Fig. 1.
How does isosystem work? Maintaining isocapnia via isocapnic rebreathing system. During the hyperpneic phase when breathing room air, end-tidal Pco2 (PetCO2) was reduced below the apneic threshold when a sufficiently large ventilatory overshoot occurred in the control condition (top panel); PetCO2 was maintained above the apneic threshold and near normocapnia via selective rebreathing during the ventilatory overshoot (bottom panel). The horizontal lines indicate the fraction of end-tidal CO2 (FetCO2) traces of the two breaths with tidal volume (Vt) > two times control. In the bottom panel, the arrows indicate a sharp increase in FiCO2 after onset of inspiration in the two augmented tidal volumes.