Cardiorespiratory I

Cardiorespiratory System: Part I - Cardiovascular System

• The cardiovascular system comprises the heart and vascular systems (pulmonary and peripheral/systemic)
• The pulmonary system includes the lungs and sites of respiration
• Cardiopulmonary describes the heart and lungs
• Cardiovascular describes the heart, blood vessels, and blood
• Cardiorespiratory encompasses cardiovascular function and respiration (internal and external)
• The cardiorespiratory system has functions for transport, homeostasis, and protection.

Learning Objectives

• Describe the components and function of the cardiorespiratory system
• Discuss cardiac muscle structure and function
• Explain cardiac muscle cell physiology, including action potential generation, propagation, mechanical contraction, and relaxation
• Summarize the events of the cardiac cycle
• Discuss the electrophysiology of the heart and its relation to the cardiac cycle and ECG reading
• Discuss measures of cardiac function, including cardiac output and ejection fraction
• Describe how the body modifies cardiac function
• Discuss the role of the autonomic nervous system on cardiac function

Functions of the Cardiorespiratory System

• Transport and delivery: Transport and exchange of respiratory gases, nutrients, waste products, and hormones.
• Homeostatic regulation: Fluid balance between compartments, maintaining pH, maintaining thermal balance, and regulating blood pressure.
• Protection: Preventing blood loss through hemostatic mechanisms and preventing infection (leukocytes, lymphatic tissue).

Myocardium Forms

• Right and left atria (thin walls)
• Two ventricles (thick walls)
• Left ventricle thicker than right ventricle
• Inter-ventricular septum (thick wall)

Coronary Blood Supply

• Right coronary artery supplies the right side. It divides into marginal and posterior interventricular arteries
• Left coronary artery supplies the left side. It divides into circumflex and anterior descending arteries

Myocardial Cell Characteristics

• Highly oxidative: Dense mitochondria
• Capillary rich: Abundant capillaries for oxygen delivery
• Highly fatigue resistant
• Slow myosin ATPase
• Lactase Dehydrogenase (LDH) has high affinity for lactate
• Entire heart - all or none

Myocardial Cell Features

• Cardiac muscle cells are connected by intercalated discs (desmosomes connect cells and gap junctions allow rapid transmission of action potentials)
• Striated appearance: Containing actin and myosin filaments.
• Requires calcium for contraction, contracting via sliding filament theory.

Cardiomyocyte Structure Review

• Sarcomere: Functional/contractile unit
• Myofibrils: Repeating sarcomeres
• Actin (thin filaments), Myosin (thick filaments), and Titin (stabilizes thick filaments)
• Striation: Visible light and dark bands indicating the arrangement of contractile proteins
• Responsible for muscle contraction via the sliding filament theory

Excitation - Conduction of Cardiac System

• The heart contracts rhythmically due to self-generation of action potentials.
• Specialized cell types:
  • Contractile (99%): Do not generate their own action potentials.
  • Autorhythmic (1%): Specialized to initiate and conduct action potentials.

Pacemaker Activity

• Cardiac autorhythmic cells do not have a resting membrane potential.
• Membrane potential slowly depolarizes between action potentials until threshold is reached.
• Important ion movements in pacemaker potential:
  • Increased inward Na+ current
  • Decreased outward K+ current
  • Increased inward Ca2+current

Action Potential of Cardiac Muscles

• Four phases (0, 1, 2, 3)
• Phase 0: Rapid depolarization
• Phase 1: Initial repolarization
• Phase 2: Plateau
• Phase 3: Rapid repolarization
• Phase 4: Pacemaker potential

ECG or EKG

• Graphic representation of the heart's electrical activity
• Used to evaluate heart's electrical activity in relation to the clinical situation at hand
• Able to detect abnormal heart function related to:
  • Cardiac rhythm
  • Electrical conduction
  • Myocardial oxygen supply
  • Tissue damage
• Does not detect whether abnormalities are old or new, or availability of a prior tracing for comparison

ECG Trace

• Signals picked up from the skin by electrodes reflecting action potential directions.
• Upward deflection, electrical activity toward a positive lead.
• Downward deflection, electrical activity away from a positive lead.

ECG Placement

• Recording heart's electrical activity by placing electrodes in specific locations on the body.
• Lead placements provide different angles of the heart.
• Standard ECG involves attaching 10 electrodes, 4 to each limb and 6 across the chest.

ECG Trace (Basic Pattern)

• P wave: Atrial depolarization
• PR interval: Impulse travelling to ventricles
• QRS complex: Ventricular depolarization
• ST segment: Ventricular systole
• T wave: Ventricular repolarization
• QT interval: Ventricular depolarization and repolarization.

Abnormal Rhythm

• Pacemaker cells outside the SA node can trigger depolarization (ectopic foci)
• Ectopic foci can occur in atria, or ventricles (slower inherent pacing rate)

Premature Ventricular Contraction (PVC)

• PVC occurs when a focus in the ventricles generates an action potential before the next SA node potential
• Wide QRS complexes; gradual spread of depolarization across the ventricles
• Premature, ectopic, and compensatory pause

Ventricular Fibrillation

• Caused by continuous rapid firing of multiple ventricular automaticity foci
• Uncoordinated heart contraction
• Causes cardiac arrest and sudden cardiac death

Myocardial Infarction (MI)

• Pattern of ST elevation, where QRS complex, ST segment and T wave merge ("tombstone")

Regulation of Cardiovascular Function

• This section covers factors controlling cardiac output (Q) and stroke volume (SV)
• Q = HR x SV: Cardiac output is heart rate x stroke volume (volume of blood pumped per minute).
• Factors include: Parasympathetic nerves, sympathetic nerves, mean arterial pressure, contraction strength, end-diastolic volume (EDV), and stretch (Frank-Starling)

Cardiac Cycle - Ventricular Diastole

• Relaxation begins, ventricular pressure drops.
• Semilunar valves close.
• Atrioventricular valves open allowing passive filling.
• At the end, blood volume in ventricle = end-diastolic volume

Cardiac Cycle - Ventricular Systole

• Contraction begins, ventricular pressure rises
• Atrioventricular valves close (heart sound 1 = "lub").
• Semilunar valves open.
• Blood ejection
• At the end, blood volume in ventricle = end-systolic volume

Stroke Volume and Ejection Fraction

• Stroke volume (SV): Volume of blood ejected by a ventricle during a single beat.
• Ejection fraction (EF): Percentage of end-diastolic volume ejected during a single beat.

Cardiac Output (Q)

• Cardiac output (Q): total volume of blood pumped by the heart per minute
• Q = Heart Rate (HR) x Stroke Volume (SV)
• Average resting cardiac output is 4.2 - 5.6 L/min

Factors Regulating Cardiac Output

• Parasympathetic nerves: Decrease heart rate
• Sympathetic nerves: Increase heart rate
• Mean arterial pressure: affects stroke volume
• Contraction strength: affects stroke volume
• End-diastolic volume (preload): affects stretch and subsequent stroke volume
• Stretch (Frank-Starling mechanism): More filling (stretch) leads to a stronger contraction and increased stroke volume.

Preload

• Volume of blood in the ventricle at the end of diastole (preload)
• Known as the end-diastolic volume (EDV)
• Stretching of the myocardial fibers during diastole: Increases preload
• Factors affecting preload include venoconstriction, skeletal muscle pump, and respiratory pump

Afterload

• Resistance left ventricle must overcome to circulate blood
• Factors affecting afterload include systemic vascular resistance (SVR), mean arterial pressure, and vasoconstriction

Ventricular Compliance

• Stiffness of ventricular walls
• Increased by hypertophohy, hypertension, myopathy, and athletic training
• Decreased by dilated cardiomyopathy and long-distance aerobic training

Inotropic State of the Heart

• Strength of ventricular contraction
• Affected by parasympathetic and sympathetic activation along with catecholamines, heart rate, afterload and disease processes.

Force-Frequency Modulation

• Conduction and contractile cells innervated by sympathetic and parasympathetic nerves
• Catecholamines increase Ca2+ uptake leading to stronger contraction

Test your knowledge of the cellular mechanisms involved in cardiac physiology, particularly the role of funny channels, pacemaker potentials, and the cardiorespiratory system. This quiz covers key concepts related to cardiac function, action potentials, and ECG interpretations. Perfect for students in advanced biology or physiology courses!