Cardiac power output (CPO) is calculated using the following formula: CPO (W) = Mean Arterial Pressure (MAP) × Cardiac Output (CO) / 451.
Here's a breakdown of the calculation:
Components of Cardiac Power Output
- Cardiac Output (CO): The volume of blood pumped by the heart per minute, typically measured in liters per minute (L/min).
- Mean Arterial Pressure (MAP): The average arterial pressure during a single cardiac cycle. It represents the driving pressure that pushes blood through the circulatory system. MAP is typically measured in mmHg (millimeters of mercury).
Calculating Mean Arterial Pressure (MAP)
MAP is estimated from systolic blood pressure (SBP) and diastolic blood pressure (DBP) using the following formula:
MAP = [(Systolic Blood Pressure - Diastolic Blood Pressure) / 3] + Diastolic Blood Pressure
Essentially, MAP is the diastolic blood pressure plus one-third of the pulse pressure (the difference between systolic and diastolic pressure).
Cardiac Power Output Formula
The formula for calculating cardiac power output is:
CPO (W) = (MAP × CO) / 451
Where:
- CPO is in Watts (W)
- MAP is in mmHg
- CO is in L/min
- 451 is a constant used for unit conversion.
Example:
Let's assume a patient has the following measurements:
- Systolic Blood Pressure (SBP) = 120 mmHg
- Diastolic Blood Pressure (DBP) = 80 mmHg
- Cardiac Output (CO) = 5 L/min
Step 1: Calculate MAP
MAP = [(120 - 80) / 3] + 80
MAP = [40 / 3] + 80
MAP = 13.33 + 80
MAP = 93.33 mmHg
Step 2: Calculate CPO
CPO = (93.33 × 5) / 451
CPO = 466.65 / 451
CPO ≈ 1.03 Watts
Significance of Cardiac Power Output
Cardiac power output is a measure of the heart's ability to pump blood and deliver oxygen to the body. It is a more direct measure of cardiac performance than cardiac output alone, as it considers both the volume of blood pumped and the pressure against which the heart must pump. Lower CPO values are often associated with increased risk of adverse outcomes in patients with heart failure.
