Lung Circulation

Abstract

The circulation of the lung is unique both in volume and function. For example, it is the only organ with two circulations: the pulmonary circulation, the main function of which is gas exchange, and the bronchial circulation, a systemic vascular supply that provides oxygenated blood to the walls of the conducting airways, pulmonary arteries and veins. The pulmonary circulation accommodates the entire cardiac output, maintaining high blood flow at low intravascular arterial pressure. As compared with the systemic circulation, pulmonary arteries have thinner walls with much less vascular smooth muscle and a relative lack of basal tone. Factors controlling pulmonary blood flow include vascular structure, gravity, mechanical effects of breathing, and the influence of neural and humoral factors. Pulmonary vascular tone is also altered by hypoxia, which causes pulmonary vasoconstriction. If the hypoxic stimulus persists for a prolonged period, contraction is accompanied by remodeling of the vasculature, resulting in pulmonary hypertension. In addition, genetic and environmental factors can also confer susceptibility to development of pulmonary hypertension. Under normal conditions, the endothelium forms a tight barrier, actively regulating interstitial fluid homeostasis. Infection and inflammation compromise normal barrier homeostasis, resulting in increased permeability and edema formation. This article focuses on reviewing the basics of the lung circulation (pulmonary and bronchial), normal development and transition at birth and vasoregulation. Mechanisms contributing to pathological conditions in the pulmonary circulation, in particular when barrier function is disrupted and during development of pulmonary hypertension, will also be discussed.

Update on novel targets and potential treatment avenues in pulmonary hypertension

“…The phenotype observed in CH models is consistent with PH that develops in humans as a result of high altitude (reviewed in Refs. 219,228). Both rats and mice are common choices for exposure to CH.…”

“…Many recent investigations have focused on the role played by exogenous signaling molecules produced by inflammatory cells in driving abnormal vascular cell function in PAH (68,228,252). Hypoxia-induced mitogenic factor (HIMF, FIZZ1), a protein secreted by M2 macrophages, promotes a proinflammatory milieu in the lung vasculature.…”

Multiple pulmonary metastases with halo‑sign from malignant mixed M?llerian tumors

“…This is mainly as the lung is the first filter in the general circulation (3,4). Secondly, the low pressure system and slow blood flow velocities of the pulmonary circulation are apt to allow tumor cells to stagnate (3,4).…”

“…This is mainly as the lung is the first filter in the general circulation (3,4). Secondly, the low pressure system and slow blood flow velocities of the pulmonary circulation are apt to allow tumor cells to stagnate (3,4). Metastatic neoplasm often present as multiple lung nodules and masses when incidental can be detected by a diagnostic chest radiography of computed tomography (CT) scan (5).…”

Measuring physiologic shunt fraction during normothermic ex‐vivo lung perfusion to assess transplantability of questionable donor lungs

“…An important aspect of pulmonary physiology in relation to gas exchange is the impact and pattern of pulmonary flow. Lower flows (especially nonpulsatile) during EVLP might result in lower vascular recruitment and simply exclude perfusion of injured regions, thereby falsely increasing P/F ratios [16,17]. Our group recently demonstrated that also the impact of flow distribution during EVLP by prone positioning might affect physiological parameters and extravascular lung water content [18].…”