Tiffeneau's index

The Tiffeneau index (TI) is the ratio between FEV1 and FVC. In spirometry, we measure the forced vital capacity (FVC), which represents the volume of exhaled air after a maximum long inhalation. When performing FVC, the forced expiratory volume in the first second (FEV1) is also measured, which is the volume of air that a person exhales in the first second of FVC. The ratio between FEV1 and FVC is called the Tiffeneau index, which in a healthy person is above 75%, meaning that a person with healthy lungs can exhale 3/4 of the air from the lungs in the first second of forced exhalation. These values vary depending on various factors, such as age, gender, and body height and weight.