What factors contribute to the development of auto-positive end expiratory pressure (PEEP)? 1. High expiratory Raw 2. High inspiratory flows 3. Inadequate expiratory time

a. 1 and 2 only
b. 1 and 3 only
c. 2 and 3 only
d. 1, 2, and 3

ANS: B
By effectively increasing the time constant of the lung, high expiratory resistance prolongs exha-lation to the point at which air trapping begins (Figure 46-21, B). Any shortening of the expira-tory time (Figure 46-21, C) aggravates the problem and increases both distal airway pressure and lung volume (auto-PEEP).