Final answer:
A flow-volume graph plots the results of a spirometry test, which is used to diagnose and monitor respiratory diseases by measuring lung volumes and capacities.
Step-by-step explanation:
A flow-volume graph is a means of plotting the results of a spirometry test. Spirometry is a common pulmonary function test that measures lung volumes and capacities. Clinicians use spirometry to diagnose respiratory diseases like asthma, emphysema, and fibrosis. In this test, two important measurements are taken: the forced expiratory volume (FEV), which quantifies how much air a person can exhale during a forced breath in a specific period, usually one second, and the forced vital capacity (FVC), the total amount of air exhaled during a forced breath.
The ratio of FEV1 (the volume exhaled in the first second of a forced exhale) to FVC is particularly useful in diagnosing respiratory conditions. A low FEV1/FVC ratio indicates obstructive lung disease, such as asthma, while a high ratio may suggest a restrictive lung disease like fibrosis. Through the plotting of these values, the flow-volume graph provides a visual tool to help assess the effectiveness of disease treatment and monitor disease progression.