Which type of resistance usually doesn't change?

• A. Airway Resistance
• B. Tissue Resistance
• C. Dynamic Resistance
• D. Vascular Resistance

Answer: (B)

In respiratory mechanics, resistance can be split into two main parts: airway resistance and tissue (parenchymal) resistance. Airway resistance changes a lot because the airways can constrict or dilate, secretions or edema can block passages, and flow conditions can alter caliber. Dynamic resistance also shifts with the breathing pattern and flow rate. Vascular resistance refers to the pulmonary blood vessels and can vary with perfusion and vasoactive factors, separate from the airways’ mechanical properties.

Tissue resistance, however, comes from the viscous damping of the lung tissue and chest wall as they stretch and recoil. Those viscoelastic properties stay largely the same under normal physiologic conditions, so tissue resistance tends to be constant and doesn’t change with typical changes in breathing pattern or airway tone. That’s why it’s the type that’s usually unchanged.