Study Notes on Stroke Volume and Cardiac Output

Blood Volume and Cardiac Output

Blood Volume in the Heart

• Atria to Ventricles:
  • Approximately 120 milliliters (ml) of blood is passed from the atria to the ventricles.
• Ventricular Residual Volume:
  • There remains about 50 ml of blood in each ventricle after this transfer.
• Stroke Volume:
  • The stroke volume is defined as the amount of blood ejected from each ventricle with each contraction (heartbeat).
  • Stroke volume can be calculated as follows:
  • $Stroke ext{ }Volume = Blood ext{ }Ejected - Blood ext{ }Remaining$
  • In usual circumstances, it is stated that this stroke volume is about 70 ml per heartbeat.

Calculating Cardiac Output

• Cardiac Output (CO):
  • Cardiac output is defined as the volume of blood pumped by the heart per minute.
  • The formula for cardiac output is:
  • $Cardiac ext{ }Output = Stroke ext{ }Volume imes Heart ext{ }Rate$
  • Where:
  • Stroke Volume = 70 ml
  • Heart Rate = beats per minute (bpm)
• Units:
  • A complete calculation will yield cardiac output in milliliters per minute as the units for stroke volume (ml) and heart rate (bpm) will combine accordingly to yield ml/min.

Practical Calculation Steps

1. Measure Heart Rate:
   • Check your partner's heart rate (bpm).
2. Calculate Cardiac Output:
   • Multiply the stroke volume (70 ml) by the heart rate (bpm) to determine cardiac output.
   • Example: If the heart rate is 60 bpm, then:
     • $Cardiac ext{ }Output = 70 ext{ }ml imes 60 ext{ }bpm = 4200 ext{ }ml/min$
3. Blood Pressure Check:
   • Measure blood pressure as a complementary parameter.
4. Document Steps:
   • It's essential to write down all the results and calculations on a piece of paper for clarity and accuracy.

Conclusion

• Each of these parameters—stroke volume, heart rate, and blood pressure—play a crucial role in understanding cardiovascular health and function. This method allows for a quantitative assessment of heart performance in terms of pumping efficiency and overall cardiovascular output.