Which type of spirometer measures volume directly?

The correct choice is the volume displacing spirometer. This type of spirometer operates by capturing the air displaced by the patient's breathing. As the patient inhales and exhales, the device measures the change in volume of the enclosed gas, producing a direct measurement of the volume of air exchanged during each breath. This method is advantageous for accurately assessing lung volumes, such as tidal volume, inspiratory reserve volume, and expiratory reserve volume.

Flow sensing spirometers, on the other hand, measure the flow rates of air rather than the volumes directly. They calculate volume based on those flow rates over time, which can introduce inaccuracies if the flow is inconsistent or not accurately recorded throughout the breathing cycle. Forced expiratory spirometers specifically assess forced vital capacity and forced expiratory volume but are not designed to measure volume directly; instead, they rely on flow measurements to calculate volume during specific maneuvers. Electronic spirometers refer to devices that may use electronic sensors to measure flow or pressure but do not necessarily provide direct volume measurements themselves. Hence, the volume displacing spirometer is distinctly recognized for its direct measurement capabilities.