Website Last Updated on March 12, 2026
When you love someone, you do everything possible to protect them. Nine years on, that has not changed. As our father's #ALS caregivers, we noticed a troubling discrepancy — his ventilator was displaying normal values while he kept telling us something was wrong. So we investigated.
The machine was lying.
A single exhalation valve substitution was silently skewing his tidal volume readings by an average of 84 mL per breath — with no alarm, no alert, and no visible indication on the display.
We did some maths and derived this from first principles. Image analysis to digitize the manufacturer's valve curve, power-law curve fitting, analytical integration, bootstrap uncertainty analysis. It confirmed what we already knew from watching him breathe.
We also propose a novel bedside correction heuristic — Pressure-Anchored Tidal Volume Correction (PAVC) — for fully passive patients on closed-loop ventilation modes (iVAPS, AVAPS, VAT etc), requiring no additional equipment and no bench measurement.
We have documented our findings in a detailed case report, intended for clinicians, respiratory therapists, and families caring for ventilator-dependent patients at home.
If it happened to our father, it is happening to others.
A pdf version of this report can be downloaded from here.