In vivo estimation of tracheal wall water: effects of histamine and carbachol

Abstract

Based on double-indicator-dilution principles we developed and validated a new method of measuring water content in the tracheal wall by inscribing time-concentration curves with the inert gas, helium and the water-soluble gas, dimethylether. In the trachea of conscious adult sheep the measurable water volume of the wall over a 15-cm length ranged between 0.50 and 0.70 ml. The tracheal radius calculated from helium volume and known tracheal length ranged between 7.4 and 9.3 mm. The corresponding measurable “water depth” ranged between 63 and 82 microns. Changes in bronchial blood flow had no consistent influence on tracheal water volume. The intravenous injection of histamine (4 micrograms/kg) increased mean water depth to between 122 and 134% of base line (P less than 0.001), whereas the intravenous injection of carbachol (4 micrograms/kg) had no effect on water depth. The production of large amounts of airway secretions produced by carbachol were removed prior to inscription of the indicator-dilution curves. These findings indicate that the double-gas-indicator technique is capable of measuring in vivo the volume of a water compartment in the tracheal wall and that this volume is increased by histamine. This method may be applicable in human subjects.