Submitted on February 3, 2006
Accepted on October 26, 2006
Time Course of Ozone-Induced Changes in Breathing Pattern in Healthy Exercising Humans
Edward Steve Schelegle1*, William F. Walby2, and William C. Adams3
1 Anatomy, Physiology and Cell Biology, University of California Davis, Davis, California, United States
2 Anatomy, physiology and Cell Biology, University of California Davis, Davis, California, United States
3 Exercise Biology, University of California Davis, Davis, California, United States
* To whom correspondence should be addressed. E-mail: esschelegle{at}ucdavis.edu.
We examined the time-course of ozone (O3)-induced changes in breathing pattern in 97 healthy human subjects (70 males and 27 females). One to five minute averages of breathing frequency (fB) and minute ventilation (VE) were used to generate plots of cumulative breaths and cumulative exposure volume versus time, and cumulative exposure volume versus cumulative breaths. Analysis revealed a three-phase response; delay, no response detected; onset, fB began to increase; response, fB stabilized. Regression analysis was used to identify four parameters: time to onset, number of breaths at onset and cumulative inhaled dose of ozone at onset of O3-induced tachypnea and the percent change in fB. The effect of altering O3 concentration, VE, atropine treatment and indomethacin treatment were eximined. We found that the lower the O3 concentration the greater the number of breaths at onset of tachypnea at a fixed ventilation, while number of breaths at onset of tachypnea remains unchanged when VE 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 fB. Atropine did not affect any of the derived parameters, while 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 fB. The results are discussed in the context of dose-response and intrinsic mechanisms of action.
