Longitudinal versus cross-sectional spirometric data

There is sufficient evidence (ref. 1) that age-related trends in cross-sectional studies of lung function differ from those found in longitudinal investigations. There are various explanations for this.

A selection effect occurs, i.e. the weakest individuals die at an early age, so that increasingly the older subjects in the population represent a positive selection (e.g. with the most favorable lung function).
A cohort effect may be involved, i.e. that persons born for example 50 years ago had a different lung development during growth than those born 20 years ago. Infectious diseases, nutrition, smoking during gestation, better survival after premature birth, exposure to environmental factors, socio-economic status (which determines bodily development in early life and leads to secular trends in body size and pulmonary function), growing up at altitude, and possibly other environmental factors, etc. might all leave their marks so that the lung function of a 40 yr old person born in 1920 would be different from that in a 40 yr old person born in 1950.
In a cross-sectional study measurements may have been influenced by seasonal and other climatological factors, whereas in longitudinal studies carried out over a sufficient time span such chance events would tend to average out.
Technical problems cannot be excluded. Unfortunately the equipment used may still play a role: it is far from easy to properly take into account the effects of gas temperature, humidity and gas composition in calibrating equipment, and even more difficult to do this reproducibly.

Implicit in most studies is that the age-related decline in lung function in adults is attributable to the effect of aging on the lung. However, there is some evidence that it may also be related to changes in body mass; in follow-up studies in males (ref. 2) a 1 kg weight gain has been found to account for a reduction in FEV1 of between 13.9 and 23 mL. However, a higher birth weight is associated with a higher adult FEV1 and FVC. This is consistent with the finding that waist circumference is negatively associated with FEV1 and FVC.

Ref. 1 - Cross-sectional versus longitudinal data
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Ref. 2 - Change in body mass and in FEV1
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5	Beverley AC, Blizzard CL, Schmidt MD, Walters EH, Dwyer T, Venn AJ. Longitudinal associations of adiposity with adult lung function in the Childhood Determinants of Adult Health (CDAH) study. Obesity 2011; 19; 2069-2075.
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7	Chen Y, Rennie D, Cormier YF, Dosman J. Waist circumference is associated with pulmonary function in normal-weight, overweight, and obese subjects. Am J Clin Nutr 2007; 85: 35-39.

Last modified on 03.07.2017 15:49