The diagnosis of emphysema has been associated with changes in the appearance of the pressure-volume (P-V) curve: reduced maximal recoil pressure, increased lung volume, and a shift in the position of the curve to the left. In our clinical practice, we have observed that patients with chronic obstructive lung disease (COPD) commonly had P-V curves with reduced maximal elastic recoil that are difficult to classify according to the classic description of the P-V curve in emphysema. In order to study the variability of P-V curves, we studied 39 cigarette smokers attending a pulmonary clinic (age, 61 +/- 1 yr; smoking history, 45 +/- 3 pack-years; mean +/- SEM) and compared them with 20 patients with alpha-1-antitrypsin deficiency (AATD) (age, 41 +/- 2 yr; 13 smokers with a smoking history of 17 +/- 2 pack-years, and seven nonsmokers). Subjects underwent spirometry, lung volume, and diffusing capacity measurements as well as static deflation P-V curves. To characterize the P-V curves, we used transpulmonary pressure at 90% of TLC (PL90) as a measure of overall recoil and specific compliance (Csp) as a measure of the slope of the initial part of the P-V curve. The curves of non-AATD smokers were classified into three groups: 13 had PL90 greater than or equal to 80% predicted (Group I), 13 had PL90 less than 80% predicted and Csp greater than or equal to 0.08 (Group II), and 13 had PL90 less than 80% predicted and Csp less than 0.08 (Group III).(ABSTRACT TRUNCATED AT 250 WORDS)