Decrease in lung recoil pressure after cessation of smoking.

Tests of lung mechanics and single-breath carbon monoxide diffusing capacity (DLCO) were done in 26 apparently healthy cigarette smokers before and 2 months after cessation of smoking. There was a significant increase in vital capacity and 1-sec forced expiratory volume as well as improvement in frequency dependence of lung dynamic compliance. Slope and phase III and density dependence of maximal expiratory flow showed a borderline improvement DLCO did not change. Static lung pressure-volume curves showed a small but significant (P less than 0.01) shift toward lower pressures. We concluded that the previously reported decrease in lung recoil pressure observed in smokers is even more accentuated after cessation of smoking.