Bainbridge Reflex - Venous Return

Venous Return

As venous return increases, the pressure in the superior and inferior vena cava increase. This results in an increase in the pressure of the right atrium, which stimulates the atrial stretch receptors (low pressure receptor zones). These receptors in turn signal the medullary control centers to increase the heart rate (Tachycardia). Unusually, this tachycardia is mediated by increased sympathetic activity to the sinoatrial node (SAN) with no fall in parasympathetic activity.

Increasing the heart rate serves to decrease the pressure in the superior and inferior venae cavae by drawing more blood out of the right atrium. This results in a decrease in atrial pressure, which serves to bring in more blood from the vena cavae, resulting in a decrease in the venous pressure of the great veins. This continues until right atrial blood pressure returns to normal levels, upon which the heart rate decreases to its original level.