Amplitude of the rest–activity cycle in chronic obstructive pulmonary disease: an exploratory study

In chronic obstructive pulmonary disease (COPD), there is large individual variability in the progression of the disease. Low amplitude of rest–activity rhythms has been associated with worse prognosis in a variety of diseases, but it has not been investigated in COPD. The first aim of this exploratory study was to compare disease severity and prognosis indicators between COPD patients with relatively high or low amplitude of their rest–activity cycle, as measured with actigraphy. As a second objective, 24-hour profiles of both activity levels and nighttime-sleep quality were compared between the two subgroups to assess the relative contribution of day- and night-activity levels to high and low rest–activity rhythm amplitude in this population. Rest–activity rhythms were measured with 8–14 days of wrist actigraphy in 14 patients (nine men), aged 58–79 years, suffering from moderate-to-severe COPD. Relative amplitude of 24-hour activity profiles ranged from 0.72 to 0.98. Participants were divided at the median into high-amplitude (mean ± standard deviation 0.9±0.04) and low-amplitude (0.79±0.05) subgroups. There was no significant difference between the two subgroups for pulmonary function or exercise capacity. However, the low-amplitude group had more severe symptoms of dyspnea and worse prognostic scores than the high-amplitude group (P<0.05). The 24-hour activity profiles revealed higher levels of activity in the high-amplitude group for the 12–3 pm interval (P<0.05). There was no significant difference between the two groups for subjective or actigraphic estimates of sleep quality, sleep duration, or proportion of daytime sleep. This exploratory study is a first step toward the identification of larger rest–activity rhythm amplitude as a marker of better prognosis in COPD and as another potential target for exercise-based rehabilitation programs in this population.