The Upper Limit of Normal Rate of Lung Function Decline in Healthy Adults in the Framingham Heart Study

Background

Lung function declines over the course of adulthood; however, a consensus on the normal range of decline in an individual’s lung function is lacking.

Research Question

What is the normal range and the upper limit of normal (ULN) decline in lung function in adults without prior tobacco use, occupational dust exposure, or a known diagnosis or symptoms of cardiopulmonary disease?

Study Design and Methods

A retrospective analysis of healthy individuals who have never smoked (N = 1,305) from the Framingham Heart Study with repeated lung function meeting standards for acceptability and reproducibility was conducted. Longitudinal change was derived using a linear mixed effects model and estimated to a 6-year interval. The ULN decline was defined as the 95th percentile.

Results

The mean follow-up between spirometry examinations was 5.5 years, whereas the mean follow-up between diffusing capacity for carbon monoxide studies was 5.9 years. Decline in FEV₁, FVC, and D accelerated with age, whereas decline in FEV₁/FVC decelerated with age. Decline varied with sex, age, and height. Over a 6-year period, the ULN decline in FEV₁ ranged from 383 to 667 mL, and the ULN decline in Dlco ranged from 3.6 to 9.5 mL/min/mm Hg. Overall, male individuals had faster absolute rates of decline than female individuals, whereas relative (%) rates of decline were similar between sexes.

Interpretation

Lung function decline is nonlinear and accelerates with age. In this cohort, the ULN decline over 6 years often exceeded current guidelines for interpreting significant longitudinal change in lung function.