Central Apnoea Fraction and CSR Interpreter
Central Apnoea Fraction and CSR Interpreter
Two separate criteria decide whether a study is centrally predominant — an index of 5 or more per hour AND more than half the events central — and a night can meet either one without the other.
Central index and central fraction
Two criteria, independently met96 central apnoeas and hypopnoeas out of 158 events, over 357 minutes of sleep, with no Cheyne-Stokes pattern reported
The two criteria, and the pattern question that follows them
| Criterion | As the consulted sources state it | Inclusivity implemented here |
|---|---|---|
| Central index | 5 or more central apnoeas and/or central hypopnoeas per hour of sleep | exactly 5.0 per hour MEETS it, because the criterion is stated as 5 or more |
| Central fraction | those central events are more than 50% of the total apnoeas and hypopnoeas | exactly 50.0% does NOT meet it, because the criterion is stated as more than 50% |
| Cheyne-Stokes pattern | three or more consecutive central apnoeas or hypopnoeas separated by a crescendo-decrescendo pattern with a cycle length of 40 seconds or more | taken from the report. It is a judgement about the shape of the trace, not arithmetic, and this page does not infer it |
Where the criteria came from, and what was not read
| Source | Index criterion | Fraction | Cycle length |
|---|---|---|---|
| ICSD-3 itself | not read — a copyrighted publication sold by the AASM | not read | not read |
| StatPearls, citing ICSD-3 | 5 or more per hour of sleep | more than 50% | 40 seconds or more |
| MDedge, citing ICSD-3 | 5 or more per hour of sleep | more than 50% | not stated |
| EBM.one, citing ICSD-3 | 5 or more per hour | more than 50% | 40 seconds or more |
Two criteria that are genuinely independent
A centrally predominant sleep study is defined by two numbers and not one, and the reason is worth seeing. The criteria the consulted sources reproduce from the International Classification of Sleep Disorders are an index — 5 or more central apnoeas and central hypopnoeas per hour of sleep — and a fraction, those events making up more than half of all apnoeas and hypopnoeas. Neither implies the other. A busy obstructive night with forty central events among three hundred meets the index and fails the fraction. A quiet night with twenty events of which eighteen are central meets the fraction and fails the index. Collapsing the two into one verdict loses which situation you are looking at, so this page reports them separately.
The inclusivity runs opposite ways, which is the detail a reimplementation usually gets wrong. The index is stated as 5 or more, so exactly 5.0 per hour meets it. The fraction is stated as more than 50%, so exactly half does not. Both boundaries are reachable from real counts — thirty central events over six hours is exactly 5.0 per hour, fifty out of a hundred is exactly 50% — and both are implemented as published rather than rounded to whichever side was convenient.
What the arithmetic cannot do is name the entity or the cause. The Cheyne-Stokes pattern — three or more consecutive central events separated by crescendo-decrescendo breathing with a cycle of 40 seconds or more — separates two different categories in the classification, and it is a judgement about the shape of the trace. This page asks for it rather than inferring it, and distinguishes not present from not reported, because the classification treats the absence of the pattern as a positive criterion and a silent report does not supply it. Beyond that, the common causes of a centrally predominant study are opioids, altitude, heart failure, stroke and a recently started positive airway pressure device, and no index tells them apart.
One limitation is structural. A central hypopnoea is distinguished from an obstructive one by the absence of respiratory effort, which requires effort belts or an oesophageal pressure measurement. A home respiratory device without them cannot make the distinction at all, so a central fraction from such a study is not a measurement of the same quantity. An index is only as meaningful as its denominator: the same event count over a shorter sleep time is a larger index, and nothing about the patient changed. The two numeric criteria used here are the International Classification of Sleep Disorders, third edition, criteria. ICSD-3 is a copyrighted publication sold by the American Academy of Sleep Medicine and was not read for this page; the criteria are taken from three independent sources that reproduce them with attribution, and all three agree on both numbers. Every number on a sleep study is scoring-rule-dependent and night-to-night variable: the same recording scored under two rules, or the same patient studied on two nights, gives different figures. This page does the arithmetic and names the body that publishes the threshold. It renders no diagnosis and no clinical decision.
Frequently asked questions
What makes a sleep study centrally predominant?
Two criteria together, as the sources consulted reproduce them from the third edition of the International Classification of Sleep Disorders: 5 or more central apnoeas and/or central hypopnoeas per hour of sleep, AND those central events making up more than 50% of all apnoeas and hypopnoeas. A night can meet one without the other, which is why this page reports them separately.
Does exactly 50% central meet the criterion?
No. The criterion is stated as more than 50% of the total apnoeas and hypopnoeas, so fifty central events out of a hundred does not meet it and fifty-one does. The index criterion goes the other way: it is stated as 5 or more per hour, so exactly 5.0 does meet it. Both conventions are implemented as published.
What is Cheyne-Stokes breathing on a sleep study?
Three or more consecutive central apnoeas or hypopnoeas separated by a crescendo-decrescendo change in breathing amplitude, with a cycle length of 40 seconds or more. Two of the three sources consulted give that cycle length and the third states none. It matters to the classification because primary central sleep apnoea is defined with no evidence of the pattern, while central sleep apnoea with Cheyne-Stokes breathing is a separate category.
Can a home sleep apnoea test measure the central fraction?
Not reliably, and for a structural reason. A central event is distinguished from an obstructive one by the absence of respiratory effort, which needs effort belts or an oesophageal pressure measurement. A home respiratory device without them cannot classify events that way, so a central fraction from such a study is not measuring the same quantity as one from an attended polysomnogram.
Why does this page ask whether the pattern was reported rather than inferring it?
Because it is a judgement about the shape of the airflow trace over a minute or more, and no count of events contains that information. The page also separates not present from not reported, because the classification treats the absence of the pattern as a positive criterion for one of its categories — and a report that says nothing about it has not supplied that absence.
Related calculators
References
- StatPearls. Central Sleep Apnea. Treasure Island, FL: StatPearls Publishing — reproducing the criteria of the International Classification of Sleep Disorders, 3rd edition, with attribution.
- Central sleep apnea in adults: diagnosis and treatment. MDedge — reproducing the International Classification of Sleep Disorders, 3rd edition criteria with attribution.
- EBM.one. Central Sleep Apnea (CSA) — reproducing the International Classification of Sleep Disorders, 3rd edition criteria, including the Cheyne-Stokes cycle length, with attribution.
- American Academy of Sleep Medicine. Summary of Updates in Version 3 of The AASM Manual for the Scoring of Sleep and Associated Events. Darien, IL: AASM; February 2023.
- Kapur VK, Auckley DH, Chowdhuri S, et al. Clinical practice guideline for diagnostic testing for adult obstructive sleep apnea: an American Academy of Sleep Medicine clinical practice guideline. J Clin Sleep Med. 2017;13(3):479–504.
- American Academy of Sleep Medicine. Sleep Apnea Severity (MIPS clinical quality measure 277, 2025 specification). Darien, IL: AASM; 2025.
Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/