In health, approximately what proportion of the total work of breathing is attributable to friction-al resistance to tissue movement?

a. 20%
b. 30%
c. 40%
d. 50%

ANS: A
Tissue resistance accounts for only approximately 20% of the total resistance to lung inflation. However, in conditions such as obesity, pleural fibrosis, and ascites, the tissue viscous resistance will increase the total impedance to ventilation.