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Hepatic arterial buffer response

The liver receives around 25% of cardiac output. The blood supply is from two sources – the portal vein contributes around 75% of blood supply and the hepatic artery around 25%. Given the higher content of oxygen in arterial blood supply, the overall distribution of oxygen supply between each source is around 50:50.

The Hepatic Arterial Buffer Response (HABR) describes the ability of the liver to alter the contribution of the hepatic artery to the blood supply. Hepatic arterial flow can double when there is a reduction in portal blood flow. The mechanism proposed for this relates to the synthesis and washout of adenosine from the periportal areas. When portal blood flow is diminished, adenosine accumulates, resulting in vasodilation of the hepatic arterioles and increasing blood flow. When venous blood flow is increased the adenosine is washed out, increasing resistance and resulting in a reduction in arterial flow.

While this doubling of blood flow in the hepatic artery cannot fully restore hepatic blood flow, it can preserve hepatic oxygen supply. However, at times of extreme physiologic stress the buffer response may be obliterated and the liver may still be vulnerable to ischemia.