The Link between Regional Tidal Stretch and Lung Injury during Mechanical Ventilation.

The aim of this study was to assess the association between regional tidal volume (Vt), regional functional residual capacity (FRC), and the expression of genes linked with ventilator-induced lung injury. Two groups of BALB/c mice (n = 8 per group) were ventilated for 2 hours using a protective or injurious ventilation strategy, with free-breathing mice used as control animals. Regional Vt and FRC of the ventilated mice was determined by analysis of high-resolution four-dimensional computed tomographic images taken at baseline and after 2 hours of ventilation and corrected for the volume of the region (i.e., specific [s]Vt and specific [s]FRC). RNA concentrations of 21 genes in 10 different lung regions were quantified using a quantitative PCR array. sFRC at baseline varied regionally, independent of ventilation strategy, whereas sVt varied regionally depending on ventilation strategy. The expression of IL-6 (P = 0.04), Ccl2 (P < 0.01), and Ang-2 (P < 0.05) was associated with sVt but not sFRC. The expression of seven other genes varied regionally (IL-1β and RAGE [receptor for advanced glycation end products]) or depended on ventilation strategy (Nfe2l2 [nuclear factor erythroid-derived 2 factor 2], c-fos, and Wnt1) or both (TNF-α and Cxcl2), but it was not associated with regional sFRC or sVt. These observations suggest that regional inflammatory responses to mechanical ventilation are driven primarily by tidal stretch.