Thirty-one young smokers (cigarette consumption; 19.7±6.8 cigarettes/day, years of smoking; 4.8±1.7 years) who were completely asymptomatic and had FEV
1.0% of greater than 80%, were compared with 29 healthy nonsmokers of the same age group, using airway resistance and maximal expiratory flow volume curves breathing air and a helium-oxygen mixture (79% He+21% O
2).
Airway resistance, Vmax and ΔVmax as well as FEV
1.0% and MMF could not distinguish smokers from nonsmokers, but the 2 groups could be distinguished on the basis of the volume of isoflow following one (Visov
1) and three (Visov
3) inhalations of helium-oxygen mixture. Visov
1 was not significantly higher than Visov
3 in nonsmokers, but it was significantly higher in smokers (P<0.02). Furthermore, Visov
1 was abnormal in 55% of smokers, whereas Visov
3 was abnormal in only 42%.
The correlation between Visov
1 and (V
75-V
50)/(V
50-V
25) which seems to express uneven distribution of time constant within lung approached statistical significance for only smokers (r=+0.33, 0.05<p<0.10, n=31), while it was significant for all subjects (r=+0.30, p<0.05, n=60). In addition, a significant correlation was found between ΔVisov (=Visov
1-Visov
3) and (V
75-V
50)/(V
50-V
25) in smokers except for the subjects whose ΔVisov is negative or zero (r=+0.51, p<0.05).
We conclude that cigarette smoking impairs peripheral airways first and that Visov
1 which reflects the maldistribution of ventilation is a more sensitive test than Visov
3 to distinguish smokers from nonsmokers.
