The modified Borg/6-min walk distance ratio: a method to assess exertional breathlessness and leg discomfort using the 6-min walk test

Abstract

BackgroundThe 6-minute walk test (6MWT) is widely used to assess exercise capacity across chronic health conditions, but is currently not useful to assess symptoms as the scores do not account for the walk distance (6MWD). We aimed to: (1) develop normative reference equations for breathlessness and leg discomfort intensity expressed as modified Borg (mBorg)/6MWD ratios; and (2) validate the equations in people with chronic obstructive pulmonary disease (COPD).MethodsAnalysis of people aged ≥40 years who performed two 6MWTs in the Canadian Cohort Obstructive Lung Disease (CanCOLD) study; a healthy cohort (n=291; aged 67.5±9.4 years; 54% male) with normal 6MWD and lung function; and a COPD cohort (n=156; aged 66.2±9.0 years; 56% male; FEV1/FVC 56.6±8.2%; FEV174.4±18.6%pred). The mBorg score was calculated as the Borg 0–10 category ratio intensity rating of breathlessness or leg discomfort recorded at the end of the 6MWT +1 (range 1–11), to avoid zeros and yield ratios proportional to the symptom score and 6MWD−1.ResultsUsing data from the healthy cohort, sex-specific normative reference equations for breathlessness and leg discomfort mBorg/6MWD ratios were developed using multivariable linear regression, accounting for age, and body mass or body mass index. In the COPD cohort, abnormal breathlessness and leg discomfort (mBorg/6MWD>upper limit of normal [ULN]) showed strong concurrent validity with worse airflow limitation, Medical Research Council (MRC) breathlessness, and COPD Assessment Test scores.ConclusionNormative references for the mBorg/6MWD ratio are presented to assess breathlessness and leg discomfort responses to the 6MWT in COPD.