Models to study mechanisms of airway collapse have been proposed. However, these models have not been tested in the human upper airway. Gas density and viscosity are different gas properties that influence upper airway collapse and are variables of different models.
In this study, subjects will breathe gas mixtures of different densities (helium and sulfur-hexafluoride) or viscosity (neon) for brief periods of time during flow-limited breaths. Flow limitation will be induced by sustained reductions of continuous positive airway pressure (CPAP). The investigators will test some models of upper airway collapse by observing if flow while breathing different gas mixtures scales according to the differences in density and viscosity.
