Fig. 1

Ventilatory responses to hypoxic gas exposure (7% O₂ + 3% CO₂ in N₂) in wild-type (WT) mice (a–d) and histamine H1 receptor-knockout (H1RKO) mice (e–h). Respiratory frequency (Rf, a, e), tidal volume (VT, b, f), minute ventilation (\( \dot{V}_{\text{E}} \), c, g), and mean inspiratory flow (d, h). Open symbols indicate values during the fed state, and closed symbols indicate values during the fasted state. Statistical results of three-way ANOVA are indicated in (e–h). Significant differences between fed and fasted states were analyzed as mean values during a 15- to 20-min period (Student’s t test, vs fed, *P < 0.05)