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Departments of 1 Chemical and Biochemical Engineering and Materials Science and of 2 Mechanical and Aerospace Engineering, University of California, Irvine, California 92697-2575
The steady-state exchange of inert gases across
an in situ canine trachea has recently been shown to be limited equally
by diffusion and perfusion over a wide range (0.01-350) of blood solubilities (
blood;
ml · ml
1 · atm
1).
Hence, we hypothesize that the exchange of ethanol
(
blood = 1,756 at 37°C) in
the airways depends on the blood flow rate from the bronchial
circulation. To test this hypothesis, the dynamics of the bronchial
circulation were incorporated into an existing model that describes the
simultaneous exchange of heat, water, and a soluble gas in the airways.
A detailed sensitivity analysis of key model parameters was performed
by using the method of Latin hypercube sampling. The model accurately
predicted a previously reported experimental exhalation profile of
ethanol (R2 = 0.991) as well as the end-exhalation airstream temperature (34.6°C). The model predicts that 27, 29, and 44% of exhaled
ethanol in a single exhalation are derived from the tissues of the
mucosa and submucosa, the bronchial circulation, and the tissue
exterior to the submucosa (which would include the pulmonary
circulation), respectively. Although the concentration of ethanol in
the bronchial capillary decreased during inspiration, the three
key model outputs (end-exhaled ethanol concentration, the slope
of phase III, and end-exhaled temperature) were all statistically
insensitive (P > 0.05) to the
parameters describing the bronchial circulation. In contrast, the model
outputs were all sensitive (P < 0.05) to the thickness of tissue separating the core body conditions
from the bronchial smooth muscle. We conclude that both the bronchial circulation and the pulmonary circulation impact soluble gas exchange when the entire conducting airway tree is considered.
mathematical model; Latin hypercube sampling; ethanol; pulmonary circulation; airways
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