Association of the six-minute walk test with severity of obstructive sleep apnea: an observational study

Obstructive sleep apnea (OSA) impairs sleep quality and exercise capacity through intermittent hypoxia and autonomic dysfunction. Simple tools that correlate objective exercise tolerance with OSA severity remain underutilized in clinical practice. The study aimed to find the association between 6-minute walk test (6MWT) performance and polysomnographic severity indices in patients with newly diagnosed OSA and whether functional exercise parameters can predict OSA severity. This cross-sectional observational study was conducted at a tertiary care center between July 2023 and January 2025. A total of 124 consecutive adults (age ≥18 years) with newly diagnosed OSA diagnosed from level I polysomnography (PSG) underwent standardized 6MWT as per American Thoracic Society Guidelines within one week of PSG testing. Primary endpoints included 6-minute walk distance (6MWD), oxygen saturation changes, post-test Borg dyspnea scale, and heart rate recovery at 1, 2, and 3 minutes. Correlations with Apnea-Hypopnea Index (AHI) and Oxygen Desaturation Index (ODI) were analyzed using Spearman's correlation, multiple linear regression, and one-way analysis of variance with Games-Howell post-hoc testing. The study included 124 participants (85.5% male, mean age 46±11.3 years, mean body mass index 33.19±5.9 kg/m²), of whom 79.8% were participants with severe OSA. Mean AHI and ODI were 52.25±23.69 and 54.04±29.22 events/hour, respectively. Mean 6MWD decreased significantly across OSA severity groups: mild 420.85±17.4 m, moderate 396.99±9.60 m, and severe 348.61±22.01 m. Strong negative correlations were found between AHI and 6MWD (ρ=-0.974, p<0.001) and ODI and 6MWD (ρ=-0.775, p<0.001). Multiple linear regression results in two important predictive models: AHI=258.65+[(0.58×Epworth Sleepiness Scale (ESS)] + (1.89×Borg dyspnea post-6MWT) - (0.1×6MWD) and ODI=207.88+(0.96×ESS) + (4.21×Borg dyspnea post-6MWT) - (0.51×6MWD). As measured by the 6MWT, functional exercise capacity is strongly and inversely associated with the severity of OSA. The derived regression equations serve as a valuable, practical adjunct for assessing the functional impairment and hypoxic burden in patients with OSA, particularly in resource-limited settings.