The 5-Minute Method
A standardized measurement protocol for recording and interpreting short-term heart rate variability.
Rationale for five-minute HRV
Twenty-four-hour Holter HRV captures circadian variation and remains necessary for several established prognostic applications. However, it is resource-intensive and often impractical for routine autonomic assessment. A standardized five-minute recording provides a pragmatic method for measuring RMSSD, short-term SDNN, pNN50, HF power, LF power and the LF/HF spectral distribution.
ECG and RR-interval acquisition
ECG directly records cardiac electrical activity and identifies the R peak of the QRS complex, enabling precise RR-interval measurement. ECG is the reference method for five-minute HRV analysis.
- Direct detection of cardiac electrical activity
- Precise RR-interval measurement
- Rhythm assessment and identification of ectopic beats
- Reliable artefact review
- Appropriate time resolution
Validated ECG chest straps may also provide accurate RR intervals when the recording can be reviewed and artefacts are handled appropriately. Photoplethysmography and wearable measurements may be useful for screening or exploratory applications, but require attention to motion, pulse-transit effects, device algorithms and artefact correction.
Direct measurement with Polar H10
5HRV can receive beat-to-beat RR intervals directly from a Polar H10 chest strap using Bluetooth. The user first rests quietly for five minutes in the supine position. The application then records slightly longer than five minutes to ensure that a complete 300-second analysis window and sufficient boundary data are available.
The received RR intervals are checked for implausible values, missed or additional beat detections, abrupt interval changes and substantial signal loss. Recordings with poor signal quality are rejected. Accepted recordings are corrected where appropriate before the HRV parameters are calculated.
Conversion from RR to NN intervals
HRV analysis begins with the detection of each heart beat from the ECG signal. The time between consecutive R peaks is the RR interval. However, not every RR interval represents normal sinus-node activation. Ectopic beats, atrial or ventricular premature complexes, and artefact from motion or electrode disturbance produce spurious intervals that must be identified and handled.
RR interval: the time between any two consecutive R peaks. NN interval: an RR interval that follows a normal sinus beat, retained after exclusion or correction of ectopic beats, arrhythmia-related intervals and artefacts. All standard HRV metrics—RMSSD, SDNN, pNN50, HF and LF power—are computed from the NN-interval time series.
Artefact and ectopic-beat handling
Artefact and ectopic beats must be identified before HRV computation. Common approaches include exclusion of non-sinus beats, interpolation of corrected intervals, and threshold-based artefact rejection. The method and threshold applied should be documented because artefact handling can significantly influence HRV values, particularly RMSSD and pNN50.
Standardized recording protocol
| Element | Standardized condition |
|---|---|
| Position | Supine, arms relaxed alongside the body, comfortable and motionless |
| Rest | Five minutes of quiet supine rest before direct Polar H10 measurement |
| Breathing | Quiet spontaneous breathing; avoid deliberate deep breathing unless part of research protocol |
| Duration | An exact 300-second analysis window. Direct Polar measurements collect a short additional margin to ensure full spectral interpolation support |
| Sampling rate | Raw ECG: preferably at least 250 Hz. Direct Polar H10 mode receives beat-to-beat RR intervals through the Bluetooth Heart Rate Service |
| Rhythm | Sinus rhythm required; do not apply standard HRV interpretation to atrial fibrillation, atrial flutter or paced ventricular rhythms |
| Quality control | Review ectopic beats; correct or exclude artefacts |
Time-domain analysis
Time-domain measures quantify the magnitude of beat-to-beat variation directly from the NN-interval time series. The principal parameters are RMSSD, SDNN and pNN50. RMSSD is the preferred primary parameter for short-term five-minute HRV assessment because it is strongly influenced by vagal modulation and is relatively robust to recording duration.
Frequency-domain analysis
After resampling and detrending of the NN-interval time series, the power spectrum is computed using fast Fourier transformation or autoregressive modelling. The HF band (0.15–0.40 Hz) reflects respiratory-frequency variability influenced by vagal modulation. The LF band (0.04–0.15 Hz) contains mixed autonomic and baroreflex-related influences. The LF/HF ratio describes the relative distribution of power between the two bands.
Very-low-frequency power (VLF, 0.003–0.04 Hz) is sometimes reported by analysis software, but a single five-minute recording contains too few slow oscillatory cycles for robust characterization. VLF is therefore not included in the practical 5HRV parameter set.
Reproducibility and reporting
Comparisons between recordings require consistent position, time of day, rest period, breathing conditions, device, analysis software and artefact-correction method. The 5HRV calculator applies the following six-measurement set: RMSSD, SDNN, pNN50, HF power, LF power and LF/HF ratio.
Practical application
Once a standardized recording has been obtained, the metrics can be entered into the calculator for age- and sex-stratified interpretation.
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