Variables of the spontaneous breathing pattern. Calves were either challenged with 108 inclusion forming units of C. psittaci or sham inoculated (controls). RR, respiratory rate; Vmin, volume of minute ventilation; Vt, tidal volume. Data are expressed as Box-and-Whisker Plots representing lower and upper quartile values (box) with median and mean (+). Whiskers extend from each end of the box to the most extreme values within 1.5 interquartile ranges. Outliers are data beyond the ends of the whiskers. In calves inoculated with C. psittaci, # indicates a significant difference at the given time point compared to controls (Mann-Whitney-Wilcoxon W test) at a probability level of p ≤ 0.01. Arrows (↑ or ↓) indicate significant increases or decreases, respectively, at the given time point compared to data ante inoculationem (a.i.) within the group (ANOVA, post hoc test: Bonferroni's multiple comparison procedure) at a probability level of p ≤ 0.05 (grey) or p ≤ 0.01 (black).