Measurement of respiratory function by impulse oscillometry in horses

Reasons for performing study: Due to technical implementations and lack of sensitivity, pulmonary function tests are seldom used in clinical practice. Impulse oscillometry (IOS) could represent an alternative method. Objectives: To define feasibility, methodology and repeatability of IOS, a forced oscillation technique that measures respiratory resistance (R-rs) and reactance (X-rs) from 5 to 35 Hz during spontaneous breathing, in horses. Methods: Using 38 healthy horses, R-rs and X-rs reference values were defined and influence of individual biometrical parameters was investigated. In addition, IOS measurements of 6 horses showing clinical signs of heaves were compared to those of 6 healthy horses. Results: Airtightness and minimal dead space in the facemask were prerequisites to IOS testing and standardisation of head position was necessary to avoid variations in R-rs due to modified upper airway geometry. In both healthy and diseased animals, measurements were repeatable. In standard-type breeds, the influence of the horse's size on IOS parameters was negligible. An increase in R-5Hz greater than 0.10 kPa/l/sec and R-5Hz>R-10Hz, combined with negative values of X-rs between 5 and 20 Hz, was indicative of heaves crisis. Conclusions: IOS is a quick, minimally invasive and informative method for pulmonary function testing in healthy and diseased horses. Potential relevance: IOS is a promising method for routine and/or field respiratory clinical testing in the equine species.