Question

A 10 Degree Centigrade decrease in temperature causes a decrease in cerebral metabolic rate by

• A. 10%
• B. 30%
• C. 50%
• D. 70%

Hint:

Cerebral metabolic rate falls about 6-7% per degree Centigrade, so a 10 degree Centigrade drop nearly halves it.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks by how much the cerebral metabolic rate falls when brain temperature drops by 10 degree Centigrade.

Step 2: Key Formula or Approach:
Cerebral oxygen consumption, which reflects the metabolic rate of the brain, follows a temperature dependent relationship described by the Q10 coefficient. For brain tissue this Q10 is close to 2 to 2.4, and the accepted clinical teaching is that cerebral metabolic rate falls by about 6 to 7 percent for every 1 degree Centigrade drop in temperature.

Step 3: Detailed Explanation:
If the metabolic rate falls by roughly 6 to 7 percent for each degree, then over a full 10 degree drop these small drops compound together. Working this out shows the cerebral metabolic rate ends up at roughly half of its starting value, in other words it falls by about 50 percent. This is why hypothermia is used clinically to protect the brain during surgery or after cardiac arrest, cooling the brain by 10 degree Centigrade roughly halves its oxygen demand, giving it more tolerance to periods of reduced blood flow.
A drop of 10 percent or 30 percent would be far too small to explain the strong protective effect seen with moderate hypothermia in clinical practice. A drop of 70 percent would be an overestimate for a 10 degree change.

Step 4: Final Answer:
A 10 degree Centigrade fall in temperature lowers the cerebral metabolic rate by about 50 percent, so the correct option is (C). Note: the source answer key marked this as option (B), 30 percent, with an uncertain mark next to it in the original scan. Based on the well established Q10 relationship for cerebral metabolism, about 6 to 7 percent fall per degree Centigrade, compounding to roughly 50 percent over 10 degrees, the medically accurate answer is 50 percent, option (C), and it has been corrected here.