Cardiovascular System (CVS) Overview

• Cardiovascular System (CVS) overview.

Heart Valves

• There are four valves in the heart.
• There are 2 atrioventricular valves which include: tricuspid and mitral
• There are 2 semilunar valves which include: pulmonary and aortic.

Systole and Diastole

• Systole refers to the contraction phase of the heart.
• Diastole refers to the relaxation phase of the heart.

Cardiovascular System Composition

• The cardiovascular system consists of a central pump (right and left sides) and a closed system of blood vessels.

Cardiovascular System Function

• Supplies organs with adequate blood flow.
• Secretes hormones to regulate blood pressure.

Systemic Circuit

• Blood travels from the left ventricle to arteries, arterioles, and capillaries.
• Blood goes to the body systems.
• Returns to the right atrium via venules and veins with deoxygenated blood.

Pulmonary Circuit

• Blood moves from the right ventricle to the lungs via pulmonary arteries.
• Oxygenated blood returns to the left heart via four pulmonary veins.

Cardiac Properties

• Include contractility, rhythmicity, conductivity an excitability.

Automaticity

• Heart's ability to initiate its own contraction independent of external stimuli. Its rate is 90-105/min
• It is a property of the SA node and is the normal pacemaker

Rhythmicity

• The heart's ability to beat regularly.

Pacemaker Action Potentials

• Both automaticity and rhythmicity result from pacemaker action potentials generated spontaneously and regularly.

Rhythmicity and Automaticity

• Defined as the heart's ability to initiate its own regular impulses independently of nerve supply.
• SAN, AVN, and Purkinje fibers are the sites
• Unstable membrane potential characterize automaticity and rhythmicity.

Node Rates

• SA node rate: 90-105/min
• AV node rate: 40-60/min.
• Purkinje fiber rate: less than 40/min.

Vagal Tone

• Is the predominance inhibitory effect of Parasympathetic nervous system on the SAN during rest.
• Vagal tone maintains a normal heart rate of 60-100 bpm.

Factors Affecting Heart Rate

• Positive chronotropic factors increase heart rate (tachycardia), and include sympathetic stimulation (adrenaline, noradrenaline).
• Negative chronotropic factors decrease heart rate (bradycardia), and include parasympathetic stimulation (acetylcholine).
• Fever increases heart rate while hypothermia decreases heart rate.
• Hyperthyroidism increases heart rate and hypothyroidism decreases it.
• L-troxin and some cold medications increase heart rate.
• Beta blockers, anesthetics, and antiarrhythmic agents decrease heart rate.
• Normal heart rate falls within the range of 60-100 bpm.

Parasympathetic Supply to Cardiac Tissues

• Affects cholinergic receptors.
• Decreases heart rate via inhibition of the sinoatrial node (SAN).
• Block adrenergic receptors.
• It can be blocked by muscarinic receptor antagonists

Conductivity

• Is the property by which the excitation wave is conducted through cardiac tissue.
• Atrial and ventricular functional syncytia are separated by fibrous rings, with the only connection being through the specialized system.

Sinoatrial (SA) Node

• It is located in the right atrium near the opening of the superior vena cava. S- The pacemaker of the heart; it has the highest automaticity.
• Action potential begins in the SA node and spreads into the atrial wall.

Internodal Tracts

• Three bundles connect the SA node to the AV node.

Atrioventricular (AV) Node

• It i located in the interatrial septum.
• The only conducting pathway between the atria and ventricles.

AV Bundle (Bundle of His)

• Continuous with the AV node.
• It gives off a left branch & right branch.

Purkinje Network

• Branches penetrate the ventricular muscle fibers and it has the fastest conduction rate.

Conduction Velocity

• Atrial fibers: 0.5 m/sec
• Internodal bundles: 1 m/sec
• AVN only pathway of transmission: 0.05 m/sec
• Bundle of His: 2 m/sec
• Purkinje fibers: 4 m/sec
• Ventricular muscles: 1 m/sec

Cardiac Excitation

• Depolarization starts in the SA node.
• AVN receives impulses, transmits them to ventricles, and delays conduction.
• Impulses from the AVN pass in the AV bundle, which divides into two bundle branches.
• Purkinje fibers distribute impulses under the endocardium and terminate on ventricular muscle fibers, they exhibit the fastest conduction rate.
• The AV node can generate impulses but at a slower rate than the SAN.

Conduction Velocity

• The delay at the AV node is to allow the atria to empty their contents into the ventricles before systole.
• Rapid conduction in Purkinje fibers ensures both ventricles contract at the same time for efficient pumping.

AV Node Function

• It prevents the atria and ventricles from contracting simultaneously.

Impulse Pathway

• SAN → AVN → AV bundle → bundle branches → Purkinje fibers.

Excitability (Ventricular Action Potential)

• Several Action Potentials are present in the heart

Action Potential Properties

• Ability of the heart to respond to an adequate stimulus by generating action potential and contraction.
• Resting membrane potential (RMP): -90 mV.
• Phase zones include: depolarization (phase 0), plateau (phase 2), and repolarization (triphasic).
• Depolarization (Phase 0) the Cause: opening of fast Na+ & Slow Ca- Na channels
• Repolarization (Triphasic)

Repolarization Phases

• Phase 1: closure of fast Na+ channels, opening of Cl- channels (influx), and opening of K+ channels (efflux).
• Phase 2 (plateau): the balance between Ca++ inflow and K+ outflow.
• Phase 3 (late repolarization): closure of Ca++ channels, allowing K+ outflow until RMP is reached (Phase 4).

Excitability Changes During Action Potential (AP)

• Absolute Refractory Period (ARP): Excitability is zero; hence, there is no response to any stimuli; coincides with systole and the beginning of diastole (phases 0-2, and half of 3); prevents tetanus.
• Relative Refractory Period (RRP): Excitability is below normal; hence, there is a response to a stronger stimulus, from the end of ARP to phase 4.
• Vulnerable Period: Occurs at the end of the AP; any stimuli can cause ventricular fibrillation (fatal condition).

Ionic Changes

• During phase 2, Na+ channels are closed, Ca2+ channels are open, and K+ channels are open.

Contractility (Inotropic State)

• Cardiac contraction lasts 1.5 times the duration of the action potential.
• Excitation-Contraction Coupling: Calcium is very important contraction, depending on extracellular Ca influx during the plateau phase.
• More Ca influx, more positive inotropics are present.
• Less Ca influx, less positive inotropics are present.

Cardiac Muscle Laws

• Starling's Law (length-tension relationship): the more initial length (end diastolic volume), the more contraction force (tension).
• All-or-None Law: whole cardiac muscle (atria/ventricles) acts as one mass: contracts to threshold stimulus, or doesn't respond to subthreshold stimulus.
• Excitation-Contraction Coupling is similar to in skeletal muscle.

Factors Affecting Contractility

• Positive Inotropics: ↑ contractility & cardiac output (COP)
• Sympathetic catecholamines norepinephrine Act on B1 receptors result more open time of Ca channels.
• Xanthines like caffeine & theophylline.
• Glucagon
• Digitalis
• ↑ ECF Ca++ stop heart in systole (Ca rigor)
• Negative Inotropics decrease contractility & COP
• Parasympathetic acetyl choline has negative effect on atrial muscle
• Ca antagonists (calcium blockers).
• Anesthetics, Anti arrhythmic agents.
• Ischemia, hypoxia, acidosis.
• ↓ ECF Ca→ stop heart in diastole.

Cardiac Resting Membrane Potential

• Not -65 mv, it is -90 mv

Ventricular Contraction Force

• The force of ventricular contraction is directly proportional to the degree of its stretch.

Ventricular Action Potential Phase Zero

• Phase zero of ventricular action potential is also called depolarization

Plateau Phase

• Is not because of balance between chloride influx and potassium efflux

Cardiac Output

• Cardiac Output (CO) is the volume of blood pumped by each ventricle per minute.

Minute Volume/Cardiac output

• Normally, venous return always equal cardiac output (COP).
• The COP of the left ventricle is typically equal to the COP of the right ventricle.
• Normal COP is approximately 5L/min.

Volumes during Cardiac Cycle

• End Diastolic Volume (EDV): 135 ml
• End Systolic Volume (ESV): 65 ml
• Stroke Volume (SV): 70 ml

Stroke Volume Calculation

• Stroke volume = End diastolic volume - End systolic volume.
• Stroke volume will be 70ml, resulting from 135ml - 65ml equation

Cardiac Output

• Cardiac Output (COP) is stroke volume X heart rate.

Factors affect the Cardiac Output

• Heart Rate
• Stroke Volume
• Autonomic innervation and hormones affect the heart rate
• End-diastolic volume and end-systolic volume determine the stroke volume.

Exercise Impact

• HR increases by 100-200% while SV increases by 50%, thus HR doubling at rest can more than double COP because SV increases.

Arrhythmias Impact

• HR increases from 75 to 150 beat/min, however it does not double CO by expectaion.
• SV decreases by 50% --> COP has no change and decrease caused by shortening of diastole.
• The increase in HR alone above 150/min results in decreased cardiac output likely due to marked decrease in SV.

Factors that lead to no change in COP

• Sleep
• Moderate temperatures

Factors that lead to higher COP

• Increased Sympathetic stimulation (Exercise, Anxiety, Excitement)
• Increases adrenaline & noradrenaline secretion
• Shifting from standing to recumbent position
• After meals
• High environmental temperature
• Pregnancy

Factors that lead to lower COP

• Standing from supine position
• Heart diseases such as: arrhythmias, ischemia, heart failure, cardiomyopathy, concentric hypertrophy

Cardiac Cycle

• Cardiac cycle is the events occurring during one heartbeat, including relaxation and contraction phases.
• If heart rate is 75/minute, the duration of each cycle is 0.8 seconds
• When the heart accelerates, the cycle shortens, mostly affecting the diastole.

Diastole Importance

• It's the period when coronary blood flow occurs.
• It allows Ventricles to rest & filling

Systole & Diastole Time

• Atrial systole (0.1 s) → evacuation of the remaining 30 % of ventricular filling
• Ventricular Diastole = 0.5 s
• Ventricular Systole = 0.3 s

Cardiac Cycle Phases (8)

• It has 8 phases
• They span across systole (S) and diastole (D)

These include

• Atrial Systole (LATE DIASTOLE)
• Isometric contraction
• Maximum ejection
• Reduced ejection
• Protodiastole phase
• Isometric relaxation
• Maximum filling
• Reduced filling (MID DIASTOLE)

Pressure

• Cardiac cycle is a balance between diastolic and systolic pressures
• Systolic pressure (SP) is the Maximum Pressure during systole 120 mmHg (90 - <140).
• Diastolic pressure (DP) is the Minimum Pressure during diastole 80 mmHg (60 – <90).
• Atrium Aortic has the lowest numbers as the values increase

Systole key points

• Heart is in contractile phase and it ejects blood into the vessels.
• Atrioventricular valves are closed, whilst Semilunar valves are open.
• Volume of the ventricles goes to ESV at the end of systole.
• 0.3s is needed

Diastole key points

• Heart muscles that are resting filling with blood
• Semilunar valves that are closed, and Atrioventricular are open
• Volume of the ventricles goes to EDV at the end of diastole
• 0.5s is needed

Venous Return

• Volume of blood retuning to heart/min is called venous return and it is a critical part of the cardiovascular system
• COP which is then equal to VR should always be 5L/min

Factors that help venous return against gravity

• Blood volume must be in consistent numbers
• Negative intrathoracic pressure must sustain and remain consistent to help cardiac. Pressure to take place
• Venous pressure must sustain to maintain healthy bodies
• Thoracic pump
• During inspiration:
• negative intrathoracic
• pressure
• ↑VR

Muscle Pump

• Help muscles return against gravity to fight resistance.
• During muscle contractions: veins are compressed and squeezed, blood in directed upward
• During muscle relaxation: healthy valves allow movement in one direction and prevent return of blood backward

Paralyzed Problems

• In paralyzed person, the leg becomes edematous and cold
• Destruction of valves leads to backwards of blood flow causes to varicose veins

Blood Flow types.

• Body must make an adequate blood flow cross a point per/min to sustain life and homeostasis

Blood type flows

• Laminar (normal, silent, flowing in one direction)
• Turbulent (abnormal flowing direction that has sound that is caused by: obstruction, ↑ velocity, ↓ blood viscosity as in anemia)

Arteriral Blood Pressure

• ABP consists of pressures exerted from vessels

Pressure levels

• Blood should be exerted when the body is at rest.
• 120/80 as a key arterial value

ABPs

• Systolic pressure (SP): Maximum Pressure during systole 120 mmHg (90 - <140).
• Diastolic pressure (DP): Minimum Pressure during diastole 80 mmHg (60 – <90).
• Pulse pressure (PP): difference between systolic & diastolic pressure
• SP – DP = 50 mmHg
• Mean arterial pressure (MAР): DP + 1/3 PP
• Blood pressure is affected by:
• Systolic arterial top and diastolic arterial bottom

Variations in ABP

• Age & Sex
• Race
• Emotions
• Exercise
• Gravity
• Circadian rhythm
• Respiration

Variation Key Points

• Age: ↑ABP with age due to loss of elasticity of blood vessels
• Sex: < 45 years females have less ABP than males as 45 years, pressure has in females due hormonal changes.
• Emotions ++ sympathetic ↑ABP especially systolic P
• Exercise static exercise ↑ABP
• Gravity 0.77 mmHg
• Circadian rhythm ( ↑ ABP at morning)
• Respiration: at the beginning of inspiration slight drop in ABP then rises to normal
• New born = 80/40 mmHg
• 20 years = 120/ 70 mmHg

ABPs determined

• ABP = COP x TPR
• ABP = SV x HR x TPR
• Elasticity of arteries helps
• atherosclerosis ++ TPR- Ineffective

Regulation of ABP through

• Nervous system
• Rapid: Nervous
• 2 areas in BRAIN STEM:
• Pressor/vasomotor
• Acts via sympathetic NS
• ↑ABP by:
• ↑ hear rate & Stroke
• volume → ↑ cardiac output
• Vasoconstriction
• Depressor/cardioinhibitory
• Acts via vagus nerve
• ↑ABP by:
• hear rate ↓cardiac
• output
• Vasodilatation
• Intermediate shift
• Capillary shift mechanism helps
• Tissue fluid is a reservoir for plasma:
• ↑ ABP
• capillary hydrostatic pressure
• filtration
• edema
• if↓ ABP: vice versa

Regulation

• Slow regulation is maintained by kidneys

Regulations in kidney

• Renal pressure regulation
• Na + excretion
• Hormones influence the balance for both.

Kidneys

• Angiotensin I must be in balance
• Help liver stay consist
• Lungs provide enzyme for the angiotensin
• The water balance in kidney will release aldosterone

Natriuresis

• ANP will always secrete from atria in response to atrial stretch for homeostasis maintenance
• Natriuresis: increase Na+ excretion & increase water excretion with kidney activation

Shock

• It's a deficiency to COP that affects how you live

Manifest

• Inadequate tissue perfusion due to inadequate cardiac output (COP).

Shock types (4)

• Hypovolemic shock which includes hemorrhage, dehydration, burn
• Distributive Shock includes anaphylactic shock, nervous shock, and septicemia
• Cardiogenic shock which includes myocardial infarction, arrhythmia
• Obstructive shock which includes pulmonary embolism

Shock types

• There are pale conditions to it.
• High respiratory rate due to tension
• Decrease output of urine to sustain levels of kidney.
• Decrease levels of consciousness due to tension
• High heart rate will be constant.
• Nausea and bad pain

Other Shock types

• Constriction/release of pressure will make levels and release the fluid