Modulation of ventilatory mechanics during exercise in ventilation-limited populations

Abstract

The aim of this thesis was to examine the impact of modifications to ventilatory constraint in populations who have reductions in expiratory flow and ventilatory limitations during exercise. The first study examined the effect of the self-contained breathing apparatus (SCBA) regulator on work of breathing (WOB) and lung volume changes in healthy subjects. The second study further examined the effect of the SCBA on the above outcomes, as well as on pulmonary function and respiratory muscle fatigue during stair-stepping (in healthy subjects). In addition, the effect of breathing heliox on the aforementioned variables was studied. The third thesis study examined the effect of heliox on ventilatory constraint, exercise tolerance, and leg muscle fatigue in patients with chronic obstructive pulmonary disease (COPD). The main results of the first study were that, compared with a low-resistance breathing valve (RV), the SCBA regulator increased inspiratory elastic (32%), expiratory resistive (59%), and total WOB (13%), and increased end-expiratory lung volume creating a plateau in end-inspiratory lung volume at approximately 90% of vital capacity. When these variables were examined with the full SCBA and compared with the RV in the second study, similar results were found. In addition, resting pulmonary function was reduced with the SCBA. Exercise with the SCBA induced reductions in both inspiratory and expiratory maximal pressures indicating the presence of respiratory muscle fatigue. When compressed air was replaced with heliox in the SCBA, end-expiratory lung volume, total WOB, and respiratory muscle fatigue were reduced. These observations regarding the effect of heliox on ventilatory function led to the third study, which found that heliox increased exercise tolerance (53%) and leg muscle fatigue (15%) in patients with COPD, but only in those limited by ventilatory constraints and who did not have a significant level of leg fatigue while breathing room air. Those patients who did have leg fatigue on room air did not increase exercise tolerance despite reduced ventilatory constraint. Together, these findings indicate that reducing ventilatory constraint during exercise can have specific positive effects on exercise performance in populations who are ventilatory limited and have implications for occupational or rehabilitation exercise training.