What physiological response occurs during prolonged standing in neuro-cardiogenic syncope?

What physiological response occurs during prolonged standing in neuro-cardiogenic syncope?

• A. Increased heart rate
• B. Vasoconstriction
• C. Vasodilation and slowing of the pulse
• D. Hypertension

Answer: (C)

In prolonged standing, especially in individuals susceptible to neuro-cardiogenic syncope, the physiological response often involves vasodilation and slowing of the pulse. When a person stands for an extended period, gravity causes blood to pool in the lower extremities. This pooling reduces venous return to the heart, leading to decreased cardiac output and blood pressure.

In response to this change, the body attempts to maintain blood flow to the brain by triggering reflex mechanisms. However, in neuro-cardiogenic syncope, these compensatory mechanisms can be impaired. Instead of adequate vasoconstriction and an increase in heart rate to counteract the effects of gravity and maintain blood pressure, there can be an inappropriate vasodilation. This vasodilation exacerbates the pooling of blood in the legs, leading to a further drop in blood pressure and potentially causing the individual to faint.

The slowing of the pulse can occur as the autonomic nervous system responds to decreased blood pressure, potentially leading to a paradoxical decrease in heart rate due to increased vagal tone. This combination of vasodilation and a slower pulse can result in inadequate blood flow to the brain, manifesting as syncope.

In contrast, increased heart rate, vasoconstriction, or hypertension do not