Water vapour and temperature dynamics in the upper airways of normal and CF subjects

Water vapour partial pressure (PH2O) and temperature (T) were measured together, continuously, at the airway opening (either lips or nares) and at the oropharynx of human subjects with normal lungs or with cystic fibrosis (CF). No apparent differences in PH2O or T were found between normal and CF groups breathing ambient air (22 +/- 2 degrees C). During inspiration the relative humidity at the pharynx for nose breathing (95%) was higher than for mouth breathing (75%). For hot air breathing (48 +/- 2 degrees C), the PH2O and relative humidity of inspired gas at the pharynx was lower for the CF group than for the normal group. Also, the CF group had a higher airway surface temperature at the airway openings on inspiration. These data suggest that when the rate of evaporation is sufficiently high, the rate-limiting step may be water transport through the mucosal tissue and/or secretions. At least for the upper airways, this rate limitation is more evident for CF patients than for normal subjects.