The goals of this study were (i) to compare the degree and (ii) temporal changes in
airway obstruction in sheep with
pulmonary injury induced by
smoke inhalation and/or
burn; (iii) to qualitatively assess the cellular and mucous content of obstructive material; and (iv) to statistically assess a possible relationship between the degree of
airway obstruction and pulmonary dysfunction. Using masked histologic slides, we estimated the degree of
luminal obstruction in all cross-sectioned airways. The mean degree of bronchial, bronchiolar, and terminal bronchiolar obstruction was significantly greater in animals with
smoke injury alone or combined
smoke inhalation and
burn (S+B) injury, compared with animals with
burn injury alone or uninjured animals (P < 0.05). In S+B animals, the degree of bronchial obstruction was maximal at 24 h, with a progressive decrease over 72 h. In contrast, the degree of bronchiolar obstruction increased over time. Qualitatively, bronchial casts were largely composed of mucus at early times after injury, whereas neutrophils were the principal component of bronchiolar obstructive material. Localization of specific
mucin subtypes in S+B tissues suggests that increasing bronchiolar obstruction is derived, in part, from upper airway material. Multiple linear regression analysis of
airway obstruction scores compared with PaO2/FIO2 values showed a correlation coefficient of r = 0.76, with bronchial and bronchiolar scores predictive of PaO2/FIO2, (P < 0.05). These results suggest that strategies to remove or decrease formation of upper airway obstructive material may reduce its deposition into small airways and parenchyma and may improve respiratory function in victims of
smoke inhalation injury.