The inhabitants of Vlaardingen and Vlagtwedde participated in a longitudinal study, which included measurements of FEV1 and FVC. After 12 years up to 5 measurements were available for each subject. This allows investigating to what extent cross-sectional and longitudinal findings disclose the same age-related trends in spirometry. The results are depicted in the animation below.
The main findings are:
- In adult non-smokers FEV1 and FVC decline with age. The decline tends to accelerate with age, but for FEV1 it decelerates in males, possibly due to selection effects.
- Longitudinally the FEV1 and FVC increase somewhat until about age 23 yr and 39 yr for FEV1 and FVC, respectively; from then on there is a decline, which increases with age.
- The same trends are observed in smokers. Particularly in male smokers the decline in FEV1 starts early, longitudinally at about age 17 yr. Smoking tends to shift the age-related decline in males by about 6 years. The same premature lung aging is not observed in women. However, these data were collected between 1970-1985, when few women smoked; it can therefore not be excluded that nowadays the same trend occurs in women.
It follows that in repeated measurements on the same person one should be careful in making comparisons with the observed longitudinal behavior and the age-related trend derived from cross-sectional studies. The latter, for one thing, comprises:
- a cohort effect
- an intra-individual effect of aging.