// HRV stress overlay
Stream your stress, not just your BPM.
An overlay driven by heart-rate variability, RMSSD, SDNN, pNN50 and a Baevsky-style stress index, so your audience sees what your nervous system is doing, computed locally in real time.
// The metrics
What HRV actually tells your stream.
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RMSSD
msThe go-to short-term HRV measure. Drops when you tense up, recovers as you settle, the backbone of the live stress score.
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SDNN
msOverall variability across the window. A broader read on how regulated vs. taxed your system is during a session.
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pNN50
%Share of beats differing by more than 50 ms. A quick, intuitive proxy for parasympathetic (calm) activity.
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Baevsky stress index
0-100A composite stress score that condenses the HRV picture into one number, what drives the gauge on screen.
Live in your overlay as CSS variables
Read --nerva-stress, --nerva-stress-pct and
the rest straight in CSS, or subscribe to the
nerva-update event in JS. Calibrates in about 30 s.
HRV stress overlay, questions.
How does Nerva measure stress on stream?
Nerva reads the beat-to-beat timing from your BLE sensor and computes heart-rate-variability metrics (RMSSD, SDNN, pNN50), then derives a Baevsky-style stress index from them. That index, alongside live BPM and zone, is exposed to overlays as CSS variables, so the overlay can react to your stress, not just your pulse.
What sensor do I need for an accurate stress reading?
A chest strap such as the Polar H10 gives the most accurate HRV, because HRV needs precise beat-to-beat timing. A watch (Garmin, Polar, COROS, Amazfit, Wear OS) gives reliable BPM and a usable stress trend, but a chest strap is the gold standard for HRV.
What's the difference between BPM and a stress score?
BPM is how fast your heart is beating. The stress score is derived from heart-rate variability, the tiny changes in timing between beats, which reflects how your nervous system is responding. Two streamers can sit at the same BPM while one is calm and the other is tense; the stress score is what tells them apart on screen.
Can I style the stress overlay myself?
Yes. Overlays are open HTML/CSS/JS folders that read the live stress value as a CSS variable, so you can drive colors, animation, gauges, or anything else from it. Restyle a bundled overlay, build your own from scratch, or commission a bespoke one.
Does the stress reading add latency?
No. Nerva computes HRV and the stress index locally and renders the overlay on your machine, with no cloud in the path. The overlay updates with no perceptible round-trip, the same as the raw BPM.
Does my heart-rate or HRV data leave my machine?
No. Heart rate, HRV, and session data are processed locally and never leave your computer. There's no cloud, no phone, and no account.