[Asthma-tobacco interaction and alterations of maximal expiratory flow in air and in helium-oxygen (author's transl)].

The eventual interaction between tobacco and asthma and the sensitivity of different functional tests on small airways are compared in 4 groups of subjects (n = 49): non-smokers and control smokers, asthmatic non-smokers and smokers. All subjects have a normal vital capacity (VC) and a normal forced expiratory volume in one second (FEV1). The measurement of mid expiratory time (MET) and maximal flow at 50% (V Max 50) and at 25% (V Max 25) of the flow volume curve in air (FEMV) does not have any discriminating advantages over the simple measurement of the ratio FEV1/VC. The latter, although always normal, differentiates the controls from the asthmatic non-smokers. Besides, helium independency (characterized by an increase in the V Max 50 air-helium less than 20% and an increase of volume iso flow [V iso V] beyond 20% of VC) is mostly linked to tobacco addiction but is definitely worsened when associated to asthma.