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A completed Neurofit Vitals scan returns up to six biometric metrics derived from a 60-second rear-camera PPG (photoplethysmography) signal. Five metrics are always populated when the scan is accepted; one — breathing rate — is confidence-gated and may be absent even in a fully accepted result. This page summarises every output, its field name, unit, and validated accuracy so you know exactly what you’re working with before diving into the per-metric detail pages.

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Metrics at a Glance

All six fields are only populated when the scan’s qualityTier is .accepted (iOS) or QualityTier.ACCEPTED (Android). If quality is insufficient, the SDK surfaces a rejection reason and none of the metric fields should be read.

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Metric Descriptions

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Heart Rate

Heart rate is the average number of cardiac beats per minute recorded across the full 60-second scan window. It is derived by detecting the peaks of the PPG waveform captured from the rear camera with the finger held over the lens. Validated against the Polar H10 chest strap, the SDK achieves a mean absolute error of just 0.47 bpm with a Pearson correlation of r = 0.999 — making it the most accurate metric in the suite.

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HRV RMSSD

RMSSD (root mean square of successive differences) is the most widely reported short-term HRV metric and is the same measure used by consumer wearables such as WHOOP, Oura, and Polar. It quantifies beat-to-beat interval variability and is strongly linked to parasympathetic nervous system activity. A higher RMSSD generally indicates better recovery and lower autonomic stress.

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HRV SDNN

SDNN (standard deviation of normal-to-normal intervals) captures overall autonomic variability across the scan window. While RMSSD emphasises short-term fluctuations, SDNN reflects the combined influence of both sympathetic and parasympathetic branches of the autonomic nervous system. It provides a complementary view of cardiovascular regulation alongside RMSSD.

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Baevsky Stress Index

The Baevsky stress index is a time-domain HRV measure that estimates autonomic nervous system strain. The SDK returns it on a natural-logarithm (ln) scale to normalise its distribution. Higher values indicate greater sympathetic activation — that is, more physiological stress or alertness — while lower values suggest a more relaxed, parasympathetically dominant state.

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Poincaré SD2:SD1

The Poincaré plot is a geometric technique that maps each RR interval against the one that follows it. The ratio of the plot’s long-axis standard deviation (SD2) to its short-axis standard deviation (SD1) reflects the balance between long-term and short-term HRV components. A higher ratio indicates that longer-timescale variability dominates; a ratio close to 1 suggests a more uniform beat-to-beat pattern.

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Breathing Rate

Breathing rate is the number of full respiration cycles per minute, estimated from the respiratory modulation embedded in the PPG signal. Because this modulation can be obscured by motion or irregular breathing, the SDK only reports a breathing rate when the signal quality is high enough to trust — it is the sole confidence-gated metric in the suite. A nil/null value should be treated as “not measured this session” rather than as an error.
Neurofit Vitals is not a medical device. None of the metrics described here are intended for clinical diagnosis, treatment, or monitoring of any medical condition.

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Explore Each Metric in Depth

Heart Rate

Accuracy details, SDK field reference, and code examples for the heartRate output.

HRV Metrics

Full reference for RMSSD, SDNN, Baevsky stress index, and Poincaré SD2:SD1.

Breathing Rate

How confidence-gating works and how to handle the nullable breathingRate field safely.