The Clinical Significance of the Pulmonary Collateral Circulation

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Abstract
The clinical significance of the normal and the expanded pulmonary collateral circulation is considered from the point of view of its nutrient, hemodynamic, and respiratory functions. In the normal lung, the collateral arterial circulation is too diminutive to serve other than a nutrient function. Its roles in preventing pulmonary infarction after embolization, in producing "ischemic lung disease," and in the direct treatment of pulmonary carcinomas are considered. The expanded collateral arterial circulation associated with localized pulmonary lesions or which occurs after ligation of a pulmonary artery seems to be without appreciable hemodynamic effect on either the pulmonary circulation, the left heart, or the systemic circulation. Only in patients with generalized suppurative disease of the lung has it been shown to affect the pulmonary circulation by diverting mixed venous blood away from diseased areas. The possibility exists that the increment in pulmonary blood flow contributed by the collateral arterial circulation may aggravate pulmonary hypertension in patients with diffuse restriction of the pulmonary vascular bed. The venous portion of the expanded collateral circulation may conceivably contribute to pulmonary hypertension by aggravating systemic arterial hypoxemia in patients with right heart failure from hypoxemic cor pulmonale. The expanded collateral arterial circulation may assume a major respiratory function in subjects with systemic hypoxemia and curtailed pulmonary blood flow. In such cases, the "effective" pulmonary collateral blood flow has been shown to equal normal values for pulmonary arterial blood flow. Different portions of the pulmonary collateral circulation may be responsible for hemoptysis in different diseases: in pulmonary disease, the arterial portion; in mitral stenosis, the venous portion; in pulmonary infarction, an imbalance between the two. The relationship between the pulmonary collateral circulation and clubbing of the digits remains uncertain. The pulmonary collateral circulation is considered, finally, with respet to (1) limitations of present methodoloy, (2) principles involved in the development of collateral circulations in general, and (3) therapeutic implications.