What is Bainbridge Reflex?
In 1915, while conducting experiments on dogs, a scientist named Francis Arthur Bainbridge discovered this reflex. Bainbridge discovered that injecting the animal with blood or saline raised the heart rate. This event happened even in the absence of a rise in arterial blood pressure. He also found that when venous pressure was high enough to distend the right atrium, the heart rate increased, but that these effects disappeared once the vagus nerve to the heart was denervated.
The Bainbridge response mainly affects the central nervous system and the cardiovascular system. But the respiratory system also plays a small role. During inspiration, intrathoracic pressure drops, which causes more blood to flow back into the veins. This, in turn, stimulates the stretch receptors, which, through the Bainbridge reflex, briefly speeds up the heart rate. This is called the respiratory sinus arrhythmia.
The rise in heart rate caused by a rise in central venous pressure is known as the Bainbridge reflex or the atrial reflex. Stretch receptors found at the venoatrial connections in both atria can detect an increase in blood volume.
Bainbridge reflex is a homeostatic reflex mechanism that causes the heartbeat to speed up when local muscle spindles are stimulated by an increase in blood pressure in the venae cavae and right atrium.
Bainbridge Reflex Location
Stretch receptors found in the cavoatrial junction and right atrial wall trigger the Bainbridge reflex. Vagal afferent signals are sent to the cardiovascular center in the medulla when right-sided filling pressure rises. These baroreceptors, also known as venoatrial stretch receptors, sense changes in the pressure and volume of blood returning to the heart. Heart rate and muscular contraction strength are both enhanced by activation of the sympathetic nervous system when information from the receptors travels through the vagus nerve to the brain.
Bainbridge Reflex Mechanism
The activation of local muscle spindles triggers the Bainbridge reflex, a homeostatic reflex mechanism that causes the heart rate to increase. Stretch receptors at the venoatrial connections on either side of the atria cause the reflex to occur. The activation of the heart’s sinoatrial node causes an increase in heart rate. Atropine can suppress the Bainbridge reflex, and cutting a vagus nerve can eliminate it. The reflex, together with the baroreceptor reflex, regulates heart rate.
The Bainbridge reflex is a compensatory mechanism because increased right atrial pressures are frequently the consequence of increased left heart pressures due to decreased cardiac output.
Clinicians are better able to grasp unique hemodynamic changes in their patients that occur in a variety of clinical circumstances by having a better understanding of the mechanism of the Bainbridge reflex. The Bainbridge reflex is responsible for regulating the rate at which the heart beats in response to changes in blood volume. Changes in blood volume are caused by a wide variety of physiological, idiopathic, and pathologic factors.
Bainbridge Reflex vs Baroreceptor Reflex
The Bainbridge reflex and the Baroreceptor reflex work in opposition to one other to control heart rate. Unlike the baroreceptor reflex, which is triggered by specialized pressure sensors called baroreceptors located in the right atrium of the heart, the Bainbridge reflex is triggered by stretch receptors at the venoatrial junctions on both sides of the atria. The baroreceptor reflex is initiated by a reduction in arterial blood pressure, whereas the Bainbridge reflex is induced by a rise in central venous pressure.
The baroreceptor reflex causes the heart rate to decrease, whereas the Bainbridge reflex causes the heart rate to increase. When blood volume is low, the baroreceptor reflex is more pronounced, and when blood volume is high, the Bainbridge reflex is more noticeable. Atropine inhibits the Bainbridge reflex, but beta-blockers suppress the baroreceptor reflex.