Figure 3. A representative example of the nasal pressure (Pn) vs. inspiratory flow (VImax) relationship in one subject. Nasal resistance (Rua) was defined as the reciprocal of the slope of the relationship between VImax and Pn, and Pcrit as the x intercept of the regression line as illustrated. In the mouth-closed condition (open circle), Pcrit was –9.4 cm H₂O and Rua was 15.8 cm H₂O/L/sec. In the moderate mouth-open condition (black circle), Pcrit was –7.0 cm H₂O and Rua was 17.0 cm H₂O/L/sec, while in the maximal mouth-open condition (open square), Pcrit was –4.0 cm H₂O and Rua was 34.6 cm H₂O/L/sec.