A Bainbridge Reflex is a positive feedback mechanism in which there is a compensatory increase in heart rate, due to a rise in right atrial pressure. It is commonly referred to as an Atrial Reflex.
How does the Bainbridge Reflex and Baroreceptor Reflex control the heart rate and ensure that blood pressure is maintained within normal homeostatic levels? The Bainbridge Reflex is triggered when the stretch receptors in the atria are triggered – this means that there is an increased level of venous blood (not to be confused with an increase in arterial blood pressure). The Bainbridge and Baroreceptor reflexes work antagonistically, meaning that if atrial blood pressure is high the Bainbridge Reflex is dominant; however, when teh corotid artery barorecptors indicate low arterial blood pressure, the Baroreceptor reflex becomes dominant.
Why does the body do this? By increasin the heart rate the left ventricles utilise more venous blood which is currently being pooled in the venacava and atria.
Clinical evidence of Bainbridge Reflex.
Bainbridge Reflex can be seen by placing a patient on a cardiac monitor and asking him or her to breath deeply. During the process of inspiration, the intrathoracic pressure is decreased (slightly), which leads to a higher venous return, which is identified by the atrial stretch receptors, which in turn cause the Bainbridge Reflex to become dominant and cause a momentary increase in heart rate. On a cardiac monitor, this can be seen as a sinus arrhythmia (a predominantly sinus rhythym, but not entirely regular – as a result of a sudden increase in heartrate).
Who first identified Bainbridge Reflex?
Francis Bainbridge first discovered the Bainbridge Reflex in 1915 while he was experimenting infusion of saline in animals (normally dogs).