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

Abstract

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 air-way 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 (Rrs) and respiratory tract system reactance Xrs) at 5 to 20 Hz by use of IOS and for total pulmonary resistance (RL) and dynamic lung compliance (Cdyn, by use of CRT. Results - Bronchoconstriction resulted in an increase in Rrs at 5 Hz (R5Hz) and a decrease in Xrs at all frequencies. Most sensitive parameters were Xrs at 5 Hz (X5Hz), R5Hz (R5Hz: R10Hz ratio; RL and the provocation concentration of methacholine resulting in a 35% decrease in dynamic compliance (PC35Cdyn) were significantly less sensitive than these IOS parameters. The TC2SD for Xrs at 5 and 10 Hz was significantly lower in group-B horses, compared with group-A horses. The lowest TC2SD was obtained for X5Hz, in group-B horses and R5Hz, 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 maybe useful in assessing subclinical changes in horses.