Vasovagal syncope is caused by which mechanism?

Vasovagal syncope is caused by which mechanism?

• A. Stimulation of the vagal nerve
• B. Increase in sympathetic activity
• C. Dehydration
• D. Brain tumor

Answer: (A)

Vasovagal syncope happens when a reflex causes the heart to slow and the blood vessels to widen, leading to a rapid drop in blood pressure and reduced blood flow to the brain. The driving factor is stimulation of the vagus nerve, which increases parasympathetic activity and decreases sympathetic activity. This produces bradycardia and vasodilation, so cardiac output falls and cerebral perfusion drops enough to cause fainting. An increase in sympathetic activity would raise heart rate and blood pressure, not produce fainting. Dehydration can lower preload and contribute to faintness, but it isn’t the immediate reflex mechanism. A brain tumor isn’t part of the reflex pathway that causes the vasovagal response.

Vasovagal syncope happens when a reflex causes the heart to slow and the blood vessels to widen, leading to a rapid drop in blood pressure and reduced blood flow to the brain. The driving factor is stimulation of the vagus nerve, which increases parasympathetic activity and decreases sympathetic activity. This produces bradycardia and vasodilation, so cardiac output falls and cerebral perfusion drops enough to cause fainting.

An increase in sympathetic activity would raise heart rate and blood pressure, not produce fainting. Dehydration can lower preload and contribute to faintness, but it isn’t the immediate reflex mechanism. A brain tumor isn’t part of the reflex pathway that causes the vasovagal response.