Morphological determinants of peripheral lung mechanical changes induced by capsaicin.

We studied the morphological elements associated with airway and pulmonary tissue responses to capsaicin in mechanically ventilated guinea pigs. Lungs were excised and frozen in liquid nitrogen 3 and 20 min after capsaicin infusion (1 or 100 micrograms/kg i.v.). Using image analysis, we obtained contraction index (CI) and peribronchial edema area (CUFF) for both central (C) and peripheral airways (P). We also assessed alveolar size (mean linear intercepts, Lm) and tissue distortion (standard deviation of the number of intercepts, SDI). Multiple regression analysis showed significant associations between pulmonary tissue resistance (Rti) and CUFFP (p < 0.001); pulmonary dynamic elastance and SDI (p = 0.002); and airway resistance and CUFFC (p < 0.0001). Our results suggest that increases in Rti observed in guinea pigs after capsaicin infusion are primarily dependent on changes in the small airways, mainly peribronchiolar edema; the increase in lung elastance is related to distortion of parenchymal tissues; and large airway edema contributes significantly to airway resistance.