Decline of FEV1 by age and smoking status: facts, figures, and fallacies.

Assessment of pulmonary function testing plays as well as in patient based research and in epidemiological studies of healthy subjects, and a central role in everyday practice of the pultherefore the items discussed will be mainly monary physician. New patients are diagnosed centred around the FEV1. and graded in severity on the basis of results from these tests, and the course of the disease in previously diagnosed patients is judged with General course of FEV1 over time the help of lung function measurements. The There is still considerable debate over the shape use of pulmonary function tests for these purof lung function increase and decline during poses requires a concept of what constitutes life. During childhood and adolescence there both a normal level and a normal decline and, is naturally a rise in lung function, the exact consequently, an unusually low level and acshape of which is beyond the scope of this celerated decline. The concept of a normal paper. For the period early in adult life, differlevel is perceived to be fairly straightforward ent shapes have been suggested. Although some and is routinely deducted from some set of authors have taken the decline in lung function reference values. The population selection of to start at 15–20 years of age, 3 others have the reference equations used is taken to be found that the FEV1 continues to rise to the sufficiently representative of the patient under age of 25 years, or even into the fourth Department of study. In this review the problems associated Pulmonology decade. 7 It is probably fair to say that in with this assumption will be discussed and the and Department of healthy individuals there is a plateau phase in Epidemiology, cut off values between normal and abnormal early adulthood in which there is little or no University of examined. The same reference equations are change in FEV1. 6 8 The European Community Groningen, often employed for the judgement of normal Groningen, for Coal and Steel stipulates that no change The Netherlands decline, assuming that the coefficient for age occurs between the ages of 18 to 25 and an H A M Kerstjens adequately represents decline in individuals. age of 25 years should be entered into the B Rijcken This approach, however, can be rather inregression equation for this whole age range. J P Schouten D S Postma adequate and this will be reviewed. AdAfter this plateau FEV1 starts to decrease, with ditionally, special reference will be given to the newer studies that exclude smokers more Correspondence to: Dr H A M Kerstjens, estimating decline in smokers. Because of its carefully suggesting a later start in nonDepartment of Pulmonology, ease of measurement and its very good resmokers. It has long been thought that this University Hospital Groningen, producibility, the forced expiratory volume in ensuing decrease is linear — that is, that FEV1 PO Box 30001, one second (FEV1) is the most widely used and decreases by the same number of ml each year. 9700 RB Groningen, The Netherlands. quoted lung function test in clinical practice However, many authors have now shown that the decline accelerates with ageing. 7 10–12 As a result of these models of change in FEV1, at any given time in adulthood FEV1 is determined by three factors: (1) the maximally attained level of lung function during early adulthood; (2) the onset of decline of lung function or, alternatively, the duration of the plateau phase; and (3) the rate of decline of lung function (fig 1). In other words, from one low measurement of FEV1 in an adult it is impossible to determine whether the reduced lung function is due to not having achieved a high maximum during early adulthood, to having had a shortened plateau phase, to having an accelerated rate of decline, or to any combination of these. c