Bernoulli Principle

As the forward velocity of a gas (or liquid) moving through a tube increases, the lateral wall pressure of the tube decreases.

Bernoulli Effect (Daniel Bernoulli)

 As velocity increases, lateral pressure (the force applied to the sides of the tube) decreases

 As gas flows through a stricture (obstruction), its velocity increases and lateral pressure decreases

 Magnitude of pressure drop is proportional to the increase in the square of the velocity.

 

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Lung pathophysiology – COPD: increased mucus in airways can cause partial obstruction, the increased velocity of gas passing by the narrowing causes a decrease in lateral pressure, and combined with the destructive changes in the lung tissue, augments airway collapse and air trapping on exhalation.