Fig 1. Curve of change in impedance (ΔZ) over the respiratory cycle of a representative horse 24 hours before anaesthesia (baseline) and one hour after recovering from anaesthesia.

Breath holding is defined as the percentage of the total breath length (t_breath) in which impedance remained higher than 50% (t_above50) of the maximum change in impedance during inspiration. Inspiratory time = tinsp; time to reach 50% of maximum impedance change during inspiration = tto50.