Respiratory impedance during expiration. Complex respiratory impedance during expiration is expressed as resistance (R) and reactance (X). d a.i., days after inoculation; dpi, days post inoculation; Rrs ex, respiratory resistance during expiration; Xrs ex, respiratory reactance during expiration. Open symbols: control calves. Filled symbols: calves inoculated with C. psittaci. Data are expressed as means per group. Significant differences between groups are indicated by *(p < 0.05), **(p < 0.01), or ***(p < 0.001) [unpaired t-test]. For reasons of visual clarity, data are expressed as means per group only. Numeric data presenting standard deviation and results of within-group comparison in addition are given in Table 2.