Nonlinearity of respiratory mechanics during bronchoconstriction in mice with airway inflammation

Respiratory system resistance (R) and elastance (E) are commonly estimated by fitting the linear equation of motion P = EV + R(V) over dot + P-0 (Eq. 1) to measurements of respiratory pressure (P), lung volume (V), and flow (V). However, the respiratory system is unlikely to behave linearly under many circumstances. We determined the importance of respiratory system nonlinearities in two groups of mechanically ventilated Balb/c mice [controls and mice with allergically inflamed airways (ova/ova)], by,g the impact of the addition of nonlinear terms (E2V2 assessing and R-2(V) over dot (V) over dot) on the goodness of model fit seen with Eq. 1. Significant improvement in fit (51.85 +/- 4.19%) was on seen in the ova/ova mice during bronchoconstriction when the E2V2 alone was added. An improvement was also observed with addition of the E2V2 term in mice with both low and high lung volumes ventilated at baseline, suggesting a volume-dependent nonlinearity of E. We speculate that airway closure in the constricted ova/ova mice accentuated the volume-dependent nonlinearity by decreasing lung volume and overdistending the remaining lung.