Asymmetrical Effects of Increases in Hydrostatic Pressure on Macromolecular Movement Across the Airway Mucosa. A Study in Guinea-pig Tracheal Tube Preparations

This study employed isolated guinea-pig tracheal tube preparations in order to examine effects of increases in hydrostatic pressure on the movement of macromolecular solutes (fluorescein isothiocyanate-conjugated dextran; FITC-D, MW 70 kD; kept either in serosal or mucosal bathing fluids) across the mucosa. An asymmetry of the mucosal barrier was demonstrated by the finding that under baseline zero-pressure difference conditions luminal entry of serosal FITC-D was greater than serosal entry of luminal FITC-D. Furthermore, an increased serosal pressure (5 cm H2O) moved significant amounts of serosal FITC-D into the lumen, whereas a corresponding pressure applied on the luminal side only marginally increased mucosal crossing of luminal FITC-D. By raising the luminal pressure to 10 and 20 cm H2O (which may be used as positive end-expiratory pressures (PEEP) in vivo in patients) mucosal penetration of luminal FITC-D was as marked as that induced in the opposite direction by the low (5 cm H2O) serosal pressure increase. Another aspect of the asymmetry of the airway mucosal barrier was evident from experiments examining the effect of a serosal pressure increase on mucosal penetration of luminal FITC-D. Neither during nor after the period of sustained serosal pressure increase was luminal FITC-D crossing the mucosa to a greater extent than under baseline zero-pressure conditions. This finding agrees with in-vivo data demonstrating that plasma exudation into the airway lumen may not be associated with an increased absorption of luminal solutes.(ABSTRACT TRUNCATED AT 250 WORDS)