The body weight-walking distance product as related to lung function, anaerobic threshold and peak (V)over dot O2 in COPD patients

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(PLT) and maximal oxygen uptake (VO2max). We further hypothesized that the D W product for a 6-min walk test (6 MWT) would correlate with the AT and VO2max because all three are markers of exercise ability. Thirty-three male chronic obstructive pulmonary disease (COPD) patients with mean forced expiratory volume in 1sec (FEV1) of 1.2+0.41 (range 0.58-1.86 1) were enrolled. Six patients were excluded due to inabiIity 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 O-2 Saturation with pulse oximetry (SPO2) were measured during both exercise tests. VO2, AT 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, VO2max and other variables. The average D and D-W were 456m and 27.5kgkm(-1), respectively. D W was superior to D alone when correlated with the VO2max and AT determined from the CPET, while modestly correlated with the change Cd) in Borg score and DeltaS(P)O(2) in the 6MWT and self-assessed every-day activities. Distance x weight product was correlated with the PIT and VO2max. 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.