Obstructed from induction. Both arms are physically identical until 7:10 — the only difference is what sits in the pharynx when each inrush happens. In the lungs, bright is oxygen, dull is nitrogen and CO₂, the dark gap is the vacuum obstruction creates, and the bases go violet as they collapse. The head turns blue on deoxygenated haemoglobin rather than saturation, so an anaemic patient never looks as bad as they are. Move the sliders and the whole simulation re-runs. Collapsibility defaults to the calibrated median; the patients who desaturate despite good tracheal oxygen sit near the top of its range.
Modelled, not measured. Saturation carries a pulse oximeter delay. There is no end-tidal CO₂ because there is no ventilation; the CO₂ and pH shown are arterial model values you would not have at the bedside. Each arm stops where the model's fixed cardiac output stops being defensible. Closing capacity and the FRC–BMI relation are parameterised, not fitted to source data.
© 2026 A. M. B. Heard. All rights reserved. Unpublished research model — not a medical device, not for patient care. Reproduction or use in any publication requires the author's written permission.