How heterogeneous bronchoconstriction affects ventilation distribution in human lungs: A morphometric model

Convective dependent flow heterogeneities associated with airways proximal to the acini are the dominant cause of abnormal ventilation distribution du ring induced bronchoconstriction (Verbanck, S., D. Schuermans, A. Van Muyle m, M. Paira, M. Noppen, and W. Vincken. Ventilation distribution during his tamine provocation. J. Appl. Physiol. 83:1907-1916, 1997). We applied a mor phometric model of the human lung to predict flow distributions among the a cini during heterogeneous bronchoconstriction and relate these distribution s to impairments in the mechanical properties of the lung. The model has an asymmetrical branching airway system. Heterogeneous constriction was invok ed by defining an airway constriction distribution with a mean (mu) and coe fficient of variation (CV) and either a Gaussian or log normal distribution . The lung resistance (R-L) and elastance (E-L) were most sensitive to seve rely heterogeneous constriction that produced a few highly constricted or c losed airways dispersed randomly throughout the periphery. Ventilation dist ribution in the healthy lung was effectively homogeneous over the frequency range of 0.1-5.0 Hz. With homogeneous or mildly heterogeneous constriction (CV less than or equal to 20%) ventilation remained fairly homogeneous at low frequencies (less than or equal to 0.1 Hz) but rapidly became heterogen eous as frequency increased. Conversely, a low mean but severely heterogene ous constriction that produced random airway closure produced abnormal vent ilation distribution in most acini at all frequencies, and some acini recei ved up to 25 times the normal ventilation. This suggests that certain forms of heterogeneity can lead to shear induced lung injury even at common mech anical ventilation rates. (C) 1999 Biomedical Engineering Society. [S0090-6 964(99)01201-1].