New perspectives in the pulmonary circulation and hypoxic pulmonary vasoconstriction

In the past few years there has been a reawakening of interest in the systems that underly pulmonary vascular control and an increased awareness of the clinical potential of pharmacological manipulation of the pulmonary circulation. Nevertheless, although so much has been learned about the physiological role of the endothelium, vasoactive substances, and neural modulation of the pulmonary vasculature; how these disparate influences interact to control the matching of ventilation to perfusion remains uncertain. Consequently, even less is known of the way in which lung injury influences these regulatory processes. It is likely that the response to hypoxia may involve a system with many pathways and much redundancy, such that blockade of the production of a single agent has only a minor effect on HPV. We speculate that the products of arachidonic acid metabolism, PAF, adenosine and EDRF, may act in concert with neural pathways in a 'microenvironment' bounded by the alveolus and endothelium to modify pulmonary vascular tone during both normoxic and hypoxic conditions.