Cardiac cycle

Cardiac Cycle Overview

Lecture Notes - Cardiac Cycle

  • Lecture 32: Focus on the cardiac cycle, including mechanics, electrical activities, pressure changes, and volume changes within the heart.

Action Potentials in Pacemaker Cells

  • Graph Analysis:

    • X-axis: Time (seconds)

    • Y-axis: Membrane Potential (mV)

    • Key components include:

    • Pacemaker potential

    • Action potential

    • Threshold

    • Key Ions Responsible: Various ions (specifically Sodium (Na extsuperscript{+}), Calcium (Ca extsuperscript{2+}), and Potassium (K extsuperscript{+})) facilitate the generation of action potentials in the Sinoatrial (SA) Node.

Ventricular Action Potentials

  • Graph Analysis:

    • Membrane potential fluctuations:

    • Starts at 0 and goes through potential reaches (e.g., Plateau, Absolute Refractory Period)

    • Phases Detailed:

    • Myocardial Contraction: Active phase where the heart contracts.

    • Myocardial Relaxation: The phase following contraction.

ECG and Pressure Dynamics

  • Key Terminology:

    • Diastole: Relaxation phase

    • Systole: Contraction phase

  • Blood Pressure Measurements (mm Hg):

    • Systolic Pressure, Diastolic Pressure, and their changes are depicted over time.

  • Heart Sounds and Electrical Activity:

    • Sound phases include S1, S2, & presence of the dicrotic notch when the aortic valve closes.

The Cardiac Cycle Phases

  • Phases:

    • Name the four phases of the cardiac cycle, which include:

    • Atrial Systole

    • Isovolumetric Contraction

    • Ventricular Ejection

    • Isovolumetric Relaxation

  • Volume Metrics:

    • End Diastolic Volume (EDV) and End Systolic Volume (ESV) can be identified on the provided graph.

Volume Changes During Cardiac Cycle

  • Metrics:

    • End Diastolic Volume (EDV): Volume in the ventricle at the end of diastole.

    • End Systolic Volume (ESV): Volume in the ventricle at the end of systole.

    • Stroke Volume (SV): Amount of blood ejected with each contraction, calculated by:
      SV = EDV - ESV

    • Ejection Fraction (EF): Percentage of EDV that is ejected, calculated by:
      EF = rac{SV}{EDV} imes 100

Ventricular Ejection Dynamics

  • During ventricular ejection:

    • AV Valve: Closed

    • Aortic Valve: Open

Cardiac Output Calculation

  • Formula:

    • C.O. = HR imes SV

    • C.O.: Cardiac Output

    • HR: Heart Rate

    • SV: Stroke Volume

  • Heart Rate (HR): Can be altered by:

    • Chronotropic effects (e.g., nervous system or hormonal influences).

Stroke Volume Determinants

  • Stroke volume is determined by three factors:

    1. Preload: The loading capacity of the heart before contraction, described by the Frank-Starling Law of the Heart.

    2. Contractility: The strength of the heart's contraction.

    3. Afterload: The resistance the heart must overcome to eject blood.

Example Calculation of Stroke Volume

  • If EDV is 150 mL and ESV is 100 mL, then:

    • SV = EDV - ESV = 150 mL - 100 mL = 50 mL

Example Calculation of Cardiac Output

  • Given:

    • HR = 100 bpm

    • SV = 90 mL

    • Cardiac Output:

    • C.O. = HR imes SV = 100 ext{ bpm} imes 90 ext{ mL}

Frank-Starling Law

  • Explains how increased Preload enhances Stroke Volume (SV).

    • Relation to Contractility and Afterload potential discussed but not emphasized as analogous.

Coronary Artery Disease Overview

  • Anatomy Samples:

    • Comparisons between Normal artery, Diseased artery with plaque, and Complicated plaque formation.

Next Lecture Preparation

  • Assigned Pages: 711-717

  • Expected Knowledge:

    1. Define cardiac output.

    2. Explain the chronotropic effects of the autonomic nervous system and chemicals.

    3. Define stroke volume and describe the three determining factors.

    4. Identify positive and negative inotropic agents.

    5. Describe the Frank-Starling law of the heart.

    6. Summarize coronary atherosclerosis progression, main risk factors, and prevention strategies.

Key Vocabulary Words

  • cardiac output

  • tachycardia

  • bradycardia

  • preload

  • contractility

  • afterload

  • chronotropic agent

  • proprioceptors

  • baroreceptors

  • chemoreceptors

  • inotropic agent

  • atherosclerosis

  • arteriosclerosis

  • plaque

  • angioplasty

  • stent