LITF-PA-2026-225 · Sleep Medicine / Predictive Maintenance

System and Method for Estimating CPAP Blower Wear and Localizing Mask Leaks via Pressure Waveform, Motor Current, and Acoustic Analysis

Defensive Prior Art Disclosure
A CPAP machine on a wooden nightstand beside a bed at night, with a sleep mask and coiled hose resting next to it under warm lamplight
⚖️ Prior Art Notice: This document is published as defensive prior art under 35 U.S.C. § 102(a)(1). The inventions described herein are dedicated to the public domain as of the publication date above. This disclosure is intended to prevent the patenting of these concepts by any party.

Medical note: this disclosure concerns machine condition, not medical advice. Therapy decisions belong to the patient and their clinician.

Abstract

Disclosed is a system and method that estimates how worn a CPAP blower is and locates where mask air is leaking, using signals the therapy already produces. A CPAP machine holds a sleeper's airway open with pressurized air, typically 4 to 20 centimeters of water, delivered all night by a small brushless blower spinning near 35,000 revolutions per minute. Two slow failures end therapy before the user notices. The blower's bearings wear, the machine gets louder, draws more current, and answers each inhalation more slowly, until one night it cannot hold pressure and stops. And the mask leaks, air escaping at the cushion, through an open mouth, or from a cracked tube, until the machine can no longer sense breathing well enough to score events. Today's machines handle both failures with blunt instruments: a timer that fires a "motor life exceeded" notice at about 21,900 hours whether the blower is healthy or dying, and a nightly leak total that says air escaped somewhere without saying where. This disclosure replaces both with measurement. It reads motor current and speed ripple, the sound of the blower, how fast pressure rises when inhalation starts, and how long the blower spins down after switch-off, and fuses them into a blower wear index with a remaining-hours estimate. It reads the pressure and flow waveform breath by breath, subtracts the mask's known vent flow, and localizes the remaining leak to the mask seal, the mouth, or the tubing by its pressure dependence, its breath-phase timing, and its acoustic signature. Both verdicts are corrected for the mimics that fake them: a clogged filter, a low humidifier chamber, a changed mask, and sleeping position.

The output is a date for the blower, a location for the leak, and a confidence score on the night's apnea-hypopnea index, so a failing machine is replaced before therapy stops and a leak is fixed at its source instead of by tightening the mask until it hurts.

Field of the Invention

This invention relates to predictive maintenance of positive airway pressure therapy devices, specifically to estimating blower bearing wear from electrical, acoustic, and pressure-transient signals and to localizing unintentional air leaks to mask seal, mouth, or tubing from breath-synchronous waveform and acoustic analysis, for replacement scheduling and therapy-integrity assessment in home sleep apnea treatment.

Background

Sleep apnea is scored by the apnea-hypopnea index, or AHI: the number of apneas and hypopneas per hour of sleep. Under 5 is normal, 5 to 15 is mild, 15 to 30 is moderate, and 30 or higher is severe. Continuous positive airway pressure, CPAP, is the first-line therapy, and the treatment goal is an AHI under 5 on therapy. The machine is therefore also the instrument that judges whether the therapy works, which makes its own measurement integrity part of the therapy. Modern machines record pressure, flow, leak, and events to an SD card every night, and free software such as OSCAR plots the full time series. The data exists. What does not exist is a system that reads it for machine health.

The blower is a brushless DC motor driving a small radial fan, typically 5 to 20 watts, running near 35,000 revolutions per minute at about 3 millinewton-meters of torque, with a design life of at least 20,000 hours. ResMed's AirSense machines display a "motor life exceeded" notice at about 21,900 hours of operation, roughly 7.5 years at 8 hours per night, and some motors run past 25,000 hours before showing trouble. The notice is a timer, not a measurement. It fires on schedule whether the blower is healthy or dying, and it says nothing about the months in between. The actual failure mode is bearing wear. Owners report the sound changing first, a high-pitched whine or a grinding rattle, then rising current draw, then sudden failure. One long-running user discussion puts it plainly: the cause of failure is most commonly the fan motor, its bearing surfaces wear out gradually, the owner hears the sound begin to change, and near the end the motor either makes so much noise no one can sleep with it or pulls more current than the power supply can handle and fails suddenly. The same discussion reports a ResMed engineer saying blower life expectancy exceeds that of the machine's other assemblies, and that machines are generally replaced for other reasons, such as size, weight, or features, before blower performance becomes an issue. That is true on average, and it is exactly why a per-unit measurement matters: an average that holds for the fleet says nothing about the tail of units that wear early, and it is the early-wearing tail that loses a night of therapy without warning. Pressure loss is a late sign, not an early one, because the machines are designed to deliver the set pressure or die trying. A machine that cannot hold pressure has already failed. A machine that holds pressure while whining, drawing excess current, and answering inhalation late is failing, and nobody is measuring it.

The leak is the second failure, and it is more common than the first. Every mask vents air by design, and the machine subtracts that expected vent flow to report unintentional leak, the air escaping because of a poor seal. ResMed treats unintentional leak at or above 24 liters per minute as a large leak. That figure originates in ResMed's Mask Fit check and is adopted here as a working threshold, not a clinical reference range. User documentation of ResMed's red-face indicator describes the trigger as unintentional leak at or above 24 liters per minute for at least 30 percent of the night, the point at which the leak is large enough and long enough to affect both the accuracy of the AHI data and the efficacy of the therapy. The machine's nightly display reports leak as a 95th percentile figure; the red-face trigger is a separate duration rule, and this disclosure adopts the 30-percent duration rule as its own large-leak flag. Push leak into the 50 to 70 liters per minute range and the machine can struggle to sense breathing accurately at all, which makes that night's AHI reading unreliable too. The causes are ordinary: a cushion that has lost its shape, headgear that has stretched, the wrong mask size, a mouth that falls open during the night on a nasal mask, a cracked tube. Current practice cannot tell these apart. The user is told to tighten the mask, which often makes the leak worse, because overtightening distorts a silicone cushion that is designed to inflate slightly under pressure and seal against the face. Or the cushion is replaced on a calendar schedule whether it needs it or not. Or the leak is ignored, and a night that looks like an AHI of 2 is actually a night the machine could not hear.

No published system fuses these signals into a measured wear index with a leak localization and an AHI confidence score. That is what this disclosure provides.

Detailed Description

1. Inputs and System Architecture

The preferred embodiment is phone-plus-data and installs no hardware in the machine. It reads the machine's own nightly data, pressure, flow, leak, and events from the SD card or the companion app, and it records blower sound with a smartphone microphone during a 30 second pre-sleep check and in short overnight samples. A second embodiment is machine-embedded: a current sensor on the blower leads, a MEMS microphone inside the housing, a pressure sensor at the blower outlet, and blower speed from back-EMF, all sampled by the machine's own controller. A third embodiment is a fleet aggregator for a durable medical equipment provider: anonymized wear curves per blower model across many machines, used to set model-specific replacement thresholds and to spot a bad batch of blowers before any single patient can see the pattern. In all embodiments only derived features leave the home: current summaries, acoustic summaries, pressure timing, and leak statistics, never audio recordings of the bedroom.

Every measurement is tagged with the variables that move it. Set pressure in centimeters of water, mask model, cushion age in days, headgear age, filter age, humidifier water level class, altitude, and sleeping position where a phone accelerometer or mask movement sensor reports it. A measurement without its tags is not used for wear or leak verdicts. It is logged as untagged and excluded from the index, because an untagged measurement is how a new mask becomes a false blower alarm.

2. Baseline Learning

Before any verdict, the system learns the machine's healthy behavior. The baseline is taken over the first two stable weeks at fixed pressure settings and one mask, and it stores six fingerprints: spin-up time from power-on to target pressure, spin-down time from switch-off to rest, RMS motor current at the set pressure, acoustic tonal peaks of the blower, pressure-rise lag from inhalation onset to 90 percent of target pressure, and unintentional leak at the reference pressure by breath phase. Wear and leak are defined strictly as drift away from this baseline under matched conditions, never as absolute numbers, because two healthy machines of different models differ more from each other than a new blower differs from a worn one of the same model. A pressure change re-baselines the pressure-dependent channels only. A mask change re-baselines the leak channels only, using the new mask's vent curve. A phone change re-baselines the acoustic channel only.

3. The Five Blower Wear Channels

Spin-up time is the channel that sees bearing drag at start. A healthy blower reaches target pressure in a consistent interval after power-on. As bearings wear, friction rises and spin-up lengthens. The system measures from power-on to the first stable second at target pressure, excluding the ramp period where the machine deliberately starts low, and it corrects for set pressure, because a higher target takes longer to reach for innocent reasons. A rise of 20 percent or more at matched pressure, sustained over at least five nights, is a wear vote, not a verdict. One slow start is a cold room. Five slow starts are a trend.

Spin-down time is the channel that sees bearing friction directly, and it is the simplest measurement in the disclosure. When the machine switches off, a healthy blower coasts for seconds on its own inertia. A worn bearing drags it to rest sooner. The system times the interval from switch-off to inaudibility or to zero back-EMF speed, and it corrects for the pressure the machine was delivering when switched off, because a faster blower coasts longer. A shortening of 25 percent or more from baseline is a wear vote. Spin-down needs no sensor the machine does not already have, which is why it is the channel a phone-only embodiment can measure with a microphone alone.

Motor current is the channel that sees effort directly. Worn bearings raise the torque needed to hold speed, so the blower draws more RMS current for the same pressure and shows larger torque ripple at the rotation frequency as the rotor drags unevenly. The system reports current only from steady-state delivery, excluding spin-up, ramp, and the pressure pulses of inhalation onset, and it normalizes by set pressure and by filter age, since a clogged filter also raises current. A sustained RMS rise of 15 percent or more with rising ripple is a wear vote. A current spike on one night is a power event or a jam, and it is flagged as an incident, not as wear.

Acoustics is the channel that hears the bearing itself. A healthy blower produces a steady tonal peak at the blade-pass frequency with low broadband noise. A worn bearing adds a high-pitched whine, in the preferred embodiment a rising tonal peak in the 2 to 6 kilohertz band, plus broadband grinding as the bearing surfaces roughen. The system summarizes each pre-sleep check with three features: the dominant tonal peak frequency and level, the high-frequency band share, and the broadband noise floor. Wear moves all three in the same direction: tonal peak level up, high-frequency share up, noise floor up. The microphone need not be calibrated in absolute decibels, because the features are ratios and shapes, not levels, and the baseline is taken on the same phone in the same bedroom.

Pressure-rise lag is the channel that sees wear in the therapy itself. When inhalation starts, airway pressure dips and the blower must accelerate to restore it. A healthy blower restores target pressure quickly. A worn blower, dragging on its bearings, restores it late. The system measures the interval from inhalation onset, detected as the start of the inspiratory flow rise, to the moment pressure recovers to 90 percent of target, and it reports the median lag over the night, corrected for set pressure and for leak, since a large leak also slows pressure recovery. A lag that grows by 50 percent or more from baseline is a wear vote, and it is the vote that matters most to the patient, because it is the only channel that measures the therapy getting slower rather than the machine getting louder.

4. Leak Separation and Localization

Leak localization starts by subtracting what is supposed to escape. Every mask model has a vent curve, the intentional vent flow as a function of pressure, published by the maker or measured once at fitting. The system subtracts the vent curve from total leak to obtain unintentional leak, breath by breath, and then localizes the remainder by three independent tests. The first test is pressure dependence. A mask seal leak grows with pressure, roughly linearly, because higher pressure pushes more air through the same gap. A mouth leak is weakly pressure dependent and strongly phase dependent. A tube leak is a nearly constant offset, present at all pressures and all phases, because a crack does not open and close with the breath. The system fits unintentional leak against pressure across the night's pressure range and reports the slope and the intercept: a steep slope with a near-zero intercept is a seal leak, a flat line with a large intercept is a tube leak.

The second test is breath-phase timing. A seal leak is continuous, present through inhalation and exhalation alike, because the gap does not close. A mouth leak appears as bursts during exhalation, when the mouth opens and expiratory pressure drives air out through the lips, and it largely vanishes during inhalation. The system computes unintentional leak separately for the inspiratory and expiratory halves of each breath and reports the expiratory-to-inspiratory ratio. A ratio near 1 with a high absolute level is a seal. A ratio well above 1 is a mouth. A ratio near 1 with a flat pressure dependence is a tube.

The third test is acoustic. A seal leak hisses at the mask, a high-frequency narrowband sound at the cushion edge, loudest to a microphone near the face. A mouth leak is a lower-frequency broadband puff at the lips. A tube leak hisses at the machine or along the hose, loudest to a microphone near the machine. A humidifier leak gurgles, a low-frequency bubbling tied to water level and to the sloshing of the chamber. The system samples sound at the pre-sleep check and in short overnight windows, computes band energies, and compares the mask-side and machine-side levels. The three tests vote independently, and the localization verdict is the source that wins at least two of the three, reported with its confidence. A leak that wins no test is reported as unlocalized with its total, not forced into a wrong location.

5. Separating Wear and Leak from Their Mimics

Four mimics make these measurements hard, and each one has a signature that separates it from the real failure. The first is a clogged filter. A dirty intake filter raises current, raises noise, and slows pressure rise, exactly like bearing wear. It differs in one respect: it resets. The system compares measurements before and after a filter change, and any step improvement is attributed to the filter and removed from the wear trend. A filter change that restores spin-down time, current, and pressure-rise lag to baseline is evidence against wear, and the wear index is lowered accordingly rather than letting a dirty filter accumulate a false wear debt.

The second is humidifier water level. A low chamber changes the acoustic coupling of the blower housing and can add gurgling that a naive acoustic channel reads as bearing noise. The system tags water level class at each check and only compares acoustic features within the same class, and it treats a gurgling signature that vanishes on refill as a water event, not a bearing event. The third is a mask change. A new mask has a new vent curve, a new cushion, and new headgear, so leak levels step-change for innocent reasons. The system re-baselines the leak channels on a mask change and never compares leak across masks. The fourth is sleeping position. Side sleeping presses the mask against the pillow and changes the seal, so leak varies with position. The system tags position where it can and only compares leak within matched positions, and where position is unknown it widens the leak uncertainty band rather than reporting a false verdict. Altitude is handled by the machine's own pressure sensor, which reports pressure relative to ambient, and the system corrects for it rather than treating a mountain trip as a machine failure. A fifth mimic is bedroom noise itself: a snoring partner, a white-noise machine, or pets can contaminate the acoustic channel, so acoustic features are only compared within the same bedroom-noise class, and a night where ambient noise dominates the blower band is flagged and excluded from the acoustic vote.

6. The Wear Index and Remaining Hours

The five blower channels are combined into a single wear index W on a 0 to 1 scale, where 0 is the healthy baseline and 1 is a blower that cannot hold set pressure. Each channel contributes a normalized drift, its current value minus its baseline divided by a channel scale set from the fleet distribution for that blower model or, where no fleet data exists, from a default scale published with the system. The channels are weighted: pressure-rise lag and spin-down time carry the most weight because they measure the therapy and the bearing directly, current and acoustics carry medium weight, and spin-up time carries the least, since it is the most sensitive to room temperature. The weights and the scales are shown to the user with the score. A black-box score that cannot be audited will not be trusted at the moment it recommends spending money, and it should not be.

Two thresholds govern action. At W of 0.5, the system issues a watch notice: wear is measurable, the blower is not yet failing, and the next replacement window is named. At W of 0.75, the system issues a replace notice: the blower is measurably degrading therapy, remaining hours are estimated from the recent slope of W against operating hours, and a replacement is scheduled. The remaining-hours estimate is reported as a range, never a point, with the range widening when the slope is estimated from few hours or across a pressure change, and it is shown next to the maker's class rating of about 21,900 hours so the owner can see whether this unit is wearing faster or slower than its class. A threshold crossed on a single channel alone does not trigger a replace notice. At least three channels must agree, or two channels plus a pressure-rise lag growth of at least 50 percent, because a single-channel verdict is how a clogged filter becomes a new machine order.

7. The AHI Confidence Score

Every AHI the system reports travels with a confidence score, because an AHI measured through a large leak is not the same number as an AHI measured through a good seal. The score is computed per night and per event cluster from the leak record. When unintentional leak is at or above 24 liters per minute for at least 30 percent of the night, the night's AHI is flagged unreliable, using the large-leak duration rule described in the Background, and the report states the fraction of the night spent in large leak next to the AHI instead of hiding it. When leak rises into the 50 to 70 liters per minute range, event detection is flagged as failed for the affected intervals, and events scored in those intervals are marked as untrusted rather than counted. When leak is under 24 liters per minute for the whole night, the AHI carries full confidence. The practical effect is a report that reads, by way of illustration, "AHI 2.1, confidence low: 41 percent of the night in large leak" instead of a bare "AHI 2.1", so a clinician does not titrate pressure on a number the machine could not hear.

8. Worked Example: The Seventh-Year Machine That Stopped Holding Its Recipe

Consider a CPAP machine in its seventh year of nightly use, at 19,400 operating hours, below the 21,900-hour timer, running a fixed pressure of 11 centimeters of water with a nasal mask. At baseline, two years earlier, spin-down took 4.2 seconds, RMS current at set pressure was its reference value, the acoustic tonal peak sat at its reference level, and pressure-rise lag after inhalation onset was 180 milliseconds. At 19,400 hours the picture has changed on every channel at once. Spin-down has shortened to 2.9 seconds, a drop of 31 percent. RMS current is up 17 percent at matched pressure with visibly larger torque ripple. The acoustic tonal peak is up 9 decibels near 3.1 kilohertz, the sound of a bearing whining. Pressure-rise lag has grown from 180 to 320 milliseconds, a rise of 78 percent. A filter change produced no step improvement, the humidifier was full, and the trend survived a mask change, so the mimics are excluded. The fused wear index reads 0.81, past the 0.75 replace threshold, with a remaining-hours estimate of roughly 400 to 1,200 hours at the recent wear slope. That it crosses the threshold at 19,400 hours, ahead of the 21,900-hour timer, is the point of measuring wear rather than counting hours: a timer describes a class average, and this unit wore faster than average. The leak record tells a second story. Median unintentional leak is 31 liters per minute, the leak grows steeply with pressure, it is continuous across breath phases, and the hiss is loudest at the mask, so the localization verdict is a cushion seal leak with high confidence. The cushion is replaced, leak falls to 8 liters per minute, and the AHI confidence score is restored. The blower is ordered the same week and swapped before it fails on a night the patient needs it. That is the entire value proposition in one paragraph: a planned replacement instead of a night without therapy, and a cushion instead of a tighter strap. The index value, remaining-hours range, and leak figures in this example are illustrative outputs of the method, not measured results.

9. Figures Description

  • Figure 1: System block diagram showing the CPAP machine, blower, mask, tube, and humidifier, the phone or embedded sensors, the SD card data import, the five blower wear channels, the leak separation and localization module, the mimic separation module, and the wear index, leak verdict, and AHI confidence outputs.
  • Figure 2: Blower wear channel trends against cumulative operating hours: spin-down time falling, RMS current rising, acoustic tonal peak rising, and pressure-rise lag rising, with the 21,900-hour class timer marked and the wear verdict crossing its threshold before the timer fires.
  • Figure 3: Leak localization diagram: vent flow subtracted from total leak using the mask vent curve, then pressure dependence, breath-phase timing, and acoustic location voting among mask seal, mouth, tube, and humidifier sources.
  • Figure 4: Confound separation diagram: filter clog as a step improvement after a filter change, humidifier level as a water-dependent acoustic change, mask change as a step change with re-baselining, and sleeping position as a leak variation that is only compared within matched positions.
  • Figure 5: Worked example dashboard: baseline versus current values for all five blower channels, the fused wear index at 0.81 against the 0.5 watch and 0.75 replace thresholds, the remaining-hours range, the localized cushion leak at 31 liters per minute falling to 8 after replacement, and the AHI with its confidence score.
  • Figure 6: Fleet view for a durable medical equipment provider: wear curves for many machines of the same blower model plotted against operating hours, showing model-specific wear rates and an outlier machine flagged for a clogged filter rather than wear.

Claims

  1. A system for estimating CPAP blower wear, comprising: a sensor set reporting at least one of blower motor current, blower acoustic output, blower speed, and delivered airway pressure; and a processor configured to compute a baseline fingerprint for a reference pressure and mask after a stabilization period, measure drift from the baseline under matched pressure and mask conditions, and convert the drift into a blower wear index.
  2. The system of claim 1, wherein the processor measures blower spin-up time from power-on to target pressure and blower spin-down time from switch-off to rest, and wherein a lengthening spin-up time or a shortening spin-down time at matched set pressure contributes to the wear index.
  3. The system of claim 1, wherein the processor measures RMS motor current and torque ripple at the rotation frequency during steady-state delivery, excluding spin-up, ramp, and inhalation-onset intervals, and wherein a sustained rise in loaded RMS current with rising torque ripple contributes to the wear index.
  4. The system of claim 1, wherein the processor computes acoustic features of blower operation comprising a dominant tonal peak level, high-frequency band share, and broadband noise floor, and wherein a rising tonal peak level with rising high-frequency share and rising noise floor contributes to the wear index as a bearing-wear signature.
  5. The system of claim 1, wherein the processor measures pressure-rise lag from inhalation onset to recovery to 90 percent of target pressure, and wherein a growth in median pressure-rise lag at matched pressure and leak contributes to the wear index.
  6. The system of claim 1, wherein the processor combines at least three wear channels into a single wear index on a fixed scale, issues a watch notice at a first threshold and a replace notice at a second higher threshold, and estimates remaining operating hours from the recent slope of the wear index against cumulative operating hours.
  7. The system of claim 1, wherein the processor subtracts expected vent flow from total leak using a mask vent curve as a function of pressure, and reports the remainder as unintentional leak.
  8. The system of claim 7, wherein the processor localizes unintentional leak to a mask seal, a mouth, a tube, or a humidifier by at least two of: pressure dependence of the leak, breath-phase timing of the leak, and acoustic location of the leak sound, and reports the localized source with a confidence.
  9. The system of claim 1, wherein the processor separates filter clog, humidifier water level, mask change, sleeping position, and altitude from blower wear and leak by comparing measurements before and after filter changes and refills, re-baselining leak channels on mask changes, comparing leak only within matched sleeping positions, and correcting pressure for altitude, and adjusts the wear index and leak verdict accordingly.
  10. The system of claim 1, wherein the processor computes an AHI confidence score from the leak record, flags a night's AHI as unreliable when unintentional leak is at or above 24 liters per minute for at least 30 percent of the night, and flags event detection as failed for intervals where leak exceeds the sensing limit, and reports the confidence score with every AHI.
  11. The system of claim 1, wherein the processor classifies a sudden single-night change in current, acoustics, or pressure-rise lag with no preceding trend as a damage incident distinct from wear, and reports an inspection prompt rather than a wear verdict.
  12. The system of claim 1, implemented as a phone-based system reading machine therapy data and smartphone microphone recordings with no machine hardware modification, or as a machine-embedded system, or as a fleet aggregator producing model-specific wear curves and replacement thresholds across many machines.

Prior Art References

  1. AirwayLab, "CPAP Leak Rate Explained: What Counts as High and Does It Matter": ResMed AirSense devices report unintentional leak separately from vent flow; a common rule of thumb treats unintentional leak above about 24 liters per minute as high; ResMed AirSense 11 Mask Fit reads leak under 24 liters per minute as a good seal and over 24 as "Adjust the mask"
  2. Jeremy Smith, "How to Interpret CPAP Data: AHI, Leak Rate, and Usage Hours": AHI under 5 normal, 5 to 15 mild, 15 to 30 moderate, 30 or higher severe; on-therapy goal under 5; ResMed treats leak at or above 24 liters per minute as a large leak, reported as a 95th percentile figure; high leak makes event detection less reliable
  3. The CPAP Shop, "How to Read Your CPAP Data and What AHI Is": target ranges of AHI under 5 and unintentional leak under roughly 24 liters per minute; once leak climbs into the 50 to 70 liters per minute range the machine can struggle to sense breathing accurately, making that night's AHI unreliable
  4. AdvanCPAP, "CPAP Stopped Working? Fix Service Required and Motor Life": ResMed motor-life alert typically triggers around 21,900 hours, about 7.5 years at 8 hours per night; some motors run past 25,000 hours; grinding, whining, or rattling points to the blower motor; worn blower motors show insufficient speed or excessive current draw
  5. CPAPtalk, "Life expectancy of a CPAP machine": the cause of failure is most commonly the fan motor, whose bearing surfaces wear out gradually; the owner hears the sound begin to change; near the end the motor makes so much noise no one can sleep with it or pulls more current than the power supply can handle and fails suddenly; machines are designed to deliver the set pressure or die trying, so pressure loss is rarely gradual
  6. Mabuchi Motor Electromag, "BLDC motors for home care ventilation (CPAP)": CPAP blowers use low-power sensorless brushless DC motors, typically 5 to 20 watts, operating at a constant speed of 35,000 revolutions per minute with torque of approximately 3 millinewton-meters, with a design lifespan of at least 20,000 hours
  7. BestCPAP.eu, "ResMed Motor Life Exceeded: What It Means and What to Do": the "motor life exceeded" message is a pre-programmed notification appearing after approximately 22,000 hours of operation, about 5 to 7 years of regular use, not an error code or a sign of immediate failure
  8. CPAPtalk, "Can mask leaks effect your treatment?": ResMed literature defines a large leak as an unintentional leak of 24 liters per minute or greater; the red-face indicator appears when leaks are at or above 24 liters per minute for at least 30 percent of the night, the point at which leaks affect both therapy efficacy and AHI accuracy; above 0.70 liters per second (42 liters per minute) the machinery may fail to sense breathing
  9. CPAP Equip, "CPAP Leak Rate: What Is Normal?": 0 to 10 liters per minute usually excellent, 10 to 20 generally acceptable, 20 to 24 worth watching, above 24 considered high leak in ResMed clinical guidance; leak duration and pattern matter as much as the level; overtightening can distort the cushion and make leaking worse

Limitations

The thresholds in this disclosure have not been validated against measured machines. The channel weights and scales that produce the wear index are to be calibrated from fleet data, and the worked example uses illustrative values, not measurements from any real machine. Acoustic performance in real bedrooms, with snoring partners, white-noise machines, and varying phone placement, is untested, and the leak localization votes have not been tested against ground-truth leak sources. The 30-percent large-leak rule is adopted from user documentation of the maker's indicator, not from a clinical study. Nothing here should be read as evidence that any particular machine will fail at any particular hour.

Implementation Notes

Build notes for whoever implements this. Ship the baseline before the score. A wear index without a two-week healthy baseline is a random number with a decimal point, and the first user who gets a replace notice on a month-old machine will never trust the second notice. Require the stabilization period, show the baseline values next to every current value, and refuse a verdict when the pressure, mask, or filter tags are missing, reporting "insufficient matched data" instead of a number. Do not ship a single-channel version. Current alone will blame every clogged filter, acoustics alone will blame every dry humidifier, and pressure-rise lag alone will blame every large leak. The three-channel agreement rule is not a nicety. It is the product. Calibrate the channel scales per blower model from fleet data as soon as the fleet exists, because blowers with different design lives wear on different clocks and a single global scale will either nag one owner or neglect the other. Present the remaining-hours estimate as a range with its slope, and say which channel drove the verdict in the notice itself, so the owner can check it with their own ears: the machine really does whine, the spin-down really is shorter, the pressure really does recover later. On a damage incident, tell the user to stop and inspect before the next night. A chipped impeller or a foreign object is not a wear trend, and sleeping through it turns a blower order into a machine replacement. Never present the wear index as a diagnosis or a prescription. The system measures machine condition, not health, and the notice should say that the blower is measurably worn and therapy delivery is measurably slower, leaving every clinical decision exactly where it belongs, with the patient and their clinician. Finally, the AHI confidence score must travel with the AHI everywhere the AHI is displayed, in the app, in the report, and in the export. An AHI without its confidence is the number that gets a pressure titrated on a night the machine could not hear.