Forced Mid-Expiratory Flow Can Predict Ventilatory Limitation and Exercise Capacity

Abstract

Background: Exercise limitation associated with most lung diseases is multifactorial and is due to complex interactions between impaired ventilatory, cardiovascular, and peripheral muscle responses. Cardiopulmonary exercise tests (CPETs) are often required to ascertain the primary cause of exercise limitation particularly in patients with multiple co-morbidities. CPETs are generally offered only at tertiary care medical centers. Objectives: To evaluate if forced expiratory flow from 25% to 75% of vital capacity (FEF25-75%) can be used to predict both reduced exercise capacity and ventilatory limitation to exercise. Methods: We retrospectively reviewed paired CPETs and spirometry tests performed on all adult patients (> 18 years of age) in the Pulmonary Physiology Laboratory at St. Elizabeth’s Medical Center between April, 2006 and April, 2016 to explore the association between spirometric parameters and ventilatory limitation to exercise. Ventilatory limitation was defined as ventilatory reserve ≤ 15% at peak exercise. We defined reduced exercise capacity as peak oxygen consumption VO(2) < 20 mL/kg/ min. Results: FEF25-75% was strongly associated with low breathing reserve (area under the ROC curve 0.81). FEF25-75% was also significantly associated with the combined outcome of low ventilatory reserve and reduced exercise capacity. The area under the ROC curve was 0.86 (p < 0.0001) suggesting excellent predictive ability. In patients with FEV25-75% ≥ 40%, exercise limitation was much more commonly non-ventilatory in nature. In patients with mid-expiratory flow, FEV25-75% ≤ 20%, nearly 7 of 10 patients had ventilatory limitations to exercise. OriGinal researCh artiCle