Frequency characteristics of lung tissue strip during passive stretch and induced pneumoconstriction

To investigate the frequency-dependent changes of lung tissue mechanics during pneumoconstriction, we studied guinea pig subpleural lung strips submitted to a multisinusoidal deformation composed of five equal-amplitude discrete frequencies ranging between 0.2 and 3.1 Hz. Strips were submitted to graded step stretch changes (SS) and to graded histamine stimulation (HS) in organ bath. Elastance, resistance, and hysteresivity were calculated at each frequency. The model accounting for the relationship between the complex Young's modulus and the angular frequency showed that the constant-phase hypothesis was satisfied in SS condition. However, HS modified all parameters in the model, and the constant-phase hypothesis could be rejected for HS of 10(-5) and 10(-3) M. The hysteresivity time course changed with angular frequency, but differently in the HS and SS conditions. Our results agree with a serial disposition of the connective matrix and contractile system in lung tissue. We conclude that pneumoconstriction induced significant structural changes at the level of the connective matrix.