The typical diameter of an alveolus is 0.3 mm. The surface tension of water is about 70 dyne cm-1. The dyne is the unit of force in the DGS system, and is equal to 1 g cm s-2. (A) What is the pressure within this alveolus assuming no surfactant at mechanical equilibrium? Give the answer in Pascals (N m-2) and in mm Hg.
(B) Surfactant lowers the surface tension to about 28 dyne cm-1. With surfactant, what would the pressure be in an alveolus with a diameter of 0.3 mm?
(C) Expanding the lungs increases the size of the alveoli and increases the surface area. How much work is necessary to expand the alveoli in a normal tidal volume of 0.5 L. Assume that the Functional Residual Capacity is 2.3 L, anatomic dead space is 150 ml, and there is surfactant. (Hint: calculate work either as PdV or gdA; use the change in volume given to calculate dV or dA, given that the rest diameter of alveoli is 0.3 mm. Assume there are 150 million alveoli in the lungs).
(D) Now, assuming there is no surfactant, re-calculate problem (C). How much does the surfactant lower the mechanical work?
(E) What are the existing synthetic lung surfactants on healthcare market? How do they perform compared to the hypothetical one here?