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Time course of ozone-induced changes in breathing pattern in healthy exercising humans

¹Department of Anatomy, Physiology, and Cell Biology, School of Veterinary Medicine, and ²Exercise Biology Program, University of California, Davis, California

Submitted 3 February 2006 ; accepted in final form 26 October 2006

We examined the time course of O₃-induced changes in breathing pattern in 97 healthy human subjects (70 men and 27 women). One- to five-minute averages of breathing frequency (f_B) and minute ventilation (E) were used to generate plots of cumulative breaths and cumulative exposure volume vs. time and cumulative exposure volume vs. cumulative breaths. Analysis revealed a three-phase response; delay, no response detected; onset, f_B began to increase; response, f_B stabilized. Regression analysis was used to identify four parameters: time to onset, number of breaths at onset, cumulative inhaled dose of ozone at onset of O₃-induced tachypnea, and the percent change in f_B. The effect of altering O₃ concentration, E, atropine treatment, and indomethacin treatment were examined. We found that the lower the O₃ concentration, the greater the number of breaths at onset of tachypnea at a fixed ventilation, whereas number of breaths at onset of tachypnea remains unchanged when E is altered and O₃ concentration is fixed. The cumulative inhaled dose of O₃ at onset of tachypnea remained constant and showed no relationship with the magnitude of percent change in f_B. Atropine did not affect any of the derived parameters, whereas indomethacin did not affect time to onset, number of breaths at onset, or cumulative inhaled dose of O₃ at onset of tachypnea but did attenuate percent change in f_B. The results are discussed in the context of dose response and intrinsic mechanisms of action.

ozone; oxidants; breathing pattern; tachypnea; kinetics

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