Investigations on the innervation of the pulmonary vasculature date back to the work of Bradford and Dean in 1894 (8), which demonstrated that gross excitation of the spinal cord caused vasorelaxation within the systemic circulation, without effect on the pulmonary circulation. Subsequently, Nissel (45) provided significant progress in our understanding of the basic mechanisms of HPV. In short, Nissel demonstrated that HPV was a local response largely, or entirely, independent ofthe autonomic nervous system. The limited influence on HPV of the innervation within the pulmonary vasculature was confirmed by denervation. First, chemical sympathectomy (using 6-hydroxy-dopamine) in the canine pulmonary vasculature was shown to be without effect on HPV (25). Naeije et al. (43) confirmed this finding, and also demonstrated that surgical denervation of the carotid and aortic chemoreceptors permitted HPV. More recently, the rise in pulmonary arterial pressure associated with HPV was shown to remain unchanged after bilateral cervical vagotomy (38).
Importantly, bilateral lung transplants allowed for the study of HPV after denervation in man. In these patients, HPV persists (54). We can conclude, therefore, that neither central nor local regulation of the autonomic nervous system plays a role in mediating HPV.
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