A subject inspires a mixture of gases containing carbon monoxide and holds his breath for 10minutes. During those 10seconds, alveolar Pco is 0.5mmHg and the CO uptake is 25ml/min. Which of the following is the diffusing capacity of the lung for CO?
A subject inspires a mixture of gases containing carbon monoxide and holds his breath for 10minutes. During those 10seconds, alveolar Pco is 0.5mmHg and the CO uptake is 25ml/min. Which of the following is the diffusing capacity of the lung for CO?
💡 Explanation
**Core Concept**
The diffusing capacity of the lung for carbon monoxide (DLCO) is a measure of the lung's ability to transfer a substance across the alveolar-capillary membrane. It is an important parameter in assessing lung function, particularly in diseases affecting the lung parenchyma or the pulmonary vasculature.
**Why the Correct Answer is Right**
The DLCO can be calculated using the formula: DLCO = (CO uptake / (alveolar Pco - inspired Pco)) * (VA / Vb), where VA is the alveolar volume and Vb is the blood volume in the lungs. In this scenario, the CO uptake is given as 25 ml/min, and the alveolar Pco is 0.5 mmHg. Assuming the inspired Pco is negligible, we can calculate the DLCO.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not take into account the alveolar Pco in the calculation. The DLCO formula requires the difference between alveolar and inspired Pco.
**Option B:** This option is incorrect because it assumes a constant alveolar volume, which may not be accurate in this scenario where the subject holds his breath for 10 minutes.
**Clinical Pearl / High-Yield Fact**
The DLCO is an important parameter in diagnosing and monitoring lung diseases such as interstitial lung disease, pulmonary fibrosis, and chronic obstructive pulmonary disease (COPD). A low DLCO indicates impaired gas exchange, which can be a sign of lung damage or disease.