Use of the impulse oscillometry system for testing pulmonary function during methacholine bronchoprovocation in horses

Objective-To compare sensitivity of the impulse oscillometry system (IOS) with that of the conventional reference technique (CRT; ie, esophageal balloon method) for pulmonary function testing in horses. Animals-10 horses (4 healthy; 6 with recurrent airway obstruction [heaves] in remission). Procedure-Healthy horses (group-A horses) and heaves-affected horses (group-B horses) were housed in a controlled environment. At each step of a methacholine bronchoprovocation test, threshold concentration (TC2SD; results in a 2-fold increase in SD of a value) and sensitivity index (SI) were determined for respiratory tract system resistance (R-rs) and respiratory tract system reactance (X-rs) at 5 to 20 Hz by use of IOS and for total pulmonary resistance (R-L) and dynamic lung compliance (C-dyn), by use of CRT. Results-Bronchoconstriction resulted in an increase in R-rs at 5 Hz (R-5Hz) and a decrease in X-rs at all frequencies. Most sensitive parameters were X-rs at 5 Hz (X-5Hz), B-5Hz and B-5Hz:R-10Hz ratio; R-L and the provocation concentration of methacholine resulting in a 35% decrease in dynamic compliance (PC35Cdyn) were significantly less sensitive than these CS parameters. The TC2SD for X-rs at 5 and 10 Hz was significantly lower in group-B horses, compared with group-A horses. The lowest TC2SD was obtained for X-5Hz in group-B horses and R-5Hz, in group-A horses. Conclusions and Clinical Relevance-In contrast to CRT parameters, IOS parameters were significantly more sensitive for testing pulmonary function. The IOS provides a practical and noninvasive pulmonary function test that may be useful in assessing subclinical changes in horses.