Hyperoxia-induced changes in mouse lung mechanics: forced oscillations vs.barometric plethysmography

Hyperoxia-induced lung damage was investigated via airway and respiratory t issue mechanics measurements with low-frequency forced oscillations (LFOT) and analysis of spontaneous breathing indexes by barometric whole body plet hysmography (WBP). WBP was performed in the unrestrained awake mice kept in room air (n = 12) or in 100% oxygen for 24 (n = 9), 48 (n = 8), or 60 (n = 9) h, and the indexes, including enhanced pause (Penh) and peak inspirator y and expiratory flows, were determined. The mice were then anesthetized, p aralyzed, and mechanically ventilated. Airway resistance, respiratory syste m resistance at breathing frequency, and tissue damping and elastance were identified from the LFOT impedance data by model fitting. The monotonous de crease in airway resistance during hyperoxia correlated best with the incre asing peak expiratory flow. Respiratory system resistance and tissue dampin g and elastance were unchanged up to 48 h of exposure but were markedly ele vated at 60 h, with associated decreases in peak inspiratory flow. Penh was increased at 24 h and sharply elevated at 60 h. These results indicate no adverse effect of hyperoxia on the airway mechanics in mice, whereas marked parenchymal damage develops by 60 h. The inconsistent relationships betwee n LFOT parameters and WBP indexes suggest that the changes in the latter re flect alterations in the breathing pattern rather than in the mechanical pr operties. It is concluded that, in the presence of diffuse lung disease, Pe nh is inadequate for characterization of the mechanical status of the respi ratory system.