Chapter_035 FA24

Cardiovascular System Overview

Heart Structure

• Four Chambers:

  • Right Atrium

  • Right Ventricle

  • Left Atrium

  • Left Ventricle

• Chamber Thickness: Different thickness across chambers, with left ventricular wall being 2-3 times thicker than the right.

• Layers of Heart:

  • Endocardium: Inner layer

  • Myocardium: Thick muscular middle layer

  • Epicardium: Outer layer

• Pericardium:

  • Visceral: Inner layer of the pericardium

  • Parietal: Outer layer

  • Pericardial Space: Space between visceral and parietal layers

Blood Flow Through the Heart

• Right Side (Unoxygenated Blood):

  • Blood returns via Superior Vena Cava (SVC) and Inferior Vena Cava (IVC) to right atrium

  • Flows through tricuspid valve to right ventricle

  • Passes through pulmonic valve to pulmonary artery and into the lungs

• Left Side (Oxygenated Blood):

  • Blood returns from lungs via pulmonary veins to left atrium

  • Flows through mitral valve to left ventricle

  • Passes through aortic valve to systemic circulation

Heart Valves and Function

• Heart Valves:

  • Atrial and ventricular valves manage blood flow through the heart, ensuring one-way movement.

  • Mitral Valve: Between left atrium and left ventricle

  • Tricuspid Valve: Between right atrium and right ventricle

  • Pulmonic Valve: Between right ventricle and pulmonary artery

  • Aortic Valve: Between left ventricle and aorta

• Chordae Tendineae & Papillary Muscles: Prevent valve inversion during contraction.

Coronary Circulation

• Major Coronary Arteries:

  • Left Coronary Artery: Branches into

    • Left Anterior Descending (supplies front of heart)

    • Left Circumflex (supplies lateral and back of heart)

  • Right Coronary Artery: Supplies right atrium, right ventricle, and parts of left ventricle.

• Coronary Veins: Drain blood into the coronary sinus.

Conduction System of the Heart

• SA Node: Initiates atrial contraction and generates electrical impulse.

• Pathway of Impulse:

  • SA Node → Interatrial Pathways → Atrial Contraction → AV Node → Bundle of His → Left & Right Bundle Branches → Purkinje Fibers → Ventricular Contraction.

• Repolarization:

  • Cells regain resting state after contraction.

  • Absolute Refractory Period: Heart muscle unresponsive to stimulation.

  • Relative Refractory Period: Heart can respond to stimulation in early diastole.

Electrocardiogram (ECG)

• Waveforms:

  • P Wave: Atrial depolarization initiated by SA node

  • QRS Complex: Ventricular depolarization

  • T Wave: Ventricular repolarization

  • U Wave: Rarely seen, associated with Purkinje fiber repolarization (may increase with hypokalemia).

• Intervals:

  • PR Interval: Time taken for impulse to travel from SA node to ventricles.

  • QRS Interval: Duration of ventricular depolarization.

  • QT Interval: Time of ventricular depolarization and repolarization.

Cardiac Mechanical Function

• Systole:

  • Contraction phase; blood ejected from ventricles.

• Diastole:

  • Relaxation phase; ventricles fill with blood.

• Stroke Volume (SV): Amount of blood ejected per heartbeat.

• Cardiac Output (CO): Amount of blood pumped per minute; calculated as:

  • CO = SV × Heart Rate (HR)

  • Normal value: 4-8 L/min.

Factors Affecting Cardiac Output

• Preload: Volume of blood in ventricles at end of diastole; influenced by venous return.

• Afterload: Pressure during ventricular contractions; affected by systemic vascular resistance and blood pressure.

• Contractility: Strength of ventricular contraction.

Regulation of Cardiovascular System

• Autonomic Nervous System (ANS):

  • Sympathetic Stimulation: Increases HR and contractility.

  • Parasympathetic Stimulation: Slows HR.

• Baroreceptors: Detect changes in blood pressure and relay information to the brain to maintain homeostasis.

• Chemoreceptors: Monitor blood chemistry, affecting respiration and blood pressure based on CO2 levels.

Blood Pressure Measurement

• Blood Pressure (BP): Force of blood against arterial walls; influenced by CO and systemic vascular resistance.

  • Systolic BP (SBP): Maximum pressure during contraction.

  • Diastolic BP (DBP): Minimum pressure during relaxation.

  • Normal values: SBP < 120 mm Hg, DBP < 80 mm Hg.

• Pulse Pressure: Difference between SBP and DBP, indicating cardiovascular health status.

Age-Related Changes in Cardiovascular System

• Increased collagen and decreased elastin affecting heart elasticity.

• Changes in vascular compliance increase SBP while maintaining DBP.

• Abnormalities such as heart murmurs, dysrhythmias, and a decreased response to stress are common.

Assessment of Cardiovascular System

• Subjective Data: Medical history, medications, and symptoms.

• Objective Data: Physical examination, vital signs, and peripheral vascular assessments.

• Common Sites for Palpating Arteries: Carotid, femoral, popliteal, brachial, radial, dorsalis pedis, posterior tibial.

Hemodynamic Monitoring

• Invasive Monitoring: Includes arterial and central venous pressure monitoring to assess heart function and fluid balance.

• Measurements: Central Venous Pressure (CVP), Pulmonary Artery Wedge Pressure (PAWP), and Cardiac Output.

• Dynamic Response Test: Used to validate pressure measurements obtained from transducers.

Patient Management Examples**

• Continuous monitoring of patients with severe cardiac conditions to manage therapy and prevent complications.

• Case Studies: Illustrate concepts in real patient scenarios, assessing risks and tailoring nursing interventions based on vital signs and hemodynamic data.