What causes Oculocardiac reflex?
The oculocardiac reflex (OCR) is a reflex resulting in severe bradycardia caused by traction applied to the extraocular muscles (especially the medial rectus muscle), pressure on the globe, ocular trauma, traction on the conjunctiva, or occasionally by placement of a retrobulbar block.
What is normal Oculocardiac reflex?
Background: A typical oculocardiac reflex (OCR) is a moderate trigemino-vagal bradycardia elicited by tension on an extraocular muscle (EOM) during strabismus surgery; however, many other orbital stimuli can elicit cardiac slowing including retinopathy of prematurity examination.
What is Dagnini aschner reflex?
The oculocardiac reflex, also known as Aschner phenomenon, Aschner reflex, or Aschner–Dagnini reflex, is a decrease in pulse rate associated with traction applied to extraocular muscles and/or compression of the eyeball.
Why does vagal stimulation cause bradycardia?
Via the vagus nerve, the parasympathetic nervous system stimulates neurons that release the neurotransmitter acetylcholine (ACh) at synapses with cardiac muscle cells. Acetylcholine then binds to M2 muscarinic receptors, causing the decrease in heart rate that is referred to as reflex bradycardia.
What is vagal nerve response?
Summary. The vagal response is a series of unpleasant symptoms that occur when the vagus nerve is stimulated. Often, this response is triggered by certain things like stress, pain, and fear. Symptoms of the vagal response include dizziness, nausea, ringing ears, and sweating. In some cases, it can make you pass out.
Does atropine block vagal response?
Atropine works by blocking peripheral muscarinic receptors of the heart and causes increased firing at the sinoatrial node as well as conduction through the AV node. This opposes the vagal response, or the efferent limb, of the OCR.
How does the vagus nerve affect the eyes?
Eye movements can increase blood flow to the vertebral artery and stimulate the vagus nerve as it passes through the upper neck. Relaxing the muscles in the eyes engages an innate reflex called the oculocardiac reflex (OCR) which initiates a parasympathetic response to slow down the heart rate and lower blood pressure.
How does the vagus nerve cause hypotension?
Vasovagal syncope is one of the most common causes of fainting, which originates in the vagus nerve. The body overreacts to certain stimuli, which stimulates the vagus nerve and causes both blood pressure and heart rate to drop.
Can the vagus nerve cause high blood pressure?
The sympathetic side increases alertness, energy, blood pressure, heart rate, and breathing rate. The parasympathetic side, which the vagus nerve is heavily involved in, decreases alertness, blood pressure, and heart rate, and helps with calmness, relaxation, and digestion.
How does atropine affect blood pressure?
Atropine in clinical doses counteracts the peripheral dilatation and abrupt decrease in blood pressure produced by choline esters. However, when given by itself, atropine does not exert a striking or uniform effect on blood vessels or blood pressure.
Why does atropine cause paradoxical bradycardia?
Bradyarrhythmia following low-dose atropine is caused by a paradoxical slowing in the sinoatrial node discharge rate. This is thought to be due to a central vagotonic effect of atropine that, at higher doses, is masked by muscarinic blockade at the sinoatrial node.
Can the vagus nerve cause hypertension?
Decreasing inflammation: The vagus nerve sends an anti-inflammatory signal to other parts of the body. Lowering the heart rate and blood pressure: If the vagus nerve is overactive, it can lead to the heart being unable to pump enough blood around the body.
Can the vagus nerve cause low blood pressure?
Vasovagal syncope The vagus nerve stimulates certain muscles in the heart that help to slow heart rate. When it overreacts, it can cause a sudden drop in heart rate and blood pressure, resulting in fainting.
How does vagal stimulation affect blood pressure?
Selective vagal nerve stimulation (sVNS) has been shown to reduce blood pressure without major side effects in rats. This technology might be the key to non-medical antihypertensive treatment in patients with therapy-resistant hypertension.
How does atropine cause reflex bradycardia?
Background: Low-dose atropine causes bradycardia either by acting on the sinoatrial node or by its effects on central muscarinic receptors increasing vagal activity.
Why atropine causes initial bradycardia and then tachycardia?
Atropine acts on the M2-receptors of the heart and antagonized the activity of Ach. It causes tachycardia by blocking vagal effects on the SA node. Ach hyperpolarize the SA node which is over come by MRA and increase the heart rate. If atropine is given by intra muscular or sub cutaneous, it causes initial bradycardia.
Does vagal stimulation cause hypertension?
How does ACh raise blood pressure?
Acetylcholine (ACh) decreases blood pressure by stimulating endothelium nitric oxide-dependent vasodilation in resistance arterioles. Normal plasma contains choline acetyltransferase (ChAT) and its biosynthetic product ACh at appreciable concentrations to potentially act upon the endothelium to affect blood pressure.
Can acetylcholine cause hypertension?
Pharmacological and biochemical studies have revealed that acetylcholine release in the RVL is increased in experimental hypertension regardless of its etiology and that this enhanced release of acetylcholine leads to hypertension.
What is the oculocardiac reflex?
Definition. This phenomenon would eventually be termed “the oculocardiac reflex” and is defined clinically as a decrease in heart rate by 10% following pressure to the globe or traction of the ocular muscles. The reported incidence of the oculocardiac reflex varies from 14% to 90%, depending on the study, making it relatively common. (Dewar KMS.
What are the risk factors for Oculocardiac reflex?
Risk Factors. The incidence of the oculocardiac reflex decreases with age and tends to be more pronounced in young, healthy patients, which is clinically significant for pediatric aanesthesiologists as it is observed with greatest incidence in young healthy neonates and infants undergoing strabismus surgery.
What is the prevalence of Oculocardiac reflex (OCR)?
The incidence of the oculocardiac reflex is reported to be anywhere from 14% to 90% and decreases with age. Therefore, pediatric populations are the most at risk. Pediatric patients are also more susceptible to the detrimental consequences of the OCR secondary to having a greater dependency on heart rate to maintain cardiac output.
How is Oculocardiac reflex used to evaluate syncope?
Historically, the oculocardiac reflex was used as a diagnostic tool to evaluate syncope, as well as to terminate supraventricular tachycardias, but this is no longer done given the limited clinical application and the associated risks.