In patients with small-airway disease breathing at higher than normal frequencies, what is likely to happen?
1. Dynamic compliance drops.
2. Oxygen consumption decreases.
3. The distribution of ventilation worsens.
4. The work of breathing increases.
a. 1 and 2 only
b. 1, 2, and 4 only
c. 2, 3, and 4 only
d. 1, 2, 3, and 4
ANS: B
Compliance of the lung appears to decrease as breathing frequency increases. This phenomenon is called frequency dependence of compliance. Compliance measured during breathing is dynamic as it includes pressure changes created by resistance to airflow. If dynamic compliance decreases as the respiratory rate increases, some lung units must have abnormal time constants. Any stimu-lus to increase ventilation, such as exercise, may redistribute inspired gas. Mismatching of venti-lation and perfusion can result in hypoxemia, severely limiting an individual's ability to perform daily activities. In addition the increased breathing frequency and decreased dynamic compliance may result in significant increases in oxygen consumption.
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