Bronchovascular role in pulmonary congestion

1. A postulated role for the bronchial circulation in the development of pu lmonary congestion may be based on recent studies of bronchovascular contro l. 2. The bronchial circulation is the nutrient blood supply of the conducting airways and, therefore, plays an important role in the function of the bro nchial mucosa. Mucosal swelling secondary to elevation of mucosal capillary hydrostatic pressure may decrease airway calibre, increase resistance to a irflow and precipitate symptoms of pulmonary congestion. 3. Resting mucosal capillary hydrostatic pressure is relatively constant du e to autoregulation of bronchial blood flow and is maintained low by nett b ronchovascular constriction due to the dominance of autonomic vasoconstrict ion over nitric oxide-dependent vasodilatation. 4. Bronchial blood flow is also regulated by cardiac afferent reflexes. Sti mulation of cardiac vagal and spinal afferents produces vasodilatation and vasoconstriction, respectively. Tonic activity of cardiac spinal afferents probably contributes to the resting autonomic vasoconstriction. 5. Therefore, mild heart failure, which is associated with abnormal cardiov ascular reflex function, may decrease cardiac spinal afferent-mediated bron chial vasoconstriction and produce active dilatation due to stimulation of cardiac vagal afferents by excessive myocardial stretch, leading to bronchi al mucosal swelling and pulmonary congestion.