Figure 17-35 Airway resistance is an increasing hyperbolic function of decreasing lung volume. Functional residual capacity (FRC) decreases when changing from the upright to the supine position. (Redrawn with modification from Lumb AB: Respiratory system resistance. In Lumb AB [ed]: Nunn's Applied Respiratory Physiology, 5th ed. London, Butterworths, 2000, p 67.)