Bronchoconstriction and the MBNW: Insights from anatomical lung modelling.
Author: Mitchell, Jennine; Tawahi MH
Type: Conference poster
Link to this item using this URL: http://hdl.handle.net/2292/17090
Bronchoconstriction and the MBNW: Insights from anatomical lung modelling. Jennine Mitchell and Dr Merryn Tawhai Auckland Bioengineering institute The multiple breath nitrogen washout (MBNW) is a global test of lung function that produces two indices Sacin and Scond that are reflective of ventilation heterogeneity arising at the level of acinus and between more spatially disparate regions of the lung respectively. An important application of the MBNW is in the study of asthma. Ventilation defects have been noted to occur in imaging studies of asthma. These regional ventilation defects have not previously been considered in relation to the MBNW indices. Scond is purported to be related to the state of conducting airways however no modelling studies exist which directly link the airway state to Scond. In this work regional ventilation defects have been simulated in an anatomically based human lung model and theoretically linked to the MBNW indices Sacin and Scond. Ventilation is simualted to the level of the acinus in a model in which acinar ventilation is considered independent of ventialtion in other acini. As previously indicated in modelling studies a high degree of constriction is required to produce a ventilation defect. The relationship between the degree of constriction in airways leading to the defect and the Scond index is however highly non-linear and shows a sharp decrease at very high levels of constriction. Ventilation defects potentially cause non-communication of gas trapped in the ventilation defects with the mouth. This may alter the calculation of FRC if nitrogen dilution is used to calculate FRC. As the indices are dependent on the phase III slope for each breath being normalised by FRC this alters MBNW results. The index Scond is not be able to be explained simply in terms of increased time constants due to increased resistance in the main conducting airway tree. The model indicates that the Scond index is more complex than current MBNW theory indicates and cannot be simply explained in terms of a longer time constant due to constriction in the conducting airway tree resulting in increased late emptying of poorly ventilated regions.
Citation: ["Medical Sciences Congress. 30 Nov 2010"]