EFFECTS OF HYPEROXIA ON BRONCHIAL WALL DIMENSIONS AND LUNG-MECHANICS IN RATS

The effects of exposure to hyperoxic conditions (> 95 kPa at normobari c pressure) on bronchial wall dimensions and lung mechanics were exami ned in adult rats. Measurements of baseline pulmonary resistance and c hanges in pulmonary resistance following acetylcholine aerosol inhalat ion were made in rats ''posed to hyperoxia for 48 and 60 h and in cont rol rats exposed to air. Exposures for 48 h were carried out in humid (80% relative humidity) or dry (35-40% relative humidity) conditions. Morphometric measurements of airway wall thickness in lobar bronchi we re made in separate groups of similarly exposed rats. Exposure to hype roxia was associated with an increase in baseline pulmonary resistance (control rats 0.043 (0.016) cmH2O ml-1 s-1, 60 h exposed rats 0.125 ( 0.042) cmH2O ml-1 s-1) but hyper-responsiveness to acetylcholine inhal ation did not occur. Thickness of the airway wall and its subdivisions , epithelium, lamina propria and muscularis, was not altered by hypero xic exposure in humid conditions. However, epithelial thickening in th e lobar bronchi was observed in rats exposed for 48 h to hyperoxia in dry conditions compared to rats exposed in humid conditions (mean (SD) thickness 13.2 (3.3) mum for controls, 14.5 (1.5) mum for humid expos ed rats and 16.5 (3.3) mum for dry exposed rats). The increase in pulm onary resistance caused by hyperoxic exposure is unlikely to be due to airway damage as airway hyper-responsiveness did not occur, and is mo re likely to be associated with the development of alveolar oedema. En vironmental humidity may modulate lung damage induced by hyperoxia, as exposure in dry conditions was associated with significant epithelial thickening.