Search of a Paradoxical Fall in Maximum Expiratory Flow After Bronchodilation in Healthy Subjects

There exists a physiological limitation of the expiratory flows because of the physical properties of the bronchial tree (flexible bronchial walls in a complex architecture subjected to variations of pressure and volume). For a given lung, in a given state, for each pulmonary volume there is a corresponding Maximum Expiratory Flow (MEF). In healthy subject, the bronchial smooth muscles have a basal tonicity which is not negligible. If the tonicity is increased, this generally leads to a reduction in MEF. If it is decreased, MEF rather tends to increase, there are healthy individuals for whom the inhibition of the contraction of the bronchial smooth muscles by inhalation of bronchodilatator leads to a reduction in the MEF: this is called "paradoxical effect". When this reduction exists, it appears it occurs at low pulmonary volumes (approximately 50% for a volume of less than 25% of the CV). Under this circumstance, it seems that the basal tonicity of the bronchial smooth muscles would fight against the expiratory collapse of the bronchi, and this would happen especially for distal bronchi, for low pulmonary volume and for forceful expiration. The existence of such a phenomenon would be in favour of a "stiffening" role of the bronchial smooth muscles. The bronchial smooth muscles would not be only harmful cells causing of the asthma attacks.