Chronic Or Passive Hyperemia is generally due to obstruction of the pulmonary veins, and is associated with disease of the aortic and mitral valves and a weakened and relaxed condition of the vessel walls. The dependent portions alone may be involved - hypostatic congestion. This predisposes to infection and may terminate in hypostatic pneumonia.

The lung in passive hyperemia is dark red in color, firm, and crepitation is less than normal. From a cut surface there escapes on pressure a frothy purplish fluid. Resulting from the congestion, there is frequently proliferation of the fibrous connective tissue, giving rise to cyanotic or brown induration of the lung. The air vesicles will contain leukocytes, red cells and desquamated epithelial cells. These latter frequently contain hematogenous pigment, resulting from the destruction of the erythrocytes. This form of hyperemia is frequently seen postmortem.

In edema of the lung there is an escape of serous fluid into the bronchi and air-vesicles. Is generally found as a result of chronic congestion following heart and kidney disease, but may follow the inhalation of very hot or very cold air, or be part of a general angio-neurotic edema. Is very frequently found as a terminal affection in many diseases. The lung may be either pale or dark, according to the amount of congestion present. Is heavy and boggy, but crepitates, and from the cut surface a thin, frothy serum escapes in large quantities.