• Long-term oxygen therapy (LTOT)

We thank Garcia-Talavera et al for their interest in our paper.1 We acknowledge their finding, in a group of chronic obstructive pulmonary disease patients with only mild hypoxaemia, of a correlation between early oxyhaemoglobin desaturation during the 6-minute walk test (6MWT) and desaturation over 24 h.2 The 6MWTs performed in our study were carried out according to American Thoracic Society guidelines.3 Given their recommendations that oxygen saturation measured by pulse oximetry (SpO₂) should not be used for constant monitoring during the test and that the technician must not walk with the patient to observe SpO₂, saturation in our study was measured at rest and immediately at the end of the 6-minute period. We are thus unable to comment upon the presence or absence of early as opposed to late desaturation in our cohort of desaturators. Nonetheless, it is likely that our group of 50 ‘end test’ desaturators would have included both early and late desaturators, according to the definition of Garcia-Talavera et al. We found no association between the degree of desaturation at the end of the 6MWT and our primary or secondary outcome criteria. Others have similarly found an absence of association between the degree of desaturation and improvement in exercise capacity with supplemental oxygen.4 Whether or not early desaturation during the 6MWT correlates with desaturation during activities of daily living or nocturnally, it remains unknown whether such early desaturation correlates with degree of dyspnoea or whether treating it with supplemental oxygen would improve this symptom.