Validity and repeatability of cardiopulmonary exercise testing in interstitial lung disease

Abstract

Background: Cardiopulmonary exercise testing (CPET), and its primary outcome of peak oxygen uptake (VO2peak), are acknowledged as biomarkers in the diagnostic and prognostic management of interstitial lung disease (ILD). However, the validity and repeatability of CPET in those with ILD has yet to be fully characterised, and this study flls this evidence gap. Methods: Twenty-six people with ILD were recruited, and 21 successfully completed three CPETs. Of these, 17 completed two valid CPETs within a 3-month window, and 11 completed two valid CPETs within a 6-month window. Technical standards from the European Respiratory Society established validity, and repeatability was determined using mean change, intraclass correlation coefcient and typical error. Results: Every participant (100%) who successfully exercised to volitional exhaustion produced a maximal, and therefore valid, CPET. Approximately 20% of participants presented with a plateau in VO2, the primary criteria for establishing a maximal efort. The majority of participants otherwise presented with secondary criteria of respiratory exchange ratios in excess of 1.05, and maximal heart rates in excess of their predicted values. Repeatability analyses identifed that the typical error (expressed as percent of coefcient of variation) was 20% over 3-months in those reaching volitional exhaustion. Conclusion: This work has, for the frst time, fully characterised how patients with ILD respond to CPET in terms of primary and secondary verifcation criteria, and generated novel repeatability data that will prove useful in the assessment of disease progression, and future evaluation of therapeutic regimens where VO2peak is used as an outcome measure.