Compliance of lung is measured by-
**Core Concept**
Lung compliance is a measure of the lung's ability to expand and fill with air. It is defined as the change in lung volume that occurs in response to a change in transpulmonary pressure. This concept is crucial in understanding the mechanics of breathing and the pathophysiology of respiratory diseases.
**Why the Correct Answer is Right**
The correct answer is the elastic recoil pressure of the lungs at a given volume. Lung compliance is calculated by dividing the change in lung volume by the change in transpulmonary pressure. In other words, more compliant lungs require less pressure to achieve the same change in volume. The elastic recoil pressure of the lungs is a measure of the lung's tendency to return to its resting volume after a change in volume. It is an important determinant of lung compliance and plays a critical role in the mechanics of breathing.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because compliance is not measured by the rate of airflow. While airflow is an important aspect of respiratory physiology, it is not directly related to lung compliance.
**Option B:** This option is incorrect because the work of breathing is not a direct measure of lung compliance. While the work of breathing can be affected by lung compliance, it is a more complex parameter that takes into account other factors such as airway resistance and respiratory rate.
**Option C:** This option is incorrect because the lung volume at the end of a normal expiration is not a measure of lung compliance. This volume is known as the functional residual capacity (FRC) and is an important parameter in respiratory physiology, but it is not directly related to lung compliance.
**Clinical Pearl / High-Yield Fact**
One important clinical correlation is that lung compliance is often decreased in patients with chronic obstructive pulmonary disease (COPD), which can lead to increased work of breathing and respiratory failure.
**Correct Answer:** D.