| Background. The small airways are often the target for air pollutants such as ozone and particulate matter and have been shown to be the initial site of injury leading to chronic airway obstruction. Spirometric measures commonly used to assess airway effects are not specific to the small airways and measures that encompass the small airway region of the lung are highly variable and, therefore, not sensitive for detecting subtle changes associated with exposure to ambient air pollution.; Objective. The objective of this study was to test a statistically refined small airway measure in the laboratory and in the field to assess its variability and sensitivity under controlled and real-world conditions.; Methods. To create the refined small airway measure, points along the flow-volume curve encompassing the small airway region of the lung (between 50 and 75% of forced vital capacity) were smoothed using a locally weighted regression and then averaged to give one flow point representative of that airway region (FEF50↔75). In the laboratory, the forced vital capacity maneuver was administered to 20 healthy, non-smoking adult volunteers (ages 25 to 40) on three separate occasions separated by no more than two weeks. The variability and sensitivity of the FEF50↔75 metric was then compared to traditional measures of small airway function. The sensitivity of the FEF50↔75 was then evaluated in the field using elite cyclists who exercise vigorously outdoors. The cyclists' exposure to ozone and particulate matter was measured along with the estimated inhaled dose of ozone.; Results. In the laboratory, the FEF50 measure provided the most sensitive measure of small airway function. It was followed in rank by FEF25-75, FEF50↔75, FEF50-75 and FEF75. In the field, airway decrements (in FVC, FEV1 and FEF50 adjusted for FVC) were associated with ozone exposure (p<0.0001) at levels below the current EPA standard of 80 ppb, in spite of improvements in airway function that can be attributed to the effect of exercise.; Conclusions. Although the FEF50↔75 measure did not offer significant improvements over traditional measures, it was slightly less variable than traditional methods that encompass the same segment of the flow-volume curve. Furthermore, decreases in pulmonary function were documented in healthy, highly-trained athletes at levels below current standards. |
