CORRELATION BETWEEN THE 2005 AND 2021 ERS/ATS CRITERIA FOR BRONCHODILATOR RESPONSIVENESS: AN ARITHMETIC SOLUTION

SESSION TITLE: Pulmonary Physiology - Rethinking Pulmonary Function SESSION TYPE: Rapid Fire Original Inv PRESENTED ON: 10/10/2023 12:00 pm - 12:45 pm PURPOSE: Bronchodilator response (BDR) to a fast-acting bronchodilator agent is routinely used as part of pulmonary function testing in patients with airway obstruction. The definition of BDR (BDRnew) has recently changed per the 2021 ATS/ERS guidelines from the previously accepted 2005 definition (BDRold) to account for the predicted values during spirometry. In contrast to what has been described in the literature, BDRold and BDRnew are not independent variables but are in fact, a function of one another. Here, we have derived a simple arithmetic method allowing the conversion between BDRold and BDRnew and their respective criteria for positivity. METHODS: BDRold is calculated as the change in forced expiratory volume in 1 second (FEV1) or forced vital capacity (FVC) after bronchodilator (BD) administration divided by the pre-bronchodilator FEV1 or FVC. For FEV1, this is represented as: BDRold = (post-BD FEV1 – pre-BD FEV1)/pre-BD FEV1 (expressed in %) (equation 1). A value of 12 % (and at least 200 ml) was considered the cut-off for a positive response. BDRnew is calculated by the change in FEV1 divided by the predicted FEV1. This is written as: BDRnew = (post-BD FEV1-pre–BD FEV1)/predicted FEV1 (expressed in %) (equation 2). A value of 10% or greater is considered a positive response. Re-writing equation 1: BDRold * pre-BD FEV1 = post-BD FEV1 – pre-BD FEV1; replacing this in equation 2: BDRnew = BDRold * pre-BD FEV1 /predicted FEV1 that is, BDRnew = BDRold* % predicted FEV1 or BDRold = BDRnew * (1/% predicted FEV1). RESULTS: Based on these new equations, BDRnew will always be lower than BDRold in patients with obstruction as the FEV1 is always lesser than the predicted FEV1, that is, FEV1/predicted FEV1 % < 100 %. The relationship between the two definitions is therefore exclusively dependent on the degree of obstruction (as defined by the % predicted value). Higher fidelity exists with lesser degrees of obstruction (i.e., higher % predicted FEV1). For example, a 15% BDRold response in an individual with 70% predicted FEV1 correlates to a BDRnew response of 15% * 70% = 10.5%, constituting a positive BDRnew. However, in an individual with greater severity of obstruction and a predicted FEV1 % of 30%, BDRold response of 15% would correspond to 15% * 30% = 4.5% which is not a positive response. CONCLUSIONS: BDRnew was introduced as a means to minimize the age and sex bias that was present with BDRold. The arithmetic relationship between BDRnew, BDRold and % predicted of FEV1 allows us to utilize the new criteria in a simple way for BDR done prior to 2021. It also shows that patients with more severe obstruction are less likely to continue to meet BDR criteria even if they did in the past. CLINICAL IMPLICATIONS: Clinical history is of paramount importance while assessing the benefit of a short-acting bronchodilator. This analysis aims to help collate data using both definitions of BDR. The clinical relevance of this data is an avenue for further research. DISCLOSURES: No relevant relationships by Mamta Chhabria No disclosure on file for Philippe Haouzi No relevant relationships by Kathryn Ickes No relevant relationships by Jonathan McCully No relevant relationships by Avantika Nathani