Redistribution of blood flow in pulmonary edema

In a normal lung, more perfusion (blood flow) occurs at the lung bases than at the apices and more ventilation (air flow) at the apices than bases.

However, in patients with pulmonary edema (left ventricular failure), this distribution of blood flow is altered. As the pulmonary venous pressure rises and fluid accumulates at the lung bases the blood flow begins to get redistributed toward the apices.

Mechanism for the redistribution of blood flow in pulmonary edema:
This is not very clearly understood but probably related to "hypoxic pulmonary vasoconstriction".
Due to alveolar wall edema, that is more significant in the lower lobes in pulmonary edema, gas exchange is reduced. This results in hypoxic vasoconstriction of lower lobes resulting in increased flow to upper lobes.

Other terms used to denote this: Cephalization of blood flow; Upper lobe blood diversion; Inverted moustache sign; Antler's horn sign

Photograph:


Click in the image for full size.

Ref: Journal of Applied Physiology

We studied the effect of edema on the regional distribution of pulmonary blood flow in 12 anesthetized dogs. Two were controls, six had low-pressure pulmonary edema, and four had high-pressure pulmonary edema. All were ventilated with 100% O2. The physiological shunt fraction (Qs/QT), as an indicator of the degree of venous admixture, was determined by measuring the arterial and venous blood gases and the hemoglobin at different times during the experiment. Cardiac output (QT) was modestly increased by opening the femoral arteriovenous shunts. The initial regional blood flow (Qi) and final regional blood flow (Qf) were marked before and after the shunts were opened, using two differently labeled macroaggregates. The dogs were then killed, and the lungs were removed and sampled completely so that Qi and Qf and the amount of regional extravascular lung water (Wdl) in each regional sample could be measured (sample size: wet wt = 5.9 +/- 2.9 g, n = 833; Wdl ranged from 5.15 +/- 1.18 to 14.42 +/- 2.34 g). The data show that QS/QT increased as QT increased in the three conditions studied. However, there was no correlation between Wdl and Qi, Qf, or the relative change in regional blood flow. The data also show that gravity affects regional blood flow more than it affects regional edema. We conclude that the increased Qs/QT seen with increased pulmonary blood flow cannot be explained by a preferential increase of blood flow to the more edematous regions.