Quantifying physical activity in chronic obstructive pulmonary disease (COPD): Accelerometer and 6-minute walk

Steele BG, Holt L, Belza B, Ferris S, Lakshminaryan S, Buchner D. Quantifying physical activity in chronic obstructive pulmonary disease (COPD): Accelerometer and 6-minute walk. Paper presented at: American Thoracic Society Annual International Conference; 1998 Sep 15; Chicago, IL.

Physical immobility is a major risk factor for a multitude of illnesses in the elderly and is the most limiting outcome of COPD and dyspnea. Precise quantitation of daily, 'free-living' activity is desired to more effectively evaluate interventions aimed at reducing physical frailty and improving mobility in these sedentary populations. The Tritrac® accelerometer, a triaxial motion sensor worn at the waist, is an appealing alternative to activity recall questionnaires and observational methods currently in use. The purpose of this preliminary investigation was to determine relationships between Tritrac® activity, measured as vector magnitude during three 6-minute walks (VM6M) and over four days (VM4D) with activity tolerance determined by the longest 6-minute walk in feet (6MDW). Nineteen COPD patients (mean age 66.5 years, + 6.8, FEV1 1.24 L +0.64, 1 woman, 18 men) were studied at entry into pulmonary rehabilitation. In addition to a four-day period of accelerometer use, a subgroup of nine also wore a Tritrac® during the 6-minute walk test. Significance was set at p < 0.05 with two-tailed probability; relationships are shown as Spearman rank (rs) and Pearson correlations (r). Correlations between VM6M and 6MDW during walks one, two and three were rs = 0.92 (p < 0.001), rs = 0.82 (p < 0.007) and rs = 0.95 (p < 0.0001), respectively. The correlation between VM4D and the maximal 6MDW was r = 0.85 (p < 0.0001). Accelerometer measurement of walking activity in COPD patients closely parallels six-minute walking distance and improves with repeated testing. As expected, activity measured over four days is less associated with 6-minute walking distance than concomitant accelerometer measurement but clearly reflects a robust correlation with everyday function in this group.