Patients with chronic obstructive pulmonary disease (COPD), facing a decline in lung function and compromised quality of life, often benefit from regular exercise (1). Assessing their cardiorespiratory fitness through maximal oxygen uptake (VO2max) is crucial (2), yet research on its validity and reliability in COPD patients remains sparse. This study aims to fill this gap, examining the content validity and test-retest reliability of the VO2-max test in COPD, comparing it with healthy controls.

Introduction and background Patients with COPD face a challenging journey characterized by a progressive loss of lung function, ultimately resulting in a diminished quality of life, exercise limitations and heightened vulnerability to disability and premature mortality. Recognizing the pivotal role of regular exercise in enhancing the well-being of COPD patients, it becomes crucial to evaluate their cardiorespiratory fitness through parameters such as maximal oxygen uptake (VO2max). This metric serves as a cornerstone in assessing the maximal capacity of the cardiovascular system to deliver oxygen to working muscles and the muscles' ability to utilize oxygen during sustained exercise.

In broader health contexts high VO2max has been established as a key indicator inversely correlated with the risk of cardiovascular diseases and mortality. However, despite the acknowledged importance of VO2max, there is a notable gap in research focusing specifically on VO2max of COPD patients. The need for a thorough examination of the content validity of the VO2-max test in the context of COPD, along with an assessment of its test-retest reliability (day-to-day variation), has not been adequately addressed, especially in comparison with healthy individuals. While regular exercise has proven to be a transformative factor in improving the quality of life for COPD patients, there remains a critical need to explore the reliability of VO2-max testing within this population. Not only does COPD induce a decline in physical activity, but it can also contribute to a reduction in VO2-max. Consequently, understanding the validity and test-retest reliability of VO2-max testing in COPD becomes paramount.

Aim To compare the validity and test-retest reliability of the VO2-max test in COPD patients compared with healthy controls.

Perspective The results are relevant for designing future studies of VO2max and VO2kinetics as outcomes in COPD patients.

Inclusion criteria - COPD patients

• Men and women
• 45-80 years
• COPD (GOLD stage I to IIII)
• Forced expiratory volume in 1 sec (FEV1)/forced vital capacity ratio (FVC) < 0.8, FEV1 < 90% of predicted value.
• Modified Medical Research Council score (mMRC 0 - 3)
• Resting arterial oxygenation > 90%

Inclusion criteria - healthy controls

• Men and women
• 45-80 years
• Normal FEV1, FVC, FEV1/FVC, and single-breath diffusion capacity
• Same sex, age (± 3 years) as the COPD patients

Exclusion criteria - COPD patients

• Symptoms of ischaemic heart disease
• Known heart failure
• Claudication
• Symptoms of disease within 2 weeks prior to the study
• Participation in pulmonary rehabilitation within 6 months
• Known malignant disease
• Pregnancy
• Unstable cardiac arrhythmic disease
• Renal or liver dysfunction

Exclusion criteria - healthy controls

• Known chronic lung disease
• Known ischaemic heart disease
• Known heart failure
• Symptoms of disease within 2 weeks prior to the study
• Known malignant disease
• Claudication
• Pregnancy
• Unstable cardiac arrhythmic disease
• Renal or liver dysfunction

Participants will be recruited through advertisements at pulmonary outpatient clinics and general practices in Greater Copenhagen, and by advertisements in newspapers, magazines, social media, and on forsøgsperson.dk as well as through forskningnu.dk. We have created a specific social media account which is used on different social medias to share knowledge and potentially recruit participants. It will not be possible to comment or tag people in our posts, and potentially interested participants will only be able to contact our research group via encrypted Region H mail. An e-mail address and telephone number will be provided by which interested participants can contact the research group.

Will be decided upon study completion.