Oxygen Uptake Efficiency Slope, an Objective Submaximal Parameter in Evaluating Exercise Capacity in Pulmonary Thromboembolism

Abstract

ObjectiveThe objective of this article was to study the oxygen uptake efficiency, an index of cardiopulmonary functional reserve that can be based upon a submaximal exercise effort, in pulmonary thromboembolism (PE) by performing the cardiopulmonary exercise test. Materials and MethodsThe cardiopulmonary exercise test with simultaneous respiratory gas measurement was performed in 50 patients with PE and in 50 healthy individuals. All subjects also underwent the pulmonary function test. Peak oxygen uptake (peak VO2), anaerobic threshold (AT), oxygen uptake efficiency slope (OUES), oxygen uptake efficiency plateau (OUEP) and oxygen uptake efficiency at anaerobic threshold (OUE@AT), were determined. Results(1) Compared with the controls, the patients with PE had lower peak VO2, AT, OUES, OUEP and OUE@AT (P < 0.001). (2) In patients with PE, oxygen uptake efficiency (OUE = VO2/VE) at warming up, AT and peak exercise but not rest, were indicated statistically lower than the controls. The OUE in normal subjects increased as unloaded exercise began, and then increased further to OUEP just before the AT. Thereafter, the OUE decreased gradually until peak exercise. In contrast, the rate of changes of the OUE in patients with PE was relatively mild during exercise. (3) Of all the submaximal parameters, OUES correlated best with peak VO2 (r = 0.712, P < 0.001). ConclusionsThe oxygen uptake efficiency of patients with PE was lower than the controls during exercise. The OUE is an objective measure of cardiopulmonary reserve that does not require a maximal exercise effort. Therefore, OUES could be helpful to assess exercise performance in patients with PE who are unable to perform a maximal exercise test in early recovery stage.