Airway pressure (Primus)¶

Airway pressure from the Primus anaesthesia machine at 62.5 Hz.

Stub

Imported from the time-source table; the full page is still to be written.


Name in the dataset	`Primus/AWP`
Type	waveform
Device	Primus anaesthesia machine
Stamped by	Recorder PC clock
Spaced by	Primus clock
Rate	62.5 Hz
Unit	hPa

Measurement space¶

Time side (after breath matching): the true time lies between -0.203 s and -0.055 s from the stamp: the delay range plus the interval one value describes.

Time¶

From UTC to the stored time stamp¶

Derived from this signal's timing table; a written chain is still to come.

The clock path first (UTC to the clock that stamps or spaces the samples), then the signal's own path to its stored time. Each bar: the time shift or error the step introduces (pale) and what is left after the atlas's correction (solid), on a log scale; dashed when estimated or assumed.

UTC

The reference every chain starts from.

Recorder PC clock

sync assumed 3 ms – 900 ms · clock link, parameter

Windows time synchronisation to the hospital's time server every 8–24 h (assumed), drifting a few ppm in between. Not observable in the release: dates are shifted to 2100. No step of 0.5 s or more was found.

Primus clock

clock measured 600 ms – 5.1 s → 55 ms – 187 ms after correction

Delay or clock offset to the stamp; removed by the breath matching to SNUADC.

Stored time stamp

window measured 16 ms

The width of the interval one value or sample stands for.

Timing¶

Against the working reference. Delay: from the end of the interval a value describes to its stamp. Interval: how wide that interval is.

Form	Delay	Interval	Clock domain	Status	Evidence
after breath matching (default)	55 ms – 187 ms	16 ms	SNUADC stamp-model time (the working reference)	measured	leave-one-out error 55 ms median, p90 187 ms, a line per stretch between AWP pauses (1,067 recordings with CVP, tools/primus_sync_accuracy.py); 74 ms with one slope per recording
raw stamps	600 ms – 5.1 s	16 ms	Primus clock	measured	offset p10-p90 0.6-5.1 s, median 1.8 s (1,061 recordings, examples/ppv-by-breath), incl. AWP-CVP physiology; drifts +104 ppm against the PC between AWP pauses

Combine it with other signals in the synchronisation planner.

Value¶

Its value side is still to be described.

Observations¶

Observation	Status	Summary
Eight recordings store whole messages twice	established	In 8 recordings 15–48% of the waveform records are byte-for-byte copies of the record before them, with the same timestamp: case 15, case 364, case 1946, case 3865, case 4857, case 5414, case 5595 and case 5619. SNUADC, Primus and BIS are affected equally, so the recorder, not a device, wrote them twice.
Primus waveform gains are wrong in every recording, for CO₂ or for AWP	established	Recordings store the Primus waveforms with one of three sets of scale factors. Checked against the Primus's own ETCO₂ and PIP numerics in all 6,388 recordings, CO₂ fits only 0.075 mmHg per code and AWP only 0.1 mbar per code with offset −20, so most recordings overstate CO₂ by a third, and the others overstate AWP by about 3% (950 recordings) or understate it about fourfold (26).
The Primus AWP stops for about 21 s every 7,230 s	established	In 5,502 recordings the Primus airway-pressure waveform has gaps of 19–23.5 s (whole messages of 0.48 s, mostly 21.12 s) that recur every 7,230 s, the Primus's correction interval; a clock correction follows about 21.6 s after. The CO₂ waveform carries on through 90% of them. The 21 s of AWP are lost, not merely re-stamped.

Studies¶

Study	Date	Status	Summary
The heartbeat in the Primus airway signals	2026-10-19	current	A pilot in 30 recordings for a heartbeat-locked route from the Primus to the SNUADC. Airway pressure shows the heartbeat in 9% of windows only. CO₂ shows a heartbeat-locked trace in 60% of windows, tight to 20 ms, but its lag does not follow the Primus drift, so it cannot time the Primus. Closed as a clock route.
Gaps and unbroken segments in every waveform	2026-10-19	draft	Every gap and every unbroken segment in the 6,388 recordings, per waveform. The curves are not smooth: a cliff at about 18 s in every device marks the recorder's pauses, SNUADC segments stop at 5 hours, Primus segments at about 2.0 hours and BIS segments at about 2.3 hours (each device's correction cycle), and BIS's short gaps grow with the time since the last one (clock resynchronisations, not lost data).
When each device's clock is corrected, in every recording	2026-10-19	draft	From the steps between records in all 6,388 recordings: the BIS is corrected every 8,192 s and the Primus every 7,230 s, on their own timers (the first correction comes at any time after the device starts); the SNUADC is reset when 0.49 s of drift has built up. With the full rerun of the correction fit, it gives each device's drift against the recorder PC in 4,728 BIS and 2,728 SNUADC recordings, and shows that the Primus's 20–23 s AWP pauses belong to its correction cycle. Every rate here is relative to the recorder PC, whose own clock drifts and is corrected.
The Primus stamp step at each airway-pressure pause	2026-10-19	current	Measured directly at 2,491 pauses in 1,021 recordings: where CO₂ carries on through the AWP pause (74%), the Primus stamps barely step (median −1 ms, p10–p90 −164 to +187 ms, close to the no-pause controls); where CO₂ stops too (26%), they step by up to seconds. No step undoes the drift built up since the last pause.
Message sizes and the steps between records	2026-10-19	draft	Every record in every waveform: SNUADC writes messages of 100 samples (0.2 s), Primus 30 (0.48 s), BIS 16 (0.125 s), CardioQ no fixed size. Backward steps outnumber gaps by about a hundred to one and come from a few recordings with duplicated or interleaved records. Primus gaps are whole lost messages; most SNUADC and BIS gaps are not.
What each break in the stamps is	2026-10-19	draft	Every step between waveform records in the release, sorted by mechanism: written twice, a SNUADC clock reset, interleaved streams, a pause shared by every device, whole messages, less than a message, or a fraction of a message beyond whole ones. A continuity test with controls shows which classes lose data: shared pauses and most longer SNUADC gaps do; steps under one message, and SNUADC's lone one-message steps, mostly do not.
Value resolution of every signal	2026-10-19	draft	How finely every waveform and numeric track in the release records its values. The SNUADC waveforms are 10-bit codes, though VitalRecorder's documentation describes the SNUADC as 12-bit; Primus waveforms use about 10 bits of 12; BIS EEG is a 16-bit grid of 0.05 µV. Numerics are 32-bit floats on decimal grids of 1, 0.1, 0.01 or 0.001, one per track; settings sit on coarser grids of 10 or 100.
How often each device is corrected	2026-10-17	current	The devices re-synchronise in different ways: SNUADC when its drift reaches about half a second, BIS on a fixed 8,192 s timer, and the Primus by small steps about every two hours that do not keep up with its drift (+104 ppm, measured later by breath matching).
Closing loops in the timing graph	2026-10-13	current	Where two independent routes reach the same clock, the offsets around the loop must sum to zero. Three measured loops close within their noise; the BIS loop closes up to a constant latency; the proposed EMR loop is not a loop at all.
How the monitors compute their numbers	2026-10-12	current	Recomputing each monitor numeric from its own waveform finds a short, simple algorithm for every one (a median, an exponential average or a time mean over 3–30 s) and a delay of 2–9 s behind the newest data it uses. No value is stamped before its data exist.
The Primus ventilator against SNUADC, by breaths	2026-10-12	open	Each breath shows in the Primus airway pressure and, through the chest, in SNUADC's central venous pressure. Tracking that lag puts the Primus on the SNUADC timeline to about 55 ms over the whole release, with a line per stretch between its AWP pauses (49 ms in the pilot). At scale it measures the Primus drifting a median +104 ppm against the recorder PC between its AWP pauses, with steps at the pauses that do not reset it.

Worked examples¶

Example	Side	Status	Summary
Pulse pressure variation gated by ventilator breaths	time	draft	Pulse pressure variation per ventilator breath, in 3,448 recordings: the ventilator's clock sits a median 1.8 s off the arterial line's, which moves half of all breaths' values by a point or more and scatters where in the breath the pulse pressure peaks; a recording's median PPV hardly changes.

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