Respiratory inductance plethysmographic (RIP) and pneumotachographic (Pn) flows were compared dynamically in horses with bronchoconstriction. On a breath-by-breath basis, RIP was normalized to inspiratory volume from Pn, and peak [peak of subtracted final exhalation waveform (SFE(max))] and selected area [integral of subtracted final waveform during first 25% of exhaled volume (SFE(int))] differences between RIP and Pn flows during early expiration were measured in three settings: 1) healthy horses (n = 8) undergoing histamine bronchoprovocation; 2) horses with naturally occurring lower airway obstruction (AO) (n = 7); and 3) healthy horses (n = 6) given lobeline. HCl to induce hyperpnea. In setting 1, histamine challenge induced a dose-dependent increase in SFE(max) and SFE(int) differences. A test index of airway reactivity (interpolated histamine dose that increased SFE(max) by 35%) closely correlated (r(s) = 0.93, P = 0.001) with a conventional index (histamine dose that induced a 35% decrease in dynamic compliance). In setting 2, in horses with AO, SFE(max) and SFE(int) were markedly elevated, and their absolute values correlated significantly (P < 0.005) with pulmonary resistance and the maximum change in transpulmonary pressure. The effects of bronchodilator treatment on the SFE(max) and SFE(int) were also highly significant (P < 0.0001). In setting 3, hyperpnea, but not tachypnea, caused significant (P < 0.01) increases in SFE(max) but not in SFE(int). In conclusion, dynamic comparisons between RIP and Pn provide a defensible method for quantifying AO during tidal breathing, without the need for invasive instrumentation.

Background: The effects of long-term environmental management on airway obstruction and inflammation in horses with recurrent airway obstruction (RAO) are unknown. Hypothesis: Horses with RAO maintained in low-dust environments have persistent airway obstruction and neutrophilic inflammation. Animals: Study horses were treated for RAO and then maintained in low-dust environments with no medical management. Horses were classified into 3 groups by years after diagnosis: 1 year (time 1, n 5 9), 2-3 years (time 2, n 5 7), and 5-6 years (time 3, n 5 8). The comparison groups were age-matched healthy horses. Methods: In this cross-sectional study, a clinical examination was performed, and the clinical score was calculated. Standard lung function, forced expiratory maneuvers, and the cytology of bronchoalveolar lavage fluid (BALF) were evaluated. Results: The clinical scores of the RAO horses were higher than those of the non-RAO horses at time 2 (P 5 .018). Standard lung function data were not different between the groups at any time point. The forced expiratory flow between 75-95% of exhaled vital capacity was lower in RAO horses than in non-RAO horses at all time points (P , .02), indicating persistent peripheral airway obstruction. Cytologic evaluation of BALF revealed no difference in total nucleated cell numbers or differential cell counts between RAO and non-RAO horses at any time point. Conclusions and Clinical Importance: The peripheral airway obstruction detected in horses with RAO maintained in low-dust environments likely is due to irreversible airway remodeling but is not associated with cytologic evidence of airway inflammation.

Background: The effects of long-term environmental management on airway obstruction and inflammation in horses with recurrent airway obstruction (RAO) are unknown.Hypothesis: Horses with RAO maintained in low-dust environments have persistent airway obstruction and neutrophilic inflammation.Animals: Study horses were treated for RAO and then maintained in low-dust environments with no medical management. Horses were classified into 3 groups by years after diagnosis: 1 year (time 1, n 5 9), 2-3 years (time 2, n 5 7), and 5-6 years (time 3, n 5 8). The comparison groups were age-matched healthy horses.Methods: In this cross-sectional study, a clinical examination was performed, and the clinical score was calculated. Standard lung function, forced expiratory maneuvers, and the cytology of bronchoalveolar lavage fluid (BALF) were evaluated.Results: The clinical scores of the RAO horses were higher than those of the non-RAO horses at time 2 (P 5 .018). Standard lung function data were not different between the groups at any time point. The forced expiratory flow between 75-95% of exhaled vital capacity was lower in RAO horses than in non-RAO horses at all time points (P , .02), indicating persistent peripheral airway obstruction. Cytologic evaluation of BALF revealed no difference in total nucleated cell numbers or differential cell counts between RAO and non-RAO horses at any time point.Conclusions and Clinical Importance: The peripheral airway obstruction detected in horses with RAO maintained in lowdust environments likely is due to irreversible airway remodeling but is not associated with cytologic evidence of airway inflammation.