Oxygen Uptake Efficiency Slope and Breathing Reserve, Not Anaerobic Threshold, Discriminate Between Patients With Cardiovascular Disease Over Chronic Obstructive Pulmonary Disease

Abstract

Objectives: The study sought to compare the relative discrimination of various cardiopulmonary exercise testing (CPX) variables between cardiac and respiratory disease.

Background: CPX testing is used in many cardiorespiratory diseases. However, discrimination of cardiac and respiratory dysfunction can be problematic. Anaerobic threshold (AT) and oxygen-uptake to work-rate relationship (VO2/WR slope) have been proposed as diagnostic of cardiac dysfunction, but multiple variables have not been compared.

Methods: A total of 73 patients with chronic obstructive pulmonary disease (COPD) (n = 25), heart failure with reduced ejection fraction (HFrEF) (n = 40), or combined COPD and HFrEF (n = 8) were recruited and underwent CPX testing on a bicycle ergometer. Following a familiarization test, each patient underwent a personalized second test aiming for maximal exercise after ∼10 min. Measurements from this test were used to calculate area under the receiver-operator characteristic curve (AUC).

Results: Peak VO2 was similar between the 2 principal groups (COPD 17.1 ± 4.6 ml/min/kg; HFrEF 16.4 ± 3.6 ml/min/kg). Breathing reserve (AUC: 0.91) and percent predicted oxygen uptake efficiency slope (OUES) (AUC: 0.87) had the greatest ability to discriminate between COPD and HFrEF. VO2/WR slope performed significantly worse (AUC: 0.68). VO2 at the AT did not discriminate (AUC for AT as percent predicted peak VO2: 0.56). OUES and breathing reserve remained strong discriminators when compared with an external cohort of healthy matched controls, and were comparable to B-type natriuretic peptide.

Conclusions: Breathing reserve and OUES discriminate heart failure from COPD. Despite it being considered an important determinant of cardiac dysfunction, the AT could not discriminate these typical clinical populations while the VO2/WR slope showed poor to moderate discriminant ability. (Identifying an Ideal Cardiopulmonary Exercise Test Parameter [PVA]; NCT01162083).

Keywords: cardiopulmonary exercise testing; chronic heart failure; exercise physiology; obstructive pulmonary disease.

Copyright © 2016 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1

Dotplots for 9 CPX Variables in Patients With COPD and HFrEF Dotplots for 9 cardiopulmonary exercise testing variables in patients with chronic obstructive pulmonary disease (COPD) and heart failure with reduced ejection fraction (HFrEF). Each dot represents an individual with mean values represented by black lines. AT = anaerobic threshold; BR = breathing rate; VO2 = oxygen uptake; VO2:WR slope = oxygen-uptake to work-rate relationship.

Figure 2

Comparison of the Area Under the ROC Curve for BNP and Percent Predicted OUES BNP = B-type natriuretic peptide; OUES = oxygen uptake efficiency slope; ROC = receiver-operating characteristic.

Figure 3

Proposed Algorithm for the Identification of Respiratory or Cardiac Disease in a Patient With Exercise Limitation Breathing reserve (%) is calculated as 100× (maximum voluntary ventilation [MVV] – peak minute ventilation)/MVV, where MVV was calculated as: 40 · FEV1 at rest. The percent predicted oxygen uptake efficiency slope (OUES) was calculated using data from Barron et al. . COPD = chronic obstructive pulmonary disease; VO2 = oxygen uptake.