"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.