Figure 70-11 Measured versus predicted PaO₂ at increased ambient pressure. Predicted PaO₂ is calculated from room-air arterial blood gases, assuming that the arterial-alveolar PO₂ ratio (PaO₂ /PAO₂ , or a/A ratio) is a constant. Data are shown both for persons with normal lungs (a/A ratio ≥0.75) and for patients with gas exchange abnormalities (a/A ratio <0.75). It is evident that PaO₂ predicted in this way is close to the actual measured PaO₂ . (From Moon RE, Camporesi EM, Shelton DL: Prediction of arterial PO₂ during hyperbaric treatment. In Bove AA, Bachrach AJ, Greenbaum LJ Jr [eds]: Underwater and Hyperbaric Physiology IX. Proceedings of the Ninth International Symposium on Underwater and Hyperbaric Physiology. Bethesda, MD, Undersea and Hyperbaric Medical Society, 1987, p 1127.)