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Figure 2 | Respiratory Research

Figure 2

From: A mathematical reason for FEV1/FVC dependence on age

Figure 2

A graphical interpretation of FEV1/FVC decline with age in healthy subjects. FEV1 and FVC for an individual can be represented by one point on the plane determined by the coordinate system: FVC and FEV1. The ratio FEV1 to FVC is equal to the tangent of the angle α contained between the horizontal axis (FVC-axis) and the vector leading out to that point from the coordinate system origin. Thus, the lower value of the angle, the smaller the FEV1/FVC value.

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