Determinants of Percent Predicted FEVi in Current Asthmatic Subjects: Discussion

Determinants of Percent Predicted FEVi in Current Asthmatic Subjects: DiscussionIn this study of a large group of asthma subjects, wheezing, dyspnea, a concurrent diagnosis of chronic bronchitis, and age were significant determinants of %FEVi. These results confirm our previous findings, in smaller groups of asthmatic subjects, that symptom severity and additional diagnoses relate to pulmonary function.’ We did not, however, anticipate the important contribution of the combination of wheezing severity and age to %FEVi, a measurement that has already been adjusted for the effect of age among our subjects. It is possible that our results have been influenced by our methodology. First, we used an arbitrary definition of asthma: subjects who responded on a questionnaire that they had asthma and were taking medication for it or were having active symptoms of the disease. It is conceivable that we would have found that other factors, serum IgE level or eosinophil count for example, were related to %FEVi, if we had defined asthma by some other method, such as airway hyperresponsiveness. Thus, our definition of asthma, which we have used throughout the years of the Tucson Study, needs to be kept in mind whenever our findings are compared with those of other investigators or are applied by clinicians to their patients. ventolin inhaler

Second, we have used %FEVi rather than absolute values of FEVi. While it is true that lower %FEVi values for older asthmatic subjects could be produced by a regression equation that distorts the contribution of age to pulmonary function, the %FEVi results in our mildly asthmatic older subjects show that such a distortion has not occurred.
As has been emphasized by the Expert Panel Report of the National Asthma Education Program, asthma patients having frequent symptoms but not acute exacerbations (referred to as “moderate asthma patients”) usually have a %FEVi of 60 to 80 percent when routinely tested. Thus, we expected that our subjects with frequent symptoms would have abnormal spirometry results.

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