Six-Minute Walk Test in Obstructive Sleep Apnoea

Introduction: The aim of this study was to assess results of 6MWT in non-selected group of obstructive sleep apnoea (OSA) patients. In healthy adult subjects 6-minute walking distance (6MWD) range from 400 to 700 m. Obesity, the main symptom of OSA, is one of the factors associated with reduction of 6MWD (another common factors: older age, shorter height, female sex, pulmonary, cardiovascular and musculoskeletal diseases). Material and methods: Subjects completed sleep questionnaire and Epworth sleepiness scale before sleep studies (full polysomnography [PSG] or PolyMesam study [PM]). Consecutive OSA subjects (AHI/RDI >10, Epworth score > 9 points) were evaluated. The 6MWT, chest X-ray, spirometry, arterial blood gases, ECG, blood morphology and biochemistry were performed during trial treatment with autoCPAP. Results: We studied 151 subjects (119 males—78.8% and 32 females—21.2%), mean age 53.4 ± 10.5 years. Subjects were obese—BMI = 35.7 ± 6.2 kg/m² and presented severe OSA—AHI/RDI = 42.4 ± 23.2. To assess relations between 6MWD and AHI/RDI, BMI, age and concomitant diseases we divided subjects in two groups: 1st with 6MWD ≥ lower limit of normal (LLN) (123 pts; 81.5%) and 2nd with 6MWD < LLN (28 pts; 18.5%). Significant differences between groups were found for BMI, FVC (% of predicted) and Borg dyspnea scale before and after 6MWT. In multiple linear regression analysis we found significant correlation between 6MWD and BMI (β = 0.41, p < 0.0001) and arterial hypertension (β = –0.16, p = 0.04). Females had significantly shorter 6MWD than males (401.1 ± 83.6 m and 451.8 ± 107 m, respectively; p = 0.01). Difference was significant after adjustment for BMI and age (analysis of covariance)—R = 0.61, R² = 0.38 (p < 0.0001). Conclusions: BMI, female sex, arterial hypertension and lower FVC (% of predicted) were related to shorter 6-minute walking distance in OSA patients.