###### Created: 2022-04-04 13:30 ###### Areas & Topics: #medicine #cardiovascular #bloodpressure ###### Note Type: #permanent ###### Connected to: [[Baroreceptors and the Baroreceptor Reflex]] [[Chemoreceptor Reflex]] [[Systemic Arterial Blood Pressure - Medical Sciences, Third Edition]] ### The Bainbridge Reflex - The Bainbridge Reflex (also known as the atrial reflex) is where heart rate increases due to increase preload (venous pressure) in the atria and vena cava. - It essentially controls heart rate in response to blood volume. - This mainly functions to maintain cardiovascular homeostasis and arterial pressure when blood is moving quickly into the venous system (e.g. during exercise). - It is important to know about because understanding it also helps to understand how blood volume changes can impact the cardiovascular system. ### Mechanism - Stretch receptors in the atria and vena cava are stimulated by increased venous system pressures. - This stimulation send afferent signals via the vagus nerve to the medulla oblongata. - This medulla then produces efferent fibres that inhibit the vagus nerve. - Because the vagus nerve is parasympathetic, inhibition of it **increases** sympathetic signals which, in turn, stimulate the SA node and other structures. - This mainly causes a reflex tachycardia, alongside other sympathetic changes to increase heart rate and blood pressure. ### StatPearl Questions #### Question 1 A 45-year-old man with a history of alcohol use disorder and liver cirrhosis is brought to the emergency department due to severe dehydration. He receives IV saline infusions, and shortly, his heart rate increases. He wants to know the reason behind this change, which he is told is most likely due to a reflex. What is the mechanism underlying this reflex? A. Increase in total peripheral resistance B. Increase in arterial pressure C. Increase in central venous pressure D. Decrease in preload ##### Answer C. Increase in central venous pressure #### Question 2 Alex is usually constipated and occasionally takes over-the-counter laxatives to relieve his problem. During a Valsalva maneuver in the bathroom, explain why Bainbridge does not occur; in other words, why does his heart rate decrease? A. A decrease in thoracic pressure, causing an increase in venous return that stretches atrial receptors B. An increase in thoracic pressure, causing a decrease in venous return that doesn't stretch atrial receptors C. A decrease in thoracic pressure, causing an increase in venous return that doesn't stretch atrial receptors D. An increase in thoracic pressure, causing an increase in venous return that stretches atrial receptors ##### Answer B. An increase in thoracic pressure, causing a decrease in venous return that doesn't stretch atrial receptors ### Resources - Physiology, Bainbridge Reflex - Statpearls https://www.ncbi.nlm.nih.gov/books/NBK541017/