Factors Affecting Pulmonary Ventilation
1) Surface Tension of Alveolar Fluid
As noted earlier the alveolar fluid exerts a force known as surface tension . Example, when liquid surrounds a sphere of air (alveolus or soap bubble), surface tension produces an inward force (higher pressure to lower pressure). Soap bubbles collapse because of this force. In the lungs the surface tension causes the alveoli to assume the smallest possible diameter. Surfactant as mentioned earlier is present in the alveolar fluid and reduces its surface tension therefore reducing the inward force.
2) Compliance of the Lungs
This refers to how much effort is needed to stretch the lungs and chest wall. Example: a thin balloon has high compliance because it is easy to blow up. A stiff balloon takes more effort and therefore has low compliance. Low compliance is often the case with pulmonary diseases, scar tissue in the lungs (tuberculosis), lungs filled with fluid (pulmonary edema), surfactant deficiency, paralysis of muscles of inspiration, etc.
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