Evidence for ozone-induced small-airway dysfunction: lack of menstrual-cycle and gender effects

Recently, we analyzed FEF25-75 isovolumetrically to assess the acute effects of ozone (O3) on small-airway function: the reduction in isovolumetric (isoV) FEF25-75 at end exposure progressed during the next 25 min even as FVC was recovering. To evaluate this effect over a longer period, we measured isovolumetric FEFs, helium-oxygen (He-O2) volume of isoflow (VisoV), the multiple breath nitrogen washout (MBNW) curve, FRC, and RV in 24 subjects 24 h after a 130-min exposure to filtered air (FA) and O3 (0.35 ppm). Men and women were studied to test for gender-based differences in response, after first determining that menstrual-cycle phase did not itself influence response. Isovolumetric FEF25-75, Vmax50, and Vmax75 were reduced about equally at 25 min after O3 exposure (p < or = 0.02) and showed no recovery at 24 h. FVC and FEV1, although still depressed after 24 h (p < 0.05), showed substantial recovery (p < 0.01). FRC, RV, and VisoV showed no effect of O3 exposure. No gender differences in O3 responsiveness were found. In summary, O3-induced reductions in isovolumetric flow rates, suggestive of small-airway dysfunction, may persist for 24 h following acute exposure to O3, a time-course consistent with inflammation.