The body weight–walking distance product as related to lung function, anaerobic threshold and peakV̇O₂in COPD patients

Abstract

The product of walking distance and body weight (D·W) mimics the work of walking. We hypothesized the superiority of D·W to walking distance (D) alone in any correlation with lung function, anaerobic threshold (AT) and maximal oxygen uptake (V̇O_2max). We further hypothesized that the D·W product for a 6-min walk test (6 MWT) would correlate with the AT andV̇O_2maxbecause all three are markers of exercise ability.

Thirty-three male chronic obstructive pulmonary disease (COPD) patients with mean forced expiratory volume in 1 sec (FEV₁) of 1·2±0·4 l (range 0·58–1·86 l) were enrolled. Six patients were excluded due to inability to achieve a maximal test. Lung function and self-assessed every-day activities using a oxygen–cost diagram were evaluated before entry of the study. A maximal effort ramp-pattern cardiopulmonary exercise test (CPET) and a 6 MWT were conducted in random order. Borg score, heart rate, and O₂saturation with pulse oximetry (S_PO₂) were measured during both exercise tests.V̇O₂AT and minute ventilation were also measured during the CPET. Correlations were sought between the distance covered in the 6 MWT, and the D·W product with AT,V̇O_2maxand other variables.

The average D and D·W were 456 m and 27·5 kgkm⁻¹, respectively. D·W was superior to D alone when correlated with theV̇O_2maxand AT determined from the CPET, while modestly correlated with the change (Δ) in Borg score and ΔS_pO₂in the 6 MWT and self-assessed every-day activities. Distance×weight product was correlated with the AT andV̇O_2max. In addition, D·W was better correlated with diffusing capacity for carbon monoxide and vital capacity than D alone.

We conclude that D·W mimics the work of walking better than D and is suggested as a parameter for evaluation of patients' fitness if gas exchange measurements are not available.