[Early respiratory function disorders secondary to tobacco smoking]

The volume of isoflow (VisoV) in 29 asymptomatic smokers with normal radiographic and pulmonary function studies was studied, with the purpose of investigating the presence of early alterations of the transitional airways in a group of 256 chronic smokers. The VisoV was measured using a body test plethysmograph, and two flow-volume curves with air and with helium were performed. 13 out of the 29 subjects (45%) showed an abnormal VisoV of between 17 and 39 per cent (normal 0-10%). This findings suggest that smoking initially damages the small transitional airways and that VisoV is an useful procedure for investigating early damage in this zone.