Struggling to understand the differences between hypopnea and apnea? You’re not alone.
Sleep-disordered breathing affects millions, yet the terms "hypopnea" and "apnea" are often misunderstood despite being key to diagnosis and treatment.
The challenge? These conditions may sound similar, but they differ significantly in their impact on breathing, health, and the effectiveness of various therapies.
This guide breaks it all down, offering clear explanations and expert-backed insights into:
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The definitions and types of hypopnea vs. apnea
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AHI scoring and how sleep studies work
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Common symptoms and health consequences
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Diagnosis methods and why they matter
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Treatment options based on event type and severity
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Pediatric considerations and special population needs
By the end of this post, you’ll know exactly how these conditions differ, what the numbers from your sleep study mean, and how to take the following steps; whether that’s treatment, consultation, or simply better understanding.
Definitions and types of hypopnea and apnea
To understand hypopnea and apnea, it is helpful to begin by defining these terms and explaining how doctors measure them.
Hypopnea is a partial reduction in airflow during sleep, characterized by a 30% or greater drop in breathing for 10 seconds or more, often accompanied by oxygen desaturation or sleep arousal. Apnea, by contrast, is a near-complete pause in airflow, usually defined as a 90% or greater reduction in airflow that lasts at least 10 seconds.
Doctors use these definitions during sleep studies to calculate the Apnea–Hypopnea Index (AHI), which measures the frequency of events per hour of sleep. The thresholds chosen, such as requiring a 3% versus 4% drop in oxygen, can alter the severity of the disorder; therefore, clinicians should always clarify the rule used.
In children, scoring is stricter: events may be measured in breaths instead of seconds, and even a single event per hour can be abnormal. The American Academy of Sleep Medicine (AASM) provides detailed scoring guidance that clinicians across Canada follow in sleep labs.
Obstructive vs central events
Not all events are the same; some originate from airway collapse, while others stem from the brain.
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Obstructive events happen when the airway collapses despite ongoing breathing effort. These often cause snoring or gasping.
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Central events occur when the brain temporarily stops sending signals to the respiratory system, resulting in reduced airflow and effort.
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Mixed events combine both, with part of the episode showing absent effort and another part showing obstruction.
Recognizing the type is essential, since treatment differs. For example, central events tied to heart failure or opioid use may require different devices than obstructive events caused by airway anatomy.
Types of hypopnea
Hypopneas can also be broken down into two categories:
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Flow-limited hypopneas: partial obstruction with snoring and flattened airflow patterns.
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Central hypopneas: reduced breathing effort without signs of airway collapse.
While not every lab distinguishes between them, identifying the type can help tailor treatment, whether the issue is anatomical primarily or driven by unstable breathing control.
Causes and risk factors for breathing events during sleep
These breathing problems don’t occur out of nowhere; several risk factors, ranging from anatomical to lifestyle factors, increase their likelihood.
Anatomical contributors
The throat is a collapsible tube, and certain features increase the chance of blockage during sleep. Enlarged tonsils, a large tongue, a long soft palate, or a receding jaw can all narrow the airway. Research has shown that obesity, which adds soft tissue around the airway, is one of the strongest risk factors for sleep apnea in Canadians (Public Health Agency of Canada).
Neck size is also a practical predictor; men with necks measuring over 43 cm and women with necks measuring over 40 cm are at a greater risk. Dentists may also look for retrognathia or a high-arched palate, which can contribute even in people who aren’t overweight.
Physiological and neurological contributors
Some people have an airway that collapses more easily because their muscles don’t respond well during sleep, especially in REM. Others have a low arousal threshold (waking too easily and fragmenting sleep) or a high loop gain (unstable breathing control that overshoots and undershoots). These patterns explain why two people with similar anatomy can have very different severities of the condition.
Medical risk factors
Obesity is the strongest modifiable risk factor for cardiovascular disease. Canadian studies estimate that moderate to severe sleep apnea affects nearly 10% of adults aged 30–70, with obesity playing a central role. Age and male sex also increase risk, though women’s risk rises after menopause.
Alcohol and sedatives worsen events by relaxing airway muscles. Chronic illnesses like COPD and heart failure also contribute.
Pediatric causes
In children, enlarged tonsils and adenoids are the most common cause. Surgery to remove them (adenotonsillectomy) often resolves pediatric sleep apnea. Childhood obesity, craniofacial conditions, and nasal obstruction can also play roles.
Symptoms and short/long-term health consequences
The signs of sleep-disordered breathing often appear both at night and during the day, and the long-term health risks extend beyond just feeling tired.
Daytime and safety consequences
Classic symptoms include loud snoring, gasping for breath, restless sleep, and waking with headaches. Daytime sleepiness can lead to poor focus, irritability, and a higher risk of motor vehicle accidents. In fact, drivers with untreated sleep apnea are at significantly greater risk of collisions (Canadian Council of Motor Transport Administrators).
Cardiovascular and metabolic risks
Interrupted breathing stresses the heart and metabolism. People with untreated apnea have higher rates of hypertension, stroke, arrhythmias, and diabetes (Heart & Stroke Foundation of Canada).
Even moderate sleep apnea can elevate blood pressure, impair blood sugar control, and exacerbate inflammation. These risks often scale with the severity of oxygen drops rather than just the event count.
Apnea vs hypopnea outcomes
Apneas tend to cause sharper oxygen drops, straining the cardiovascular system, while hypopneas more often fragment sleep. Both can be serious, and both count toward overall disease severity.
Diagnosis: sleep studies, scoring, AHI and RDI explained
Obtaining a precise diagnosis typically involves conducting a sleep study, during which specialists track breathing patterns and convert them into numerical values, such as the AHI.
In-lab polysomnography vs home testing
The gold standard for sleep studies is polysomnography (PSG) in a sleep laboratory. It measures brain waves, airflow, effort, oxygen, and other vital signs. Because it tracks sleep stages, PSG can capture arousal-linked hypopneas that home tests miss.
Home sleep apnea testing (HSAT) is more accessible and widely used in Canada for diagnosing suspected moderate to severe obstructive sleep apnea. According to the Canadian Thoracic Society, HSAT is an appropriate first-line tool in uncomplicated cases, but PSG remains necessary when results are negative or inconclusive. This aligns with the AASM’s clinical practice guideline, which recommends PSG when patients have comorbidities or suspected central events.
Canadian provinces also provide local guidance. For instance, BC’s provincial guideline notes that a negative HSAT doesn’t rule out OSA, reinforcing the importance of PSG in borderline cases.
What sleep studies measure
Key signals include:
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Airflow (nasal pressure and thermistors)
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Respiratory effort (chest and abdomen belts)
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Oxygen saturation (continuous oximetry)
Lab studies also record EEG, ECG, and sleep position to provide a more comprehensive picture.
How events are scored
Apnea is scored when airflow falls by ≥90% for at least 10 seconds. Hypopnea is scored as a ≥30% reduction in airflow for at least 10 seconds, accompanied by either ≥3% oxygen desaturation or an arousal. Some clinics still use the older ≥4% oxygen desaturation rule, which counts fewer events. The AASM clarified that both definitions remain acceptable, but reports should specify which rule was used, as prevalence and severity can differ substantially.
AHI and RDI
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AHI (Apnea-Hypopnea Index): total apneas + hypopneas ÷ hours of sleep
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RDI (Respiratory Disturbance Index): includes apneas, hypopneas, and effort-related arousals
Severity is typically classified as:
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Normal: <5
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Mild: 5–14.9
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Moderate: 15–29.9
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Severe: ≥30
In children, even one event per hour can be abnormal. Experts also emphasize that AHI alone doesn’t tell the whole story. A review in the Canadian Medical Association Journal notes that oxygen desaturation burden and arousal frequency may better predict long-term cardiovascular and neurocognitive outcomes than AHI alone.
Treatment options and how choices differ by event type
Once doctors determine the cause, several treatment options are available, ranging from simple lifestyle changes to advanced devices and surgery.
Hypopnea
People with hypopnea-predominant disease may respond well to less invasive options:
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Positive airway pressure (PAP): often effective at reducing events.
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Oral appliances, such as mandibular advancement devices, can help in mild to moderate cases.
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Positional therapy: avoiding back-sleeping reduces supine-related events.
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Lifestyle: weight loss, limiting alcohol, and improving sleep hygiene.
Apnea
For apnea-predominant disease, stronger measures are often needed:
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Continuous Positive Airway Pressure (CPAP) is the gold standard for treating sleep apnea.
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Bilevel PAP or adaptive devices may help in complex cases.
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Surgery or hypoglossal nerve stimulation may be considered if CPAP fails, though these are reserved for select patients.
Both types aim to lower the AHI below five and improve symptoms.
Special populations and measurement nuances
Children, older adults, and individuals with specific conditions require distinct approaches, resulting in variations in how these disorders are measured and treated.
Pediatric differences
In children, even a small number of breathing events can matter. An AHI of 1 or greater is generally considered abnormal because disrupted sleep can affect growth, attention, and development. Treatment often happens earlier than in adults, with adenotonsillectomy recommended when enlarged tonsils and adenoids are the cause.
The American Academy of Sleep Medicine emphasizes that polysomnography (PSG) is the gold standard for pediatric diagnosis, and that scoring rules differ from those used in adults. Canadian research has also highlighted variability in how children are treated after surgery, especially when residual sleep apnea remains (Canadian Pediatric Society).
Neck circumference as a marker
Neck size is one of the risk factors included in screening tools like STOP-BANG, since larger necks often suggest more soft tissue around the airway. However, experts note that it is not reliable on its own and must be interpreted in conjunction with BMI, symptoms, and other factors (Canadian Thoracic Society).
Central sleep apnea
Unlike obstructive apnea, central sleep apnea happens when the brain temporarily stops sending signals to breathe. It’s often seen in people with heart failure, stroke, or opioid use. Treatment typically focuses on correcting the underlying condition first.
In some cases, advanced devices like adaptive servo-ventilation (ASV) can be beneficial; however, studies, such as the SERVE-HF trial, have found that it can be harmful for patients with reduced heart function, indicating that it should be prescribed cautiously under specialist care (Canadian Sleep Society).
Testing limitations
HSATs work well for common obstructive sleep apnea but can miss central events or arousal-only hypopneas. In-lab PSG remains the gold standard for children and adults with complex needs.
Practical guidance: screening, interpreting results, and next steps
If you or someone you know might have sleep-disordered breathing, there are practical tools, screening tests, and next steps to consider.
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Screening tools, such as the STOP-BANG and Epworth Sleepiness Scale, are quick ways to identify high-risk patients.
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Device reports: Residual AHI <5, consistent nightly use, and minimal leaks mean therapy is working.
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Coverage: In most provinces, public or private insurance coverage for CPAP requires a sleep study showing an AHI of 15 or more, or five or more if symptoms or comorbidities are present. For example, British Columbia’s guidelines outline when CPAP is covered and when further testing is needed.
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Referral: If CPAP therapy fails or if central events or comorbidities complicate treatment, specialists may recommend advanced devices or surgery.
How providers and device-based care support breathing during sleep
Sleep clinics, providers, and technology all work together to ensure that treatment is effective and comfortable over the long term.
Accurate diagnosis informs device choice: CPAP for most obstructive cases, bilevel or ASV for central cases, and oral appliances for milder disease. Proper mask fitting and pressure titration are essential, since leaks can reduce effectiveness. Follow-up is just as necessary.
FAQs
What’s the difference between apnea and hypopnea?
Apnea is a complete pause in airflow (at least 90% reduction for 10 seconds or longer), while hypopnea is a partial reduction (at least 30% reduction with a drop in oxygen or an arousal). Both disrupt sleep, but in slightly different ways.
How is sleep apnea diagnosed?
Diagnosis is typically determined through a sleep study. In-lab polysomnography (PSG) is the gold standard for sleep studies. At the same time, home sleep apnea testing (HSAT) is often used in Canada for adults at risk of moderate to severe obstructive sleep apnea (Canadian Thoracic Society). If a home test is negative but symptoms remain, doctors usually recommend an in-lab study. This guideline outlines when to use PSG versus HSAT and when PSG should follow a negative HSAT.
What’s a normal AHI?
For adults, an AHI under five is considered normal. For children, the cutoff is much stricter: an AHI of less than 1. Even low numbers in kids can be clinically significant, since sleep-disordered breathing can affect growth, attention, and behaviour.
Are home tests accurate?
HSATs are accurate for many adults with straightforward obstructive sleep apnea, but they can underestimate severity because they don’t measure brain activity (EEG). That means they miss arousals and may not detect central sleep apnea. If results don’t match symptoms, a full PSG is recommended.
Get the proper treatment and support for sleep-disordered breathing
Throughout this post, we’ve explored the critical distinctions between hypopnea and apnea, two pillars of sleep-disordered breathing. You now understand how they’re defined, what causes them, how they’re diagnosed, and which treatments are most effective based on your individual condition.
Bottom line? While both conditions disrupt sleep and health, recognizing their distinct differences is essential for selecting the appropriate treatment and enhancing long-term outcomes.
Sleep is not optional; it’s foundational. Whether you’re dealing with symptoms yourself or supporting someone who is, taking steps toward better sleep care can significantly boost daily function and long-term health.
Ready to take control of sleep-disordered breathing? Browse CPAP machines, CPAP masks, and CPAP accessories from YourCPAPShop, book an online consultation with our sleep specialists, or order supplies with fast, Canada-wide shipping from our Richmond, BC warehouse.
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