After exhalation, human alveoli have an average radius of approximately 0.05 mm. When inflated by inhalation, the radius increases to about 0.10 mm. The normal mucous tissue fluid surrounding the alveoli has a nominal surface tension of about 50 dynes/cm. The presence of the natural surfactant decreases this to about 3.3 dynes/cm (a factor of 15!). Note that the lungs are inflating by applying a negative pressure to body cavity around them, so the signs of your pressure changes might look a little odd at first.
a. The units "dynes/cm" do not look right for surface energy at first glance because of the linear cm units. Convert the two given surface tensions (with and without surfactant) to units of J/m2 to show why dynes/cm units make sense.
b. Using the converted J/m2 units, calculate the applied pressure necessary to inflate the alveoli without the surfactant, in units of Torr.
c. Calculate the applied pressure necessary to inflate the alveoli with the surfactant, in units of Torr.
d. By what factor has the addition of the surfactant changed the inhalation pressure?