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Figure 1. Graph shows PaO₂/FiO₂ level at six time points of the protocol. In prone group, PaO₂/FiO₂ at time point of prone positioning for 1 hour to approximately time of return to supine positioning for 1 hour exceeded baseline value. PaO₂/FiO₂ in prone group was significantly higher than that of supine group at time point of prone positioning for 3 hours. _* indicates P value less than .05 in comparison with baseline values. indicates P value less than .05 in comparison with supine group at same time point. Error bars indicate standard deviations.