Relationship between frequency and amplitude dependence in the lung: a nonlinear block-structured modeling approach

Area of Science:

• Pulmonary Physiology
• Respiratory Mechanics
• Nonlinear Systems Analysis

Background:

• Lung constriction alters lung tissue resistance (Rti) and elastance (Eti) frequency and tidal volume (VT) dependencies.
• These changes suggest coupled linear and nonlinear mechanisms in lung tissue mechanics.

Purpose of the Study:

• To investigate the coupled frequency and VT dependencies of Rti and Eti during lung constriction.
• To differentiate between linear (L) and nonlinear (N) system models (Hammerstein vs. Wiener) in describing lung tissue mechanics.

Main Methods:

• Utilized nonlinear block-structured systems theory (Hammerstein and Wiener models).
• Combined models with a nonlinear airway compartment.
• Fitted models to canine airway pressure-flow data before and after histamine-induced constriction.

Main Results:

• The Wiener model (L-N structure) best described the coupled frequency and VT dependencies of Rti and Eti.
• This suggests coupled linear and nonlinear characteristics of lung tissues during normal and constricted states.
• Histamine induced greater changes in linear tissue parameters than nonlinear coefficients.

Conclusions:

• Lung tissue resistance and elastance dependencies are coupled during constriction.
• A linear airway compartment coupled with a Wiener-structured lung tissue model accurately represents these dynamics.
• Histamine significantly impacts linear lung tissue properties.