UBC Theses and Dissertations
Heart-lung interactions following cervical spinal cord injury Gee, Cameron Marshall
Cervical spinal cord injury (C-SCI) is a devastating condition that leads to significant impairments in both the cardiovascular and respiratory response to aerobic exercise. As the heart and lungs share space within the thoracic cavity it follows that changes in one system will affect the other. Therefore, the purpose of this thesis was to examine heart-lung interactions in C-SCI and to utilize this knowledge to enhance exercise capacity in athletes with C-SCI. The aims of this thesis were to (1) compare the cardiorespiratory response to maximal and sub-maximal exercise following C-SCI to able-bodied individuals, with a particular focus on operating lung volumes (Study #1, Chapter 3); (2) to examine the effects of respiratory loading on lung volumes and left-ventricular function during head-up tilt (Study #2, Chapter 4); and (3) to assess the effects of a combined inspiratory and expiratory respiratory muscle training (i.e. RMT) intervention in elite athletes with C-SCI (Study #3, Chapter 5). Laboratory-based incremental arm ergometry testing demonstrated that C-SCI is associated with a limited exercise capacity compared to able-bodied individuals along with an altered respiratory pattern that is characterized by dynamic hyperinflation and reduced tidal volume. By manipulating inspiratory and expiratory esophageal pressure in individuals with C-SCI, it was demonstrated that expiratory loading elicited dynamic hyperinflation that was associated with impaired left-ventricular filling, likely due to direct ventricular interaction and/or mediastinal constraint. Finally, a six-week RMT intervention in elite athletes with C-SCI was found to significantly enhance respiratory muscle strength and measures of pulmonary function and prevent dynamic hyperinflation during exercise. These changes in pulmonary function were accompanied by enhanced exercise capacity during an incremental arm ergometry test and were partly ameliorated following six-weeks of wash-out (i.e., no RMT). This thesis demonstrates that dynamic hyperinflation in individuals with C-SCI, which likely occurs due to expiratory muscle weakness, limits left ventricular filling and is associated with an attenuated exercise capacity compared to able-bodied individuals. RMT improved respiratory muscle strength and prevented dynamic hyperinflation in individuals with C-SCI and enhanced exercise capacity.
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