L6 part 2 physiology

Cardiac Output

• Defined as the volume of blood pumped by the heart every minute.
• Measured in Litres/minute ( L/min)
• Calculated by multiplying Stroke Volume (SV) by Heart Rate (HR): CO = SV x HR
• Normal cardiac output is approximately 5 L/min.

Cardiac Indices and Values

• Ejection Fraction (EF): Percentage of blood ejected from the ventricle during each contraction.
  • Measured using echocardiography.
  • Calculated using the formula: EF = (SV/EDV) * 100% (where SV is Stroke Volume, EDV is End-Diastolic Volume)
  • Normal EF is greater than 60%.
• Stroke Volume (SV): Volume of blood ejected from the ventricle with each heartbeat.
  • Calculated by subtracting End-Systolic Volume (ESV) from End-Diastolic Volume (EDV): SV = EDV - ESV.
• End-Diastolic Volume (EDV): Volume of blood in the ventricle at the end of diastole (relaxation).
• End-Systolic Volume (ESV): Volume of blood remaining in the ventricle at the end of systole (contraction).

Factors Affecting Stroke Volume

• Preload: The degree of stretch of the ventricle muscle fibers before contraction.
• Afterload: The resistance the ventricle must overcome to eject blood (arterial pressure).
• Contractility: The intrinsic strength of the ventricle muscle.

Frank-Starling Principle

• The heart pumps more blood with a greater preload (increased EDV), as long as contractility is not depressed.
• This mechanism regulates the heart to maintain a steady cardiac output.

Cardiac Reserve

• Represents the difference between resting cardiac output and maximum cardiac output.
• Represents how much more the heart can pump when needed (e.g., during exercise).

Cardiac Output

• Cardiac output refers to the volume of blood pumped each minute and is expressed by the equation: CO = SV x HR.
• Normal cardiac output is approximately 5 L/min.
• SV represents stroke volume, which is the amount of blood pumped per beat, and HR is the heart rate, or the number of beats per minute.

Ejection Fraction

• Ejection fraction is a measure of the heart's pumping efficiency.
• It is the percentage of blood ejected from the left ventricle with each contraction.
• It is most commonly measured using echocardiography.
• A normal ejection fraction is greater than 60%.

Stroke Volume

• Stroke volume is the amount of blood ejected from the heart with each beat.
• It is determined by three factors: preload, afterload, and contractility.
• Preload: The volume of blood in the ventricle at the end of diastole
• Afterload: The pressure the heart must overcome to eject blood.
• Contractility: The force of contraction of the heart muscle.
• Formula: SV = EDV - ESV.
• EDV: End-diastolic volume, the amount of blood in a ventricle at the end of diastole.
• ESV: End-systolic volume, the amount of blood remaining in a ventricle after contraction.

Cardiac Reserve

• Cardiac reserve is the difference between resting heart output and the maximum achievable cardiac output.
• This represents the ability of the heart to increase its output during exercise or stress.

Test your knowledge about cardiac output, stroke volume, and ejection fraction. This quiz covers the definitions, calculations, and normal values for various cardiac indices. It's a great resource for students studying cardiovascular physiology.