Evaluation of a movement detector to measure daily activity in patients with chronic lung disease

This study was designed to evaluate the performance of movement detectors (pedometers) in measuring daily activity of patients with chronic lung disease. Three groups of subjects were studied: group 1: 25 patients with stable nonhypercapnic chronic obstructive pulmonary disease (COPD) (forced expiratory volume in one second (FEV1) = 47+/-9% predicted) studied twice, one month apart; group 2: 25 patients with chronic respiratory failure studied before and three months after nasal nocturnal mechanical ventilation; and group 3: 25 normal healthy subjects studied once. The median level of activity in the healthy subjects (group 3) was three times greater than in either group of patients (groups 1 and 2). Activity levels were not correlated with age, sex or employment status. The repeatability of the activity counts in the nonhypercapnic COPD patients was high (intraclass correlation coefficient=0.94) and in these patients activity correlated significantly with FEV1 (r=0.54, p=0.006). In the respiratory failure patients, daytime arterial carbon dioxide pressure (Pa,CO2) improved following nasal nocturnal mechanical ventilation (NMV) (pre NMV: 8.5+/-1.2 kPa; post NMV: 6.2+/-0.5 kPa), health status improved (p<0.004) and daily movement count doubled (p<0.0001). This increase correlated with change in Pa,CO2 (r-0.53, p=0.006), but not with improved health status. We conclude that motion detectors may provide repeatable measures of daily activity that are related to physiological impairment and improvement following treatment. Activity counts appear to be complementary to estimates of exercise limitation obtained using health questionnaires.