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J Appl Physiol 94: 1003-1011, 2003; doi:10.1152/japplphysiol.00569.2002
8750-7587/03 $5.00
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Vol. 94, Issue 3, 1003-1011, March 2003

Impedance, gas mixing, and bimodal ventilation in constricted lungs

Ron C. Anafi1, Kenneth C. Beck2, and Theodore A. Wilson1

1 Department of Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis 55455; and 2 Thoracic Diseases, Department of Internal Medicine, Mayo Clinic and Foundation, Rochester, Minnesota 55905

To evaluate the effect of increasing smooth muscle activation on the distribution of ventilation, lung impedance and expired gas concentrations were measured during a 16-breath He-washin maneuver in five nonasthmatic subjects at baseline and after each of three doses of aerosolized methacholine. Values of dynamic lung elastance (EL,dyn), the curvature of washin plots, and the normalized slope of phase III (SN) were obtained. At the highest dose, EL,dyn was 2.6 times the control value and SN for the 16th breath was 0.65 liter-1. A previously described model of a constricted terminal airway was extended to include variable muscle activation, and the extended model was tested against these data. The model predicts that the constricted airway has two stable states. The impedances of the two stable states are independent of smooth muscle activation, but driving pressure and the number of airways in the high-resistance state increase with increasing muscle activation. Model predictions and experimental data agree well. We conclude that, as a result of the bistability of the terminal airways, the ventilation distribution in the constricted lung is bimodal.

mathematical model; human; helium washin; asthma; phase III


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