Sharma and Goodwin V o l u m e T V IRV ERV RV Lung volumes Lung capacity VC IC FRC TLC Figure 2 Relationship between lung volumes and lung capacities. Abbreviations: ERV, expiratory reserve volume; FRC, functional residual capacity; IC, inspiratory capacity; IRV, inspiratory reserve volume; RV, residual volume;TLC, total lung capacity;TV, total volume;VC, vital capacity. a defined time period that may not be present in successive generations explains why younger individuals now have a higher lung function compared with 50 years ago. The cumulative cohort effect is estimated to be 5 ml/yr. This means that each former 25 year old generation had a vital capacity which is lower by 125 ml compared with the present generation (Xu et al 1995). On the contrary, period effects include changes in techniques, equipment, and “learning effect” from 120 100 d te 80 c i d e r 60 p % 1 40 V E F 20 0 repeated measures that can all improve the lung function measurement on subsequent studies. Studies estimating the period effect on lung function showed an average FEV1 increase by 250 ml in men and 219 ml in women during two different survey periods (from 1973–1978 and 1985–1990) (Xu et al 1995). Most cross-sectional studies s h o w e d l i n e a r d e c l i n e i n F E V 1 w i t h a g e a n d , underestimated the rate of decline. Longitudinal studies showed a nonlinear decline with age. The estimated rate of decline in FEV1 is 25–30 ml/yr starting at age 35–40 years and can double to 60ml/yr after age 70 years. Precise rate of decline is difficult to assess as inter- individual variability (up to 125 ml) far surpasses the estimated annual decline by various regression equations (Morris et al 1971; Crapo et al 1981; Knudson et al 1983; Dockery et al 1985; Burrows et al 1986; Ware et al 1990; Roberts et al 1991; Enright et al 1993; Kerstjens et al 1997) (Table 4). Lung volumes depend on body size, especially height. Total lung capacity (TLC) corrected for age remains unchanged throughout life. Functional residual capacity and residual volume increase with age, resulting in a lower vital capacity. Gas exchange in the lungs occurs across the alveolar capillary membrane. It is measured by diffusing capacity of carbon monoxide (DLCO). The DLCO is dependant upon 0 10 20 30 40 50 60 70 80 90 Age in years Figure 3 Age-related decline in forced expiratory volume in one second (FEV1)% predicted plotted as % of maximal at age 20 years against age. Note: Adapted from Ware JH, Dockery DW, Louis TA, et al. 1990. Longitudinal and cross-sectional estimates of pulmonary function decline in never-smoking adults. Am J Epidemiol, 132:685-700. Copyright © 2004. Reprinted with permission from Oxford University Press. 256 Clinical Interventions in Aging 2006:1(3)