An acute spinal cord injury above T4–T6 produces a sympathectomy below the level of injury with vasodilation and hypotension, a condition known as spinal shock. Which statement best describes this physiologic change?

An acute spinal cord injury above T4–T6 produces a sympathectomy below the level of injury with vasodilation and hypotension, a condition known as spinal shock. Which statement best describes this physiologic change?

• A. Increased systemic vasomotor tone
• B. Increased vasopressor reflexes
• C. Sympathectomy below the level of injury with vasodilation and hypotension
• D. Enhanced cardiac output

Answer: (C)

The key idea is that a high spinal cord injury disrupts the brain’s control of the sympathetic nervous system to the parts of the body below the injury. When the injury is above T4–T6, the descending sympathetic outflow to vessels below the lesion is lost. Without this sympathetic input, peripheral vessels dilate (vasodilation), which lowers systemic vascular resistance and blood pressure, producing hypotension. At the same time, the heart loses much of its sympathetic stimulation, and parasympathetic (vagal) influence can predominate, contributing to a tendency toward bradycardia and blunted pressor responses. This is why the statement describing sympathectomy below the level of injury with vasodilation and hypotension best captures the physiological change. Other options imply preserved or enhanced sympathetic activity (increased vasomotor tone or vasopressor reflexes) or an increase in cardiac output, which conflicts with the loss of sympathetic control and the resulting vasodilation and hypotension seen in spinal shock.

The key idea is that a high spinal cord injury disrupts the brain’s control of the sympathetic nervous system to the parts of the body below the injury. When the injury is above T4–T6, the descending sympathetic outflow to vessels below the lesion is lost. Without this sympathetic input, peripheral vessels dilate (vasodilation), which lowers systemic vascular resistance and blood pressure, producing hypotension. At the same time, the heart loses much of its sympathetic stimulation, and parasympathetic (vagal) influence can predominate, contributing to a tendency toward bradycardia and blunted pressor responses.

This is why the statement describing sympathectomy below the level of injury with vasodilation and hypotension best captures the physiological change. Other options imply preserved or enhanced sympathetic activity (increased vasomotor tone or vasopressor reflexes) or an increase in cardiac output, which conflicts with the loss of sympathetic control and the resulting vasodilation and hypotension seen in spinal shock.