Which statement correctly defines cardiac index?

Which statement correctly defines cardiac index?

• A. Cardiac output per square meter of body surface area
• B. Cardiac output divided by body weight
• C. Stroke volume per square meter
• D. Heart rate times stroke volume

Answer: (A)

Cardiac index is the cardiac output adjusted for body size. It takes the amount the heart pumps each minute (cardiac output) and divides it by the body's surface area, giving units of liters per minute per square meter (L/min/m^2). This normalization lets you compare hearts of people with different sizes on a common scale. So, the best definition is cardiac output divided by body surface area. It’s not cardiac output divided by body weight, not stroke volume per square meter (that would be stroke volume index), and not heart rate times stroke volume (that equals cardiac output without adjusting for body size). For context, if the cardiac output is 5 L/min and the body surface area is 1.8 m^2, the cardiac index would be about 2.8 L/min/m^2, which falls within a typical normal range of roughly 2.5–4.0 L/min/m^2.

Cardiac index is the cardiac output adjusted for body size. It takes the amount the heart pumps each minute (cardiac output) and divides it by the body's surface area, giving units of liters per minute per square meter (L/min/m^2). This normalization lets you compare hearts of people with different sizes on a common scale.

So, the best definition is cardiac output divided by body surface area. It’s not cardiac output divided by body weight, not stroke volume per square meter (that would be stroke volume index), and not heart rate times stroke volume (that equals cardiac output without adjusting for body size).

For context, if the cardiac output is 5 L/min and the body surface area is 1.8 m^2, the cardiac index would be about 2.8 L/min/m^2, which falls within a typical normal range of roughly 2.5–4.0 L/min/m^2.