Veterinary research communications
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The effects of histamine and methacholine aerosols and of a fixed inspiratory resistance on tidal breathing flow-volume loops (TBFVL) were investigated using 18 unsedated, standing, healthy thoroughbred horses. The data were first analysed using traditional flow-volume loop indices and then reduced using standardized factor scoring coefficients obtained in a previous study in this laboratory using similar experimental techniques. On the basis of resting TBFVL analysis, the degree of pulmonary dysfunction caused by inhalation of histamine and methacholine aerosols with concentrations of 10 and 2 mg/ml, respectively, was similar. ⋯ The close agreement between the factor scores obtained under controlled conditions in this study and in a previous study in this laboratory confirms that the factor analysis used for both of these studies provides an adequate means of reducing TBFVL data obtained from thoroughbred horses. The large intra- and inter-individual variation observed both with the indices of TBFVL and with the factor scores limits the potential of these variables for detecting individual animals with obstructive airway disease. Re-evaluation of these indices under the stress of exercise may reduce the variability observed in these data and may increase the magnitude of differences between different animals, providing a means of detecting individual animals with subclinical obstructive airway conditions.