The Relationship Between Heart Rate, Cardiac Output, and Stroke Volume
Key Definitions
Before diving into the relationships, let's quickly define our key terms:
- Heart Rate (HR): Number of heartbeats per minute
- Stroke Volume (SV): Amount of blood pumped out by each ventricle per beat
- Cardiac Output (CO): Total volume of blood pumped by the heart per minute
The fundamental equation connecting these variables is: $CO = HR × SV$
At Rest
During resting conditions:
- Heart Rate: typically 60-80 beats per minute
- Stroke Volume: approximately 70-80 mL per beat
- Cardiac Output: about 5 L per minute
For a person with a resting heart rate of 70 bpm and stroke volume of 70 mL: $CO = 70 \text{ bpm} × 70 \text{ mL} = 4900 \text{ mL/min} = 4.9 \text{ L/min}$
During Exercise
Initial Response
When exercise begins:
- Heart rate increases rapidly
- Stroke volume increases due to:
- Enhanced venous return
- Stronger myocardial contractions
- More complete emptying of ventricles
Progressive Changes
As exercise intensity increases:
