Airway responses to histamine aerosol in clinically normal foals

Abstract

Abstract Objective To describe the spectrum of nonspecific airway reactivity in a group of clinically normal foals. Animals 12 clinically normal mixed-breed foals, 48 to 92 days old, without history of clinical lung disease. Procedure Nonspecific airway reactivity was determined by measuring the extent of changes in dynamic compliance during nebulization of incrementally increasing concentrations of histamine aerosol. Degree of airway reactivity was expressed as the dose of histamine that evoked a decrease in dynamic compliance (Cdyn) to 65% of the after saline nebulization value (PC65Cdyn) or increase in pulmonary resistance (RL) to 135% of baseline (PC135RL). Results In all foals, it was possible to induce a decrease in Cdyn in dose-dependent manner to ≤ 65% of baseline. Response of foals in terms of RL was more erratic, and, in 1 foal, RL decreased after histamine exposure. Mean ± SD PC65Cdyn was 5.43 ± 1.74 (range, 0.77 to 19.56) mg/ml, and mean PC135RL was 3.34 ± 1.52 (range, −0.749 to 17.35) mg/ml. Body weight was not correlated to baseline Cdyn, RL, PC65Cdyn, or PC135RL. Conclusions and Clinical Relevance Clinically normal foals had a wide range of airway reactivity, which may contribute to variation in clinical responses of foals to otherwise similar stimuli, such as infection, inflammation, and challenge exposure with environmental irritants. (Am J Vet Res 1999;60:965-968)