Fig. 4. Plot of the systematic error in the partial rebreathing measurements of PBF as a function of simulated true PBF. Line with open square = no recirculation model, differential Fick equation evaluated using Paco²and alveolar carbon dioxide flux with 50 s rebreathing time; line with open circle = no recirculation model, differential Fick equation evaluated using Paco²and alveolar carbon dioxide flux with 300 s rebreathing time.