Cardiac Output

Cardiac Output

• Definition: Cardiac output is defined as the volume of blood that each ventricle pumps out in one minute (60 seconds).

• Equality of Ventricles: The volume of blood pumped by the right ventricle into the pulmonary trunk in one minute is equal to the volume of blood pumped by the left ventricle into the aorta in one minute. Therefore, the cardiac output of the two sides of the heart is the same.

Components of Cardiac Output

• Stroke Volume (SV):

  • Definition: The amount of blood that is ejected by a ventricle each time it contracts.

• Heart Rate (HR):

  • Definition: The number of times the ventricle contracts in one minute.

• Formula for Cardiac Output:

  • $CO = SV \times HR$
    Where:
  • CO: Cardiac Output
  • SV: Stroke Volume
  • HR: Heart Rate

Calculating Stroke Volume

• To determine the stroke volume, we need the following information:

  • End Diastolic Volume (EDV): The volume of blood inside the ventricle at the end of its relaxation (diastole).
  • End Systolic Volume (ESV): The volume of blood left in the ventricle at the end of its contraction (systole).

• Formula for Stroke Volume:

  • $SV = EDV - ESV$

Example of Stroke Volume Calculation

• Assume each ventricle had:
  • EDV: 150 ml
  • ESV: 50 ml
• Calculation:
  • $SV = 150 \, ml - 50 \, ml = 100 \, ml$
• Thus, the stroke volume for each ventricle is 100 ml.

Calculating Heart Rate

• A common method for determining heart rate is by taking the pulse.
• Critical Consideration: When measuring pulse, it is essential to know the duration for which it was measured.
  • Example 1: If the pulse is taken for 15 seconds, the heart rate should be multiplied by 4 since there are four 15-second intervals in one minute.
  • Example 2: If the pulse is taken for 30 seconds, the number counted should be multiplied by 2 to get the heart rate.

Example of Heart Rate Calculation

• Counted pulse in 15 seconds: 20 beats
• Conversion:
  • $HR = 20 \, beats \times 4 = 80 \, bpm$

Total Cardiac Output Calculation

• To find cardiac output, use the values derived above:
• Given that:
  • Stroke Volume: 70 ml
  • Heart Rate: 80 bpm
• Calculation:
  • $CO = SV \times HR = 70 \, ml \times 80 \, bpm = 5600 \, ml/min$

Converting Units

• To convert from milliliters to liters:

  • Formula:
  • Divide the volume in milliliters by 1000.
  • Example: 5600 ml = $\frac{5600}{1000} = 5.6 \, liters$

• In conclusion, understanding cardiac output involves comprehending how stroke volume and heart rate work together to provide vital information regarding cardiovascular function.