The Apnea-Hypopnea Index (AHI) is the headline number on every sleep-study report in India, but it is not by itself the device selection. AHI sets severity. Device selection is set by AHI plus the central-vs-obstructive breakdown plus the titrated pressure plus any overlap with COPD, hypercapnia, or neuromuscular disease. Buyers who match a CPAP to “AHI 35” without reading the rest of the report frequently buy the wrong machine class.
This guide walks through how a polysomnography report becomes a device prescription, where the genuine CPAP-to-BiPAP transition points sit, and what is specific to the Indian sleep-medicine market.
AHI severity tiers and what they actually mean
AASM scoring defines an apnea as a ≥90% drop in airflow lasting ≥10 seconds, and a hypopnea (most commonly used definition) as a ≥30% drop in airflow lasting ≥10 seconds with associated ≥3% desaturation or arousal (AASM Scoring Manual). AHI is the sum of apneas plus hypopneas per hour of sleep.
The conventional severity bands:
- AHI < 5: normal
- AHI 5-15: mild OSA
- AHI 15-30: moderate OSA
- AHI ≥ 30: severe OSA
A second number, the Respiratory Disturbance Index (RDI), adds Respiratory Effort-Related Arousals (RERAs). RDI is always ≥ AHI. Indian PSG reports typically include both. For first-line therapy decisions, the clinically actionable threshold for CPAP initiation is AHI ≥ 15 (or AHI 5-14 with daytime sleepiness, cognitive impairment, mood disturbance, hypertension, ischaemic heart disease, stroke, or atrial fibrillation) (AASM Practice Guidelines).
Below that threshold the patient may still benefit from positional therapy, weight loss, mandibular advancement, ENT evaluation for upper-airway anatomy, but does not strictly need PAP.
The central-AI breakdown
A buyer who reads only the headline AHI misses the most decision-relevant section of the report: the breakdown of apneas into obstructive, central, and mixed.
Obstructive apnea: airway collapses; the patient continues to make respiratory effort that is visible on chest/abdominal belts but no airflow gets through. This is the type that CPAP solves.
Central apnea: brainstem fails to send drive-to-breathe; effort and airflow both stop simultaneously. CPAP does not help and can sometimes worsen central events (treatment-emergent central sleep apnea).
Mixed apnea: event begins as central (no effort), then transitions to obstructive (effort returns against a closed airway). Counted toward central in many scoring conventions.
The selection rule:
- If centrals are < 50% of all apneas AND the absolute central index (CAI) is < 5/hour, treat as conventional OSA. CPAP first-line.
- If centrals are ≥ 50% of all apneas OR CAI ≥ 5/hour, treat as central or complex sleep apnea. BiPAP-ST or ASV — not CPAP (AASM Practice Guidelines).
Some Indian PSG reports surface this only in the long-form scoring tables rather than the front-page summary. The right step before any device purchase: ask the sleep physician explicitly for the obstructive-vs-central split.
Pressure titration outcomes
A Type-1 in-lab titration study finds the pressure at which obstructive events are eliminated. The titration ends with a recommended therapeutic pressure (or a min/max range for APAP). Where that pressure lands changes the device class.
Titrated pressure under 12 cmH2O: CPAP or APAP is the standard first-line answer. Most patients in this band do well on auto-CPAPs run between 5-12 cmH2O.
Titrated pressure 12-15 cmH2O: still CPAP/APAP territory clinically, but tolerance becomes the issue. Some patients adapt; others find sustained 14-15 cmH2O on expiration uncomfortable enough that adherence collapses below the 4-hours-per-night threshold that drives outcome benefit (Weaver TE et al, Sleep).
Titrated pressure 15-18 cmH2O: BiPAP becomes more tolerable than CPAP. Dropping the expiratory pressure to 11-12 cmH2O while maintaining 16-17 cmH2O on inspiration restores comfort without losing therapeutic effect.
Titrated pressure > 18 cmH2O: strongly favours BiPAP. Single-pressure CPAP at this level is rarely sustained.
The transition point is therefore not a magic number — it is the inflection where expiratory burden tips a patient out of adherence. For most adult OSA patients, that inflection sits in the 14-16 cmH2O band.
APAP vs fixed CPAP for first-line OSA
For uncomplicated OSA without significant central events, hypercapnia, or COPD overlap, auto-CPAP (APAP) is the first-line PAP device in 2026 practice. The argument is mechanical: APAP varies pressure breath by breath within a prescribed min/max window to track airway resistance, lowers the average pressure delivered across the night, and tolerates positional and REM-related variability that fixed CPAP must oversize for.
Fixed CPAP at a lab-titrated pressure is non-inferior to APAP on AHI reduction in head-to-head trials, but APAP shows better adherence in many studies — typically a 30-45 minute increase in nightly use. Adherence is the outcome variable that drives clinical benefit, so APAP wins on revealed preference.
Where fixed CPAP still wins: patients who have already titrated successfully on a fixed pressure and have stable AHI control, patients who are price-sensitive and the additional cost of an APAP is the difference between buying and not buying, and certain post-stroke or heart-failure populations where the literature is thinner on APAP.
The Indian market reflects this: APAP-capable units (ResMed AirSense 11, Philips DreamStation 2, BMC G3 Auto, Home Medix HM-CV-20) cost ₹45,000-₹80,000 and dominate first-line prescription. Fixed-pressure CPAPs from second-tier brands run ₹25,000-₹40,000 and persist in price-sensitive segments.
Central, complex, and overlap exceptions
Pure central sleep apnea. Causes include heart failure with Cheyne-Stokes respiration, chronic opioid use, brainstem stroke, and idiopathic central apnea. CPAP is not first-line. Adaptive servo-ventilation (ASV) is the standard if heart failure is absent or compensated; BiPAP-ST is a step down.
Complex sleep apnea (CompSAS). Patient has predominantly obstructive events on diagnostic PSG, but on CPAP titration develops persistent or new central events at therapeutic pressure. Often resolves with continued CPAP over 4-12 weeks; if it does not, transition to ASV or BiPAP-ST.
COPD-OSA overlap syndrome. Both diseases coexist in roughly 1% of the general population and a much higher fraction of the moderate-severe COPD pool. Overlap patients have worse outcomes on CPAP alone than on BiPAP because the expiratory pressure relief of BiPAP reduces work-of-breathing in the COPD background while the EPAP component still splints the airway.
Obesity hypoventilation syndrome (OHS). BMI > 30, daytime PaCO2 > 45 mmHg without other cause. CPAP works for the OSA component but does not address the hypoventilation. BiPAP, often with AVAPS or TVAPS volume-target overlay, is the standard (Masa JF et al, Pickwick trial (Lancet 2019)).
Neuromuscular disease. ALS, muscular dystrophy, post-polio. Respiratory muscle weakness causes nocturnal hypoventilation that CPAP cannot fix. BiPAP-ST with a backup rate is the entry-level home ventilation setup.
Reading an Indian PSG report
Indian sleep labs follow AASM scoring with reasonable consistency, but report formats vary. The fields that matter:
- AHI (overall and by sleep stage; REM-AHI > 30 with overall AHI < 30 is “REM-predominant OSA” and still warrants therapy)
- Obstructive AI / Central AI / Mixed AI breakdown
- Lowest SpO2 during sleep
- Time below 90% SpO2 as a percentage of total sleep time
- Sleep architecture (stage percentages, REM latency, sleep efficiency)
- Limb movements (PLMI for restless-leg overlap)
- Body position-dependent AHI (supine vs lateral)
A complete report tells you whether OSA is severe, whether centrals matter, whether nocturnal hypoxaemia is significant beyond the apneas (suggesting hypoventilation overlay), and whether the disease is positional (which can shift the threshold for surgical or appliance options).
Indian sleep-medicine market specifics
PSG vs home sleep test (HSAT) availability. Tier-1 cities have multiple Type-1 in-lab PSG providers (typical price ₹6,000-₹15,000 for a single-night study). Type-3 home sleep tests are now widely available at ₹3,000-₹6,000. HSAT is acceptable for high-pre-test-probability uncomplicated adult OSA without significant comorbidity; it underestimates AHI, cannot measure sleep stages, and misses central events. For any complex or non-routine case, in-lab PSG remains the right study (AASM Practice Guidelines).
Sleep-physician routing. Pulmonology, ENT, and neurology all run sleep practices in Indian Tier-1 cities. The physician’s specialty influences the workup direction — pulmonologists tend to think about COPD overlap and hypoventilation first, ENTs about anatomical surgery and appliances, neurologists about central and movement disorders. For a primary OSA presentation a pulmonologist is usually the right first call.
Titration patterns. Many Indian sleep labs run a split-night study (diagnostic in the first half, titration in the second) for cost efficiency. Split-night is acceptable when the diagnostic half clearly shows AHI ≥ 40 within the first 2 hours of sleep; otherwise a full night of titration on a separate occasion is more reliable.
Device pricing in 2026. The bands are stable: APAP ₹45,000-₹80,000, BiPAP-S ₹50,000-₹1,20,000, BiPAP-ST ₹80,000-₹1,60,000, BiPAP with volume assurance ₹1,40,000-₹2,50,000, ASV ₹1,60,000-₹3,00,000+. Hospital-channel pricing typically runs 10% above retail; specialised PAP-clinic pricing usually 5-10% below.
The takeaway
AHI severity sets the trigger to treat. The choice between CPAP and BiPAP is set by a small set of secondary findings: titrated pressure, central-vs-obstructive breakdown, hypercapnia, COPD overlap, neuromuscular weakness. Read the full PSG report, ask the sleep physician for the central-AI split and the titrated pressure, then pick the device class that matches both. Within a class, brand choice runs on accuracy, ecosystem, and service.
This guide is editorial opinion and general information. It is not medical advice. Consult your physician for therapy decisions, and verify all specifications with the manufacturer before purchase.