11. Vasovagal syncope.

Vasovagal syncope: What happens after loss of consciousness?

After loss of consciousness you will lose muscle tone, causing you to fall and assume a supine position. This evens out the distribution of blood, causing consciousness to be quickly regained. There will be no later symptoms. However, if you for example faint while sitting in your bed and don't fall to a supine position the cerebral hypoperfusion will remain and severe symptoms can develop.

In standing position, when blood pressure at the level of the heart is 120/80 mmHg, is the MAP:

At the level of the head: 60-80 (70) mmHg At the level of the heart: 80-100 (90) mmHg At the level of the feet: 180-190 (185) mmHg

What is precollapse?

Before vasovagal syncope occurs people often experience precollapse, a collection of symptoms related to decreased cerebral perfusion. Common symptoms include: -Blackening vision -Sounds becoming faint -Nausea -Pallor -Diaphoresis (sweating) -Lightheadedness If you ever felt like fainting but lie down just before it happens, you may have experienced that you regain consciousness and feel better shortly after lying down. That is because the supine position improves the venous return and the cardiovascular parameters, and the brain finally gets enough blood.

Why is orthostatic syncope in some elderly?

Elderly have decreased sensitivity of the baroreceptors, which impairs the immediate adaptation.

Causes of vasovagal syncope:

Etiology: Strong psychogenic effects -Strong emotions -Severe pain -Fear Smell of blood Sight of blood Heat exposure

When do orthostatic syncope occur?

If syncope occurs right after standing up from supine position

Not all cases of loss of consciousness are cases of syncope

It's important to note that not all cases of loss of consciousness are cases of syncope. A coma for example isn't a type of syncope even though both include loss of consciousness.

What is the mechanism of vasovagal syncope?

Like the name implies the circulation and vagus nerve are involved. It occurs when the body overreacts to certain triggers, such as the sight of blood or extreme distress.

What happens when the vagus nerve is overreacted?

Something causes the vagus nerve to be overactivated. The vagus nerve causes bradycardia and systemic vasodilation. Vasodilation causes the blood pressure and venous return to decrease suddenly. This causes a massive but temporary hypoperfusion of brain, which results in a syncope with loss of consciousness.

Syncope

Syncope (or fainting) is a sudden, completely reversible loss of consciousness due to an acute reduction of cerebral perfusion. It may last from several seconds up to minutes. It occurs exclusively in orthostatic (standing or sitting where the head is up) posture. Along with the loss of consciousness is there also a loss in skeletal muscle tone, which causes the affected person to fall and assume a supine position where the circulation normalizes and consciousness is regained.

Risk factors for syncope:

Syncope is more expected in: -people whose immediate adaptation is impaired -people that have diseases giving them hypotension -pregnancy, where there is a physiological decrease in blood pressure (usually around 110/70) Other factors may be: -Exhausting exercise (vasodilation) -Valsalva maneuver -Loss of blood -Obstruction in venous return -Sympathectomy -Some drugs and medicines -Hyperventilation

What happens when you're standing up to maintain enough blood flow to the brain?

The baroreceptor-triggered sympathetic reflex mechanism will react, and cause either arteriolar or venous constriction. This is called immediate adaption

decortication syndrome

The cortex is the least-perfused part of the brain, so it's affected the most by this. In fact, a 5-minute-long cerebral hypoperfusion causes the cortex to die completely, causing decortication syndrome! Try to google "decortication syndrome" literally and note how the term hasn't been used since the 60s.

How have vasovagal syncope got its name?

The name comes from how the afferent part of the reflex comes from the vessels (vaso), while the efferent part comes from the vagus (vagal).

Vascular adaptation in the legs

This high MAP in the lower extremities means that there is a tendency for blood to pool there. Vascular adaptation in the legs is the key to maintaining cerebral blood flow, and therefore, when standing up after supine posture, the body must adapt and increase the vascular tone in the legs. When standing up, the baroreceptor-triggered sympathetic reflex mechanisms will react, and cause either arteriolar or venous constriction. This is called immediate adaption and prevents a sudden drop in venous return to the heart and blood pressure, and ensures that enough blood will flow to the brain.

Why do orthostatic syncope occur?

This is often due to an impairment of the immediate adaptation, which is often seen in elderly.

What is the most common syncope?

Vasovagal syncope is the most common cause of syncope.