Prediction of exercise respiratory limitation from pulmonary function tests

Background: Evaluation of unexplained exercise intolerance is best resolved by cardiopulmonary exercise testing (CPET) which enables the determination of the exercise limiting system in most cases. Traditionally, pulmonary function tests (PFTs) at rest are not used for the prediction of a respiratory limitation on CPET. Objective: We sought cut-off values on PFTs that might, a priori, rule-in or rule-out a respiratory limitation in CPET. Methods: Patients who underwent CPET in our institute were divided into two groups according to spirometry: obstructive and non-obstructive. Each group was randomly divided 2:1 into derivation and validation cohorts respectively. We analyzed selected PFTs parameters in the derivation groups in order to establish maximal and minimal cut-off values for which a respiratory limitation could be ruled-in or ruled-out. We then validated these values in the validation cohorts. Results: Of 593 patients who underwent a CPET, 126 were in the obstructive and 467 in the non-obstructive group. In patients with obstructive lung disease, forced expiratory volume in 1 second (FEV₁) ≥ 61% predicted could rule out a respiratory limitation, while FEV₁ ≤ 33% predicted was always associated with a respiratory limitation. For patients with non-obstructive spirometry, FEV₁ of ≥ 73% predicted could rule-out a respiratory limitation. Application of this algorithm might have saved up to 47% and 71% of CPETs in our obstructive and non-obstructive groups, respectively. Conclusion: Presence or absence of a respiratory limitation on CPET can be predicted in some cases based on a PFTs performed at rest.