Effects of hyperoxia on bronchial wall dimensions and lung mechanics in rats

Abstract

The effects of exposure to hyperoxic conditions (> 95 kPa at normobaric pressure) on bronchial wall dimensions and lung mechanics were examined in adult rats. Measurements of baseline pulmonary resistance and changes in pulmonary resistance following acetylcholine aerosol inhalation were made in rats exposed to hyperoxia for 48 and 60 h and in control 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 were made in separate groups of similarly exposed rats. Exposure to hyperoxia 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 inhalation did not occur. Thickness of the airway wall and its subdivisions, epithelium, lamina propria and muscularis, was not altered by hyperoxic exposure in humid conditions. However, epithelial thickening in the 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) microns for controls, 14.5 (1.5) microns for humid exposed rats and 16.5 (3.3) microns for dry exposed rats). The increase in pulmonary resistance caused by hyperoxic exposure is unlikely to be due to airway damage as airway hyper-responsiveness did not occur, and is more likely to be associated with the development of alveolar oedema. Environmental humidity may modulate lung damage induced by hyperoxia, as exposure in dry conditions was associated with significant epithelial thickening.

Respiratory function and blood gas variables in cystic fibrosis patients during reduced environmental pressure

“…In animals inspiratory hypoxia has a direct impact on the tone of bronchial smooth muscles resulting in an increase in airway resistance (D'Brot and Ahmed 1991;Dewachter et al 1992), whereas inspiratory hyperoxia induced slight bronchodilation (D'Brot and Ahmed 1991;Libby et al 1981;Murchie et al 1993). In healthy subjects, a slight hypoxia-induced increase in airway resistance was observed whereby pronounced inter-individual differences were found (Dillard et al 1998;Saunders et al 1977;Teague et al 1988).…”

“…Inspiratory hypoxia has impact on the tone of the bronchial smooth muscles resulting in hypoxia-induced bronchoconstriction accompanied by an increase in airway resistance (D'Brot and Ahmed 1991;Dewachter et al 1992;Saunders et al 1977;Teague et al 1988) and, conversely, inspiratory hyperoxia reduces the hypoxiainduced increase in pulmonary resistance (D'Brot and Ahmed 1991;Murchie et al 1993). This study followed changes in blood gases in arterialized capillary blood and lung function in CF patients under moderate inspiratory isocapnic hypoxia by hypobaric conditions.…”

Anti‐remodelling drugs for the treatment of asthma: requirement for animal models of airway wall remodelling

“…70 In a similar model, smooth muscle expansion is evident after 5 days exposure to hyperoxia, although the epithelial area is unaffected. 70 In a similar model, smooth muscle expansion is evident after 5 days exposure to hyperoxia, although the epithelial area is unaffected.…”

“…Using hyperoxia as a stimulus, 48-60 h exposure to > 95 kPa O2 in relatively dry air conditions (approximately 35-40% humidity) causes an increase in the volume occupied by the epithelium in Sprague-Dawley rats. 70 In a similar model, smooth muscle expansion is evident after 5 days exposure to hyperoxia, although the epithelial area is unaffected. 71 Studies in immature (21-day-old) Sprague-Dawley rats have shown that hyperoxia stimulates an expansion in volume occupied by both epithelial and smooth muscle after only 6 days exposure.…”

Humidity does not affect central nervous system oxygen toxicity

“…It may also be possible that dry normobaric oxygen is more deleterious to lung surface tension than humidified oxygen in the anesthetized dog after 12 h (11). Exposure of rats to dry normobaric oxygen for 48 h caused epithelial thickening in the lobar bronchi, which was not the case with humidified oxygen (12). In patients treated daily with 256 kPa of oxygen for 95 min, humidified oxygen increased the forced expiratory volume in the first second as opposed to dry oxygen (13).…”