The Peculiarities of Six-Minute Walk Test in Patients with Chronic Obstructive Pulmonary Disease, Some with Normal Weight and Some Overweight

Background: The combination of chronic obstructive pulmonary disease (COPD) and overweight/obesity is a common clinical situation in modern healthcare. The objective of this study was to conduct a comparative analysis of exercise tolerance in normal body weight (NBW) and overweight patients with COPD in the 6MWT using the original device for cardiorespiratory analysis and a method for assessing the cardiorespiratory condition. Methods and Results: The study included 194 patients with COPD. The patients were divided into two groups. Group 1 consisted of 96 COPD patients with NBW: 77(80.21%) men and 19(19.79%) women aged 41 to 73 years (mean age of 63.33 ± 8.44 years). Group 2 consisted of 98 overweight COPD patients: 74(75.51%) men and 24(24.49%) women aged 55 to 71 (mean age of 64.84 ± 5.46 years). To assess tolerance to physical activity and to objectify the functional status of patients, the 6MWT was used and carried out according to generally accepted principles. The distance covered in 6 minutes (6MWD) was measured in meters and compared with the proper 6MWD(i). The developed device for cardiorespiratory analysis was used to obtain the most accurate 6MWT result. All patients in the study groups underwent an analysis of the composition of the body by the bioelectrical impedance method using a fat mass analyzer BC-555 (Tanita Corporation, Tokyo, Japan). The percentages of fat, water, muscle mass (MM), and bone mass were evaluated. The average value of the 6MWD/6MWD(i) ratio in COPD patients with NBW was significantly lower than in COPD patients with overweight (P=0.0121). Before the test, the study groups did not differ in the level of SpO2. However, according to the results of comparative analysis, this parameter was significantly lower in patients with NBW immediately after the 6MWT (P=0.0000), which, along with a lower value of the distance traveled as a percentage of the proper value in Group 1 patients, may indicate a lower tolerance to physical activity in COPD patients with NBW than in patients with overweight. In COPD patients with NBW, the percentage of fat and MM were significantly lower than in COPD patients with overweight (P=0.0000 in both cases). There was a direct correlation between 6MWD and body mass index (r=0.56, P=0.003) and between 6MWD and MM percentage (r=0.59, P=0.016). Conclusion: Higher exercise tolerance is found in overweight COPD patients than in COPD patients with NBW. This phenomenon can be explained to some extent by the compositional components of the body, in particular, by a significantly lower percentage of lean MM in patients with NBW.