title: Six-minute walk distance in patients with chronic obstructive pulmonary disease: Which reference equations should we use?
abstract: The use of different 6-min walk distance (6MWD) reference equations probably results in different predicted 6MWD reference values. We wished to investigate the impact of several 6MWD reference equations for adults in patients with chronic obstructive pulmonary disease (COPD) and factors accountable for different 6MWD% predicted values. Twenty-two 6MWD reference equations were applied to a data set of 2757 patients with COPD. The predicted 6MWD reference value of Troosters and colleagues was used as the point of reference. Four out of 21 remaining equations resulted in comparable 6MWD% predicted, 16 equations resulted in significantly higher 6MWD% predicted and 1 equation resulted in a significantly lower 6MWD% predicted. Similar differences in 6MWD% predicted were observed after stratification by sex. Body mass index and global initiative for chronic obstructive lung disease (GOLD) stage classification demonstrated varying results within and between the groups; 9 out of 21 equations resulted in comparable 6MWD% predicted in underweight patients but only 1 equation demonstrated comparable result in obese. Eight equations in GOLD I, whilst 5 out of 21 equations in GOLD IV resulted in comparable 6MWD% predicted. Existing 6MWD reference equations will give varying results. The choice of 6MWD reference equation should consider the consistency of 6-min walk test operating procedures and at least be specific for the country/region of origin.
authors.affiliation: Department of Research and Education, CIRO+, Centre of Expertise for Chronic Organ Failure, Hornerheide, Horn, The Netherlands vasilisandrianopoulos@ciro-horn.nl.
authors.forename: Vasileios
authors.initials: V
authors.lastname: Andrianopoulos
authors.affiliation: Department of Physiotherapy, Alfred Health and La Trobe University, Melbourne, Australia.
authors.forename: Anne E
authors.initials: AE
authors.lastname: Holland
authors.affiliation: Department of Respiratory Medicine, University Hospitals of Leicester NHS Trust, Leicester, UK.
authors.forename: Sally J
authors.initials: SJ
authors.lastname: Singh
authors.affiliation: Department of Research and Education, CIRO+, Centre of Expertise for Chronic Organ Failure, Hornerheide, Horn, The Netherlands.
authors.forename: Frits M E
authors.initials: FM
authors.lastname: Franssen
authors.affiliation: Department of Respiratory Medicine, Laurentius Hospital, Roermond, The Netherlands.
authors.forename: Herman-Jan
authors.initials: HJ
authors.lastname: Pennings
authors.affiliation: Department of Respiratory Medicine, St Anna Hospital, Geldrop, The Netherlands.
authors.forename: Arent J
authors.initials: AJ
authors.lastname: Michels
authors.affiliation: Department of Respiratory Medicine, Catharina Hospital, Eindhoven, The Netherlands.
authors.forename: Frank W J M
authors.initials: FW
authors.lastname: Smeenk
authors.affiliation: Department of Physical Education and Sport Sciences, National and Kapodistrian University of Athens, Athens, Greece.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Vogiatzis
authors.affiliation: Department of Research and Education, CIRO+, Centre of Expertise for Chronic Organ Failure, Hornerheide, Horn, The Netherlands Department of Respiratory Medicine, Maastricht University Medical Centre (MUMC+), Maastricht, The Netherlands.
authors.forename: Emiel F M
authors.initials: EF
authors.lastname: Wouters
authors.affiliation: Department of Research and Education, CIRO+, Centre of Expertise for Chronic Organ Failure, Hornerheide, Horn, The Netherlands.
authors.forename: Martijn A
authors.initials: MA
authors.lastname: Spruit
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005080:Exercise Test / Q000379:methods*; D017079:Exercise Tolerance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000145:classification / Q000503:physiopathology*; D012015:Reference Standards; D012016:Reference Values; D012189:Retrospective Studies; D012720:Severity of Illness Index; D016138:Walking
keywords: 6-min walk test; 6MWD predicted values; 6MWD reference equations; COPD; exercise capacity