Heart Function and Heart Failure Detailed Notes

Basics of Heart Function

  • Heart Pumps Blood to Two Main Places:

    • Body:

      • Oxygenated blood is pumped from the left side.

      • Body uses oxygen and sends deoxygenated blood back to the right side.

    • Lungs:

      • Deoxygenated blood is pumped from the right side to the lungs to be reoxygenated.

      • Returns to the left side to be pumped through the body again.

Blood Demand

  • Amount of blood pumped depends on body's demand for blood.

    • Demand changes based on activity level (e.g., exercising increases demand).

    • Heart can adjust pumping rate to meet these demands.

Heart Failure Overview

  • Heart Failure: Heart cannot meet body's blood demands.

  • Two main types of heart failure:

    1. Systolic Heart Failure:

      • Refers to systole phase when heart pumps blood.

      • Heart muscles are weakened/smaller, failing to pump blood forcefully.

      • Results in less blood ejected with each contraction.

        • Visualize as squeezing a partially pinched bottle: harder to get the fluid out.

      • Characterized by enlarged lower chambers and thin muscle walls.

    2. Diastolic Heart Failure:

      • Refers to diastole phase when heart fills with blood.

      • Heart cannot fill adequately due to larger muscles taking up space.

      • Even with the same force, less blood is ejected due to lower filling capacity.

        • Visualize holding a half-filled water bottle, squeezing won't yield enough fluid.

Isolated Heart Failure

  • Heart failure can occur in isolation on either side (left or right).

    • Usually, left-sided insufficiency occurs first, potentially leading to right-sided failure.

    • Can happen with systolic or diastolic

Left-Sided Heart Failure

  • Blood backs up into the lungs since left side pumps to the body.

    • Results in fluid buildup in lungs, termed congestion.

  • Symptoms may include:

    • Shortness of breath.

    • Coughing due to congestion.

Right-Sided Heart Failure

  • Blood backs up into the body since right side pumps to the lungs.

    • Results in fluid buildup in feet, legs, lungs, and abdomen.

  • Symptoms may include:

    • Swelling in legs and feet (edema).

    • Congestion in abdominal areas.

Measurement of Heart Function: Cardiac Output

  • Cardiac Output: Total blood pumped by the heart per minute (in liters).

    • Normal range is approximately 5 liters/minute.

    • Calculated from:

      • Stroke Volume: Amount of blood pumped per beat.

      • Heart Rate: Beats per minute.

    • Formula: Cardiac Output = Stroke Volume x Heart Rate.

  • Effects of Heart Failure on Cardiac Output:

    • Heart failure typically leads to lower cardiac output due to:

      • Reduced stroke volume or heart rate.

    • Often secondary to preexisting conditions that damage cardiac muscle (cardiomyocytes).

      • Damage leads to:

        • Reduced strength of heart muscle.

        • Lower stroke volume and cardiac output.

Compensatory Mechanisms in Heart Failure

  • Following a decline in function, heart attempts to compensate:

    • Increase stroke volume (e.g., by squeezing harder).

    • Increase heart rate (e.g., by beating faster).

  • Compensation can initially be effective but may worsen condition over time due to:

    • Increased oxygen demand on surviving muscle cells.

    • Further cell death from insufficient oxygen supply, leading to a worsening cycle of heart failure.