Arterial pressure as a check on the PPG correction¶
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.
| Date | 2026-10-11 |
| Status | current |
| Methods | Clocks carried in the signal, One event, two clocks |
| Techniques | Beat matching, Null controls |
| Clocks | Pulse oximeter frame clock, SNUADC sample clock |
| Devices | SNUADC, Solar8000 monitor |
| Variables | Plethysmogram (SNUADC), Arterial pressure (SNUADC), ECG lead II (SNUADC) |
Data¶
201 cases with an arterial line; an injected-sawtooth benchmark on 28 of them (84 runs).
Method¶
At every ECG→PPG slip, the step in ECG→ABP and in ABP→PPG was measured. A real slip is a one-frame step in ABP→PPG with ECG→ABP unchanged; a tooth's creep shows as a slope in ABP→PPG that the correction should flatten.
Results¶
- ART is clean: raw ART peaks do not lock to the 33.3 ms frame (resultant 0.02, the same as the control). Its median R-to-upstroke delay of 212 ms is physiological, so any arterial path delay is small.
- At 351 ECG→PPG slips, ECG→ABP steps by a median 0.4 ms and ABP→PPG by 32.6 ms. In 3% ECG→ABP also jumps by more than 15 ms: physiological changes that had passed as slips.
- Detected slips are real in 97–100% of cases; slips inferred from ECG→PPG alone are real in only 62%.
- Tier A leaves about 2 ms of drift mid-tooth (an upper bound that includes physiology).
Discussion¶
Used in physiosync as an optional reference, arterial pressure raises confidence and rejects physiological jumps, but adds little coverage.
Observations it supports¶
| Observation | Status | Summary |
|---|---|---|
| The ECG→PPG delay is a sawtooth | established | 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. |
Worked examples¶
| Example | Side | Status | Summary |
|---|---|---|---|
| Pulse arrival time against blood pressure, before and after synchronisation | time | draft | In 3,270 recordings, PAT tracks systolic pressure only once each pulse is paired with its own beat: the hourly correlation moves from a mean of −0.04 to −0.21 (88% of recordings negative), reproducing Ruffolo et al. 2025 in a second dataset; paired naively, PAT is a heart-rate signal. |
| Pulse arrival time in two correction steps | time | draft | The time from the ECG R wave to the pulse at the finger, as stored, after the PLETH's sawtooth is removed, and after its device offset is removed, smoothed by maximum likelihood, with the arterial line as the reference. |