[1] Univ Alberta, Dept Med, Div Cardiol, Pulm Hypertens Program, Edmonton, AB T6G 2B7, Canada
[2] Univ London Imperial Coll Sci Technol & Med, Div Expt Med, London, England
[3] Stanford Univ, Dept Pediat, Cardiopulm Res Program, Stanford, CA 94305 USA
[4] Pulm Vasc Res Inst, Canterbury, Kent, England