Chap015_Cardiovascular_Function

Chapter 15: The Heart and Cardiovascular Function

Principles of Cardiovascular Function

• Calcium is Key: Essential for muscle contraction.

• Water Flows Downhill: Blood moves from high to low pressure.

• Capillary Fluid Exchange: Increased pressure results in more fluid loss.

• LaPlace’s Law: Tension = Pressure x Radius / Wall Thickness.

• More In, More Out: Higher end-diastolic volume increases output.

Pressure Changes in the Cardiovascular System

• Major drop in pressure occurs at arterioles.

• Blood flows from areas of high to low pressure.

• Heart Systole: Phase when the heart contracts.

• Heart Diastole: Phase when the heart relaxes.

Phases of the Cardiac Cycle

Systole

• Heart contracts, blood pressure increases, blood moves into vessels.

Diastole

• Heart relaxes, blood pressure decreases, heart fills with blood.

Position of the Heart in the Thoracic Cavity

• Key anatomical structures include:

  • Parietal pleura, aorta, pulmonary trunk, diaphragm, apex of the heart.

Heart Chambers

• Four main chambers:

  • Atria: Right and left atria (superior chambers) receive blood.

  • Ventricles: Right and left ventricles (inferior chambers) pump blood into arteries.

Heart Anatomy

• Structures include:

  • Vena cavae, pulmonary arteries and veins, heart valves (tricuspid, mitral, aortic, and pulmonary semilunar), papillary muscles, and myocardium.

• Key resource: Heart Anatomy Video

Blood Flow Through the Heart

• Sequence of blood flow:

  1. Blood enters right atrium from superior and inferior venae cavae.

  2. Flows through right AV valve into right ventricle.

  3. Contraction forces pulmonary valve open.

  4. Blood flows to lungs via pulmonary trunk for gas exchange.

  5. Oxygenated blood returns to left atrium via pulmonary veins.

  6. Flows through left AV valve into left ventricle.

  7. Contraction forces aortic valve open, distributing blood to the body.

  8. Returns to right atrium via venae cavae.

The Pulmonary and Systemic Circuits

• Left Heart: Sends oxygenated blood from lungs to the body via aorta.

• Right Heart: Sends deoxygenated blood to the lungs via pulmonary trunk.

• Arteries that you can palpate:

  • temporal, carotid (neck), brachial, radial, femoral, pedal, posterior tibial

Ventricular Comparison

• Right Ventricle: Thinner wall; pumps blood to nearby pulmonary circuit.

• Left Ventricle: Thicker wall; pumps blood through systemic circulation requiring more pressure.

Cardiac Muscle Contraction Mechanisms

• Key aspects:

  • Decrease in cross-sectional area during contraction.

  • Shortening of the heart's dimensions and twisting motion.

Heart Layers

• Endocardium, myocardium (muscle layer), and epicardium (outer layer).

The Pericardium

• Double-walled sac surrounding the heart; allows for frictionless movement while limiting expansion.

• Issues like pericarditis can disrupt heart function.

Arterial Blood Pressure Basics

• Systolic Pressure: Pressure during heart contraction.

• Diastolic Pressure: Pressure during heart relaxation.

• Pulse Pressure: systolic - diastolic

• Mean Arterial Pressure (MAP): Average pressure in a patient's arteries.

  • MAP = 1/3 systolic + 2/3 diastolic

• Cardiac output: heart rate x stroke volume

• Blood Pressure: Cardiac output x total peripheral resistance

Steps of Cardiac Muscle Cell Action Potential

1. Rapid Depolarization: Triggered by the influx of sodium (Na+) ions through voltage-gated sodium channels, leading to a rapid increase in membrane potential.

2. Plateau Phase: Calcium (Ca2+) ions enter the cell through voltage-gated calcium channels, balancing the outward flow of potassium (K+) ions, which prolongs depolarization and prevents rapid repolarization.

3. Repolarization: Inactivation of calcium channels and activation of potassium channels lead to an efflux of K+ ions, resulting in a return to resting membrane potential.

Electrocardiography

• Definition: A diagnostic tool that records the electrical activity of the heart over time using electrodes placed on the skin.

• Purpose: Used to detect heart rhythm abnormalities, issues with the heart's electrical conduction, and effects of drugs or heart diseases.

• Components of ECG:

  • P Wave: Represents atrial depolarization.

  • QRS Complex: Represents ventricular depolarization.

  • T Wave: Represents ventricular repolarization.

  • QT Interval: Electrical systole of the ventricles (varies inversely with HR)

  • PR Interval: time from the onset of atrial activation to onset of ventricular activation

Specialized Conduction System of Heart

The specialized conduction system of the heart refers to the network of cells and fibers responsible for controlling the heart's rhythmic contractions by coordinating the electrical impulses that trigger the heart to beat. This system ensures the heart beats in a regular and synchronized manner.

1. SA Node (Sinoatrial Node):

   • Often referred to as the "natural pacemaker" of the heart.

   • Located in the right atrium, near the opening of the superior vena cava.

2. Atrial Internodal Pathways:

   • These are specialized pathways of conductive fibers that carry the electrical signal from the SA node to the AV node.

   • They help ensure the electrical impulse spreads quickly and evenly across both atria so they contract together.

3. AV Node (Atrioventricular Node):

   • Located at the junction of the atria and the ventricles, near the interatrial septum.

   • The AV node acts as a "gatekeeper," briefly delaying the electrical signal before it moves to the ventricles. This delay allows the atria to fully contract and fill the ventricles with blood before the ventricles contract.

   • The AV node also has a backup pacemaker function if the SA node fails.

4. Bundle of His:

   • After the AV node, the electrical impulse moves to the Bundle of His, a bundle of specialized fibers located in the interventricular septum (the wall between the left and right ventricles).

   • The Bundle of His transmits the electrical signal from the AV node to the ventricular muscle.

5. Ventricular Bundle Branches:

   • The Bundle of His splits into two branches: the left bundle branch and the right bundle branch.

   • These branches conduct the electrical signal down to the left and right ventricles, respectively.

6. Purkinje Fibers:

   • The bundle branches further divide into Purkinje fibers, which are fine, specialized fibers that spread throughout the walls of the ventricles.

   • Purkinje fibers transmit the electrical signal very rapidly to the myocardial cells (heart muscle cells) of the ventricles, causing them to contract and pump blood out of the heart.

Autonomic Regulation of Rhythmicity

• Sympathetic Nervous System: Increases heart rate and contraction force through norepinephrine.

• Parasympathetic Nervous System: Decreases heart rate and conduction speed via acetylcholine.

1. Rapid Depolarization: Triggered by the influx of sodium (Na+) ions through voltage-gated sodium channels, leading to a rapid increase in membrane potential.

2. Plateau Phase: Calcium (Ca2+) ions enter the cell through voltage-gated calcium channels, balancing the outward flow of potassium (K+) ions, which prolongs depolarization and prevents rapid repolarization.

3. Repolarization: Inactivation of calcium channels and activation of potassium channels lead to an efflux of K+ ions, resulting in a return to resting membrane potential.

• Definition: A diagnostic tool that records the electrical activity of the heart over time using electrodes placed on the skin.

• Purpose: Used to detect heart rhythm abnormalities, issues with the heart's electrical conduction, and effects of drugs or heart diseases.

• Components of ECG:

  • P Wave: Represents atrial depolarization.

  • QRS Complex: Represents ventricular depolarization.

  • T Wave: Represents ventricular repolarization.

• Types of ECG:

  • 12-lead ECG: Provides a comprehensive view of the heart's electrical activity from multiple angles.

  • Portable ECG: Smaller devices that can be used for continuous monitoring.

• Clinical significance: Helps in diagnosing conditions such as arrhythmias, myocardial infarctions (heart attacks), and electrolyte imbalances.

Bradycardia

• Definition: A slower than normal heart rate, typically defined as fewer than 60 beats per minute.

• Causes: Can result from sleep, medications, or heart conditions.

• Symptoms: May include fatigue, dizziness, or fainting.

Tachycardia

• Definition: An abnormally fast heart rate, generally above 100 beats per minute.

• Causes: Can be caused by stress, anxiety, fever, or heart abnormalities.

• Symptoms: May include palpitations, shortness of breath, or chest pain.

Ventricular Fibrillation

• Definition: A life-threatening heart rhythm that results in a rapid, uncoordinated contraction of the ventricles, preventing effective blood circulation.

• Symptoms: Sudden cardiac arrest, loss of consciousness, or no pulse.

• Treatment: Requires immediate medical intervention with CPR and defibrillation.

Cardiac Performance

• Important variables include:

  • Preload: Amount of blood filling the heart before contraction.

  • Afterload: Pressure the heart must work against to eject blood.

  • Contractility: Strength of heart muscle contraction.

Factors Influencing Stroke Volume

• Involves preload, contractility, and afterload adjustments.

  • Higher preload leads to increased stroke volume according to Frank-Starling law.

    • greater the ED volume the larger the stroke volume

Tests of Cardiac Function

• Echocardiography: Ultrasound technique for heart imaging and functionality assessment.

• Cardiac Catheterization: Procedure to diagnose and visualize heart structures and blood flow.

  • Directly measures cardiac pressures and evaluates coronary ateries.

Important Conditions

• Atherosclerosis: Buildup of plaques in arteries causing narrowed flow and potential heart attacks.

• Myocardial Infarction (MI): Blood flow obstruction leading to cardiac tissue death.

• Angina: Chest pain indicative of heart muscle's oxygen deficit.

1. Rapid Depolarization: Triggered by the influx of sodium (Na+) ions through voltage-gated sodium channels, leading to a rapid increase in membrane potential.

2. Plateau Phase: Calcium (Ca2+) ions enter the cell through voltage-gated calcium channels, balancing the outward flow of potassium (K+) ions, which prolongs depolarization and prevents rapid repolarization.

3. Repolarization: Inactivation of calcium channels and activation of potassium channels lead to an efflux of K+ ions, resulting in a return to resting membrane potential.

• Definition: A diagnostic tool that records the electrical activity of the heart over time using electrodes placed on the skin.

• Purpose: Used to detect heart rhythm abnormalities, issues with the heart's electrical conduction, and effects of drugs or heart diseases.

• Components of ECG:

  • P Wave: Represents atrial depolarization.

  • QRS Complex: Represents ventricular depolarization.

  • T Wave: Represents ventricular repolarization.

• Types of ECG:

  • 12-lead ECG: Provides a comprehensive view of the heart's electrical activity from multiple angles.

  • Portable ECG: Smaller devices that can be used for continuous monitoring.

• Clinical significance: Helps in diagnosing conditions such as arrhythmias, myocardial infarctions (heart attacks), and electrolyte imbalances.

Bradycardia

• Definition: A slower than normal heart rate, typically defined as fewer than 60 beats per minute.

• Causes: Can result from sleep, medications, or heart conditions.

• Symptoms: May include fatigue, dizziness, or fainting.

Tachycardia

• Definition: An abnormally fast heart rate, generally above 100 beats per minute.

• Causes: Can be caused by stress, anxiety, fever, or heart abnormalities.

• Symptoms: May include palpitations, shortness of breath, or chest pain.

Ventricular Fibrillation

• Definition: A life-threatening heart rhythm that results in a rapid, uncoordinated contraction of the ventricles, preventing effective blood circulation.

• Symptoms: Sudden cardiac arrest, loss of consciousness, or no pulse.

• Treatment: Requires immediate medical intervention with CPR and defibrillation.