Respiratory mechanics: modelling, measurement and clinical applications—a review

The mechanical properties of the airways significantly impact respiration, and estimating respiratory mechanics provides important insights for diagnosing and monitoring respiratory diseases, such as asthma and chronic obstructive pulmonary disease. Here, we review electrical equivalent models of human respiratory mechanics and derive the mathematical expressions of their impedance. We describe the necessity of transitioning from a basic single-compartment model to a multi-frequency constant-phase model to represent respiratory mechanics in both health and disease. We review the forced oscillation technique and impulse oscillometry systems, which are clinically used to measure respiratory mechanics via respiratory impedance, and examine their roles in respiratory diseases. We also describe how respiratory impedance can be interpreted using these electrical analog representations to estimate key mechanical parameters. Attention is given to the limitations arising from device-specific variability and intra- and inter-breath fluctuations, where frequency-compensation filters and modelling strategies incorporating nonlinear resistance and compliance models could enhance the robustness and standardization of impedance-based analysis.