Which tool is used to measure respiratory airflow?

The spirometer is the correct tool for measuring respiratory airflow because it is specifically designed to assess lung function by measuring the volume of air that is inhaled and exhaled. This device is crucial for evaluating respiratory conditions and determining how well the lungs are performing. It provides vital information on various lung metrics, such as tidal volume, vital capacity, and forced expiratory volume, which help in diagnosing conditions like asthma or chronic obstructive pulmonary disease (COPD).

In contrast, a sphygmomanometer is intended for measuring blood pressure, and a stethoscope is used to listen to internal body sounds, including heartbeats and lung sounds, but it does not provide quantitative measurements of airflow. A thermometer measures body temperature, which is not related to airflow measurement. Thus, the spirometer stands out as the appropriate choice for assessing respiratory airflow.