Estimation of respiratory control loop gain from pseudorandom forcing of inhaled CO2

The authors have developed a method for deriving estimates of respiratory control loop gain (LG) from the ventilatory response to inhaled CO₂, randomly modulated between 0 and 5%. The corresponding changes in alveolar (and thus, arterial) CO₂ results from two components: (1) the direct effect of breath to breath changes in inhaled CO₂, and (2) the chemoreflex-mediated changes in ventilation. LG is estimated by computationally delineating the first component from the overall ventilatory response. The method was tested against simulated and experimental data. In both cases, the authors found strong correlations between their predictions and LG estimates derived by other methods. The authors conclude that their method, which uses data from a single test procedure lasting <10 minutes, represent a simple yet improved means of quantifying respiratory control stability