Relative Flow-Time Relationships in Single Breaths Recorded After Treadmill Exercise in Thoroughbred Horses

Effects of sedation and salbutamol administration on hyperpnoea and tidal breathing spirometry in healthy horses

Sedation is often required to perform pulmonary function testing (PFT) in horses, but drug effects may influence respiratory function. The current study was designed to characterise the effects of sedation and bronchodilator administration on absolute and relative indices of pulmonary function during eupnoeic respiration and carbon dioxide-induced hyperpnoea (rebreathing) in healthy horses using a pneumotachographic spirometry system. Sedation with acetylpromazine (ACP), xylazine, or both drugs in combination was associated with significant reductions in respiratory frequency, minute ventilation and peak airflows during eupnoeic respiration. Peak expiratory airflow occurred later in the respiratory cycle than was observed in untreated horses, and expiratory relative flow-time indices were also affected during eupnoeic respiration. Rebreathing attenuated the effects of sedation on indices of pulmonary function, suggesting that future studies should consider the use of induced hyperpnoea as part of the spirometry protocol. Based on the finding that all sedative agents had some effect on eupnoeic respiration, albeit least pronounced with ACP, the latter drug should be considered for sedation of horses undergoing PFT. Salbutamol increased peak inspiratory flow during eupnoeic respiration in healthy horses.

Reliability of breath by breath spirometry and relative flow-time indices for pulmonary function testing in horses

Background

Respiratory problems are common in horses, and are often diagnosed as a cause of poor athletic performance. Reliable, accurate and sensitive spirometric tests of airway function in resting horses would assist with the diagnosis of limitations to breathing and facilitate investigations of the effects of various treatments on breathing capacity. The evaluation of respiratory function in horses is challenging and suitable procedures are not widely available to equine practitioners. The determination of relative flow or flow-time measures is used in paediatric patients where compliance may limit conventional pulmonary function techniques. The aim of the current study was to characterise absolute and relative indices of respiratory function in healthy horses during eupnoea (tidal breathing) and carbon dioxide (CO₂)-induced hyperpnoea (rebreathing) using a modified mask pneumotrachographic technique well suited to equine practice, and to evaluate the reliability of this technique over three consecutive days. Coefficients of variation, intra-class correlations, mean differences and 95% confidence intervals across all days of testing were established for each parameter.

Results

The technique provided absolute measures of respiratory function (respiratory rate, tidal volume, peak inspiratory and expiratory flows, time to peak flow) consistent with previous studies and there was no significant effect of day on any measure of respiratory function. Variability of measurements was decreased during hyperpnea caused by rebreathing CO₂, but a number of relative flow-time variables demonstrated good agreement during eupnoeic respiration.

Conclusions

The technique was well tolerated by horses and study findings suggest the technique is suitable for evaluation of respiratory function in horses. The use of relative flow-time variables provided reproducible (consistent) results, suggesting the technique may be of use for repeated measures studies in horses during tidal breathing or rebreathing.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0893-3) contains supplementary material, which is available to authorized users.

Pulmonary function measurements immediately after exercise are correlated with neutrophil percentage in tracheal aspirates in horses with poor racing performance

Inflammatory airway disease (IAD) is common in racehorses, and is a cause of wastage in the industry. IAD has been diagnosed by measurement of percent neutrophils (N%) in tracheal aspirates (TA). The aim of this study was to investigate whether spirometric indices of pulmonary function were correlated with N% in TAs. Limits to breathing were measured by analyses of relationships between relative times and relative respiratory gas flows during inspiration and expiration in individual breaths recorded after exercise. Horses with higher N% had significantly lower relative gas flows at the same relative times during inspiration and expiration, suggesting a limit to breathing. These findings confirm a physiological basis for the measurement of N% in TA after exercise for diagnosis of IAD. Spirometric pulmonary function testing using analyses of individual breaths after exercise has application for assessment of pulmonary function and poor exercise performance.