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

Magnus Ekström; Pei Zhi Li; Hayley Lewthwaite; Jean Bourbeau; Wan C Tan; Dennis Jensen

doi:10.1183/23120541.00281-2023

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

ERJ Open Res. 2023 Sep 25;9(5):00281-2023. doi: 10.1183/23120541.00281-2023. eCollection 2023 Sep.

Authors

Magnus Ekström¹, Pei Zhi Li², Hayley Lewthwaite^{3

4

5}, Jean Bourbeau^{2

6}, Wan C Tan⁷, Dennis Jensen^{6

8}

Affiliations

¹ Lund University, Faculty of Medicine, Department of Clinical Sciences Lund, Respiratory Medicine, Allergology and Palliative Medicine, Lund, Sweden.
² Montreal Chest Institute, McGill University Health Center Research Institute, McGill University, Montréal, QC, Canada.
³ Centre of Research Excellence Treatable Traits, University of Newcastle, Newcastle, Australia.
⁴ Asthma and Breathing Research Program, Hunter Medical Research Institute, Newcastle, Australia.
⁵ UniSA: Allied Health and Human Performance, Innovation, Implementation and Clinical Translation in Health, University of South Australia, Adelaide, Australia.
⁶ Research Institute of the McGill University Health Centre, Translational Research in Respiratory Diseases Program and Respiratory Epidemiology and Clinical Research Unit, Montréal, QC, Canada.
⁷ University of British Columbia Centre for Heart Lung Innovation, Department of Medicine, Vancouver, BC, Canada.
⁸ Clinical Exercise and Respiratory Physiology Laboratory, Department of Kinesiology and Physical Education, Faculty of Education, McGill University, Montréal, QC, Canada.

Abstract

Background: The 6-min 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 6-min 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 COPD.

Methods: Analysis of people aged ≥40 years who performed two 6MWTs (on a 20-m course) in the Canadian Cohort Obstructive Lung Disease (CanCOLD) study: a healthy cohort (n=291; mean±sd age 67.5±9.4 years; 54% male) with normal 6MWD and lung function, and a COPD cohort (n=156; age 66.2±9.0 years; 56% male; forced expiratory volume in 1 s (FEV₁)/forced vital capacity 56.6±8.2%; FEV₁ 74.4±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.

Results: Using 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) showed strong concurrent validity with worse airflow limitation, Medical Research Council breathlessness and COPD Assessment Test scores.

Conclusion: Normative references for the mBorg/6MWD ratio are presented to assess breathlessness and leg discomfort responses to the 6MWT in COPD.