MEASUREMENTS OF MAXIMAL EXPIRATORY FLOW-RATES IN CIGARETTE SMOKERS AND NON-SMOKERS USING GASES OF HIGH AND LOW-DENSITIES

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Abstract
Maximal expiratory flow (.ovrhdot.Vmax) measurements were made at various lung volumes in 29 smokers and 29 nonsmokers with normal spirometric test results, while the subjects breathed a mixture of 80% He and 20% O2 (He + O2), 70% sulfur hexafluoride and 30% O2 (SF6 + O2), or air. No significant difference was noted between nonsmokers and smokers for expiratory flows while breathing air. .ovrhdot.Vmax while breathing He + O2, although generally less in smokers, was statistically less for .ovrhdot.Vmax at 25% of vital capacity (P < 0.05). The percent of difference in flow rate (.DELTA..ovrhdot.Vmax%) while subjects breathed He + O2, as compared to the flow rates observed while subjects breathed SF6 + O2 (.DELTA..ovrhdot.Vmax He + O2-SF6 + O2) was the most sensitive test and was statistically less in smokers than in nonsmokers. Values were statistically less for .DELTA..ovrhdot.Vmax at 70 (P < 0.01), 75 (P < 0.05) and 50% (P < 0.05) of total lung capacity, but only for .DELTA..ovrhdot.Vmax50 (P < 0.025) with He + O2 and air. The breathing of He + O2 and SF6 + O2 while performing maximal expiratory flow-volume measurements seems to provide a safe and sensitive method for identifying pulmonary function differences in smokers and nonsmokers. The response noted with (He + O2) and (SF6 + O2) may offer some additional advantage in detecting small-airway disease over .ovrhdot.Vmax measurements using (He + O2) and air.