Measurement of the distensibility of the parabronchi in duck lungs

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Abstract

Air flow resistance in the parabronchial lung of the duck was measured at various pressure differences between the lung and the body surface (Prs) using a body plethysmograph. One lung of the anesthetized animal was ventilated at a steady flow rate, from trachea, through the parabronchial lung, and out via a cannula in the caudal thoracic air sac (TrCS flow), or vice versa (CSTr flow), all flow being directed over the parabronchi (Pb) by blocking the main bronchus between the medioventral (MV) and mediodorsal secondary bronchi (MD). Pressure differences were measured between MV and MD (Plot), and between the clavicular air sac and MD giving the pressure drop along the parabronchial tubes (PPb). The pressure drop along MV, PVb, was derived as Ptot-PPb. Air flow resistances, Rtot, RPb, RVb, were calculated from the ratio of the corresponding pressure difference to the flow rate.

Results show: (1) All resistances decreased with increasing distending pressure (Prs) from −20 to +20 cm H2O, this change being most pronounced around Prs = 0; (2) The flow resistance of these structures depended on the flow direction, being smaller with TrCS flow during distension than in the opposite direction; (3) Arterial blood gases did not significantly change with varying distending pressure, suggesting unimpaired gas exchange even when the lung is significantly compressed. The results indicate that the parabronchi and the secondary bronchi of the duck lung have a finite compliance but that changes in intrapulmonary pressure, particularly compression of the lung, do not result in significant collapse of the air capillarities with ensuing impairment of gas exchange.

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1

Present address: Meakins Christie Laboratories, McGill University Clinic, Royal Victoria Hospital, Montreal, Quebec H3A 2B4, Canada.

2

Present address: Abteilung Physiologie, Max-Planck-Institut für experimentelle Medizin, D-3400 Göttingen, F.R.G.

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