What is "congested" in cardiac failure? A newer approach to plain film interpretation of cardiac failure.

The amount and location of intra- and extravascular fluids varies for the type and duration of heart failure. In some instances (acute LHF) pulmonary and systemic blood volume actually diminishes, and in others (chronic LHF) pulmonary blood volume diminishes at the bases while increasing in the upper lobes. It is only in right heart failure that clinically visible "congestion" occurs and the phrase congestive failure should be reserved for right heart failure. It is more valuable clinically for the film reader to analyze which compartments contain increased or diminished fluid and from this analysis, to decide whether the patient is in left, right or biventricular failure and whether this is acute or chronic. Upper lobe engorgement, (flow inversion) is not caused by basal edema, as previously hypothesized, but by reflex vasoconstriction secondary to chronic elevation of left atrial pressure. The mechanism is designed to improve left atrial function.