A man has intrapleural pressure of (-5 cm H20) before inspiration and (-10cm H20) at the end of inspiration and he inspires 1200 ml from a spirometer. What shall be the the compliance of lungs?
## **Core Concept**
The compliance of the lungs is a measure of the lung's ability to expand, defined as the change in lung volume that occurs per unit change in the transpulmonary pressure. It is an important parameter in respiratory physiology, reflecting the lung's distensibility. The formula for lung compliance is (C = Delta V / Delta P), where (C) is compliance, (Delta V) is the change in volume, and (Delta P) is the change in pressure.
## **Why the Correct Answer is Right**
Given that the intrapleural pressure (also known as intrathoracic pressure) changes from -5 cm H2O before inspiration to -10 cm H2O at the end of inspiration, and the volume inspired is 1200 ml, we can calculate the lung compliance. The change in pressure ((Delta P)) is (-10 - (-5) = -5) cm H2O. To use the formula (C = Delta V / Delta P), we convert (Delta P) to cm H2O and (Delta V) to ml. So, (C = 1200 / 5 = 240) ml/cm H2O.
## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it doesn't match our calculated value of 240 ml/cm H2O.
- **Option B:** This option is incorrect for the same reason as Option A; it does not align with the calculated compliance.
- **Option D:** This option suggests a much lower compliance than calculated, which would not be correct given the provided numbers.
## **Clinical Pearl / High-Yield Fact**
A normal lung compliance is approximately 200 ml/cm H2O. Compliance can be decreased in conditions like pulmonary fibrosis and increased in conditions such as emphysema. Remembering that lung compliance reflects how easily the lungs expand is crucial.
## **Correct Answer:** . 240 ml/cm H2O