Which technique is NOT used to measure Functional Residual Capacity (FRC)?

Functional Residual Capacity (FRC) refers to the volume of air remaining in the lungs after a normal expiration. The measurement of FRC is critical for assessing lung function and can be determined using various techniques.

The technique that is not used to measure FRC is simple spirometry. Spirometry primarily measures the volume of air that is inhaled and exhaled during forced maneuvers, such as the forced vital capacity (FVC) or forced expiratory volume in one second (FEV1). It does not assess the total lung volume or the residual volume specifically, making it unsuitable for directly measuring FRC.

In contrast, body plethysmography, gas dilution techniques, and closed-circuit helium dilution are all valid methods for measuring FRC. Body plethysmography utilizes changes in pressure within a sealed chamber to calculate lung volumes, including FRC. Gas dilution techniques involve inhaling a known concentration of an inert gas (like helium), which helps to assess the volume of the lungs based on the dilution of the gas. Closed-circuit helium dilution specifically uses a closed system where the initial concentration of helium is compared to the final concentration after the patient breathes from it, allowing for the calculation of lung volume, including FRC