Viscoplasticity of respiratory tissues

Area of Science:

• Physiology
• Biomechanics
• Respiratory Mechanics

Background:

• Low-frequency mechanical behavior of respiratory tissues exhibits similarities.
• Understanding these behaviors is crucial for respiratory system analysis.

Purpose of the Study:

• To test the hypothesis that rate-independent plastic and rate-dependent viscoelastic processes explain respiratory tissue mechanics.
• To analyze oscillatory responses of various respiratory tissues using a established model.

Main Methods:

• Collected and analyzed oscillatory data from excised cat lung, human chest wall, excised dog rib cage, and excised rabbit abdominal viscera.
• Applied Hildebrandt's viscoplastic model, comprising parallel plastoelastic and viscoelastic compartments in series with lumped inertia.
• Utilized a least-squares technique to fit the model to the oscillatory data and performed stress relaxation tests for verification.

Main Results:

• The viscoplastic model provided a qualitatively consistent and quantitatively good fit to the mechanical data of respiratory tissues.
• Stress relaxation functions calculated from cat lung data aligned well with observed stress relaxation.
• Both plasticity and viscoelasticity were identified as key factors in low-frequency respiratory tissue mechanics.

Conclusions:

• Plasticity and viscoelasticity are significant determinants of respiratory tissue mechanical behavior at low frequencies.
• Inertial effects play a negligible role in this mechanical behavior.
• The viscoplastic model effectively characterizes the complex mechanical responses of respiratory tissues.