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

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