Airway rapidly adapting receptors--sensors of pulmonary extra-vascular fluid volume

The factors regulating transfer of fluid into the pulmonary extra-vascular space and the role of sensory receptors of the airways in detecting such fluid fluxes are reviewed and discussed. It is concluded that the rapidly adapting receptors (RARs) located in apposition to bronchial venules are highly sensitive to changes in the pulmonary extra-vascular space produced by mild elevations of left atrial pressure, plasmapheresis and pulmonary lymphatic obstruction and their activation causes respiratory stimulation, an increase in tracheal tone and cough. There is a reflex diuresis also following the stimulation of these receptors by pulmonary lymphatic obstruction. It is proposed that the RARs function as a sensory component of the pulmonary defence mechanisms which preserve the 'milieu interior'.