A heartbeat-locked trace in the CO₂ waveform that ignores the Primus clock¶
Averaged on the ECG's R peaks, the Primus CO₂ waveform shows a heartbeat-locked signal in 60% of 10-minute windows (30-recording pilot), tight to about 20 ms. Unlike the breath, its lag does not drift with the Primus clock: it stays fixed on the SNUADC timeline.
| Status | open: seen, not explained. |
| Clocks | Primus clock, SNUADC sample clock |
| Devices | Primus anaesthesia machine |
| Variables | Capnogram (Primus) |
What it means¶
The trace cannot be used to time the Primus. An analysis that looks for cardiac effects in CO₂ should expect a heartbeat-locked component whose timing does not follow the Primus's other data.
What is done about it¶
None yet; flagged for anyone using CO₂ at beat resolution.
Detail¶
A cardiogenic oscillation in expired CO₂ is physiological, but it would arrive on the Primus's stamps and drift with them. A trace fixed to the SNUADC timeline suggests something timed outside the Primus clock: electrical crosstalk from the ECG, or a component of the signal that is re-timed at the recorder. Neither has been tested.
Evidence¶
| 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. |