Measuring Gas Exchange with Step Changes in Inspired Oxygen: An Analysis of the Assumption of Oxygen Steady State

The ALPE system provides model estimates of pulmonary shunt, and V/Q mismatch within 10 to 15 minutes, using 3 to 5 steps of FIO2 and assuming whole body oxygen steady state at each step. In patients suffering from COPD, arterial oxygenation equilibrium can take 30 minutes. This paper investigates whether data suitable for ALPE can be obtained at non-steady state conditions. A calibration algorithm is proposed and it is shown in COPD patients that breath-by-breath data can be successfully calibrated for ALPE, potentially omitting the need for oxygen steady state and allowing the system to be applied in COPD.