Two types of resistance are what?

• A. Amplitude and Phase shift
• B. Conductance and Viscosity
• C. Airway and Tissue
• D. Ventilation and Perfusion

Answer: (C)

In breathing mechanics, the opposition to airflow comes from two distinct sources: the airways and the lung tissue. Airway resistance is the friction air experiences as it moves through the conducting tubes; it depends on airway diameter, branching, flow pattern, and anything that narrows or obstructs the tubes. Tissue resistance comes from the viscoelastic properties of the lung parenchyma and chest wall—the energy lost as these tissues stretch, compress, and rearrange during inspiration and expiration. Together they make up the total respiratory system resistance, with the pressure needed to move air proportional to the sum of these resistances (plus the elastic recoil opposing expansion). That’s why the two types are airway resistance and tissue resistance. The other options describe concepts that aren’t sources of resistance in the respiratory system.