For each 1°C decrease in body temperature, by what percentage is CMRO2 diminished?

For each 1°C decrease in body temperature, by what percentage is CMRO2 diminished?

• A. 3%
• B. 5%
• C. 6%
• D. 10%

Answer: (C)

Temperature sharply influences brain metabolism. The cerebral metabolic rate for oxygen (CMRO2) slows as body temperature falls, following a roughly linear fall with temperature. The widely used rule is about a 6% decrease in CMRO2 for each 1°C drop in temperature. This is explained by the Q10 effect, where enzymatic reactions and neuronal activity slow as temperature decreases, reducing the brain’s oxygen demand. For example, lowering temperature by 3°C from normal would reduce CMRO2 by about 18%, and a larger drop would yield progressively larger reductions. This metabolic slowdown underpins why hypothermia is used to protect the brain during certain surgical and pathologic conditions. Among the options, 6% per degree is the standard figure, whereas 3% or 5% would underestimate the change, and 10% would overestimate it.

Temperature sharply influences brain metabolism. The cerebral metabolic rate for oxygen (CMRO2) slows as body temperature falls, following a roughly linear fall with temperature. The widely used rule is about a 6% decrease in CMRO2 for each 1°C drop in temperature. This is explained by the Q10 effect, where enzymatic reactions and neuronal activity slow as temperature decreases, reducing the brain’s oxygen demand.

For example, lowering temperature by 3°C from normal would reduce CMRO2 by about 18%, and a larger drop would yield progressively larger reductions. This metabolic slowdown underpins why hypothermia is used to protect the brain during certain surgical and pathologic conditions.

Among the options, 6% per degree is the standard figure, whereas 3% or 5% would underestimate the change, and 10% would overestimate it.