Figure 17-24 For any given O₂ concentration in inspired gas, the relationship between alveolar ventilation and PAO₂ is hyperbolic. As the inspired O₂ concentration is increased, the amount that alveolar ventilation must decrease to produce hypoxemia is greatly increased. BTPS, body temperature, ambient pressure, saturated. (Redrawn from Lumb AB: Respiratory system resistance: Measurement of closing capacity. In Lumb AB [ed]: Nunn's Applied Respiratory Physiology, 5th ed. London, Butterworths, 2000, p 79.)