Abstract

The aim of this thesis was to investigate the clinical implications of diurnal variations in physiological, behavioral and psychological measures in a Chronic Obstructive Pulmonary Disease (COPD) population. In a sample of 14 moderate-to-severe COPD participants we first evaluated the effect of time of day on the acute response to incremental exercise in COPD. We found that a majority of individuals exceeded clinically significant changes in their pulmonary function and peak exercise capacity measures. A peak in exercise capacity was observed in the afternoon in the subgroup of individuals who demonstrated increased variability, similar to the timing of peak exercise performance previously documented in healthy individuals. We then investigated if high or low relative amplitude (RA), a marker of internal synchronization, was associated with disease severity or prognosis in COPD. Lower RA was associated with higher ratings of dyspnea and worse scores on prognostic indexes. The amplitude difference between the two sub-groups appears to be due to increased physical activity at midday in the high-RA sub-group. Lastly, we investigated whether diurnal variation in depression symptoms would be associated with depression symptoms severity. We found larger diurnal variation in depression symptoms to be associated with worse depression symptom severity in COPD patients. This association seemed independent of pulmonary function and exercise capacity.
The results presented in this thesis were the first to report on diurnal variations in various common clinical measures in COPD and to explore the link between amplitude of the rest-activity cycle and indexes of disease prognosis. Based on our findings, accounting for the timing of repeated exercise testing is suggested. RA of the rest-activity cycle may be a useful marker in COPD prognosis. Lastly, identifying diurnal variation in depressive symptoms may help detect depression in COPD.