Question

You are a Biomedical Engineer interested in developing new drugs to help breathing in premature babies. Surfactant is a complex mixture of phospholipids, ions and proteins. It plays a critical role in increasing oxygen exchange in the alveoli of the lungs, by decreasing the surface tension of water on the alveoli surfaces. If surfactant is at abnormally low levels, then the attraction of water molecules for each other, and hence the surface tension, increases. This increased surface tension causes increased pressure in the alveoli, leading to their malfunction, breathing problems, and possible lung collapse.

Assume that:

a) The normal surface tension in the fluids that line the alveoli is about 12 dynes/cm, when there are normal levels of surfactant present.

b) Without surfactant, the surface tension goes up to about 58 dynes/cm.

c) P = pressure, ơ = surface tension, r = radius of the alveolus; P = 2ơ/r

d) Diameter = 220 µm for a typical alveolus

e) Surfactant usually does not start to be secreted until the 6th month of gestation for human infants

Problem

1) What is the surface-tension pressure (P) for the lungs of an adult with the normal amount of surfactant?

2) What is the surface-tension pressure (P) for the lungs of an adult with no surfactant?

3) If a baby is born prematurely at 4 months, would the baby have trouble breathing? Explain why or why not.

4) Premature babies have alveoli with radii one quarter the size of adults. Calculate the premature baby’s surface-tension pressure (P) if born at 5 months?

5) Calculate the volume of an alveolus of a premature baby (assume its shape is approximated by a sphere).

Answer 1