Steady pressure-flow relationship of a model of the canine bronchial tree

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Abstract
Static pressure differences (.DELTA.P) across the entire length and portions of a latex reproduction of a canine bronchial tree were measured during steady inspiratory or expiratory flow (.ovrhdot.V). The reproduction consists of a 10-cm length of trachea through bronchi of .apprx. 2 mm in diameter. The airflow was simulated by a water flow with tracheal Reynolds number (Re0) in the range from 1500-10,000. Loss in total pressure (.DELTA.Pt) was computed by summing .DELTA.P and tracheal kinetic energy (KE0) loss. Relationships between .DELTA.Pt and .ovrhdot.V were well described (r > 0.98) by a dimensionless Rohrer equation .DELTA.Pt/.DELTA.Pd0 = A + B Re0 applicable to gas flow, in which .DELTA.Pd0 is a Poiseuille pressure drop. For expiratory .DELTA.Pt, A was about twice that for inspiration, while the values for B were nearly equal. Differences in kinetic energy between sites of static pressure measurement are important in determining loss in total pressure. Rohrer''s equation is a good approximation to the phenomenological laws of steady inspiratory and expiratory flow-pressure relations in the canine bronchial tree for the range of Reynolds number investigated.