U01.21.020 Cardiac Output (CO)

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Learning Objective:
Understand and apply the formulas for cardiac output (CO), which measures the volume of blood the heart pumps per minute.

Formulas:

CO = \frac{\text{Rate of O}_2 \text{ consumption}}{\text{Arterial O}_2 \text{ content} - \text{Venous O}_2 \text{ content}}

CO = \text{Stroke Volume} \times \text{Heart Rate}

Explanation:

  • \text{Stroke Volume (SV)} = volume of blood ejected by the heart per beat
  • \text{Heart Rate (HR)} = number of heartbeats per minute
  • \text{Rate of O}_2 \text{ consumption (VO}_2\text{)} = oxygen uptake per minute
  • The first formula uses Fick’s principle: CO is proportional to oxygen consumption divided by the arteriovenous oxygen difference.
  • The second formula is the basic physiological definition of CO as the product of SV and HR.

Example (Stroke Volume × Heart Rate):

Given:
SV = 70 \text{ mL}
HR = 75 \text{ beats/min}

CO = 70 \times 75 = 5250 \text{ mL/min} = 5.25 \text{ L/min}

✅ Answer: Cardiac Output = 5.25 L/min

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