Which of the following pathophysiologic conditions can result from acute airway narrowing and increases in airway resistance during respiratory failure caused by airflow obstruction? I. lung regions that cannot be completely emptied II. decreased pulmonary compliance III. respiratory muscle overload IV. impaired cardiac filling

A. I, III only
B. I, II, IV only
C. I, III, IV only
D. II, III, IV only

?ANS: C
A. Incorrect response: See explanation C.
B. Incorrect response: See explanation C.
C. Correct response: Respiratory failure from airflow obstruction is a direct consequence of acute airway narrowing and increases in airway resistance. These changes lead to two mechanical alterations. First, the increased pressures required for airflow may overload respiratory muscles, producing ventilatory pump failure with spontaneous minute ventilation inadequate for gas exchange. Second, the narrowed airways create regions of the lungs that cannot be properly emptied and returned to their normal resting volume. This occurrence is called air trapping and produces elevated end-expiratory pressures (i.e., auto-PEEP). Overinflated regions may compress more healthy regions of the lung, and impair ventilation–perfusion matching. The high intrathoracic pressures may also impair cardiac filling.
D. Incorrect response: See explanation C.?