Cardiac Output + Ejection Fraction

Key Terms in Cardiology

Basic Terms

• Systole

  • Definition: The contraction phase of the heart when blood is pumped out of the ventricles.

  • Importance: Critical for understanding blood pressure readings; systolic pressure is the maximum pressure during this contraction.

• Diastole

  • Definition: The relaxation phase of the heart, where the ventricles fill with blood.

  • Importance: Understanding diastolic pressure is important as it represents the lowest pressure within the arteries.

Hemodynamic Definitions

• Preload

  • Definition: The volume of blood returning to the heart, specifically into the right atrium and ventricle.

  • Concept: Think of it as the "filling" phase of the heart.

  • Key Medication: Nitroglycerin, which decreases preload by reducing the volume of blood returning to the heart.

• Afterload

  • Definition: The force against which the left ventricle must pump blood during systole.

  • Concept: It’s primarily influenced by the pressure in the aorta and systemic vascular resistance.

  • Clinical Significance: Increased afterload can lead to conditions like pulmonary edema if the left ventricle fails.

Advanced Cardiac Terms

• Contractility

  • Definition: The strength of ventricular contractions.

  • Clinical Relevance: Increasing contractility can be achieved with medications like epinephrine, improving cardiac output during emergencies.

• Automaticity

  • Definition: The ability of cardiac muscle cells to contract independently of external stimuli.

  • Importance: Essential for maintaining rhythm and pace of the heart.

Cardiac Output, Stroke Volume, and Heart Rate

• Cardiac Output (CO)

  • Definition: The total volume of blood pumped by the heart in one minute, measured in liters per minute.

  • Formula: CO = Stroke Volume × Heart Rate

  • Normal Adult CO: 5 to 6 liters per minute at rest.

• Stroke Volume (SV)

  • Definition: The amount of blood ejected by the heart per contraction, typically measured in milliliters.

  • Normal Range: 50 to 100 mL per contraction.

• Heart Rate (HR)

  • Definition: The number of heartbeats per minute (BPM).

  • Normal Range: 60 to 100 BPM at rest.

Calculating Cardiac Output

• Example:

  • Stroke Volume = 100 mL, Heart Rate = 60 BPM

  • Calculation: 100 mL × 60 BPM = 6000 mL = 6 liters per minute (normal).

  • Another Example: Stroke Volume = 75 mL, Heart Rate = 72 BPM

  • Calculation: 75 mL × 72 BPM = 5400 mL = 5.4 liters per minute (normal).

Ejection Fraction (EF) and Diastolic Volume

• Ejection Fraction

  • Definition: The percentage of blood ejected from the left ventricle with each contraction.

  • Normal EF: 50 to 75%

  • Importance: An indicator of heart health, especially in heart transplant patients.

• Diastolic Volume

  • Definition: The volume of blood in the ventricles just before contraction (during diastole).

  • Normal Measurement: 120 mL.

• Ejection Fraction Formula

  • EF = (Stroke Volume / End Diastolic Volume) × 100

  • Example Calculation:

    • Stroke Volume = 70 mL, End Diastolic Volume = 120 mL

    • Calculation: (70 / 120) × 100 = 58% (within normal range).