The effect of acute, intensive cigarette smoking on maximal expiratory flows and the single-breath nitrogen washout trace.

The effect of acute, intensive cigarette smoking on forced vital capacity and the single-breath expired N2 trace was studied in 82 smokers. There were significant decreases in the "effort-dependent" tests, such as peak flow and 1-sec forced expiratory volume, but no change in the more "effort-independent" tests, such as maximal mid-expiratory flow and maximal expiratory flow at 25 per cent of the vital capacity. Closing volume was unchanged in absolute terms and as a percentage of vital capacity. Closing capacity was unchanged in absolute terms and as a percentage of total lung capacity, but there was a significant increase in the slope of Phase III of the N2 washout curve after the acute smoking session. The tests of function that changed significantly after acute, intensive smoking were the ones that improved in 52 subjects who modified their smoking habits. The data suggest that acute, intensive cigarette smoking may be associated with an increase in resistance to air flow in the larger airways or a reduction in effort, and with increased nonuniformity of intraregional distribution of ventilation.