The ECG→PPG delay is a sawtooth¶
Inside the oximeter the PPG content creeps 18–52 ppm against its 30 Hz frames; every 11–31 minutes a frame repeats and the delay jumps up by 33 ms. The rate is fixed per recording setup.
| Status | established: shown on many cases, with a control. |
| Clocks | Pulse oximeter frame clock |
| Devices | Solar8000 monitor, SNUADC |
| Variables | Plethysmogram (SNUADC) |
What it means¶
Uncorrected, pulse arrival time from VitalDB carries a 0–33 ms sawtooth (about 9.5 ms RMS) on top of its hardware delay; trends in PAT over tens of minutes can be the sawtooth, not physiology.
What is done about it¶
physiosync removes it tooth by tooth; labels give each tooth's confidence tier.
Evidence¶
| Study | Date | Status | Summary |
|---|---|---|---|
| Arterial pressure as a check on the PPG correction | 2026-10-11 | current | Arterial pressure is sampled by the same converter but has no frame and no sawtooth, so every PPG slip leaves ECG→ABP unchanged. Against it, detected slips are 97–100% real and tier A leaves about 2 ms of drift mid-tooth. |
| The PPG sawtooth and its correction | 2026-10-10 | current | The ECG→PPG delay creeps at 18–52 ppm and jumps up by one 33.3 ms frame at each slip, every 11–31 minutes. A tooth-by-tooth model removes it; where the correction is confident it is essentially exact on injected test data. |