Which of the following has/have been shown to injure the alveolar-capillary membrane? 1. Excessive pressures 2. Excessive tidal volumes 3. Increased intracranial pressures 4. Pulmonary hypertension

a. 1, 2, and 4 only
b. 2 and 3 only
c. 4 only
d. 1, 2, 3, and 4

ANS: A
Conditions of pulmonary hypertension (e.g., capillary pressure >30 mm Hg during congestive heart failure and high-altitude pulmonary edema) and excessive tidal volume and airway pressure during positive-pressure ventilation (e.g., tidal volume >6 ml/kg and airway pressures >30 cm H2O) can result in stress failure of the blood-gas membrane. Stress failure results in endothelial and/or type I cell stretching and shearing injuries.