Targeting Constricted Airways

In diseased lungs, the airways are often more constricted relative to healthy lungs, so one might expect significant differences in lung deposition fraction and deposition pattern (101). The impact of constriction on aerosol deposition is discussed below. We present deposition data based on models of constricted airways as well as experimentally derived data, taken from healthy subjects in which constriction was induced by methacholine provocation, and from patients who are constricted in their baseline state. 

Kim et al. developed a lung model based on the Weibel-A model in which they decreased airway diameter by 25 or 40% in both the peripheral and central airways (102). Then they calculated the increases in resistance and deposition. Their results are presented in Fig. 14A and B. The upper graph represents the situation after a diameter reduction of 25%, the lower one after a 40% reduction. It is clear from the graphs that there is no simple one-to-one relationship between the increase in resistance and deposition. This is to be expected, because resistance relates to airway diameter raised to the fourth power, while deposition does not. Nevertheless, from both graphs, it is clear that the model predicts that as resistance increases, the increase in deposition will occur mainly in the larger airways (generations 0-7). Deposition in generations 8-16 will be less affected by the inaease in resistance. 

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Svartengren and coworkers (103) quantified deposition in eight healthy subjects under control conditions and after constriction was induced by methachofine challenge. In both situations, inspiratory flow rate was regulated at 0.5 L/s. Under control conditions, alveolar deposition of b-pm-labeled Teflon particles labeled with In ranged from 38 to 68% in these subjects. At the same time. 

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Because the respiratory tract is an initial target of any air pollutant challenge, it usually receives primary attention in tests to determine irritant effects of exposure. Other aspects of interest include hematology, blood enzyme biochemistry, eye irritation, and p chomotor performance. Constriction of the large airways, maldistribution of ventilation due to narrowing in some small airways, constriction of peripheral lung units, and mechanical or gas diffusion impairment due to edema are possible effects of insult by pollutants. A variety of pulmonary tests is required to examine the possibilities. 

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