EC

Heart Sounds and Cardiac Output

Overview of Heart Sounds

  • Heart Sounds Definition: Heart sounds are audible noises produced by the heart during its functioning, primarily related to the closing of valves.

Primary Heart Sounds

  • S1 (First Heart Sound):

    • Created by the closing of the atrioventricular (AV) valves during ventricular contraction.
    • Commonly referred to as "lub".

  • S2 (Second Heart Sound):

    • Produced by the closing of the semilunar valves during ventricular diastole.
    • Referred to as "dup" or "dub".

  • Variations in Notation:

    • Sometimes written as "PP" or "lub lub dup"; differences in representation do not imply correctness.

Additional Heart Sounds

  • S3 (Third Heart Sound):

    • Not commonly heard in healthy individuals; may indicate abnormality when present.
    • Indicates:
      • Blood flow into atria.
      • Blood movement in ventricles.
      • Tensing of chordae tendineae.
    • Commonly heard in:
      • Younger patients
      • Athletes
      • Pregnant women
    • When heard in older adults, often indicates congestive heart failure (CHF).

  • S4 (Fourth Heart Sound):

    • Related to atrial contraction pushing blood into stiff or hypertrophic ventricles.
    • Indicates left ventricular failure.

  • Collective Reference:

    • S1, S2, and S3 combined are sometimes referred to as "Kentucky gallop", due to their rhythmic resemblance to galloping horses.

Heart Murmurs

  • Definition: Abnormal sounds from the heart due to turbulent blood flow.
  • Grading Scale for Murmurs:
    • Graded from 1 to 6:
      • 1: Very faint, difficult to detect; least serious.
      • 6: Very loud; most serious.
  • Causes of Murmurs:
    • Incompetent valves (e.g., regurgitation).
    • Increased turbulence due to various conditions (e.g., illness).
    • Treatment varies based on cause; from monitoring to surgical intervention.

Cardiac Output

  • Definition: Measurement of blood volume pumped by each ventricle in one minute.

Calculation of Cardiac Output

  • Formula:
    ext{Cardiac Output (CO)} = ext{Heart Rate (HR)} imes ext{Stroke Volume (SV)}

Stroke Volume (SV)

  • Definition: Amount of blood ejected from each ventricle during one contraction.
  • Calculation of SV: ext{SV} = ext{End Diastolic Volume (EDV)} - ext{End Systolic Volume (ESV)}
    • Example Calculation:
      • EDV = 130 mL
      • ESV = 60 mL
      • ext{SV} = 130 ext{ mL} - 60 ext{ mL} = 70 ext{ mL}

Overall Calculation Example

  • Using a typical resting heart rate:

    • HR approximately 75 beats/min.
    • CO Calculation:
      ext{CO} = 75 ext{ beats/min} imes 70 ext{ mL/beat} = 5250 ext{ mL/min} or 5.25 ext{L/min} .

  • Human Blood Volume: Approximately 5 liters; at rest, almost the entire blood supply circulates through the heart once per minute.

Physiological Changes in Cardiac Output

  • During Exercise: Heart rate can increase to approximately 150 beats/min; stroke volume may increase up to 130 mL.
    • Resulting CO may reach up to 19-20 L/min (approximately five times the resting output).
  • Regulation of Cardiac Output:
    • Intrinsic Controls: Regulated by normal heart function, focusing on preload and afterload.
    • Extrinsic Controls: Involves neural (sympathetic and parasympathetic nervous systems) and hormonal regulation.

Intrinsic Regulation of Cardiac Output

  • Preload:

    • Amount of stretch of the ventricular walls during filling.
    • Greater stretch leads to stronger heart contractions (Starling's Law).

  • Afterload:

    • Pressure necessary for the ventricles to eject blood against aorta pressure.
    • High blood pressure increases afterload, making the heart work harder.

Extrinsic Regulation of Cardiac Output

  • Sympathetic Control:

    • Norepinephrine and epinephrine increase heart rate and force of contraction by binding to beta-1 adrenergic receptors on pacemaker cells.

  • Parasympathetic Control:

    • Acetylcholine binds to muscarinic receptors, hyperpolarizing pacemaker cells, leading to a decrease in heart rate.

Heart Failure

  • Definition: Inability of the heart to meet metabolic demands due to inadequate cardiac output.

Signs/Symptoms of Heart Failure

  • Common Symptoms:
    • Shortness of breath (especially when lying down).
    • Fatigue/weakness.
    • Swelling in the legs/ankles.
    • Rapid and irregular heartbeat.
    • Cough and wheezing.

Causes of Heart Failure

  1. Persistent Hypertension: Increased workload causes heart muscle wear and potential failure.
  2. Arteriosclerosis: Thickening and stiffness of blood vessels limiting blood flow.
  3. Atherosclerosis: Build-up of fatty plaques leading to narrowed arteries and increased pressure.
  4. Myocardial Infarction (Heart Attack): Damage from blocked coronary arteries leading to scar tissue that does not contract effectively.

Effects of Left vs Right Ventricular Failure

  • Left-Sided Weakness:
    • Results in pulmonary congestion (fluid backup in lungs leading to pulmonary edema).
  • Right-Sided Weakness:
    • Causes peripheral congestion (blood backup in systemic circulation, leading to swelling in limbs).

Treatment of Heart Failure

  • Diuretics: Reduce swelling and fluid buildup.
  • Beta Blockers: Lower blood pressure and heart rate.
  • ACE Inhibitors: Open blood vessels and improve flow.
  • Lifestyle Changes: Dietary recommendations and exercise as advised by healthcare professionals.
  • Surgical Options: Potential heart transplantation in severe cases.

Conclusion

  • Understanding the mechanisms and dynamics of heart sounds, murmurs, cardiac output regulation, and implications of heart failure is essential for diagnosing and managing cardiovascular health effectively.