Pulmonary Vascular Reactivity in Primary Pulmonary Edema

The entire cardiac output traverses only one organ, the lung; thus, pulmonary blood flow equals cardiac output. Changes in blood flow through the lung can have profound effects on left ventricular filling (preload), systemic pressures, cardiac output, and tissue perfusion. Within the lung, the distribution of blood flow, in relation to the distribution of ventilation, determines oxygenation of the blood and elimination of carbon dioxide. Normal arterial oxygenation requires that pulmonary blood flow in its entirety must be matched to ventilation; this requirement is easily met in health, but requires compensatory mechanisms in disease. The distribution of blood flow is partly determined by pulmonary vascular responses (reflexes), and derangement of these regulatory responses can lead to hypoxemia, especially if there are concurrent airway abnormalities. The purpose of this section is to review the characteristics of normal pulmonary pressures and blood flow, describe mechanisms and effects of abnormal vascular responses in primary pulmonary edema, and suggest strategies for management of patients who demonstrate these abnormalities.