The Flow Resistance Across a Set of Airways is Lowest

Question

The flow resistance across a set of airways is lowest under which of the following conditions?
A)Airway radius is large and airways are in series.
B)Airway radius is large and airways are in parallel.
C)Airway radius is small and airways are in series.
D)Airway radius is small and airways are in parallel.

Accepted Answer

The flow resistance across a set of airways is inversely proportional to the fourth power of their radius. Therefore, larger airway radius will result in lower resistance. When airways are in parallel, the total flow resistance is lower than when they are in series. Therefore, option B (large airway radius and in parallel) has the lowest flow resistance.