Pulmonary reflexes after human heart-lung transplantation.

Heart-lung transplantation involves denervation of the lungs below the tracheal anastomosis, with associated permanent loss of all pulmonary innervation except post-ganglionic efferent nerves. This is supported by loss of the cough reflex to inhaled USNDW, which also implies that the RARs which mediate this cough mechanism lie in the central airways. Bronchoconstriction following inhalation of USNDW developed only in those HLT recipients with acute lung rejection; this was not related to methacholine responsiveness and may therefore represent a pathologic vascular response. Hyperresponsiveness to methacholine has been reported following HLT, which we found unrelated to inflammation or acute rejection. A similar hyperresponsiveness to histamine was seen, which correlated with the response to methacholine. This also implies that histamine may act directly on smooth muscle receptors, and not solely via a cholinergic reflex. Hyperresponsiveness following HLT may be due to development of a generalized denervation hypersensitivity. Bronchodilation following capsaicin inhalation has been observed in HLT recipients, and may be due to unopposed release of VIP from retained post-ganglionic efferent nerves.