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Andrew Pollack-Gray

Nursing Notes

Cardiac Output

2 min read

What is it?

Cardiac output (CO) is the volume of blood pumped by one ventricle of the heart per minute.
It depends on:

  • Heart Rate (HR): Number of heartbeats per minute.
  • Stroke Volume (SV): Amount of blood ejected by one ventricle with each heartbeat.

How does it work?

Formula:
CO = HR × SV
Example:

  • Heart rate = 70 beats/min.
  • Stroke volume = 70 mL/beat.
  • Cardiac output = 70 × 70 = 4,900 mL/min = 4.9 L/min.
    A typical resting adult cardiac output is approximately 4–8 L/min, although it varies with body size, activity, and health.

Factors Affecting Cardiac Output

Heart Rate:

  • Increasing HR can increase CO.
  • Extremely high HR may reduce ventricular filling and lower stroke volume.
    Stroke Volume:
  • Preload: Ventricular filling and stretch before contraction.
  • Contractility: Strength of heart muscle contraction.
  • Afterload: Resistance the ventricle must overcome to eject blood.

Relationship to Blood Pressure

  • Higher CO generally increases arterial pressure when other factors remain constant.
  • Lower CO may contribute to hypotension.
  • Blood pressure also depends on Systemic Vascular Resistance.

Why does it matter clinically?

Cardiac output helps determine whether enough blood reaches the body’s tissues.
Reduced cardiac output may contribute to:

  • Dizziness or weakness.
  • Reduced organ perfusion.
  • Cool extremities.
  • Low blood pressure.
  • Altered mental status.
    These findings have multiple possible causes and do not independently establish low cardiac output.

Sources

  • Anatomy and physiology — cardiovascular circulation

Flashcards

What is the cardiac output formula?01-foundations / anatomy-physiology / cardiovascular
Answer

Heart rate × stroke volume.

What is stroke volume?01-foundations / anatomy-physiology / cardiovascular
Answer

Blood ejected by one ventricle per beat.

Why can an extremely high heart rate reduce cardiac output?02-mechanisms / anatomy-physiology / cardiovascular
Answer

Too little ventricular filling can lower stroke volume.

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