PSIO 532 Study Guide - Midterm Guide: Alveolar Pressure, Atelectasis, Surface Tension
PSL – Respiratory Physiology
Alveolar Stability
▪ The diagram shows the effect of
surfactant on alveolar stability. To
understand this effect, you must
know the equation that is used to
describe the alveolar conditions of
interest:
P = 2T/R (LaPace Law)
▪ P is the intra-alveolar pressure, T is
the tension of the alveolus (resistance that acts to preserve the integrity of the surface),
and R is the radius of the alveolus.
▪ In the example shown on the top right, the alveoli are assumed to be without
surfactant. In the example shown, the surface tensions are equal. Based on the above
equation, you can see that the smaller alveolus will have a larger intraluminal
pressure. Because gas flows from regions of high pressure to low pressure, gas will
flow from the smaller alveolus to the larger alveolus. (One alveolus will be deflated or
collapsed). When alveoli are collapsed, they are said to be atelectic.
o Whenever the radius is reduced, that will increase the pressure within the
alveolus
o An aveolus with a larger radius, the aveolar pressure is going to be less on the
larger aveolus compared to the smaller aveolus
o This will cause one aveolus to collapse → Atelectic
o We want the aveolus to be expanded → we want stability existing within the
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Document Summary
Alveolar stability: the diagram shows the effect of surfactant on alveolar stability. To understand this effect, you must know the equation that is used to describe the alveolar conditions of interest: P = 2t/r (lapace law: p is the intra-alveolar pressure, t is the tension of the alveolus (resistance that acts to preserve the integrity of the surface), and r is the radius of the alveolus. In the example shown on the top right, the alveoli are assumed to be without surfactant. In the example shown, the surface tensions are equal. Based on the above equation, you can see that the smaller alveolus will have a larger intraluminal pressure. Because gas flows from regions of high pressure to low pressure, gas will flow from the smaller alveolus to the larger alveolus. (one alveolus will be deflated or collapsed). First, look at the alveolus on the right. Note that the presence of surfactant decreased the surface tension.
