PhD Oral Exam - Emilie Chan-Thim, Individualized Program

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

The aim of this thesis was to investigate the implications of diurnal variations in the clinical assessment of physiological, behavioral and psychological measures in a Chronic Obstructive Pulmonary Disease (COPD) population. We evaluated the effect of time of day on the acute response to incremental exercise in COPD. In a sample of 14 moderate-to-severe COPD participants we found a majority of individuals exceeded clinically significant variability 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. The timing of this peak coincides with the peak in body temperature, which is a measure of the underlying biological rhythm. Relative amplitude (RA) of the rest-activity cycle may be used as a marker of internal synchronization with physiological measures. Therefore, we investigated if high or low RA was associated with disease severity or prognosis in COPD. Lower RA was associated with more dyspnea and worse prognosis. The high amplitude group demonstrated increased activity levels in the afternoon. No significant difference was found in sleep quality. Depression severity was not found to have a significant association with amplitude, which is contrary to what has been reported in the literature. Therefore, we investigated whether diurnal variation in depression symptoms would be associated with depression severity. We found larger diurnal variation in depression symptoms to be associated with worse depression severity in COPD patients. Pulmonary function and exercise capacity did not have a significant role in the relationship.

The results presented in this thesis were the first to use diurnal variations to investigate the implications on assessments measures and clinical outcomes in COPD. Based on our findings new methodological recommendations such as accounting for the timing of repeated exercise testing is suggested, RA of the rest-activity cycle may be a useful marker in COPD prognosis, and identifying diurnal variation in depressive symptoms may be a novel way of identifying depression severity in COPD. Additionally, identifying the timing of peak exercise capacity and pattern of elevated physical activity in the afternoon may be a target for pulmonary rehabilitation programs.