The Effect of Pulmonary Rehabilitation on Carotid Chemoreceptor Activity and Sensitivity in Chronic Obstructive Pulmonary Disease

• Author / Creator

  Byers, Bradley W

• Chronic obstructive pulmonary disease (COPD) is associated with increased cardiovascular (CV) risk, which may result from heightened sympathetic nerve activity secondary to elevated carotid chemoreceptor (CC) activity/sensitivity. Our recent work indicates that CC activity/sensitivity is elevated in COPD compared to controls, which appears to contribute to increased CV risk resulting from tonic vasoconstriction. Exercise training has been shown to normalize CC activity/sensitivity in other populations characterized by elevated CC activity/sensitivity. COPD patients are commonly referred to pulmonary rehabilitation (PR), an exercise-based intervention shown to improve dyspnea, exercise tolerance, and quality of life. The purpose of this study was to determine whether PR can reduce CC activity/sensitivity in COPD. A pre-post case-control study design was used; COPD patients on the PR waiting list were enrolled in the experimental group, while COPD patients not enrolled in PR were recruited as controls. CC activity/sensitivity, exercise tolerance, resting dyspnea, quality of life, arterial stiffness, and autonomic function were assessed before and after the intervention period. CC activity was determined by the reduction in minute ventilation (ΔV̇E) while breathing transient hyperoxia (FIO2=1.0). CC sensitivity was evaluated by the increase in V̇E relative to the drop in arterial saturation while breathing hypoxic gas (ΔV̇E/ΔSpO2). Functional exercise tolerance was assessed by six-minute walk distance, the modified Medical Research Council questionnaire was used to determine resting dyspnea, and quality of life was assessed with the St. George’s Respiratory Questionnaire. Arterial stiffness was assessed using carotid-radial pulse wave velocity while autonomic function was examined with heart-rate variability and baroreceptor sensitivity. Data from 45 patients completing PR and 15 COPD controls were analyzed. Patients completing PR improved exercise tolerance (p=0.01), resting dyspnea (p=0.03), and health-related quality of life (p=0.03). There was no effect of PR on CC activity or CC sensitivity in stable COPD patients. When stratified by the degree of baseline CC activity, individuals with greater baseline CC activity significantly reduced CC activity following PR (p<0.01); however this improvement in CC activity occurred independently of changes in arterial stiffness or autonomic function. These data indicate that, despite improving exercise tolerance, resting dyspnea, and health-related quality of life, PR does not appear to affect CC activity/sensitivity in COPD. PR may normalize CC activity in stable COPD patients, however this is independent of changes in indicators of CV risk. It is possible that the exercise training stimulus achieved during PR is insufficient to elicit changes in CC activity/sensitivity, or unlike what has been observed in experimental heart failure, exercise training may not be an appropriate intervention in reducing CC activity/sensitivity and the associated CV risk in stable COPD patients.

• Subjects / Keywords

  • COPD
  • Pulmonary Rehabilitation
  • Chemoreceptor

• Graduation date

  Spring 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3X05XR05

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.