Figure 3.

Relationship between maximal inspiratory flow (V_Imax ± standard deviation) and upstream nasal pressure (P_US) during NREM sleep. Inspiratory flow limitation in a non-apneic normal individual was induced by sequentially lowering P_US. Under these conditions, V_Imax is linearly dependent on P_US. The reciprocal of the line slope represents the upstream resistance (R_US). The critical pressure (P_CRIT) is the zero-flow intercept, −21 cmH₂O (indicated by arrow), indicating total upper airway occlusion. Adapted from Schwartz et al. 1988 (27).