Which of the following factors would tend to increase the frictional component of the work of breathing?

1. Decreased compliance of the lungs or thorax
2. High frequencies of breathing
3. Increased Raw
a. 1 and 2 only
b. 1, 2, and 3
c. 1 and 3 only
d. 2 and 3 only

ANS: D
In healthy individuals, the mechanical work of breathing depends on the pattern of ventilation. High breathing rates (and hence, high flows) increase frictional work. Patients who have airway obstruction (i.e., increased Raw) also experience increased frictional work of breathing.