This issue includes an important paper by Barry et al. 1 in which the changes in nasal peak inspiratory flow (NPIF), and oral peak inspiratory flow (OPIF), during acclimatized exposure to low barometric pressure (equivalent to a simulated altitude of 8000 m, about the height of Mount Everest) of subjects in a hypobaric chamber were analysed. The changes were presumably due to hypoxia and its chemical sequelae, and influenced by the processes of acclimatization. They show that NPIF increases by a mean of 16%, whereas OPIF increases by 47%, and conclude that these results are consistent with a decrease in upper airways luminal calibre at altitude, correlating with the symptomatic nasal blockage and impairment of mucociliary function seen in similar conditions. The changes must be due to chronic hypoxia rather than to inhalation of cold and dry air, since environmental temperature and humidity were maintained at values close to those found at sea level. The study is important because it may point to physiological mechanisms determining airway calibre at altitude, and to changes in the airways that will influence breathing at altitude. The authors must have confronted formidable problems in experimental design, since their subjects were confined to a hypobaric chamber for over a month, and the apparatus which could be used to assess their airway mechanics must inevitably have been limited. The authors fully justify their use of rather simple methods to assess airways' resistances. However, while these limitations can be appreciated, there are important considerations about the methodology and interpretation of results. A clear distinction between airways' conductance, airways' resistance and airways' calibre needs to be made. The former two are reciprocally related and depend, inter alia, on the viscosity and density of the transmitted gas, and other aerodynamic features; however calibre will affect both …