Airway resistance

In respiratory physiology, airway resistance is the resistance of the respiratory tract to airflow during inspiration and expiration. Airway resistance can be measured using body plethysmography.

Analogously to Ohm's Law:

Where:

So:

Where:

N.B. P_A and ${\displaystyle {\dot {V}}}$ change constantly during the respiratory cycle.

There are several important determinants of airway resistance including:

In fluid dynamics, the Hagen–Poiseuille equation is a physical law that gives the pressure drop in a fluid flowing through a long cylindrical pipe. The assumptions of the equation are that the flow is laminar viscous and incompressible and the flow is through a constant circular cross-section that is substantially longer than its diameter. The equation is also known as the Hagen–Poiseuille law, Poiseuille law and Poiseuille equation.

Where:

Dividing both sides by ${\displaystyle {\dot {V}}}$ and given the above definition shows:-

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