The multilevel mechanical behaviour of the lung during induced bronchoconstriction

The standard way of simulating obstructive lung disease in animals is by induced bronchoconstriction, where a bronchoactive agent is applied to the lungs either by inhaled aerosol or i.v. injection. This paper reviews some of the recent advances in our understanding of how lung mechanics in animals are affected by bronchoconstriction at both the microscopic and macroscopic levels. At the microscopic level, the alveolar capsule oscillator technique provides mechanical information at the level of a single acinus, and has shown that bronchoconstriction causes both spatial and temporal inhomogeneities throughout the lung. These inhomogeneities become more profound as lung volume is reduced, presumably because of reduced mechanical interdependence between adjacent lung regions. At the macroscopic level, studies of the time-evolution of lung impedance following a sudden application of bronchial agonist have provided evidence that regional mechanical inhomogeneities are the major contributor to impedance changes. Thus, an important general problem is to find out how the distributed regional (microscopic) mechanical properties of the lung determine its macroscopic properties. Computer models of the lung, such as those based on branching airway trees terminating in complex tissue impedances, are beginning to make this link.