Locating and selecting appraisal studies for reviews.

lung (an increase in forced VC). Dr. Petty’s preference to use the FEV1/FVC ratio is wellunderstood. It has been well-described that subjects with airway obstruction, that is, a low FEV1/FVC ratio, are more likely to have airway hyperresponsiveness (AHR). We evaluated the association between the “new” ratio (ie, FEF25–75/FVC) and AHR because we believed that it describes a potentially different mechanism that leads to AHR. A low FEF25–75/FVC ratio may identify subjects who have relatively small airways for their lung size but do not have airway obstruction, whereas the FEV1/FVC ratio would identify subjects with airway obstruction. The purpose of our article was not to advocate the use of FEF25–75 or the FEF25–75/FVC ratio in the clinical interpretation of pulmonary function test results. We agree that these parameters have not been shown to be good predictors of the development of obstructive airway disease. Rather, the focus of our article was to demonstrate that small airway size relative to lung size was a more important determinant than the absolute airway size alone for AHR. This relationship between dysanapsis and AHR may provide another potential mechanism for the pathogenesis of asthma.