Lung function in young adults: evidence for differences in the chronological age at which various functions start to decline.

In order to gather prospective information on the chronological age at which lung functions start to decline, follow-up measurements were carried out on 38 young adults (30 men and eight women) whose respiratory and cardiac function had been studied previously in the course of a survey of high school students. In the 15 subjects who had reached adult height at the time of the first study, only the vital capacity showed no change between studies, while forced expiratory flow rates (FEV1, MMEF), transfer factor (TLCO) and alveolar volume (VA) all decreased. By contrast, in the 23 subjects who had grown in stature since the previous tests, there was an increase in the slow and forced vital capacity, no consistent change in FEV1 and MMEF, and a decrease in TLCO. The findings are consistent with the view that the age-related decline does not start at the same chronological age for all lung functions, and suggest that structural changes associated with biological "aging" affect some functions before others. The results also illustrate the inadequacy of predicting values for early adulthood by backward extrapolation from later decades or forward extrapolation from the teens, and underline the need for comprehensive studies to elucidate the pattern of change which accompanies growth, maturation, and early adulthood.