Ventilation: Static Forces. Lung Compliance Elastic Recoil Surface Tension. Lung Compliance. Air flow in lungs: no muscles in the alveoli; air passively moves in/out of the lungs in response to pressure gradients. Forces are present that resist the opening of the lungs, I.e., the alveoli
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pressure within the alveoli themselves tend to keep the lungs inflated
Reduced surface tension within the alveoli
(more about this later)
Changes in transpulmonary pressure opposing the elastic (static) forces of lung tissue.Lung CL
Surface tension develops at every liquid-air interface (static) forces of lung tissue.
it takes a certain inflation pressure to maintain or support a liquid bubbleLaPlace’s Law & Surface Tension
P = 2ST/r (static) forces of lung tissue.
P = pressure
ST = surface tension
r = radius
Pressure is needed to keep an bubble (I.e., alveoli) inflated
This pressure is directly affected by the surface tension of the bubble
Inversely affected by the size of the bubbleHow does it affect lung expansion?
As the surface tension of a liquid bubble increases, distending pressure needed to hold the bubble open increases
The higher the surface tension, the more pressure required to inflate the bubbleThe effects of increasing surface tension on pressure
As radius of a bubble increases, distending pressure needed to hold bubble open decreases
As radius decreases, pressure to hold bubble open increasesSurface tension and bubble size