Assessing the effect of deep inhalation on airway calibre: a novel approach to lung function in bronchial asthma and COPD

Bronchoconstriction in bronchial asthma and chronic obstructive pulmonary d isease (COPD) may be due to decreased airway calibre and/or to the inabilit y of the airways to distend after a deep inhalation (DI), The purpose of th is review is to discuss the physiological and clinical relevance of this la tter mechanism. During induced constriction, DI shows remarkable bronchodilatation in norma l subjects, but a blunted or null effect in asthmatics, In contrast, during spontaneous bronchospasm DI tends to decrease airway calibre, From a funct ional point of view, airway inflammation, remodelling, and peripheral bronc hoconstriction could prevent airway smooth muscle from stretching. Therapeutic intervention improving lung function may change the response to DI, For example, bronchodilators allow expiratory airflow before DI to inc rease more than after DI, because of decreased bronchial hysteresis, This s uggest that bronchodilation might be systematically underestimated from par ameters derived from maximal expiratory manoeuvres. Inhaled corticosteroids tend to increase the dilator effect of DI,likely due to decreased bronchia l and peribronchial oedema, In conclusion, measuring the effects of deep inhalation on lung function is an easy and simple test able to evaluate the structural changes occurring in the airways and to monitor the effectiveness of therapy.