Cardiovascular Physiology

Objectives

• Review the basic anatomy and

physiology of the cardiovascular

system.

• Describe the electrical and mechanical

events involved in the cardiac cycle.

Objectives

• Discuss the factors that alter or impact the

electrical and mechanical events of the

cardiac cycle.

• Explain the physiology of circulation and

perfusion.

Anatomy

Did you know???Your heart is about the size of your clenched fist

It beats about 4000 times an hour and about 100,000 times a day

It will beat over 2 billion times in a lifetime

Each heartbeat pumps half a cup of blood

The force of your heartbeat is sufficient to shoot blood 30 feet into the air

Anatomy Review - The Heart

Right atrium

• Incoming blood supply

• Tricuspid valve

• Chordae tendinae and

papillary muscles

• Right Ventricle

• Pulmonary artery

Anatomy Review - The Heart

Left atrium

• Receives supply

from the pulmonary

vein

• Left ventricle

• Bicuspid (mitral) valve

• Aorta

Anatomy Review - The Heart

Heart wall

• Endocardium

• Myocardium

• EpicardiumSplits into another

outside layer – the

pericardium

The Pericardium

• Fixates the heart to thethoracic cavity

• Relatively inflexible tissue• Pericardial sac holds

30-50mL of serousfluid between thepericardium andepicardium,prevents friction during contraction

Valves of The Heart

Pulmonic

Aortic

Mitral

Tricuspid

Circulation through HeartCirculation through Heart

Pulmonary

Right side of the heart

Blood from the body, low O2 high CO2, right atriumright ventriclelungs via pulmonary trunk.

Unloading of CO2 pick up O2 to left side of the heart.

Arteries carry De-Oxygenated blood

Veins carry oxygen rich blood

Systemic

Left side of heart

Oxygen rich blood - lungs- left atrium- left vent. - aorta

Blood transported via systemic arteries to body tissues, gas and nutrient exchange across capillary walls

Blood is then returned to the right side of the heart through superior and inferior venae cavae.

Circulation through HeartCirculation through Heart

Although equal volumes of blood are flowing in the pulmonary and systemic circuits, the two ventricles have uneven workloads.

Pulmonary Circuit: right, short low pressure circulation.

Systemic Circuit: left, long pathway, five times as much resistance to blood flow, high pressure

Coronary CirculationCoronary Circulation

The functional supply of the heart, is the shortest circulation in the body.

The arterial supply of coronary circulation is provided by the right and left coronary arteries arising from the base of the aorta, and encircle the heart in the atrioventricular groove.

Coronary ArteriesCoronary Arteries

• The coronary arteries provide an intermittent, pulsating blood flow to the myocardium.

• Actively deliver blood when the heart is relaxed, ineffective when the ventricles are contracting because:– compressed by contracting myocardium– entrances to the coronary arteries is

blocked by the open Aortic valve.

Coronary Artery SuppliesRight C.A.

Right atrium andventricle

Inferior portion ofthe left ventricle

Interventricularseptum

Conductionsystem

Coronary Artery Supplies

Left Main C.A.

Left atrium

Nearly all of theleft ventricle

Circumflex and LAD Branch

AV node in halfof the population

Cardiac Physiology

• Electrical components

• Electrophysiology

• The Cardiac Cycle

• Mechanical Events of the Cardiac Cycle

• Influences of Electrical and Mechanical

• Heart Function

Electrical Conduction System

Action Potential

Upstroke depolarisation

Early repolarisation

Notch Plateau

Late rapid Repolarisation

Resting potential

Intracellular

Extracellular

Ref: Woods et al (2005) Cardiac Nursing 5th ed Lippincott, Wilkins & Williams: Philadelphia p 23

Cardiac Cell Types

Electrical cells• Generate andconduct impulsesrapidly• SA and AV nodes• Nodal pathways• Interventricularseptum• No contractileproperties

Cardiac Cell Types

Muscle (myocardial) cells• Main function iscontraction• Atrial muscle• Ventricular muscle• Able to conductelectrical impulses• May generate its ownimpulses with certaintypes of stimuli

Unique Properties of Cardiac Cells

• Automaticity

SA and AV nodes

• Excitability (all cells)

Points of stimulation

• Nervous system

• Physical cell damage

• Ischemia

• Electrolytes

• Conductivity (all cells)

Points of stimulation• Nervous system

• Electrolytes

Slowing of conductivity• Ischemia

• Calcification of nodal

pathways

Contraction• Muscle cells

Mechanical Functionof the Heart

The Cardiac Cycle

2 components

Diastole Filling of the chamber

Systole Contraction of the chamber and ejection of

blood

Cardiac Output

• The amount of blood ejected from the

ventricle in one minute

• Elements of cardiac output

Stroke volume CO = SV x HR• Amount of blood ejected from the

ventricle in one contraction

Heart rate

• The number of cardiac cycles in one minute

Determination of Stroke Volume

PreloadAmount of blood delivered to the chamber.Depends upon venous return to the heart.Also dependent upon the amount of blood

delivered to the ventricle by the atrium.Contractility

The efficiency and strength of contractionFrank Starling’s Law

AfterloadResistance to forward blood flow by the vessel

walls

Cardiac Feedback Loops

• Master controller: the medullaIncoming input

• ChemoreceptorsSense changes in pH, PaCO2 and PaO2

• BaroreceptorsSense changes in arterial pressure

Response of the medulla• Stimulate the autonomic nervous system

Autonomic Nervous System

Sympathetic Nervous System

Extensively innervates the SA node and ventricular cells

• Increase in heart rate

• Increase in conduction and contractility in the ventricles

Parasympathetic Nervous System

Innervates the SA and AV nodes

• Decreases heart rate

• Decreases conduction times through the AV node

Chemical Factors

• Hormones

Adrenaline

• Stimulation of beta receptors in the

myocardium

• Increase in contractility of the ventricles

• Increase in conduction throughout the

ventricles

Chemical Factors

Electrolyte Concentrations

Calcium

• Impacts the strength of contractions

• High calcium may cause irritability of electrical cells

Chemical Factors

PotassiumImpacts the rates of firing and recovery of thecardiac cells

• High potassium• Irregular firing of cardiac cells• Dysrhythmias and ventricular fibrillation potentials

• Low potassium• Longer delays in the firing of cardiac cells• May be caused by diuretic use• Bradycardia• Hypotension (systemic complication)• Poor cardiac output results

The Vascular System

The Vascular System

• The vascular system is composed of the systemic and pulmonary circulation.

• Both systems consist of arteries, capillaries and veins.

• Arterial system: away from the heart

• Venous system: capillary beds to heart

• Anatomical differences of arteries and veins

Factors Contributing to Arterial Blood Pressure

BP = CO x TPR• Cardiac Pump

• Blood Volume

• Peripheral Resistance

• Elasticity of Arterial Walls

• Viscosity of Blood

Factors Aiding Venous Return

1) Cardiac Pump

2) Respiratory Pump

3) Muscular Pump

Control Of Blood Pressure

• Cardioacceleratory & Cardioinhibitory centres in the Medulla.

• Chemicals, Temperature, Sex, Emotions and age, effect heart rate

• Vasomotor centre, pressoreceptors (baroreceptors), chemoreceptors - chemical and autoregulation

Pathophysiology

When it all goes wrong

Pathophysiology – Pericardial, Myocardial and Endocardial

Disease • Pericarditis – inflammation of the pericardium

• Effusion – excess fluid/blood/pus in the pericardial sac

• Tamponade – significant compression of the heart due to pericardial effusion

• Myocarditis – inflammation of the myocardium

• Cardiomyopathies – dilatation, hypertrophy or non-compliance of the myocardium

• Infective Endocarditis – infective organisms invade the endothelial lining of the heart involving the valves, causing vegetation

Pathophysiology - Valvular Heart Disease

• Stenotic – unable to open fully restricting forward blood flow afterload and cause hypertrophy (enlarged muscle)

• Regurgitant, incompetent or insufficient– Unable to close fully permit backward blood flow– volume load and cause dilation of chambers

• Rheumatic Heart Disease – extensive inflammatory changes scarring of the

valves

• Infective Endocarditis– Endovascular infection vegetation on a heart valve

• Degenerative Changes

Physiology of Ischaemia

Atherosclerosis – HardeningAtheroma (plaque) builds up in the coronary arteries and reduces blood flow and O2 supply to the heart muscle, resulting in angina pain. Prolonged ischaemia or plaque rupture leads to myocardial infarction and loss of myocardial function (heart failure). The extent of damage depends on which artery is affected and time to treatment.

References

• Darovic, G. (2002). Hemodynamic Monitoring invasive and noninvasive clinical application 3rd ed. W.B. Saunders Company.

• Marieb, E.N. (2001). Human Anatomy and Physiology 2nd ed. The Benjamin/Cummings Publishing Company: California.

• Stinson Kidd, P.& Dorman, Wagner, K. (2001). High Acuity Nursing 3rd ed. Prentice Hall: New Jersey.

• Thelan, L.A., Urden, L.D., Lough, M.E. & Stacy, K.M. (1998). Critical Care Nursing Diagnosis and Management 3rd ed. Mosby: St Louis.

• Tortora, G.J. & Grabowski, S.R. (1993). Principles of Anatomy & Physiology 7th Ed. Harper Collins: New York