A 62-year old patient has been diagnosed with a restrictive pulmonary disease. Which of his following measurements is likely to be normal?
**Core Concept**
The question is testing the understanding of the pathophysiology of restrictive pulmonary disease, which is characterized by a reduction in lung volume and capacity due to various causes such as interstitial lung disease, sarcoidosis, or pulmonary fibrosis.
**Why the Correct Answer is Right**
Restrictive lung disease leads to a decrease in lung volumes, including the total lung capacity (TLC), vital capacity (VC), and residual volume (RV). However, the functional residual capacity (FRC) is often preserved or even increased due to the increased elastic recoil of the lung parenchyma. This is because the lung is stiffer in restrictive lung disease, resulting in a higher FRC at the end of expiration.
**Why Each Wrong Option is Incorrect**
* **Option A:** TLC is likely decreased in restrictive lung disease due to the reduction in lung volume and capacity.
* **Option B:** VC is also decreased in restrictive lung disease as it is a measure of the maximum amount of air that can be exhaled from the lungs after a maximum inhalation.
* **Option C:** RV is decreased in restrictive lung disease as the lung is stiffer and less compliant, leading to a reduction in the residual volume.
**Clinical Pearl / High-Yield Fact**
In restrictive lung disease, the lung compliance is reduced, leading to an increase in the elastic recoil of the lung parenchyma, which can result in an increased FRC.
**Correct Answer: D. Functional Residual Capacity (FRC)**