Procedures (methods): 7% hypertonic saline (HS) aerosol containing the radio tracer Tc99m-sulfur colloid will be delivered via the tPAD and compared to the well characterized PARI LC Star nebulizer using planar gamma scintigraphy (i.e. particle clearance). The fraction of sulfur colloid particles that clear over the ensuing 24 hours with each device will indicate the fraction deposited in conducting airways.