Thursday 2 June 2016
Vagus nerve and the heart
Heart Disease
The Importance of the Vagus Nerve
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The Vagus Nerve. BSIP/UIG/Getty Images
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By Richard N. Fogoros, MD - Reviewed by a board-certified physician.
Updated April 26, 2016
The vagus nerve is the longest, and one of the most important, nerves in the body. The vagus nerve helps regulate many critical aspects of human physiology. For this reason, medical science has long sought ways of modulating the function of the vagus nerve.
What Is the Vagus Nerve?
The vagus nerve (also known as the 10th cranial nerve) is a very long nerve that originates in the brain stem and extends down through the neck and into the chest and abdomen.
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While there are actually two vagus nerves (the left and the right), doctors usually refer to them together as “the vagus nerve.”
The vagus nerve helps control several muscles of the throat and of the voicebox. It also supplies the heart, lungs, major blood vessels of the chest, and the gastrointestinal tract. The vagus nerve has a major role in regulating the heart rate, and keeping the gastrointestinal tract in working order. The vagus nerves also carry sensory information from the internal organs back to the brain.
Why Is The Vagus Nerve Significant?
Perhaps the greatest significance of the vagus nerve is that it is the body’s major parasympathetic nerve, supplying parasympathetic fibers to all the major organs of the head, neck, chest and abdomen. The vagus nerve is responsible for the gag reflex (and the cough reflex when the ear canal is stimulated), slowing the heart rate, controlling sweating, regulating blood pressure, stimulating peristalsis of the gastrointestinal tract, and controlling vascular tone.
Vagus Nerve Stimulation
Sudden stimulation of a vagus nerve can produce what is called a "vasovagal reflex," which consists of a sudden drop in blood pressure and a slowing of the heart rate. This reflex can be triggered by gastrointestinal illness or in response to pain, fright or sudden stress. Some people are particularly prone to the vasovagal reflex, and their blood pressure and heart rate changes can cause loss of consciousness - a condition called "vasovagal syncope."
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AdvertisementRead about vasovagal syncope.
Excessive activation of the vagus nerve is also seen in certain medical conditions, especially the dysautonomias.
Stimulating the vagus nerve can have therapeutic effects (such as stopping episodes of supraventricular tachycardia or hiccups), and can help doctors diagnose certain kinds of heart murmurs. Vagal stimulation can be achieved quite easily by employing the Valsalva maneuver.
The Vagus Nerve and the Heart
The right vagus nerve supplies the sinus node, and its stimulation can produce sinus bradycardia. The left vagus nerve supplies the AV node, and its stimulation can produce a form of heart block.
The Vagus Nerve In Medical Therapy - VNS Therapy
Because the vagus nerve has so many important functions, medical science has been interested for decades in the idea of employing vagus nerve stimulation, or vagus nerve blocking, in medical therapy.
For decades, the vagotomy procedure (cutting the vagus nerve) was a mainstay of therapy for peptic ulcer disease, since this was a way of reducing the amount of peptic acid being produced by the stomach.
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However, the vagotomy had several side effects, and with the availability of more effective treatment has now become much less commonly used.
Today, there is great interest in using electronic stimulators (essentially, modified pacemakers) to chronically stimulate the vagus nerve in an attempt to treat various medical problems. Such devices (referred to generically as vagus nerve stimulating devices, or VNS devices) have been used successfully to treat people with severe epilepsy that is refractory to drug therapy. VNS therapy is also sometimes used to treat refractory depression.
Because when you have a hammer everything looks like a nail, companies that make VNS devices are investigating their usage in several other conditions including hypertension, migraines, tinnitus, fibromyalgia and weight loss. There is indeed promise in such applications of VNS. However, the true potential of VNS will emerge once the hype is replace by firm clinical evidence.
Sources:
Henry TR. Therapeutic mechanisms of vagus nerve stimulation. Neurology 2002; 59:S3.
Shuchman M. Approving the vagus-nerve stimulator for depression. N Engl J Med 2007; 356:1604.
Waxman MB, Wald RW, Sharma AD, et al. Vagal techniques for termination of paroxysmal supraventricular tachycardia. Am J Cardiol 1980; 46:655.
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Vasovagal Syncope - What You Need To Know
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Heart Disease
Vasovagal (Cardioneurogenic) Syncope
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Fainting. Betty Dupuis/E+/Getty Images
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By Richard N. Fogoros, MD - Reviewed by a board-certified physician.
Updated December 16, 2014
Vasovagal syncope (also called cardioneurogenic syncope) is a condition in which temporary loss of consciousness (syncope) occurs due to a neurological reflex that produces either sudden dilation of the blood vessels in the legs or a very slow heart rate (bradycardia), or both.
Vasovagal syncope is by far the most common cause of syncope and probably accounts for more than 50% of all episodes. While doctors often refer to it as a "simple fainting spell," the mechanism of vasovagal syncope actually is not particularly simple.
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In fact, many doctors seem not to grasp how vasovagal syncope occurs, which too often leads to problems in making the correct diagnosis or in determining adequate treatment.
What Causes Vasovagal Syncope?
Vasovagal syncope occurs when, due to a reflex, the blood vessels in the legs suddenly dilate, causing a significant proportion of the blood volume to pool in the legs. This blood pooling is often accompanied by a slowing of the heart rate. The blood pressure subsequently drops and fainting occurs.
The reflex responsible for vasovagal syncope works like this: First, a person is exposed to some stimulus (such as a painful needle stick in a finger) that triggers the reflex. The triggering event stimulates certain nerves (the pain nerves of the finger), which send an electrical signal to the vasomotor center in the brainstem, the portion of the brain that determines the body's vascular (blood vessel) tone.
The vasomotor center, in response, sends signals to the blood vessels in the legs, causing them to dilate. This produces blood pooling, which leads to syncope. The same stimulation of the brainstem may also send signals to the heart to produce a drop in the heart rate.
In most people with vasovagal syncope, the dilation of blood vessels appears to be the predominant mechanism that causes loss of consciousness.
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In some people, however, the slowing of the heart rate plays the major role.
The "trigger" that initiates a vasovagal reflex can be any of a number of different things. Pain is a particularly common cause of fainting. Other common triggering events include having your blood drawn, being exposed to the sight of blood, having difficult urination or defecation, severe coughing, painful swallowing, receiving upsetting news, sudden fright or standing motionless for long periods of time. (This is why soldiers standing at parade rest, or singers in a choir, will sometimes faint.) In fact, if fainting follows any of these events, vasovagal syncope is extremely likely to be the cause.
What Are the Symptoms of Vasovagal Syncope?
While the loss of consciousness with vasovagal syncope can be quite sudden, more typically it is preceded by a few seconds or a few minutes of warning symptoms. These warning symptoms often include lightheadedness, ringing in the ears, visual disturbances, sweating and/or nausea.
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This is followed by a sensation of "graying out," followed immediately by loss of consciousness.
Vasovagal syncope almost always occurs when the victim is standing or sitting upright (when blood pooling in the legs can occur), and it virtually never happens when lying down.
People who have vasovagal syncope usually regain consciousness after a few seconds, once they have fallen (or, if they're lucky, are helped) to the ground. This is because once on the ground, gravity no longer causes the blood to pool in the legs and the blood pressure improves almost immediately. When somebody passes out, the right thing to do is to get their head down and elevate their legs. Holding them in an upright position - even if you add the additional "treatment" of yelling in their ears or slapping them - is not helpful.
After an episode of vasovagal syncope, many individuals will feel terrible for a few hours or even for the next day or two. During this time they commonly experience extreme fatigue, nausea, dizziness and loss of appetite. Until these symptoms disappear they are particularly prone to fainting again.
People who have had one or two episodes of vasovagal syncope are frequently able to recognize the warning symptoms, so they will know when another event is about to occur. More important, if they do recognize the warning symptoms, they can prevent the blackout simply by lying down and elevating their legs. (Stopping an episode is not possible with most other forms of syncope.) Further, if they can avoid actually blacking out, they can usually also avoid the period of feeling "sick" that often follows such and episode.
On the other hand, trying to "fight off" an impending episode of vasovagal syncope - by forcing yourself to remain upright and willing yourself not to faint - almost never works out very well.
Older individuals with vasovagal syncope are more likely to have an "atypical" form of this condition, in which syncope may occur without any identifiable trigger and without any warning symptoms. Making the correct diagnosis in these individuals can present a real challenge to the doctor.
In general, vasovagal syncope is not itself life-threatening - but injuries that result from falling may be.
Who Gets Vasovagal Syncope?
The reflex that causes vasovagal syncope can occur to some extent in everyone, so almost anyone can have an episode as long as a strong enough triggering event occurs. Indeed, it is likely that most people will have a fainting episode at least once in their lives.
Vasovagal syncope can occur at any age, but it is much more common in adolescents and young adults than in older people.
Some people are particularly prone to vasovagal episodes and often faint even with relatively mild triggering events. These individuals tend to relate histories of syncope dating back to adolescence. They frequently will describe several episodes, often with several different kinds of triggering events.
In some people, vasovagal syncope is so frequent and so difficult to treat that they become virtually disabled by it. These individuals often have a form of dysautonomia (imbalance of the autonomic nervous system) that makes them very prone to the reflex that causes this condition. They also often have other persistent symptoms typical of the dysautonomias, such as abdominal bloating or cramps, diarrhea, constipation, extreme fatigue and various aches and pains.
In fact, the several-hour period of symptoms that can follow an episode of vasovagal syncope (mentioned above) strongly mimics many of the symptoms experienced chronically by people with dysautonomia.
Read about dysautonomia.
How Is Vasovagal Syncope Diagnosed?
Doctors who are good at correctly diagnosing vasovagal syncope understand that this condition is almost always situational. Vasovagal syncope is particularly likely to occur after a viral illness, after exercise, after a warm shower or early in the morning - in other words, any time relative dehydration is likely to be present. (When you are dehydrated, dilation of the blood vessels in the legs is more likely to produce a significant drop in your blood pressure.)
Given these characteristic features and the situational nature of this condition, doctors should be able to make the correct diagnosis in the vast majority of patients simply by asking right questions and listening carefully to the answers. Unfortunately, too many doctors fail to take a careful enough medical history in their patients with this condition; as a result, they end up doing unnecessary tests and procedures for cardiac or neurological disease.
The physical examination of people with vasovagal syncope is usually completely normal. However, the exam is very helpful in diagnosing the similar conditions of orthostatic hypotension or postural orthostatic tachycardia syndrome (POTS), and thus in helping the doctor sort through the likely possibilities.
While in most cases the diagnosis of vasovagal syncope ought to be made by taking a medical history and doing a physical examination, testing is sometimes helpful. In particular, a tilt table study can be helpful if the history is not typical for vasovagal syncope or if it is difficult to distinguish between vasovagal syncope and orthostatic hypotension.
How Is Vasovagal Syncope Treated?
There are several approaches to treating vasovagal syncope, and while the condition cannot be "cured," in the vast majority of people with vasovagal syncope it can be controlled sufficiently to allow for a completely normal life.This article discusses the treatment of vasovagal syncope.
Sources:
Task Force for the Diagnosis and Management of Syncope, European Society of Cardiology (ESC), European Heart Rhythm Association (EHRA), et al. Guidelines for the diagnosis and management of syncope (version 2009). Eur Heart J 2009; 30:2631.
Chen-Scarabelli C, Scarabelli TM. Neurocardiogenic syncope. BMJ 2004; 329:336.
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By Richard N. Fogoros, MD - Reviewed by a board-certified physician.
Updated May 08, 2016
Sinus bradycardia is the most common type of bradycardia, or slow heart rate.
In sinus bradycardia, the sinus node - the structure in the right atrium that generates heart’s electrical impulses - is firing at relatively reduced rate. Thus, the heart rate becomes “slow.”
Read about the heart's electrical system.
Read about the heart’s chambers and valves.
In most circumstances, sinus bradycardia is entirely normal.
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In other cases, however, sinus bradycardia can be caused by a diseased or damaged sinus node and may require treatment with a pacemaker.
Normal vs. Abnormal Sinus Bradycardia
At rest, the electrical impulses from the sinus node typically occur between 50-60 and 100 times per minute. This is called "normal sinus rhythm." When the sinus rate is faster than 100 times per minute, it is referred to as "sinus tachycardia." And a sinus rate slower than 50-60 times per minute is called "sinus bradycardia."
Sinus bradycardia is often completely normal. The healthy body is very good at regulating the heart rate to be whatever it needs to be to support the body’s functions. And often, this normal heart rate is within the range of what is “officially” sinus bradycardia. So healthy young people, and even older people when they are in good physical condition, will frequently have resting heart rates in the 40s or 50s.
It is also common (and normal) for many people to have heart rates in this range while sleeping.
However, if the heart rate is too slow to meet the body’s needs, symptoms can develop. Most typically, these symptoms are lightheadedness, fatigue, poor exercise tolerance, or syncope (transient loss of consciousness).
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Usually, sinus bradycardia is not considered to be a serious problem unless it is producing one or more of these symptoms.
What Causes Abnormal Sinus Bradycardia?
Transient, abnormally slow sinus bradycardia is most often caused by increased tone in the vagus nerves, which often occurs with nausea or vomiting, or in response to pain or sudden stress. This form of sinus bradycardia is a normal response to elevated vagal tone and disappears as soon as the cause of the increased vagal tone has subsided.
The most common cause of persistent sinus bradycardia is intrinsic sinus node disease -- disease within the sinus node itself. Usually, sinus node disease is caused by an age-related fibrosis of the sinus node; it is a disorder of aging. Intrinsic sinus node disease is most commonly seen in people who are 70 years old or older.
People who have intrinsic sinus node disease, especially when it is associated with symptoms, are often said to have "sick sinus syndrome."
Read more about sick sinus syndrome.
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Other cardiac conditions can also produce persistent sinus bradycardia. These conditions include coronary artery disease, pericarditis, myocarditis, and trauma due to injury or to cardiac surgery. Sinus bradycardia is also associated with more generalized medical conditions, including amyloidosis, hypothyroidism, dysautonomia, and various infections. Drugs are another cause of sinus bradycardia. These drugs include beta blockers, calcium channel blockers, and antiarrhythmic drugs.
When Should Sinus Bradycardia Be Treated?
Sinus bradycardia should be treated whenever it is producing a heart rate that is slow enough to cause fatigue, lightheadedness, or syncope, either at rest or during exertion.
How Is Sinus Bradycardia Treated?
The first step in treating sinus bradycardia is to determine whether it has a reversible underlying cause. If the sinus bradycardia is due to increased vagal tone, drug therapy, an infectious disease, pericarditis, myocarditis or hypothyroidism, then addressing the underlying problem is usually the only treatment that is necessary.
But if the sinus bradycardia is caused by intrinsic sinus node disease, or by some other medical problem that cannot be easily reversed, then treatment will require the placement of a pacemaker.
Read the basics about pacemakers.
Read about living with a pacemaker.
So if you have sinus bradycardia, you will need to work with your doctor to determine why you have it, and whether it is causing symptoms. While most people with sinus bradycardia do not require a pacemaker, if you do have symptoms from sinus bradycardia you can be confident that a pacemaker will completely eliminate those symptoms.
Read about heart block, the other major cause of bradycardia.
Sources:
Tresch DD, Fleg JL. Unexplained sinus bradycardia: clinical significance and long-term prognosis in apparently healthy persons older than 40 years. Am J Cardiol 1986; 58:1009.
Epstein AE, DiMarco JP, Ellenbogen KA, et al. ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices): developed in collaboration with the American Association for Thoracic Surgery and Society of Thoracic Surgeons. Circulation 2008; 117:e350.
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Treating Vasovagal (Cardioneurogenic) Syncope
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By Richard N. Fogoros, MD - Reviewed by a board-certified physician.
Updated January 01, 2016
Vasovagal (or cardioneurogenic) syncope, often called a "simple fainting spell," is the most common cause of temporary loss of consciousness. It is so common, in fact, that most people will have at least one episode of vasovagal syncope in their lives.
Read about the evaluation of syncope.
Read about vasovagal syncope.
People who have a single, isolated episode generally do not require any medical therapy at all.
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But if you have had recurrent episodes, you have identified yourself as a person who is particularly prone to this condition. Fortunately treatment is likely to be quite helpful.
There are four general types of therapy for vasovagal syncope: education, medication, exercise and pacemakers. Of these, education is by far the most effective for the majority of people.
Educating Yourself About Vasovagal Syncope
People who are prone to vasovagal syncope need to know five important facts about this condition:
1. Vasovagal syncope is produced by a reflex that causes sudden dilation of the blood vessels in the legs, causing the blood to pool there.
2. Any condition that causes a bit of dehydration (which reduces blood volume) will make you more prone to have a syncopal episode.
3. Most people will have a brief "prodrome" (in other words, a set of characteristic symptoms) that precedes the loss of consciousness. These are called “prodromal” symptoms. The key is: there is usually some kind of a warning.
4. If you lie down and elevate your legs when you experience the prodrome, you can prevent the syncopal episode.
5. People will often have occasional periods of days or weeks in which they are particularly prone to vasovagal episodes.
How can these five facts be put to work? The best way to prevent vasovagal syncope is to avoid situations that produce the syncope.
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If you understand the five facts just listed, the following guidelines become immediately apparent.
First and foremost, avoid dehydration. Dehydration (and therefore syncope) most commonly occurs after strenuous exercise, after any kind of illness, and early in the morning after an overnight fast. Coffee, tea and diuretic drugs can also produce dehydration. If you are in a situation where dehydration is likely, you should take pains to rehydrate yourself. You should drink plenty of fluids in general, but if you think you may be dehydrated this is particularly important. And you must avoid prolonged standing while you are dehydrated.
Pay close attention to any prodromal symptoms you may experience. Vasovagal syncope is usually preceded by at least a few seconds of symptoms that commonly may include visual disturbances, buzzing in the ears, lightheadedness, sweating, and/or nausea. People who have had syncopal episodes usually have an excellent idea of what prodromal symptoms they should expect.
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AdvertisementIt is important to recognize your prodromal symptoms, because if you do, you can avoid syncope by lying down and elevating your legs. On the other hand, if you choose to ignore the warning symptoms, you are likely to pass out in the frozen foods section, and the store manager will insist (for well-founded legal reasons) on shipping you to the E.R. in an ambulance, where you'll be subjected to a battery of unnecessary tests and probably an overnight stay in the hospital. Another advantage of avoiding the actual syncope by lying down is that when you do, you will also avoid the prolonged period of feeling "sick" (wasted, washed out, nauseated and dizzy) that often follows a vasovagal episode.
Some people have been able to abort an episode of vasovagal syncope (or more often, delay it long enough to reach a convenient spot to lie down) by immediately engaging in muscle-tensing exercises. These exercises apparently reduces blood vessel dilation and increases the amount of blood being returned to the heart. Such exercises may include leg-crossing while tensing the legs, abdominal area and buttocks; tensing the arms with clenched fists; leg pumping; or squeezing rubber balls.
People who are prone to vasovagal syncope may experience periods of time, lasting days or weeks, in which syncope is particularly prone to occur. These "sensitive periods" often seem to occur for no identifiable reason. Sometimes, however, they may be related to a viral illness, to menstrual cycles, to periods of being fatigued or run down; or to gastrointestinal, urinary or gynecological problems. If you have had one or two recent syncopal episodes, it pays to be particularly vigilant for prodromal symptoms that might herald another episode. It also pays during these times to make special efforts to remain well hydrated by drinking plenty of fluids.
Drug Therapy
In some people, vasovagal syncope occurs with disturbing frequency even when all appropriate precautions are taken. For these individuals, drug therapy is often helpful.
The drugs that have been most commonly used for vasovagal syncope are the beta blockers, but several recent studies have failed to show any benefit and they are currently not recommended.
Drugs that have been shown to be of at least some help include midodrine (a drug that tends to limit the dilation of blood vessels), disopyramide (Norpace, an antiarrhythmic drug that also has some vagal-blocking properties), serotonin re-uptake inhibitors (drugs in the Prozac category) and theopylline (a drug most commonly used to treat asthma).
While one or more of these drugs will often help reduce episodes of syncope, finding the "right" combination of drugs is usually a matter of trial and error. Patience is required on the part of both the doctor and patient in order to find the best therapy.
Exercise Therapy
Many people who have dysautonomia also display a tendency to have vasovagal syncope; indeed, it seems likely that people who have frequent vasovagal syncope (instead of single, isolated episodes), may have a form of dysautonomia. Since some dysautonomias are known to respond favorably to exercise training (which can improve vascular function and "readjust" the autonomic nervous system), some experts have suggested that exercise might similarly benefit people with vasovagal syncope. And indeed, the limited data that are currently available suggest this is the case. So, if you have recurrent vasovagal syncope, you should discuss aerobic exercise training (such as walking, jogging or bicycling) with your doctor.
Read about getting an exercise prescription.
Pacemaker Therapy
Several years ago there was a lot of enthusiasm for using pacemakers to treat vasovagal syncope. The rationale for pacemakers is that vasovagal syncope is usually accompanied by a sudden drop in heart rate. The enthusiasm for pacemaker therapy dropped off rapidly, however, after it was finally noted that many patients with vasovagal syncope who received pacemakers continued to pass out - they just did it with better heart rates. As it turns out, in many, if not most people with vasovagal syncope, it is the pooling of blood in the legs, and not the slow heart rate, that produces syncope.
Still, there are people with vasovagal syncope in whom the drop in heart rate is the predominant reason for passing out. In these people, pacemakers can indeed reduce the frequency of syncope. Unfortunately, it is very difficult to determine whether the slow heart rate alone is the culprit.
Currently, pacemakers are recommended for people with vasovagal syncope only if a) significant slowing of the heart rate is documented during episodes, either during a tilt-table test or during ambulatory ECG monitoring, and b) avoidance behavior (that is, taking the steps described above to avoid or abort vasovagal syncope) is ineffective.
Summary
Vasovagal syncope is a very common condition. Fortunately, it usually occurs in rare, isolated episodes or during a limited period of time.
If you have had vasovagal syncope - especially more than one episode - you should learn as much as you can about your condition, including what kinds of things provoke it, how to recognize the warning symptoms and how you might stop an episode.
If you have repeated episodes of syncope, you should talk to your doctor about whether something more than mere “avoidance therapy” is needed.
Sources:
Task Force for the Diagnosis and Management of Syncope, European Society of Cardiology (ESC), European Heart Rhythm Association (EHRA), et al. Guidelines for the diagnosis and management of syncope (version 2009). Eur Heart J 2009; 30:2631.
Chen-Scarabelli C, Scarabelli TM. Neurocardiogenic syncope. BMJ 2004; 329:336.
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