Which of the following statement(s) is/are true concerning pulmonary mechanics?

b. The decreased compliance in acute respiratory failure occurs because the lung is smaller not stiffer

c. In acute respiratory failure, higher pressures are required to achieve the same level of inflation

d. Areas of normal lungs are more vulnerable to overdistention which may lead to progressive lung dysfunction

The standard compliance or volume pressure curve is drawn by measuring volume and pressure at stages of lung deflation after total inflation. The decreased compliance in acute respiratory distress syndrome occurs because the lung is smaller, not stiffer. In acute respiratory failure, the cause of decreased compliance is almost always associated with a decrease in functional residual capacity (FRC). The decreased FRC represents lost alveoli which are either collapsed or filled with fluid but still perfused with blood. Because the lung is smaller, the compliance curve has shifted to the right and much higher pressures are required to achieve the same level of inflation. Lung damage can be caused by high airway pressure, so that overdistension is not merely inefficient but actually detrimental. Since the most normal areas of lung have the best compliance, they are most vulnerable to overdistension, contributing to the steady progression of lung dysfunction in patients ventilated at high peak pressure.