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Limitations of 6-minute walk test-based equations in predicting peak oxygen uptake and risk assessment in patients with pulmonary hypertension and COPD
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DOI：10.1016/j.rmed.2026.108738.png)
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Abstract
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Background: Peak oxygen uptake (VO2 peak) is essential for assessing exercise capacity and mortality risk in chronic respiratory diseases. Due to limited accessibility, VO2 peak is often estimated using prediction equations from the 6-min walk test (6MWT). We evaluate the accuracy of VO2 peak prediction equations from the 6-min walk distance (6MWD) in patients with pulmonary hypertension (PH) and/or chronic obstructive pulmonary disease (COPD), and risk assessment. Methods: Patients with PAH, COPD with PH (COPD-PH), and COPD without PH were followed at Hospital Clinic, Barcelona, Spain. All underwent the 6MWT and direct VO2 peak measurement via CPET. Estimated VO2 peak from 6MWD-based equations was compared with measured values. Reliability and agreement were assessed using intraclass correlation coefficients (ICC) and Bland-Altman analysis. We also evaluated the accuracy of VO2 peak estimation in identifying high-risk patients. Results: A total of 225 patients participated: 81 with PAH, 64 with COPD-PH, and 80 with COPD without PH. ICC values showed moderate reliability for VO2 peak prediction in all groups, and despite moderate overall agreement, variability indicated inconsistencies. The equations consistently underestimated mortality risk. Conclusions: Our findings revealed moderate reliability, poor agreement, and a high bias, with 6MWD-based equations overestimating VO2 peak and underestimating risk classification. While the 6MWT is useful when CPET is unavailable, clinicians should interpret these equations cautiously for risk stratification and decisionmaking.
Keywords:
Peak oxygen uptake
6-min walk test
Prediction equations
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