What does a spirograph measure?

A spirograph measures the volume and speed of air during breathing. It is commonly used in pulmonary function tests to assess lung capacity and the efficiency of the respiratory system. The data collected can help identify various respiratory conditions, such as asthma or chronic obstructive pulmonary disease (COPD), by quantifying the amount of air a person can inhale and exhale, as well as the flow rates during these processes.

This choice is correct because spirographs specifically focus on respiratory metrics, reflecting how well the respiratory system is functioning, rather than measuring circulatory metrics or oxygen levels, which are associated with other tools and methods. In contrast, devices that measure blood pressure, heart rate, or oxygen saturation are designed for cardiovascular or blood analysis and do not assess lung function, which is the primary purpose of a spirograph.