Trial Comparing Effect of He/O2 to Medical Air on Pulmonary Function Disease

Two types of measurements will be performed with each of the three evaluated gases: * pulmonary function measurements at rest to establish the resistance to airflow in a reproducible way, including the measurements of Inspiratory Capacity (IC), Forced Expiratory Volume in 1 second (FEV1), Forced Expiratory Flows (FEF) at different lung volumes (25 to 75% of the vital capacity), and Forced Vital Capacity (FVC), * Tidal Volume (TV) measured at rest and during light cycling exercise. The results of this study should be useful to evaluate the extent of influence on gas concentration, since none of the previous trials have been performed with He/O2 65:35, as well as the extent of influence on the lung disease, since none of the previous trials have been performed with asthmatic patients at various disease stages. The working hypothesis is that when using He/O2 mixtures 78:22 and 65:35, the flow resistance decreases as compared to medical air because low density helium replaces nitrogen, thus resulting in a lower workload of breathing for asthmatic and COPD patients. For patients with reduced pulmonary function, this difference might result in greater Inspiratory Capacity. That is why Inspiratory Capacity will be measured as primary efficacy criterion, but also Tidal Volume and other pulmonary function parameters on 3 types of subjects/patients : * healthy volunteers, * patients with moderate and severe persistent asthma, * patients with moderate and severe COPD.