Fig 3. An inspired CO₂ of 3.2% causes isocapnic hypoxemia in mice concurrently exposed to 7.0% O₂.

A scatter plot (A) showing arterial CO₂ tensions (P_aCO₂; y-axis) in mice exposed to 7.0% O₂ and a range of inspired CO₂ levels (% CO₂; x-axis) was fit using linear regression (solid line, equation displayed on the graph). The dotted lines on the graph indicate the average baseline P_aCO₂ (horizontal) measured during exposure to room air, and the estimated inspired CO₂ required to maintain this P_aCO₂ level (vertical) during exposure to 7% O₂ based on the linear regression. Arterial blood samples from WT mice exposed to 7.0% O₂, 3.2% CO₂, balance N₂, were analyzed to assess P_aO₂ (B), P_aCO₂ (C), and pH_a (D). (E) Representative whole-body plethysmography traces from a WT mouse show the ventilatory response to 7.0% O₂, 3.2% CO₂, balance N₂. Values are individual measurements (A) or means ± SE (B-D); n = 5–6 animals per group (B-D). *P < 0.05 vs. baseline (paired, two-tailed Student’s t-test).