Effects of Inhaled Ondansetron on Perceived Respiratory Discomfort (Dyspnea) During Exercise in the Presence of External Thoracic Restriction

"Dyspnea" refers to the awareness of breathing discomfort that is typically experienced during exercise in health and disease. In various participant populations, dyspnea is a predictor of disability and death; and contributes to exercise intolerance and an adverse health-related quality-of-life. It follows that alleviating dyspnea and improving exercise tolerance are among the principal goals of disease management. Nevertheless, the effective management of dyspnea and activity-limitation remains an elusive goal for many healthcare providers and current strategies aimed at reversing the underlying chronic disease are only partially successful in this regard. Thus, research aimed at identifying dyspnea-specific medications to complement existing therapies for the management of exertional symptoms is timely and clinically relevant. The purpose of this study is to test the hypothesis that single-dose inhalation of nebulized ondansetron (a serotonin 5-HT3 receptor antagonist) will improve the perception of dyspnea during strenuous exercise in health, young men. To this end, the investigators will compare the effects of inhaled 0.9% saline placebo and inhaled ondansetron (8 mg) on detailed assessments of neural respiratory drive (diaphragm EMG), ventilation, breathing pattern, dynamic operating lung volumes, contractile respiratory muscle function, cardio-metabolic function and dyspnea (sensory intensity and affective responses) during symptom-limited, high-intensity, constant-work-rate cycle exercise testing in healthy, men aged 20-40 years.