Reflex and nervous control of the tracheobronchial circulation.

Determinants of blood flow through the tracheobronchial vasculature include systemic arterial blood pressure, airway pressure, central venous and pulmonary vascular pressures, alveolar and arterial gas tensions, neural influences and chemical and humoral mediators. There is anatomical and physiological evidence of a role for cholinergic, adrenergic and peptidergic nerves in the control of the vasculature. Physiologically, adrenergic and peptidergic influences appear to be more important than cholinergic. The vasodilator response to inhalation of cold or dry air observed in the tracheobronchial vasculature of several species is unaffected by cholinergic or adrenergic blockade, but is attenuated by pretreatment with lignocaine, suggesting that it may be related to axon reflexes in sensory nerves resulting in release of tachykinins. This may also be the mechanism of the tracheobronchial vasodilator response to allergen challenge. The role of peptidergic nerves in other reflex responses of the tracheobronchial vasculature is at present unknown.