Bainbridge reflex
Encyclopedia
The Bainbridge reflex, also called the atrial reflex, is an increase in heart rate
due to an increase in central venous pressure. Increased blood volume is detected by stretch receptor
s located in both atria at the venoatrial junctions.
reported this reflex in 1915 when he was experimenting on dogs. Bainbridge found that infusing blood or saline into the animal increased heart rate. This phenomenon occurred even if arterial blood pressure did not increase. He further observed that heart rate increased when venous pressure rose high enough to distend the right atrium, but denervation of the vagi to the heart eliminated these effects.
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 decrease parasympathetic tone via the vagus nerve to the heart, leading to increased heart rate.
Increasing the heart rate serves to decrease the pressure in the superior and inferior vena 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.
. During inhalation
intrathoracic pressure decreases. It triggers increased venous return which is registered by stretch receptors, which via Bainbridge Reflex increases the heart rate momentarily during inspiration. This is not to be confused with stage 4 of the Valsalva maneuver
, in which the release of high intrathoracic pressure previously generated by forced expiration against a closed glottis, now restores venous return and cardiac output into a vasoconstricted circulation, stimulating the vagus nerve and leading to a slowing of the heart, or bradycardia.
Heart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....
due to an increase in central venous pressure. Increased blood volume is detected by stretch receptor
Stretch receptor
Stretch receptors are mechanoreceptors responsive to distention of various organs and muscles, and are neurologically linked to the medulla in the brain stem via afferent nerve fibers...
s located in both atria at the venoatrial junctions.
History
A scientist by the name of Francis Arthur BainbridgeFrancis Arthur Bainbridge
Francis Arthur Bainbridge FRS FRCP was an English physiologist.Bainbridge was born in Stockton-on-Tees in 1874 and educated at The Leys School. He entered Trinity College, Cambridge in 1893, graduating BA in 1896 and earning a doctorate in 1904. In 1911 he became a professor of physiology at...
reported this reflex in 1915 when he was experimenting on dogs. Bainbridge found that infusing blood or saline into the animal increased heart rate. This phenomenon occurred even if arterial blood pressure did not increase. He further observed that heart rate increased when venous pressure rose high enough to distend the right atrium, but denervation of the vagi to the heart eliminated these effects.
Control of heart rate
The Bainbridge reflex and the baroreceptor reflex act antagonistically to control heart rate. The baroreceptor reflex acts to increase heart rate when blood pressure drops. When blood volume is increased, the Bainbridge reflex is dominant; when blood volume is decreased, the baroreceptor reflex is dominant. The Bainbridge reflex is seen in dogs, but experiment has shown that it is not as significant in primates. There is evidence, however, that the Bainbridge reflex does occur in humans, as in after delivery of an infant when a large volume (up to 800 mL) of uteroplacental blood is put back into the mother's circulation, resulting in tachycardia.Venous return
As venous return increases, the pressure in the superior and inferior vena cavaInferior vena cava
The inferior vena cava , also known as the posterior vena cava, is the large vein that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart....
increase. This results in an increase in the pressure of the right atrium, which stimulates the atrial stretch receptors (low pressure receptor zones
Low pressure receptor zones
Low pressure receptor zones are areas with baroreceptors located in the venae cavae and the pulmonary veins, and in the atria. They are also called volume receptors. These receptors respond to changes in the wall tension, which is proportional to the filling state of the low pressure side of...
). These receptors in turn signal the medullary control centers to decrease parasympathetic tone via the vagus nerve to the heart, leading to increased heart rate.
Increasing the heart rate serves to decrease the pressure in the superior and inferior vena 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.
Respiratory Sinus Arrhythmia
Bainbridge Reflex is involved in Respiratory Sinus ArrhythmiaRespiratory sinus arrhythmia
Respiratory sinus arrhythmia is a naturally occurring variation in heart rate that occurs during a breathing cycle. RSA is also a measure of parasympathetic nervous system activity - which denotes "rest and digest" behaviours.-Overview:...
. During inhalation
Inhalation
Inhalation is the movement of air from the external environment, through the air ways, and into the alveoli....
intrathoracic pressure decreases. It triggers increased venous return which is registered by stretch receptors, which via Bainbridge Reflex increases the heart rate momentarily during inspiration. This is not to be confused with stage 4 of the Valsalva maneuver
Valsalva maneuver
The Valsalva maneuver or Valsalva manoeuvre is performed by moderately forceful attempted exhalation against a closed airway, usually done by closing one's mouth and pinching one's nose shut...
, in which the release of high intrathoracic pressure previously generated by forced expiration against a closed glottis, now restores venous return and cardiac output into a vasoconstricted circulation, stimulating the vagus nerve and leading to a slowing of the heart, or bradycardia.