What is the effect of increasing airway area on velocity, assuming volume is constant?

When the airway area increases while maintaining a constant volume, the velocity of air flowing through that airway decreases. This concept can be understood by applying the principle of continuity in fluid dynamics, which states that for an incompressible fluid, the product of cross-sectional area and velocity remains constant.

In simple terms, if you think of a garden hose: when the nozzle is constricted (decreased area), the water flows out at a higher velocity. Conversely, if you were to widen the nozzle (increase the area) while keeping the overall flow of water (volume) the same, the water would exit the nozzle at a lower velocity.

Thus, increased airway area allows more space for the air to pass through, resulting in a decrease in velocity in order to maintain the same flow rate (volume). This relationship is crucial in understanding respiratory mechanics and how changes in airway resistance can impact airflow velocity.