Purpose. To assess the physical stability and aerosol characteristicsof suspensions of hollow porous microspheres (PulmoSpheres™) inHFA-134a.

alkane propellants have now been approved: HFA-134a Luis A. Dellamary,1 Thomas E. Tarara,1 (1,1,1,2-tetrafluoroethane), and HFA-227 (1,1,1,2,3,3,3 hepDan J. Smith,1 Christopher H. Woelk,1 tafluoropropane). Unfortunately, the transition to the new more Anastasios Adractas,1 Michael L. Costello,2 environmentally acceptable HFA propellants has been difficult, Howard Gill,1 and Jeffry G. Weers1,3 due in large part to the poor solvency of the HFA, which limits