## **Core Concept**
Spirometry is a common pulmonary function test that measures lung function, specifically the volume and/or flow of air that can be inhaled and exhaled. It assesses the functional capacity of the lungs and airways. Spirometry can provide various parameters, including Forced Vital Capacity (FVC), Forced Expiratory Volume in one second (FEV1), and peak expiratory flow rate.

## **Why the Correct Answer is Right**
Residual Volume (RV) represents the volume of air remaining in the lungs after maximum exhalation. Spirometry cannot directly measure RV because it measures the air that can be exhaled or inhaled, not the air left in the lungs after a maximal exhalation. Specialized tests like helium dilution, nitrogen washout, or body plethysmography are required to measure RV.

## **Why Each Wrong Option is Incorrect**
* **Option A:** Forced Vital Capacity (FVC) can be measured by spirometry. It is the total volume of air that can be forcibly exhaled from the lungs after a maximal inhalation.
* **Option B:** Forced Expiratory Volume in one second (FEV1) is also measured by spirometry. It represents the volume of air that can be forcibly exhaled in the first second of a forced exhalation.
* **Option D:** Peak Expiratory Flow Rate (PEFR) can be determined through spirometry. It is the maximum rate of airflow achieved during a forced exhalation.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that spirometry is crucial for diagnosing and monitoring obstructive lung diseases (like asthma and COPD) and restrictive lung diseases. However, for certain parameters like RV and Total Lung Capacity (TLC), additional tests are needed.

## **Correct Answer:** . Residual Volume (RV)