance, or hypoglossal nerve stimulation can help: they splint or stiffen the airway.

In central sleep apnea, the brainstem’s output to the breathing muscles dips or stops. Effort belts go quiet with the airflow. There is no blockage to push against. Classic settings include heart failure with Cheyne-Stokes respiration, chronic opioid use, high altitude, and treatment-emergent central events after PAP is applied to an obstructive airway. Mixed apneas start with a central pause and pick up obstructive effort before airflow returns. Scoring manuals treat mixed events as their own category because both mechanisms showed up in the same breath.

The AASM Scoring Manual’s apnea rule is a drop of at least 90 percent of pre-event airflow for at least 10 seconds, then a classification by effort: obstructive if effort continues, central if effort is absent, mixed if it starts absent and returns. Hypopneas are a 30 percent flow drop for at least 10 seconds plus a 3 percent desaturation or an arousal (recommended rule), or a 4 percent desaturation without requiring an arousal (the CMS-friendly alternative). Optional rules let a lab mark a hypopnea as obstructive or central using flattening, snoring, or paradox. A home test that cannot see arousals and may not see paradox cleanly is working with half of that toolkit.

Why does the label change treatment?

Because the treatments are not interchangeable. PAP that stents an obstructive airway is first-line for garden-variety OSA in the Patil 2019 guideline. Central syndromes are a different AASM document. The 2012 practice parameters, updated in 2016 after the SERVE-HF safety signal, drew a hard line on adaptive servo-ventilation in a specific heart-failure group: ASV targeted to normalize AHI should not be used for central sleep apnea related to congestive heart failure in adults with ejection fraction of 45 percent or less and moderate or severe CSA-predominant sleep-disordered breathing. That is a standard-level recommendation against, based on increased cardiovascular mortality in that phenotype. ASV remained an option-level choice when ejection fraction is above 45 percent or the CSA is mild.

Opioid-related central apnea, primary CSA, and treatment-emergent CSA each have their own levers: lowering the opioid when that is safe, oxygen in selected patients, BPAP with a backup rate, ASV in people who are not in the SERVE-HF exclusion, or treating the heart failure that is driving Cheyne-Stokes breathing. Sticking a standard CPAP on a Cheyne-Stokes tracing and calling it a night is not “close enough.” It may leave residual central events, fragment sleep, or, in the reduced-ejection-fraction ASV story, be the wrong advanced device entirely.

If your report says “complex sleep apnea” or “treatment-emergent central,” that is a lab observation after PAP was applied, not a consumer brand. It means the obstructive events improved and central events declared themselves. The follow-up is a different titration, not a pep talk about mask leak. Opioids are a separate, common driver of central events: they blunt respiratory drive. Kapur lists chronic opioid use among the reasons to skip a home test and go to the lab. If the medication cannot be reduced, the device choice has to respect central physiology rather than pretending the events are obstructive because the AHI looks similar.

Why can a home test miss central apnea?

The 2017 AASM diagnostic guideline (Kapur) is built around obstructive disease, and it still spends pages on when a home sleep apnea test is the wrong tool. HSAT devices that use conventional sensors cannot detect hypopneas that are scored only with cortical arousals, which the recommended AASM hypopnea rule includes. Sensor dislodgement and poor signal quality add measurement error. The guideline’s term for the home-test index is often REI (respiratory event index), counted per hour of recording, not per hour of sleep. All of that underestimates the “true” AHI relative to attended polysomnography.

Kapur’s strong recommendation 4 is the central-apnea paragraph in all but name: use PSG, rather than HSAT, in significant cardiorespiratory disease, potential respiratory muscle weakness, awake hypoventilation or suspected sleep-related hypoventilation, chronic opioid use, history of stroke, or severe insomnia. Those are the populations in which central events, hypoventilation, and mixed physiology are common. The task force reviewed limited HSAT accuracy data in heart failure and noted, in one oximetry study, that specificity for identifying CSA from desaturation/resaturation patterns was 0.17: ten of twelve patients with OSA were labeled as having CSA. Pattern-matching from a finger probe is not a respiratory-effort diagnosis.

A negative or “mild” home test in a patient on methadone, or a patient with systolic heart failure and witnessed pauses without snoring, has not ruled out central disease. Kapur’s strong recommendation 3 already says that a single negative, inconclusive, or technically inadequate HSAT should be followed by PSG when you are hunting OSA. That advice is even more important when the differential includes CSA. This is why sleep testing in this practice is not automatically a mail-order box.

What does the lab actually look at?

Attended polysomnography records airflow (usually nasal pressure plus a thermal sensor for apneas), effort (chest and abdominal belts, ideally respiratory inductance plethysmography), oxygen saturation, EEG for sleep stage and arousals, EMG, and usually snore and body position. Central versus obstructive is a belt-and-flow call, sometimes supported by snore and flattening. REM versus NREM matters because obstructive events often worsen in REM, while Cheyne-Stokes central events often dominate NREM and can spare REM.

Home tests vary. Some are type III devices with nasal pressure, belts, and oximetry. Some are peripheral-arterial-tonometry watches that estimate obstruction from pulse-wave attenuation and do not measure effort the way RIP belts do. Kapur’s remarks for an adequate HSAT name either nasal pressure plus chest and abdominal RIP plus oximetry, or PAT with oximetry and actigraphy. Neither montage is a full EEG. Neither is a CO2 channel. If the question is “does this patient hypoventilate” or “are these events central,” the watch is the wrong instrument.

People sometimes arrive with a consumer ring that plotted “apneas.” Consumer devices are not the AASM diagnostic pathway. They can start a conversation. They cannot classify effort. A ring that reports “30 events” without belts has not told you whether the chest was fighting a closed throat or sitting still. Ordering CPAP from that plot is how mixed and central disease get mistreated for a year.

Can you have both?

Yes. Many adults have predominantly obstructive events with a minority of centrals. Heart-failure patients can show both obstruction from a crowded airway and Cheyne-Stokes central cycles from a delayed, unstable ventilatory control loop. Starting CPAP therapy for the obstructive component is often the first experiment. If the download or a titration night then fills with central events, the diagnosis has shifted, and so should the device algorithm.

The AHI on the summary page will not tell you the mix. The event table will: obstructive apnea count, central apnea count, mixed, hypopneas, and sometimes a Cheyne-Stokes comment. If your one-page summary only prints a single AHI, ask for the full report before anyone orders a machine.

For sleep apnea that might not be purely obstructive, the useful appointment is the one that reviews the tracing, not only the number. Call Westerville Sleep Center at (614) 898-9340. Bring the raw report if you already had a home test, especially if you have heart failure, take opioids, or had a stroke. We would rather repeat an in-lab study than treat a guessed mechanism.