Clinical Application of Pulmonary Function Testing in Horses

Pulmonary function tests are emerging as an essential tool in equine referral practice. Indications include intermittent cough, excess mucus, abnormal breathing pattern, presence of wheezes or crackles on auscultation, or exercise intolerance. Since non-infectious airway obstruction and inflammation are the most common problems encountered in the lower respiratory tract of horses, tests are largely aimed at describing the severity, anatomical pattern, stability (reactivity) and reversibility of airway constriction. A comprehensive approach often requires multiple tests, since the information gained from each method is different. Four important tests of mechanical function are discussed in this chapter. They include (1) conventional lung mechanics using pleural pressure measurements, (2) forced oscillatory mechanics, (3) flowmetrics ("boxless" plethysmography) and (4) forced expiratory maneuvers. The implementation of bronchoprovocation to assess airway reactivity is reviewed. The flowmetric test can be employed in the field, while the other methods are suitable for specialists and researchers in the pulmonary laboratory. The importance of pulmonary function testing to the early diagnosis of lower airway obstruction is emphasized, since this is the widest application.