What is the Bainbridge reflex?

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The Bainbridge reflex is the adjustment of heart rate that occurs when venous return to the heart increases. When more blood returns to the right atrium, the atrial walls stretch, activating stretch receptors. These receptors send signals to the cardiovascular centers in the brainstem, leading to a rise in sympathetic activity (and a reduction in parasympathetic influence) to the heart. The outcome is an increased heart rate so the heart can pump the extra returned blood effectively. This reflex helps match the heart’s rate to the amount of blood returning to it, preventing congestion and maintaining proper cardiac output. It’s different from changes in stroke volume driven by the Frank-Starling mechanism, and it’s not about a reflex that decreases heart rate in response to pooling. The essential idea is heart-rate adjustment in response to venous return.