Moriya, HT; Lemos, M; Rivero, DHRF; Hizume, DC; Alencar, AM
RATIONALE: Exposure to air pollution is associated with several diseases in the respiratory system. These diseases may be better understood by multi scale assessment of lung mechanics. Here, we investigated the outcome of acute exposure to Diesel Exhausted Particles (DEP) in ex vivo lung, and in vitro parenchyma tissue mechanics.
METHODS: Ten male Wistar rats randomly received a tracheal instillation of either 1mL of DEP solution (200 μg/mL) or PBS (saline buffered phosphate). After 24h, animals were anesthetized with intraperitoneal ketamine (75mg/kg) and xylazine (15mg/kg) and mechanically ventilated with pure oxygen, 80 breaths per minute and tidal volume of 7mL/kg for 10 minutes. For each animal, end-inspiratory occlusion was performed. After the lungs were completely collapsed, a letal dose KCl 0.2% was administrated. Ex vivo respiratory mechanics were assessed analyzing lung inflation data from collapsed state. The lungs were inflated at very low speed (0.14mL/s). During the inflation, lung pressure increased monotonically until it reached the pressure threshold to trigger the first avalanche of openings which recruit a large portion of the lung. After the first opening threshold was reached, the pressure decreased and started to fluctuate around a critical pressure. During this process, several regions of the lung were continuously recruited, each of them in a process called avalanche shock. We calculated the elastance (E = dP/dV) in subsequent portions of the PV curve, yielding negative, Eneg, and positive values of E. tissue mechanics were assessed using In vitro parenchyma strips mounted in organ chambers in Krebs-Henseleit solution at 37^C and connected to force transducers. After an equilibration period, the tissue strips were exposed to different amounts of acetylcholyne (10^-7 M, 3·10^-7 M, 10^-6 M, 3·10^-6 M, 10^-5 M, 3·10^-5 M, 10^-4 M, and 3·10^-4 M).
RESULTS: The distribution of the Eneg for both cases showed a power law behavior, with similar slopes but DEP curve was shifted to the left. No difference was found in the in vitro mechanics tissue strips.
CONCLUSION: Acute exposure to DEP affected ex vivo lung mechanics but did not affect the tissue strip properties. We interpreted these results using a model of airway opening in a tree like structure and we concluded that the properties of the lining lung fluids were changed possibly due to inflammation. In addition, instabilities in the PV curve could give new insights in lung/tissue mechanics.
