OXYGENATION: CARDIAC FUNCTIONS

Review of Cardiac Anatomy and Physiology

Throughout a person’s life, the heart and blood vessels work together as the main component of the cardiovascular system. The primary function of this system is to transport oxygen and nutrients to the tissues and to deliver the end-products of tissue metabolism to appropriate organ for their excretion The proper functioning of every organ and tissue depends on the efficiency and the effectiveness of the cardiovascular system. A healthy vessel distributes the blood at precisely the amount of blood available to every tissue of the body.

Cardiac Structures The cardiovascular system consists of the heart, the major blood vessels that empty

into or exit directly from the heart, and a vast network of smaller peripheral blood vessels.

The hearts ability to pump blood is the result of the five qualities unique to cardiac tissue:o Automaticity – the ability to initiate electrical stimulus independentlyo Excitability – the ability to respond to electrical stimulationo Conductivity – the ability to transmit electrical stimulus from the cell in the hearto Contractility – the ability to stretch as a single unit and recoilo Rhythmicity – the ability to repeat the cycle with regularity

The heart is a four chambered muscular pump about the size of a fisto Upper Chambers – receiving chambers for blood

Right Atrium Left Atrium

o Lower Chambers – the heart’s pumping chambers Right Ventricle Left Ventricle

The interventricular septum divides the heart into two: the right side and left sideo Right side: conducts pulmonary circulationo Left-side: responsible for systemic circulation

It is surrounded by the pericardium, which is a saclike structure that surrounds and supports the heart. It has two membranes:

o Parietal (outer) pericardium – the tough, outer layer. Its density safeguards the heart from invasion by infectious microorganisms

o Visceral (inner) pericardium – inner, serous layer. Serous fluid fills the pericardial space between the two layers lubricating the heart and reducing friction with each heart beat.

The heart has three layerso Epicardium (visceral pericardium) – the outer layer, composed of fibrous and

connective tissueo Myocardium – the middle layer, consists of muscle tissue and is the force behind

the heart’s pumping action. o Endocardium – the inner, thin, smooth layer of endothelial cells. The endocardium

is in direct contact with the blood that passes through the heart. The valves of the heart are membranous structures that ensure that blood passes through

the heart in a one-way forward direction. The heart has four valves. o Atrioventricular valves – separate the atria from the ventricles. They prevent

blood from returning to the atria when the ventricles contract. Tricuspid valve – between the right atrium and the right ventricle Bicuspid / Mitral valve – valve between the left atrium and the left ventricle

o Semilunar valves – resemble portion of the moon, prevent blood from flowing back into the ventricles after the heart contracts.

Pulmonic valve – valve between the right ventricle and pulmonary artery Aortic valve – between the left ventricle and aorta

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Myocardial Blood Supply The left coronary artery branches out into the left anterior descending (LAD) artery

and the circumflex artery.o The LAD artery supplies blood to the anterior wall of the ventricle, the anterior

ventricular septum, and the bundle branches. o The circumflex artery provides blood to the lateral and posterior portions of the left

ventricle. The right coronary artery (RCA) fills the groove between the atria and ventricles and

gives rise to the right marginal artery, ending as the posterior descending artery. o The RCA sends blood to the sinus and atrioventricular nodes to the right atrium. o The posterior descending artery supplies the posterior and inferior wall of the left

ventricle and the posterior portion of the right ventricle. Coronary arteries receive blood primarily during ventricular relaxation (diastole) Blood is pumped out to the systemic circulation during contraction of the ventricles

(systole)

Circulation Inferior and superior vena cava to right atrium Through tricuspid valve to right ventricle Through pulmonic valve to pulmonary artery To lungs Through pulmonary veins to left atrium Through mitral valve to left ventricle Through aortic valve to aorta To systemic circulation

Electrical Conduction The heart contains specialized muscle fibers that generate and conduct their own electrical

impulses spontaneously The following make up the system that conducts electrical impulses and coordinates

chamber contractions:o SA Node (Sinoatrial) – is an area of nerve tissue located in the posterior wall of

the right atrium. It is also called the pacemaker of the heart. It produces 62 -100 impulses per minute, the average of which is around 72 impulses.

o AV Node (AV Junction) – located in the lower aspect of the atrial septum. It can be a secondary cardiac pacemaker, but normally receives electrical impulses from the SA Node and it is the only pathway for conducting impulses from the atria to the ventricles. The slow rate of action potential conduction in the AV node allows the atria to complete their contraction before action potentials are delivered to the ventricles.

o Bundle of His – it is the intraventricular septum, which is relatively short, branching into right and left segments.

o Purkinje Fibers – are diffuse network of conducing strands beneath the ventricular endocardium; they rapidly spread the wave of depolarization through the ventricles.

Impulses follow a right-to-left, top-to-bottom path A normal electrical impulse is initiated at the SA node, the heart’s intrinsic pacemaker. Once generated, the normal impulse must move forward through the conduction system to

the ventricles. Numerous events occur almost simultaneously in the following order after the initiation of

the impulse at the SA node. o Atrial depolarizationo Atrial contractiono Impulse transmission to the AV nodeo Impulse transmission to the bundle of His, bundle branches, and Purkinje fiberso Ventricular depolarizationo Ventricular contractiono Ventricular repolarization.

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Cardiac Function Cardiac Output (CO) – total amount of blood ejected per minute (4-8 L / min; ave: 5L) Stroke Volume (SV) – amount of blood ejected with each beat (ave: 65 – 70 mL) Cardiac output equals stroke volume times heart rate (HR)

Cardiac Output = Stoke Volume x Heart Rate Alterations in cardiac output affect every body system Ejection fraction is the percent of left ventricular end-diastolic volume ejected during

systole (60 to 70%)

Cardiac Cycle It refers to the contraction (systole) and relaxation (diastole) of both atria and both

ventricles. The contraction of the left ventricle can be felt as a wave-like impulse (pulse) in the

peripheral arteries. Starling’s Law – the greater the stretch of the myocardium as the ventricles fill with

blood, the stronger is the ventricular contraction.

Heart Rate The normal heart rate is 60 – 100 beats per minute. Sinus tachycardia is a rate of more than 100 BPM Sinus bradycardia is a rate of lower than 60 BPM Intrinsic heart rate is 90 BPM. At rest, the heart rate of 70 BPM reflects the dominant control by the parasympathetic

nervous system.

Arterial Pressure It is the pressure of blood against the arterial walls. Systolic pressure is the maximum pressure of the blood exerted against the artery walls

when the heart contracts (normally 100 – 140 mm Hg) Diastolic pressure is the force of blood exerted against the artery walls during the

heart’s relaxation (or filling) phase (normally 60 -90 mm Hg). Blood pressure is expressed as systolic / diastolic pressure (e.g. 120 /80)

Blood Vessels Arteries are three-layered vessels that carry oxygenated blood from the heart to the

tissues. Arteries have thicker walls but are smaller in diameter.o Tunica Adventitia – the outer layer, consists of the connective tissueo Tunica Media – middle layer, consists of smooth muscleo Tunica Intima – the inner layer, composed of endothelial cells

Arterioles are small resistance vessels that feed into capillaries Capillaries join arterioles to venules (larger, lower-pressured vessels that arterioles),

where nutrients and wastes are exchanged. Venules join capillaries to veins Veins are large-capacity, low-pressure vessels that return unoxygenated blood to the

heart. Veins have thinner walls than arteries because venous pressure is lower than arterial pressure. Despite being having thinner walls, veins, in turn, have larger diameters than those of arteries.

The Factors Affecting Normal Cardiovascular Function: Age – the rapid metabolic rate of newborns demands tremendous blood flow to the

developing tissues. Their heart rate is considerably faster. In old age, the vascular system has naturally narrowed and stiffened, thus the BP somewhat increases.

Activity and Exercise – increased metabolic demands from the exercising muscles will force the heart to beat faster. The increased temperature causes vasodilation, increasing local blood flow.

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Gender – heart rate and BP vary slightly among men and women. Men have usually lower heart rates but higher BPs. Menopausal women however, have comparably higher BP.

Body Position – blood tends to pool to the lower gravity-dependent extremities. The heart usually must work harder to force blood through the system.

Temperature – when the body temperature begins to rise, the autonomic system signals the arerioles to open wide (dilate) to allow heat loss. The opposite occurs when the body is exposed to cold.

Lifestlyle and Habits – smoking increases heart rate and BP.

PHYSICAL ASSESSMENT FINDINGS

History Dyspnea Paroxysmal nocturnal dyspnea Orthopnea Fatigue and weakness Cough Chest pain Syncope Palpitations Leg Pain

Physical Examination Blood pressure changes Pulse changes including rate, rhythm, and quality Skin color and temperature Abnormal heart sounds Edema Arrythmias Jugular vein distention Respiratory distress Vascular bruits Point of maximal impulse alterations Pruritus

DIAGNOSTIC TESTS AND PROCEDURES

Electrocardiography (ECG) Non-invasive test Graphical representation of the heart’s electrical activity Nursing Interventions:

o Determine the patient’s ability to lie stillo Reassure the patient that electrical shock won’t occuro Interpret ECG for changes

Ambulatory Electrocardiography (Holter monitoring) Non-invasive test Records the heart’s electrical activity and cardiac events for 24 hours Nursing Interventions:

o Advise the patient on activity limitations while wearing monitor: Instruct the patient not to bathe, shower, operate machinery, or use a

microwave oven or an electric shaver while wearing the monitor. o Instruct the patient to keep an activity diary.

Cardiac Catheterization Invasive, fluoroscopic procedure Examines intracardiac structures, pressures, oxygenation, and cardiac output Nursing Intervention:

o Before the procedure: Withhold the patient’s food and fluids after midnight.

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Take baseline vital signs and palpate peripheral pulses. Place obtained written informed consent in the patient’s chart. Inform the patient about possible nausea, chest pain, flushing of the face, or

throat irritation form the injection of radiopaque dyes. Note the patient’s allergies to seafood, iodine or radiopaque dyes

before testing Shave and scrub the insertion site as ordered Mark peripheral pulses with an “X” Administer sedation as prescribed Remove all jewelry, and prosthetic devises. Ensure patent I.V. access

o After the procedure: Monitor vital signs, peripheral pulses, and insertion site for bleeding Maintain a pressure dressing and bed rest for 4 to 8 hours, or as ordered. Increase fluid intake unless contraindicated. Allay the patient’s anxiety. Monitor for complaints of chest pain, a possible sign of myocardial

infarction (MI) – a serious complication of cardiac catheterization – and report immediately!

Keep affected leg extended Assess peripheral pulses in both legs and compare to baseline Monitor urinary output Monitor for delayed reaction for radiopaque dye

Coronary Arteriography Invasive, fluoroscopic procedure Examination of coronary arteries Nursing Interventions:

o Before the procedure: Note the patient’s allergies to iodine, seafood, or radiopaque dyes Monitor the patient’s vital signs Allay the patient’s anxiety. Inform the patient about possible flushing of the face or throat irritation from

the injection. o After the procedure:

Check the insertion site for bleeding Assess peripheral pulses Maintain a pressure dressing at bed rest

Digital subtraction angiography Invasive procedure using a computer system and fluoroscopy with an image intensifier Allows for complete visualization of the arterial blood supply to a specific area especially

the carotid and cerebral arteries Nursing Interventions:

o Before the procedure: Place obtained written informed consent in the patient’s chart Monitor the patient’s vital signs Remove all jewelry in the are to be imaged Perform a baseline neurologic examination before cerebral

angiography Administer sedation, as ordered

o After the procedure: Check the insertion site for bleeding Instruct the patient to drink at least 1 L of fluid Monitor delayed reaction to radiopaque dye

Echocardiography Non-invasive examination of the heart

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Uses echoes from sound waves to visualize intracellular cardiac structures and direction of blood flow.

Nursing Interventions: o Determine the patient’s ability to lie stillo Explain the procedure

Exercise (Stress) Testing Non-invasive test of the heart Study of the heart’s electrical activity and ischemic events during prescribed levels of

exercise Nursing Interventions:

o Withhold food and fluids, especially those that contain caffeine, for 1 hour before the test

o Instruct the patient to wear loose-fitting clothing and supportive shoes o Explain the procedure

Nurclear Cardiology Visual examination of the heart using radioisotopes Imaging of myocardial perfusion and contractility after I.V. injection of isotopes Nursing Interventions:

o Explain the procedureo Allay the patient’s anxietyo Determine the patient’s ability to lie still during the procedure

Hemodynamic Monitoring (Single procedure or continuous monitoring) Invasive procedure involving balloon-tipped, flow-directed catheter placed in pulmonary

artery (pulmonary artery catheter) Allows for examination of intracardiac pressures and cardiac output Nursing Interventions:

o Before the procedure: Place the obtained written informed consent in the patient’s chart Explain the procedure and its purpose to the patient

o After the procedure: Check the insertion site for infection Monitor the pressure tracings and record readings

Putting hemodynamic monitoring to use:o To understand intracardiac pressures, picture the cardiovascular system as a

continuous loop with constantly changing pressure gradients that keep the blood moving.

Right Atrial Pressure (RAP) or Central Venous Pressure (CVP)The RAP reflects right atrial, or right heart function and end-diastolic pressure Normal: 1 to 6 mm Hg / 1.34 to 8 cm H20 Elevated value suggests: right sided heart failure, fluid volume

overload, tricuspid valve stenosis or insufficiency, constrictive pericarditis, pulmonary hypertension, cardiac tamponade, or right ventricular infarction

Low value suggests: reduced circulating blood volume

Right Ventricular Pressure (RVP)Right ventricular (RV) systolic pressure normally equals pulmonary artery pressure; RV end-diastolic pressure, which equals right atrial pressure, reflects RV function Normal: systolic: 15 to 25 mm Hg; diastolic: 0-8 mm Hg Elevated value suggests: mitral valve stenosis or insufficiency,

pulmonary disease, hypoxemia, constrictive pericarditis, chronic heart failure, atrial and ventricular septal defects, and patent ductus arteriosus

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Pulmonary Artery Pressure (PAP)Pulmonary artery systolic pressure reflects right ventricular function and pulmonary circulation pressures. Pulmonary artery diastolic pressure reflects left ventricular pressures, specifically left-ventricular end-diastolic pressure. Normal: Systolic, 15 to 25 mm Hg; Diastolic: 8 to 15 mm Hg; mean:

10 to 20 mm Hg Elevated value suggests: Left-sided heart failure, increased

pulmonary blood flow (left or right shunting as in artial or ventricular septal defects), or any condition causing increased pulmonary arteriolar resistance.

Pulmonary Artery Wedge Pressure (PAWP)PAWP reflects left atrial and left ventricular pressures unless the patient has mitral stenosis. Changes in PAWP reflect changes in left ventricular filling pressure. The heart momentarily relaxes during diastole as it fills with blood from the pulmonary veinsl this permits the pulmonary vasculature, left atrium, and left ventricle to act as a single chamber. Normal: mean pressure: 6 to 12 mm Hg Elevated value suggests: left-sided heart failure, mitral stenosis or

insufficiency, and pericardial tamponade Low value suggests: hypovolemia

Left Atrial PressureThis value reflects left ventricular end-diastolic pressure in patients without mitral valve disease. Normal: 6 – 12 mm Hg

Cardiac OutputCardiac output is the amount of blood ejected by the heart each minute Normal: 4 to 8 L; varies with the patient’s weight, height, and body

surface area. Adjusting the cardiac output to the patient’s size yields a measurement called the cardiac index

Chest X-ray (CXR) Non-invasive test Provides radiographic picture of the heart and lungs Nursing Interventions:

o Determine the patient’s ability to hold his breatho Ensure that the patient removes jewelry before the test

Blood Tests Laboratory test of a blood sample Blood Chemistries:

Sodium Glucose BUN (Blood Urea Nitrogen) Troponin TPotassium Cholesterol Creatinine BilirubinMagnesium Triglicerides CK (creatinine kinase) AST (aspartate amino-

transferase)Calcium Uric Acid CK isoenzymes Alanine amino-transferase

Phosphorus Bicarbonate Troponin I

Nursing Interventions: o Note any drugs that may alter test resultso Restrict the patient’s exercise before the blood sample is drawno Withold I.M. injections or note the time of the injection on the laboratory slip

(alter CK levels)o Withhold any food and fluids as orderedo Assess the venipuncture site for bleeding

Hematologic Studies:

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RBCs ESR (Erythrocyte Sedimentation Rate)

PTT (Partial Thromboplastin Time)

Hemoglobin

WBCs PT (Prothrombin time) Platelets HCT (Hematocrit) Nursing Interventions:

o Note any drugs that may alter test results before the procedureo Assess the venipuncture site for bleeding after the procedure

Arterial Blood Gas (ABG) Analysis Assessment of tissue oxygenation, ventilation, and acid-base status Test of arterial blood Nursing Interventions:

o Before the procedure: Note whether the patient needs supplemental oxygen or mechanical

ventilation Perform Allen’s test prior to obtaining sample Avoid using a limb with an arteriovenous shunt

o After the procedure: Check the site for bleeding Maintain a pressure dressing Check peripheral pulses in the affected limb

Doppler Ultrasound Non-invasive test that transforms echoes from soundwaves into audible sounds Examination of blood flow in peripheral circulation Nursing Interventions:

o Determine the patient’s ability to lie stillo Explain the procedure

Venogram Visualization of the veins after I.V. injection of a dye Diagnosis of deep vein thrombosis or incompetent valves Nursing Interventions:

o Before the procedure: Withhold food and fluids after midnight Record the patient’s baseline vital signs and peripheral pulses Place obtained written consent in the patient’s chart Note the patient’s allergy to seafood, iodine, or radiopaque dye

before the test Inform the patient about possible flushing of the face or throat irritation form

the injection Ensure the patient is adequately hydrated

o After the procedure: Check the injection site for bleeding and hematoma Force fluids unless contraindicated Evaluate for signs of delayed reaction to radiopaque dye Assess vital signs and compare to baseline

Pulse Oximetry Non-invasive procedure using infrared light to measure arterial oxygen saturation in the

blood Continuous assessment of oxygen saturation assists in pulmonary assessment of patient

and weaning patient from a ventilator. Nursing Interventions:

o Avoid placing the pulse oximetry sensor on an extremity that has impeded blood flow.

o Protect sensor from bright lighto Attach the monitoring sensor to a fingertip, earlobe, or toe. o Consider using the earlobe if the patient has artificial nails, nail tips, or nail polish,

as these may interfere with light transmission.

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Some sensors can accurately read through these as long as polish is removed, but this isn’t recommended.

PSYCOSOCIAL IMPACT OF A CARDIOVASCULAR DISORDER Developmental Impact

o Fear of rejectiono Lowered self-esteemo Fear of dying o Role conflict

Economic Impacto Disruption or loss of employmento Cost of hospitalization, medications, and special diets

Occupational and Recreational Impacto Restrictions in work activityo Changes in leisure activityo Restrictions in physical activity (walking, climbing stairs)o Restrictions in activity related to environmental temperature; for example, hot or

cold weather may interfere with patient’s ability to take walks or go outside Social Impact

o Changes in dietary habits such as dining outo Changes in sexual functiono Changes in role performance including work, family roleso Social isolation

MODIFIABLE RISK FACTORS NON-MODIFIABLE RISK FACTORS Smoking Hypertension Hypercholesterolemia Obesity Physical inactivity Emotional stress

Gender and Age Family history of cardiovascular disease Childhood history of cardiovascular

illness Ethnicity Race

ALTERED CARDIAC FUNCTIONS Decreased pumping ability of the heart – can be a result of conduction problems

termed as cardiac arrhythmias, making the heart unable to pump coordinately. Another cause of pump failure is valvular dysfunction wherein the valves which guard the chambers may be damaged such as in myocardial infarction, which can weaken the pump action of the heart.

Altered blood flow – d/t obstruction & narrowing which can affect tissue oxygenation. Altered blood composition – alteration in RBC, plasma, or circulating volume

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