Rationale:~Carbon dioxide partial pressure (PCO2) varies significantly in patients with advanced chronic obstructive pulmonary disease (COPD). Data from the Swedish LTOT Registry showed that PCO2 is an independent predictor for mortality and that there is a U-shaped relationship. Patients with advanced COPD who are still normocapnic at rest may still develop a clinically relevant, exercise-induced carbon dioxide (CO2) retention during exercise/ activity. It is also known that altered breathing patterns at night in COPD patients can lead to nocturnal hypercapnia, especially during REM sleep. The course of PCO2 cannot be reliably predicted by lung function parameters or resting blood gas analysis. Since exercise tests with blood gas control or nightly PCO2 monitoring are rarely performed in clinical routine, exercise induced CO2 retention often remains undetected. In the literature, there is little information on PCO2 behaviour under everyday conditions (with or without LTOT) such as rest, physical exertion and nightly sleep. Therefore, predictors that could describe the PCO2 patterns are missing. However, one former study by O'Donnel from 2002 showed that the change in CO2 under hyperoxia conditions could provide predictive information for the change in CO2 with exercise.~Objective:~Primary aim of this study is to investigate whether the change of PCO2 during a hyperoxia-test (10l/min O2 at rest) correlates with the change of PCO2 during walking exercise with either a: l/min O2 as prescribed; b: medical air; c: 10l/min O2.~Design:~This study is a randomized, controlled cross-over trial. Following an initial maximal incremental shuttle walk test (ISWT), the participant will perform 3 endurance shuttle walk tests (ESWT) at 85% of the maximum ISWT pace on three consecutive days (24h break between ESWTs). In a randomized order, participants will perform one ESWTs with O2-flow as prescribed (e.g. study day 1), one with medical air (same flow rate as prescribed oxygen) (e.g. study day 2) and one with 10l/min O2 (e.g. study day 3). An additional hyperoxia test (10l/min O2 for ten minutes; at resting condition) will be perfomed on each day prior to performing an ESWT.
The aim of the study is to investigate a possible correlation between the change in PCO2 during a hyperoxia-test and the change in PCO2 during walking in people with COPD