Beats per minute, from the interval between systolic peaks in the pulse waveform. The most direct and most reliable of the five — it needs only that peaks be locatable, not that their shape or amplitude be calibrated.
Source: finger PPG · rPPG · SCG
Measurements
Five vital signs, one minute
Each estimate comes from a specific signal and carries its own limitations. This page sets out what VitalVein measures, what it derives, and how much weight each result deserves.
The variation between consecutive beat intervals, reported as RMSSD and SDNN. A window onto autonomic balance — it responds to sleep, stress, illness, and training load, which makes it most informative when tracked against your own baseline rather than a population norm.
Source: finger PPG · rPPGEstimated from the ratio of pulsatile to steady absorption across colour channels. A dedicated oximeter uses two precisely known wavelengths; a phone camera has three broad, overlapping ones, so this estimate is more sensitive to calibration, ambient light, and skin tone.
Source: finger PPGDerived from pulse transit time — the delay between the heartbeat at the chest and the pulse wave arriving at the fingertip — combined with waveform morphology. Requires the optional chest capture, and is best used to watch for change over time rather than as an absolute figure.
Source: finger PPG + chest SCGEstimated from colour-channel absorption characteristics in the fingertip signal, aimed at flagging possible anaemia for follow-up. The hardest of the five and the most exploratory — useful as a screening prompt, never as a substitute for a blood test.
Source: finger PPGNot a vital sign in itself, but the quantity the blood pressure estimate rests on, and an indicator of arterial stiffness in its own right. Reported alongside BP whenever a chest capture is included in the session.
Source: finger PPG + chest SCG
Signal matrix
What each capture mode gives you
The finger capture alone covers four of the five. Adding the chest capture unlocks transit-time-based blood pressure; the facial capture trades some precision for requiring no contact at all.
| Measurement | Finger PPG | Remote PPG | Chest SCG | Typical capture |
|---|---|---|---|---|
| Heart rate | Primary | Yes | Yes | 30–60 s |
| HRV | Primary | Reduced precision | Supporting | 60 s |
| SpO2 | Primary | — | — | 60 s |
| Blood pressure | Required | — | Required | 60 s, simultaneous |
| Haemoglobin | Primary | — | — | 60 s |
Confidence
A number without a confidence score is a guess in a costume
Every VitalVein estimate is reported with a quality grade, and a poor capture is labelled as one rather than dressed up as a result.
The grade combines three things: how clean the raw waveform was, how consistent the beat-to-beat intervals were across the capture, and how far the extracted features sit from the range the estimator was calibrated over. A reading taken with a cold finger, through movement, in poor light will say so.
This matters more for screening than for consumer tracking. A false reassurance is worse than no reading at all, because it stops someone from seeking the check they needed.
Signal qualityPerfusion, noise floor, saturation of the sensor
Beat consistencyAre successive intervals physiologically plausible?
Capture durationShort captures cannot support HRV at all
Calibration distanceHow far inputs sit from validated ranges
Grades are surfaced next to the number, not buried in a details screen.
Validation
Where we are honest about the state of the evidence
Estimating vital signs from consumer optics is an active research area, and the five measurements above are not equally mature. Heart rate from contact PPG is well established in the literature. Blood pressure from pulse transit time and haemoglobin from optical absorption are promising but far more sensitive to calibration, individual physiology, and capture conditions.
VitalVein is being validated against reference equipment — clinical pulse oximetry, a validated oscillometric cuff, and laboratory haemoglobin assays — across a range of skin tones, ages, and device models. That work is ongoing, and skin tone in particular is treated as a first-class variable rather than an afterthought, because optical methods have a documented history of performing worse on darker skin when it is not.
Until that evidence is in hand and published, treat every number the app produces as a prompt to investigate rather than a conclusion to act on.
VitalVein is a wellness and screening tool, not a medical device. It is not cleared or approved by any regulator, and it must not be used to diagnose, treat, or make decisions about a medical condition — including decisions about medication. If a reading concerns you, or if symptoms are present regardless of what the app says, seek care from a qualified clinician.
Help us validate it properly
We are looking for clinics, community health programmes, and research groups willing to run VitalVein alongside reference equipment.