Cardiovascular Physiology-B Notes

Cardiovascular Physiology-B

Overview

• Lecturer: Dr. R. Ahangari

• Institution: University of Central Florida, Orlando

• Text Reference: Human Physiology by Linda S. Constanzo

• Source: Medline Plus

• Transcript ID: 20000

Structure of the Heart

• Location: Positioned between the lungs in the middle of the chest.

• Components:

  • Aortic arch

  • Pulmonary artery

  • Pulmonary vein

  • Superior (anterior) vena cava

  • Inferior (posterior) vena cava

  • Atria:

  • Left atrium

  • Right atrium

  • Ventricles:

  • Left ventricle (largest and strongest chamber)

  • Right ventricle

  • Valves:

  • Bicuspid (mitral) valve

  • Tricuspid valve

  • Supporting Structures:

  • Chordae tendineae

  • Papillary muscle

  • Septum: Muscle wall separating left and right atria and ventricles.

Heart Valves

• Function: Regulate blood flow within the heart.

• Types of Valves:

  1. Tricuspid Valve: Between the right atrium and right ventricle.

  2. Pulmonary Valve: Controls blood flow from right ventricle to pulmonary arteries for lung oxygenation.

  3. Mitral Valve: Allows oxygen-rich blood from the lungs to flow from the left atrium to left ventricle.

  4. Aortic Valve: Permits oxygen-rich blood to leave left ventricle into the aorta, the largest artery.

Circulation Through the Heart

• Blood Flow Pathway:

  1. Deoxygenated blood enters the Right Atrium.

  2. Blood moves through the Right Atrioventricular Valve to the Right Ventricle.

  3. Upon contraction, blood exits the right ventricle via the Pulmonary Valve to the Pulmonary Artery.

  4. At the lungs, CO2 is expelled and O2 is absorbed.

  5. Oxygenated blood returns through the Pulmonary Vein to the Left Atrium.

  6. Blood flows into the Left Ventricle via the Left Atrioventricular Valve.

  7. Left ventricle contraction ejects blood through the Aortic Valve into the Aorta for distribution throughout the body.

Systemic Circulation

• Definition: Carries oxygenated blood from the heart to the body and returns deoxygenated blood to the heart.

• Pathway:

  • Oxygenated blood exits the left heart through the Aorta.

  • Distributed to organs and tissues through arteries, arterioles, and capillaries.

  • Deoxygenated blood is collected by venules, flowing into veins, culminating in the Superior and Inferior Venae Cavae returning blood to the right heart.

  • Blood is re-oxygenated in pulmonary circulation.

Pulmonary Circulation

• Definition: Carries oxygen-depleted blood from the heart to the lungs and returns oxygenated blood back to the heart.

• Pathway:

  • Deoxygenated blood flows from the right heart via Pulmonary Arteries to the lungs.

  • In the lungs, red blood cells release carbon dioxide and pick up oxygen during respiration.

  • Oxygenated blood exits the lungs through Pulmonary Veins to the left heart.

• Blood cycles back into systemic circulation from the left heart.

Hemodynamics

Components of the Vasculature

1. Arteries:

   • Deliver oxygenated blood.

   • Thick-walled with elastic tissue and smooth muscle.

   • Under high pressure; blood volume here is called stressed volume.

2. Arterioles:

   • Smallest artery branches; site of highest resistance.

   • Innervated by autonomic nerve fibers.

   • Resistance regulated by the autonomic nervous system (ANS).

   • Alpha1-Adrenergic receptors: Found in skin, splanchnic, and renal circulation.

   • Beta2-Adrenergic receptors: Present in skeletal muscle arterioles.

3. Capillaries:

   • Composed of a single layer of endothelial cells and basal lamina.

   • Thin-walled, site of nutrient, water, and gas exchange.

4. Venules:

   • Formed from merging capillaries.

5. Veins:

   • Merge to form larger veins; largest is the Vena Cava.

   • Thin-walled, under low pressure; contain the highest blood volume (unstressed volume).

   • Have alpha1-adrenergic receptors.

Blood Flow and Velocity

• Velocity of Blood Flow Equation: $V = rac{Q}{A}$

  • Where:

  • $V$ = velocity (cm/sec)

  • $Q$ = blood flow (ml/min)

  • $A$ = cross-sectional area (cm²)

• Principles:

  • Velocity is directly proportional to blood flow and inversely proportional to cross-sectional area.

  • Higher velocity in the aorta compared to capillaries; lower capillary velocity enhances substance exchange.

Cardiac Output and Blood Flow

• Blood Flow Equation: $Q = rac{P}{R}$

  • Where:

  • $Q$ = flow or cardiac output (ml/min)

  • $P$ = pressure gradient (mm Hg)

  • $R$ = resistance (mm Hg/ml/min)

• Analogy to Ohm's Law:

  • $I = rac{V}{R}$

  • Flow (Q) analogous to current (I); pressure (P) analogous to voltage (V).

• Flow Drivers:

  • Blood flows from high to low pressure; inversely proportional to vessel resistance.

Resistance in Blood Vessels

• Poiseuille's Equation: $R = rac{8 imes n imes l}{r^{4}}$

  • Where:

  • $R$ = resistance

  • $n$ = viscosity of blood

  • $l$ = length of blood vessel

  • $r$ = radius of blood vessel

• Principles:

  • Resistance directly proportional to blood viscosity and vessel length.

Capacitance and Compliance

• Definition: Describes blood vessel distensibility; inversely related to elastance.

• Capacitance Equation: $C = rac{V}{P}$

  • Where:

  • $C$ = capacitance or compliance (ml/mm Hg)

  • $V$ = volume (ml)

  • $P$ = pressure (mm Hg)

• Characteristics:

  • Directly proportional to volume; inversely proportional to pressure.

  • Veins generally exhibit greater capacitance than arteries.

• Aging Effect: - Arterial capacitance decreases with age as arteries become stiffer.

Pressure Profile in Blood Vessels

• Pressure Dynamics:

  • Blood pressure decreases progressively throughout systemic circulation due to resistance.

  • Highest pressure located in the aorta and large arteries, lowest in vena cavae.

• Mean Pressure Values:

  • Aorta: 100 mm Hg

  • Arterioles: 50 mm Hg

  • Capillaries: 20 mm Hg

  • Vena Cava: 4 mm Hg

Arterial Pressure

• Blood Pressure Definition: Force exerted by circulating blood on vessel walls.

• Characteristics:

  • Pulsatile, varies within every cardiac cycle.

• Systolic Pressure: Highest pressure during cardiac contraction.

• Diastolic Pressure: Lowest pressure when the heart relaxes.

• Pulse Pressure: Difference between systolic and diastolic pressure; primarily affected by stroke volume.

• Mean Arterial Pressure Calculation: Approximately equals diastolic pressure plus one-third of pulse pressure.

Venous Pressure

• Characteristics: Very low pressure; high capacitance allows retention of large blood volumes.

• Atrial Pressure: Estimated by pulmonary wedge pressure; low compared to venous pressure.

Hypertension

Primary Hypertension

• Definition: Of unknown etiology; environmental factors like dietary sodium, obesity, and stress linked.

• Mechanisms:

  • Increased total peripheral vascular resistance via vasoconstriction or increased cardiac output or both.

  • Sympathetic nervous system and renin-angiotensin-aldosterone system contribute to hypertension.

• Sodium Transport Abnormalities:

  • Issues with Na+/K+ pump increase intracellular Na+, hence increased sympathetic response and Ca²+ sensitivity.

  • Deficiency: Lack of vasodilators such as prostaglandins; bradykinin impact.

Secondary Hypertension

• Causes: Conditions influencing kidneys, arteries, heart, endocrine system.

• Examples:

  1. Adrenal disorders

  2. Cushing's syndrome (cortisol overproduction)

  3. Hyperaldosteronism (excess aldosterone)

  4. Pheochromocytoma (adrenal gland tumor)

  5. Kidney diseases

  6. Medication effects (e.g., corticosteroids or NSAIDs)

  7. Coarctation of the aorta

  8. Preeclampsia during pregnancy

  9. Thyroid and parathyroid problems

Symptoms of Hypertension

• Often asymptomatic, may include:

  • Headache

  • Fatigue

  • Shortness of breath

  • Dizziness

  • Convulsions

  • Vision changes

  • Nausea and vomiting

  • Anxiety and increased sweating

  • Nosebleeds and palpitations

  • General unwellness and increased urination

  • Flushed face and pale skin

Pharmacological Treatment for Hypertension

• Drug Classes Include:

  • ACE Inhibitors: Captopril, Ramipril

  • ARBs: Valsartan

  • Diuretics: Thiazide types like Hydrochlorothiazide

  • Calcium Channel Blockers: Felodipine, Benidipine

  • Beta-Blockers: Propranolol

Cardiac Electrophysiology

ECG Components

1. P Wave:

   • Represents atrial depolarization; duration 0.08 to 0.1 seconds.

   • P-R Interval (0.12 to 0.20 seconds) measures atrial depolarization to ventricular depolarization onset.

   • If P-R interval >0.2 sec, AV conduction block is indicated.

2. QRS Complex:

   • Duration normally 0.06 to 0.1 seconds; reflects rapid ventricular depolarization.

   • Prolonged QRS (>0.1 sec) indicates conduction impairment, such as in bundle branch block or ectopic foci.

3. ST Segment:

   • Interval from S to T wave, indicating period of complete ventricular depolarization.

   • Elevation or depression indicates ischemia or hypoxia.

4. T Wave:

   • Represents ventricular repolarization; longer than depolarization phase.

   • Presence of U wave may suggest repolarization issues.

5. QT Interval:

   • Encompasses both ventricular depolarization and repolarization (0.2 to 0.4 seconds).

   • Prolonged QT may signify susceptibility to tachyarrhythmias.

Cardiac Action Potentials

1. Stable Resting Potential:

   • Ventricles, atria, and Purkinje system maintain about -90mV, influenced by K+ equilibrium.

2. Action Potential Phases:

   • Phase 0 (Upstroke): Caused by Na+ conductance increase resulting in depolarization.

   • Phase 1 (Initial Repolarization): Brief outward K+ current.

   • Phase 2 (Plateau): Stabilization due to equal inward Ca²+ and outward K+ currents.

   • Phase 3 (Repolarization): Decrease in Ca²+ conductance and increased K+ current leading to hyperpolarization.

   • Phase 4 (Resting): Balance of inward and outward currents reaching K+ equilibrium.

3. SA Node Specifics:

   • Serves as the heart's pacemaker; unstable resting potential.

   • Conductance during upstroke (phase 0) from Ca²+, differing from ventricle mechanism (Na+).

Conduction Velocity and Excitability

• Conduction Velocity:

  • Time for excitation across cardiac tissue; fastest in Purkinje fibers, slowest in AV node to facilitate filling.

• Excitability:

  • Ability for cardiac cells to generate action potentials based on inward current.

  • Refractory Periods:

  1. Absolute Refractory Period (ARP): No action potential initiation.

  2. Effective Refractory Period (ERP): No conducted action potential.

  3. Relative Refractory Period (RRP): Possible action potentials requiring increased inward current; begins at end of ARP and lasts until about -70mV.