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

Abstract 

Analysis of individual breaths after exercise has potential for pulmonary function testing. The aims of this study were to investigate the dependence of measurements of pulmonary function in single breaths on time postexercise and tidal volume (V_T) after treadmill exercise. Five Thoroughbred horses without evidence of airway disease were used. Horses had been previously acclimated to treadmill exercise and to wearing a face mask. A Quadflow spirometer recorded airflow rates continuously during 90 seconds after intense treadmill exercise to fatigue. Indices of function were based on ratios of times within each breath and analyses of the shape of relative flow–time curves within inspiration and expiration. Restricted maximum likelihood, general linear regression, repeated-measures one-way analysis of variance (ANOVA), and two sample t-tests were used, with statistical significance at P < .05. Time postexercise had no effect on several ratios based on time for inspiration (T_I) and expiration (T_E), and times to peak flows (T_I/T_T, T_E/T_T, T_E/T_I, Tpef [peak expiratory flow]/T_E, and Tpif [peak inspiratory flow]/T_I). Many variables were significantly dependent on V_T. Occasional big respiratory cycles with V_T more than 10% greater than in the previous breath had significantly different means for relative flow (Rf)/(T_E/T_I), epz_50% (50% of the time from Tpef to end of expiration), epz_75% (75% of the time from Tpef to end of expiration), and ipz_75% (75% of the time from Tpif to end of inspiration). Predicted means for these variables differed by 10–20%. This study establishes guidelines for the selection of breaths after exercise, and describes a new approach to measurement of relative flow and time relationships. It was concluded that several time-based ratios have potential for measuring pulmonary function. However, care is needed when selecting breaths for calculation of most of the new relative flow–time variables.

Keywords: Respiratory, Physiology, Pulmonary, Breathing, Exercise