> ## Documentation Index
> Fetch the complete documentation index at: https://help.apnealytics.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Metrics explained

> Usage and adherence, leak, pressure (P95 and EPR), event composition, oximetry (SpO2, ODI, T90), and per-night waveforms — what each metric in Apnealytics means and how to read it.

Beyond [AHI](https://help.apnealytics.com/guides/understanding-ahi.md), Apnealytics tracks the other numbers that
describe a night of therapy. Here's what each one means.

> [!NOTE]
>
> These metrics are for tracking and coaching, not diagnosis. Prescribed settings
> come from your clinician — use Apnealytics to see how therapy is going over time,
> and make prescription changes with your provider, not on a hunch.

## Usage & adherence

Usage is simply how long you wore the mask each night. The common adherence
benchmark — used by many insurers, DOT medicals, and clinics — is the
**4-hour / 70% rule**: using the machine at least 4 hours a night on at least 70%
of nights, often measured over a rolling 30-day window.

> [!TIP]
>
> Partial nights still count toward the 70% — even a nap-length session helps. The
> **Reports** page produces a compliance summary you can save for your provider.

## Leak

Leak is air escaping the mask, measured in **L/min**. Apnealytics tracks the
**95th-percentile** leak per night (the level your leak stayed below for most of
the night). High leak matters for two reasons: it disrupts therapy, and it makes
AHI and pressure readings unreliable — so it's usually the first thing to fix.

Quick wins: re-seat the mask lying down, try a different cushion size, replace a
worn cushion, and for mouth leak on a nasal mask add a chin strap or switch to
full-face.

## Pressure, EPR & ramp

> [accordion] Pressure and P95
>
> Pressure is measured in **cmH₂O**. Auto machines vary it through the night;
> the **95th-percentile pressure (P95)** summarizes how hard your machine was
> working most of the time. Apnealytics also shows the median so you can see the
> typical vs. the busy end of the night.

> [accordion] EPR — expiratory pressure relief
>
> EPR drops the pressure slightly when you exhale, so breathing out feels less
> like pushing against the machine. It's a comfort setting, typically 1–3 cmH₂O.

> [accordion] Ramp
>
> Ramp starts at a low, easy pressure and gradually rises to your therapy
> pressure over a set time, so you can fall asleep before it reaches full
> strength.

## Event composition

The same AHI can be made of very different events. Apnealytics shows the split
between obstructive, central, hypopnea, and unclassified events so you can see
what's driving a night. The sub-indices are covered in
[Understanding AHI](https://help.apnealytics.com/guides/understanding-ahi.md).

## Oximetry — SpO₂, ODI & T90

If you add a recording pulse oximeter (such as a Wellue O2Ring or CMS50) or sync
blood-oxygen from Apple Health / Health Connect, Apnealytics charts your overnight
oxygen on the **Vitals** page and overlays it on the per-night waveform.

> [accordion] SpO₂ — blood oxygen
>
> The percentage of your blood's oxygen-carrying capacity in use. Healthy
> overnight values usually sit in the mid-to-high 90s. Apnealytics charts your
> nightly average alongside the nightly low.

> [accordion] ODI — oxygen desaturation index
>
> How often your oxygen dropped by a meaningful amount per hour (desaturations).
> Where AHI counts breathing events, ODI counts their effect on your oxygen — so
> the two together tell you more than either alone.

> [accordion] T90 — time below 90%
>
> How much of the night your oxygen spent below about 90%. Brief dips are
> normal; frequent or sustained time below 90% is what matters.

> [!NOTE]
>
> SpO₂ tells you what AHI can't: AHI counts events, oximetry shows their impact on
> your body. An oxygen dip with no matching flow change is more likely a sensor
> artifact than a real apnea.

## Waveforms

The **per-night view** stacks flow rate, pressure, leak, and (if you have oximetry)
SpO₂ and pulse on a shared timeline. Line them up vertically: a real event usually
shows across several strips at once — a flow drop that recovers with a big
"catch-up" breath, a matching pressure response, and, a beat later, an SpO₂ dip.

> [!WARNING]
>
> Always read the **leak** strip first. A high-leak stretch makes every other number
> on that night unreliable.

Waveforms load that night's detailed files on demand, so the first time you open
an older night it may take a moment to fetch and render in your browser.


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