A 27-year-old woman has intense fear of receiving an injection. She experiences immediate fear, dizziness, and often faints when she sees a needle. This pattern also occurs when she watches medical procedures on television. What physiological mechanism uniquely predisposes her to syncope in this specific phobia?
- A Prolonged sympathetic activation causing supraventricular tachycardia
- B Vasovagal (diphasic) response: initial sympathetic activation followed by parasympathetic predominance causing bradycardia and hypotension ✓
- C Adrenal insufficiency triggered by phobic stimuli
- D Cerebral vasoconstriction from hyperventilation-induced hypercapnia
Explanation
Blood-injection-injury (BII) phobia is unique among specific phobias in its association with a biphasic cardiovascular response. Initial exposure to the phobic stimulus triggers a sympathetic surge with tachycardia and elevated blood pressure, followed rapidly by a vagally mediated parasympathetic rebound causing bradycardia, hypotension, and syncope. This vasovagal or vasodepressor fainting response is not seen in other specific phobia subtypes and has a strong genetic loading. Applied tension technique is the preferred psychological treatment, counteracting the hypotensive phase.
Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.
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