Title: Investigating Changes in Responses to Controlled Effective Doses of Ozone at Different Exercise Intensities
Thesis Supervisor: Dr. Michael Koehle
Committee members: Dr. Valérie Bougault, Dr. Donald McKenzie
Defence Chair: Dr. Darren Warburton
Abstract:
Background: While exposure to greater effective doses of ozone (O3) (product of the concentration of O3, ventilation, and duration of exposure) during exercise results in greater decrements in pulmonary function, the effect of matched effective doses of O3 at different exercise intensities on pulmonary function has seldomly been explored.
Aim: To investigate whether exercise performed in O3 results in greater decrements in forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1) when performed at a higher-intensity for a shorter duration compared to a moderate-intensity exercise performed longer when the effective dose of O3 is matched across intensities.
Methods: Fourteen endurance-trained athletes (6 female, VO2peak=56.9±9.6 ml/kg/min) completed steady-state exercise bouts at a moderate-intensity (average duration =43:53) and heavy-intensity (average duration =66:07) with different air conditions (180ppb O3 and room air ≤10 ppb) in a randomised fashion. Cumulative ventilation was controlled across trials to control for effective dose. Spirometry and dyspnea were assessed before, during, and after each exercise bout, while breathing mechanics were only assessed during exercise.
Results: Compared to baseline measures using mixed-effects modeling, O3 exposure resulted in worsened measures of FEV1 (-7.48%, p-value<0.001) and FVC (-2.55%, p-value=0.014) independent of intensity immediately post-exercise. Independent of pollution exposure immediately post-exercise, moderate-intensity exercise resulted in worsened FEV1 (-2.89%, p-value=0.026) and FVC (-2.07%, p-value=0.043). While differences in spirometry from moderate-intensity O3 exposure were not significantly worse than heavy-intensity O3 exposure immediately post-exercise, when all post-exercise timepoints were included in the model, differences in FEV1 (-3.80%, p<0.001) and FVC were significant. Changes in breathing frequency and tidal volume were only seen with comparison of the moderate-intensity O3 exposure to the room air, moderate-intensity control.
Conclusion: Differences in FEV1 and FVC were observed with O3 exposure and moderate-intensity exercise immediately post exercise and between O3 exposures (in favour of worsened responses during moderate-intensity exercise) when a model that included measurements from all post-exercise timepoints was used. Findings from this study suggest that to minimize the effect of O3 pollution on acute lung function, endurance athletes should aim to exercise for a shorter duration at a higher intensity.