Summary
The waveform pipeline is vulnerable to two related failure modes:
- A missed systolic boundary causes two cardiac cycles to be treated as one long beat.
- Motion-related spikes or dips can become the global maximum, minimum, or derivative extremum of a beat.
This is not limited to heart-rate reporting. It can propagate into per-beat waveform averaging, timing endpoints, RI/PI, and most waveform-shape metrics.
Current behavior
Systoles are detected from peaks in the arterial-velocity derivative using a global 95th-percentile height threshold. A weaker but valid upstroke can be missed. The detected indexes are then used directly as beat boundaries and the intervals between them are accepted without period or morphology validation.
A missed boundary therefore produces a double-length beat containing two physiological cycles. That malformed beat is resampled and passed to the metric calculator as a valid single beat.
Several metrics also use unconstrained global extrema or derivative extrema within the beat:
vmax = nanmax(v), vmin = nanmin(v)t_max/T = nanargmax(v) / nt_min/T = nanargmin(v) / n- Rise/fall slopes and their timing use the global maximum/minimum of
dv/dt
A short motion dip can therefore be interpreted as the physiological trough, while a spike or rebound can be interpreted as the systolic maximum or steepest slope.
Affected outputs
Directly affected by missed beat boundaries
- Heart rate and beat-period counts
- Average-cycle construction
- Arterial time from peak to descent and venous time from minimum to peak
- Phase and distribution metrics:
MuTOverT, SigmaTOverT, GammaT, T10/T25/T50/T75/T90OverT, QtWidth, and QtSkew
- Cumulative-distance metrics:
DeltaDTI, D10/D25/D50/D75/D90OverD, QdWidth, QdSkew, RVTI, and SFVTI
- Extrema and kinetics metrics:
TMaxOverT, TMinOverT, SRise, SFall, TRiseOverT, TFallOverT, ESlope, and VEndOverVbar
- Spectral metrics, especially
ELFOverEHF, because the true cardiac fundamental moves from the first to the second harmonic of a double-cycle interval
Some amplitude-distribution metrics such as RI, PI, CF, W50OverT, W80OverT, NEffOverT, and NtOverT may be approximately invariant when the malformed beat contains two identical, artifact-free cycles. They are still affected when the two cycles differ or contain motion.
Particularly sensitive to motion-driven extrema
- Full-trace velocity maximum and minimum
- Waveform
RI and PI
W50OverT, W80OverT, and CFTMaxOverT and especially TMinOverTSRise, SFall, TRiseOverT, TFallOverT, and ESlope- Peak-to-trough timing endpoints
ELFOverEHF and EtaH through added broadband energy
Integral and cumulative metrics are generally less sensitive to a single-sample artifact, but remain vulnerable to multi-sample motion disturbances and incorrect beat boundaries.
Summary
The waveform pipeline is vulnerable to two related failure modes:
This is not limited to heart-rate reporting. It can propagate into per-beat waveform averaging, timing endpoints, RI/PI, and most waveform-shape metrics.
Current behavior
Systoles are detected from peaks in the arterial-velocity derivative using a global 95th-percentile height threshold. A weaker but valid upstroke can be missed. The detected indexes are then used directly as beat boundaries and the intervals between them are accepted without period or morphology validation.
A missed boundary therefore produces a double-length beat containing two physiological cycles. That malformed beat is resampled and passed to the metric calculator as a valid single beat.
Several metrics also use unconstrained global extrema or derivative extrema within the beat:
vmax = nanmax(v),vmin = nanmin(v)t_max/T = nanargmax(v) / nt_min/T = nanargmin(v) / ndv/dtA short motion dip can therefore be interpreted as the physiological trough, while a spike or rebound can be interpreted as the systolic maximum or steepest slope.
Affected outputs
Directly affected by missed beat boundaries
MuTOverT,SigmaTOverT,GammaT,T10/T25/T50/T75/T90OverT,QtWidth, andQtSkewDeltaDTI,D10/D25/D50/D75/D90OverD,QdWidth,QdSkew,RVTI, andSFVTITMaxOverT,TMinOverT,SRise,SFall,TRiseOverT,TFallOverT,ESlope, andVEndOverVbarELFOverEHF, because the true cardiac fundamental moves from the first to the second harmonic of a double-cycle intervalSome amplitude-distribution metrics such as
RI,PI,CF,W50OverT,W80OverT,NEffOverT, andNtOverTmay be approximately invariant when the malformed beat contains two identical, artifact-free cycles. They are still affected when the two cycles differ or contain motion.Particularly sensitive to motion-driven extrema
RIandPIW50OverT,W80OverT, andCFTMaxOverTand especiallyTMinOverTSRise,SFall,TRiseOverT,TFallOverT, andESlopeELFOverEHFandEtaHthrough added broadband energyIntegral and cumulative metrics are generally less sensitive to a single-sample artifact, but remain vulnerable to multi-sample motion disturbances and incorrect beat boundaries.