BACKGROUND: Emphysema is defined as the abnormal enlargement of airspaces distal to the terminal bronchiole, but the limits of normality of airspace size have never been defined. The aims of the study were to examine the effects of age and sex on airspace size in non-smokers and to define the limits of normal airspace size. METHODS: Airspace size was measured in terms of airspace wall surface area per unit volume of lung tissue (AWUV). AWUV was measured on histological sections of lung tissue with an automated scanning system, the fast interval processor. Thirty eight lifelong non-smokers were studied, 15 male and 23 female, with an age range of 21-93 years. Macroscopic emphysema was assessed semi-quantitatively on the midsagittal slice of each lung specimen. RESULTS: The relation between mean AWUV and age was negative (r = -0.78). This relation was linear, and the 95% prediction limits of its regression line were used as the limits of normality of AWUV in this sample. The AWUV-age relationship was similar in the men and women studied. Localised areas of macroscopic emphysema were found in three specimens whose mean AWUV measurements were within the normal range. CONCLUSIONS: There is a normal increase in airspace size associated with advancing age in adult lungs. The limits of normal AWUV between ages 21 and 93 years have been defined, and it is proposed that lungs with a mean AWUV below the 95% prediction limit should be considered as having emphysema.
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