MICROSCOPIC EMPHYSEMA IN RELATION TO AGE AND SMOKING HABIT

Background-The increases in airspace size within the human lung associ ated with microscopic emphysema can be assessed by measuring the airsp ace wall surface area per unit volume of lung tissue (AWUV). In a prev ious study the limits of normality of AWUV with age were estimated in lifelong non-smokers by the 95% prediction limits of the regression li ne for these variables. The aims of this study were to study the incid ence of microscopically assessed emphysema in a group of smokers and t o examine the influence of smoking habit on the susceptibility to and severity of microscopically assessed emphysema. Methods-AWUV was measu red on tissue sections from 125 lung specimens obtained from tobacco s mokers (mean age 61.1 (range 33-85) years) with the fast interval proc essor, a rapid automatic scanning device. The mean AWUV value was calc ulated for each specimen and this figure was plotted against the age o f the subject. The limits of normal AWUV were plotted, and AWUV values below these limits were taken as indicative of microscopically assess ed emphysema. Details of the number of cigarettes smoked each day were obtained for 97 of the smokers. These subjects were grouped according to smoking habit: group 1, 1-19 cigarettes/day; group 2, 20-29 cigare ttes/day; group 3, at least 30 cigarettes/day. The AWUV results from e ach of these groups were then assessed. Results-Mean AWUV decreased wi th age in this group of smokers, but only 26% had microscopically asse ssed emphysema, indicating that within the group there were two subgro ups of smokers with differing susceptibility to microscopically assess ed emphysema. There were no sex differences in the incidence of micros copically assessed emphysema, nor were the incidence and severity incr eased with increased daily cigarette consumption. Conclusions-Suscepti bility to microscopically assessed emphysema was found to be similar i n male and female smokers. Daily cigarette consumption did not appear to be the primary factor influencing the susceptibility to or severity of microscopically assessed emphysema. Susceptibility differences wit hin the smoking population should be taken into consideration in studi es of the pathogenesis of emphysema.