Normal Cardiovascular System

Normal Cardiovascular System

• The cardiovascular system perfuses organs and tissues with blood and consists of the heart, blood, and blood vessels.

Cardiac Structure and Function

• The heart resides in the mediastinum within the thoracic cavity.
• The heart is enclosed by the fibrous pericardium, parietal pericardium serous membrane, and visceral pericardium (epicardium).
• Serous fluid between the parietal and visceral layers prevents friction during heartbeats.
• The heart chamber walls consist of cardiac muscle (myocardium), lined with endocardium to prevent abnormal clotting.
• Epithelium covering the heart valves and blood vessels is referred to as endothelium.
• Coronary circulation delivers oxygenated blood to the myocardium and returns deoxygenated blood to the right atrium via the coronary sinus.
• The two main coronary arteries branch off the ascending aorta just outside the left ventricle.
• The interatrial septum separates the right and left atria (superior chambers), while the interventricular septum separates the right and left ventricles (lower chambers).
• Both septa consist of myocardium.

Coronary Blood Flow

• The right atrium receives deoxygenated blood from the coronary sinus, superior vena cava (upper body), and inferior vena cava (lower body).
• Blood flows from the right atrium, through the tricuspid valve, and into the right ventricle.
• The tricuspid valve prevents backflow during ventricular systole.
• The right ventricle pumps blood through the pulmonary semilunar valve to the lungs via the pulmonary trunk and arteries.
• The pulmonary semilunar valve prevents backflow during ventricular diastole.
• The left atrium receives oxygenated blood from the lungs via the four pulmonary veins.
• Blood flows through the mitral (bicuspid) valve into the left ventricle.
• The mitral valve prevents backflow during ventricular systole.
• The left ventricle pumps blood through the aortic semilunar valve to the body via the aorta.
• The aortic valve prevents backflow during ventricular diastole.
• Chordae tendineae and papillary muscles anchor the tricuspid and mitral valves to the ventricle floor, preventing hyperextension during ventricular systole.
• The left ventricle pumps with approximately five times the force of the right ventricle to circulate blood throughout the body, resulting in a large difference between systemic and pulmonary blood pressure.

Cardiac Conduction Pathway and Cardiac Cycle

• The cardiac conduction pathway is the route of electrical impulses that generate each heartbeat.
• The sinoatrial (SA) node in the right atrium wall depolarizes about 100 times per minute, initiating each heartbeat.
• Parasympathetic fibers slow the SA node to about 75 beats per minute at rest.
• The SA node is known as the pacemaker, producing a normal sinus rhythm.
• Impulses travel from the SA node along a specific path.
• If the SA node is nonfunctional, the AV node can initiate heartbeats at a slower rate of 40 to 60 beats per minute.
• The bundle of His can generate ventricular beats, but at an even slower rate of about 20 to 35 beats per minute.
• A cardiac cycle involves the simultaneous contraction of both atria, followed by the simultaneous contraction of both ventricles.
• Systole is the contraction/emptying phase, while diastole is the relaxation/filling phase for each set of chambers.
• The first major heart sound ("lub") is caused by the closure of the AV valves during ventricular systole.
• The second sound ("dub") is created by the closure of the aortic and pulmonary semilunar valves.

Cardiac Output

• Cardiac output is the amount of blood ejected from the left ventricle in 1 minute.
• Cardiac output is calculated by multiplying stroke volume by heart rate.
• Stroke volume is the amount of blood ejected by a ventricle in one contraction.
• Stroke volume It averages 60 to 80 mL/beat.
• Average resting cardiac output is 5 to 6 L, which is approximately the total blood volume, with an average resting heart rate of 75 beats per minute.
• Ejection fraction measures ventricular efficiency, normally 55% to 70%.
• Starling’s law of the heart explains that during exercise, increased venous return stretches the ventricular myocardium, causing more forceful contractions and increased stroke volume.
• During exercise, heart rate increases, resulting in a cardiac output increase by as much as four times the resting level (or more for athletes).

Regulation of Heart Rate

• The heart generates its electrical impulse at the SA node.
• The nervous system can modify the heart rate in response to environmental factors.
• The medulla oblongata in the brain processes sensory input and regulates heart function.

Hormones and the Heart

• Epinephrine, secreted by the adrenal medulla during stress, increases heart rate and contraction force, and dilates coronary vessels, leading to increased cardiac output and systolic blood pressure.
• Aldosterone, from the adrenal cortex, regulates blood levels of sodium and potassium, which are essential for normal myocardial electrical activity.
• Atrial natriuretic peptide/hormone, secreted by the atria, increases sodium excretion by the kidneys by inhibiting aldosterone secretion.
• Atrial natriuretic peptide is secreted in response to higher blood pressure or blood volume stretching the atrial walls, which leads to increased water loss in urine and decreased blood volume and blood pressure.

Blood Vessels

• Arteries and arterioles carry blood from the heart to capillaries and have relatively thick walls composed of three layers, which carry blood under high pressure.
• The outer layer of fibrous connective tissue prevents arterial rupture.
• The middle layer of smooth muscle and elastic connective tissue contributes to blood pressure, specifically diastolic pressure, by altering the artery's diameter.
• The sympathetic nervous system primarily regulates artery diameter.
• Arteries can direct blood volume using smooth muscle.
• The inner layer, or lining, of the artery is simple squamous epithelium called endothelium to prevent abnormal clotting.
• Veins and venules carry blood from capillaries to the heart.
• Veins have thinner walls with less smooth muscle than arteries, but sympathetic impulses can constrict them.
• Vein linings have endothelium to prevent abnormal clotting and valves to prevent backflow, especially in the extremities.
• Capillaries connect arterioles to venules, forming networks in most tissues except cartilage, covering/lining epithelia, and the lens and cornea of the eye.
• Capillary walls consist of a single cell layer to facilitate gas, nutrient, and waste exchange between blood and tissues.
• Precapillary sphincters regulate blood flow through capillary networks, contracting or relaxing based on tissue needs.
• Active tissues cause dilation of precapillary sphincters to increase blood flow.
• Inactive tissues cause constriction of precapillary sphincters to reduce blood flow.
• The redirection of blood flow ensures that the fixed blood volume is directed to where it is most needed.
• Exchange between blood and tissue fluids primarily involves diffusion of gases and filtration for extracellular fluid homeostasis.
• Tissue fluid returns to the capillaries and lymph capillaries, with lymph returned to the blood via lymph vessels.
• Increased capillary blood pressure can lead to excess tissue fluid formation, potentially causing edema if lymph vessels cannot collect it all.

Blood Pressure

• Blood pressure refers to the force of blood against blood vessel walls, measured in millimeters of mercury (mm Hg), systolic over diastolic.
• The standard average systemic arterial pressure is 120/80 mm Hg.
• Blood pressure decreases in arterioles and capillaries, merging systolic and diastolic pressures.
• Blood pressure falls further as blood enters the veins, approaching zero as it flows into the right ventricle.
• Normal capillary blood pressure permits appropriate tissue nourishment via filtration, while being low enough to prevent rupture.
• Arterioles (and veins during sympathetic stimulation) are usually slightly constricted, maintaining normal blood pressure, especially diastolic pressure.
• Peripheral resistance is regulated by the vasomotor center of the medulla, which receives input via the glossopharyngeal and vagus nerves.
• Blood pressure is also affected by heart rate and force.
• Rapid heart rates can decrease cardiac output and blood pressure because the ventricles do not fill completely.
• Adequate venous return ensures strong heart contractions, while decreased venous return results in weaker contractions.
• Venous return relies on constriction of the veins, skeletal muscle pumping, and the diaphragm's pressure during inhalation.
• Venous valves prevent backflow and aid in blood return to the heart.
• Arterial elasticity absorbs some force during ventricular contraction and exerts pressure during ventricular relaxation, contributing to normal blood pressure and pulse pressure.
• Normal systolic to diastolic to pulse pressure ratio is 3:2:1.

Renin-Angiotensin-Aldosterone Mechanism

• Decreased blood flow through the kidneys triggers renin secretion, initiating the renin-angiotensin-aldosterone mechanism to raise blood pressure.
• Other hormones affecting blood pressure include norepinephrine and epinephrine from the adrenal medulla, which increase cardiac output and cause vasoconstriction.
• Antidiuretic hormone, released from the posterior pituitary, increases water reabsorption by the kidneys, increasing blood volume and blood pressure.
• Atrial natriuretic peptide, secreted by the heart's atria, inhibits aldosterone secretion, increasing renal excretion of sodium and water, decreasing blood volume and subsequently blood pressure.

Circuits of Circulation

• Pulmonary circulation begins at the right ventricle, which pumps deoxygenated blood toward the lungs for gas exchange, and oxygenated blood returns to the left atrium via the pulmonary veins.
• Low pressure in the pulmonary capillaries prevents filtration and keeps fluid from accumulating in the alveoli of the lungs.
• Systemic circulation starts in the left ventricle, pumping oxygenated blood into the aorta, which branches into capillaries within tissues, and deoxygenated blood returns to the right atrium via the vena cava and coronary sinus.
• The hepatic portal circulation is a part of the systemic circulation where blood from the digestive organs and spleen flows through the portal vein into the sinusoids in the liver before returning to the heart.
• The liver regulates blood levels of nutrients and removes potential toxins.

Aging and the Cardiovascular System

• Aging of blood vessels, particularly arteries, begins in childhood, with effects becoming apparent later in life.
• Atherosclerosis is the deposition of lipids in artery walls over years, which narrows the lumens and forms surfaces that may stimulate intravascular clot formation.
• Atherosclerosis decreases blood flow to affected organs.
• With age, the heart muscle becomes less efficient, decreasing maximum cardiac output and heart rate.
• Valves may thicken due to fibrosis, causing heart murmurs.

Cardiovascular Disease

• An estimated 121.5 million American adults have one or more types of cardiovascular disease.
• Lifestyle and access to health care greatly influence cardiovascular disease risk factors.
• Ways to improve cardiovascular health include not smoking, exercising, eating healthy, and maintaining normal blood pressure, blood glucose, total cholesterol levels, and weight.
• Culturally competent engagement in health promotion and disease prevention education is important to address and reduce heart disease risk in all racial and ethnic groups.
• Cardiovascular disease is the greatest cause of death in women.

Cardiovascular System Data Collection

• Data collection for cardiovascular disorders entails a patient health history and physical examination.
• Focus on the most serious signs, symptoms, and physical findings until the patient is stabilized if they have an acute problem.
• Older adults may show atypical signs and symptoms of myocardial infarction.
• Data collection focuses on allergies, medications, medical disorders, surgeries, and functional limitations.
• Observe the patient’s general appearance and record height, weight, and vital signs.

Health History Questions

• Focus on pain WHAT'S UP: where, how, aggravating/alleviating factors, timing, severity, useful data, perception.
• Assess dyspnea: what increases or relieves shortness of breath?
• Assess palpitations or irregular heartbeats: heart racing, pounding, or skipping beats?
• Assess fatigue: change in energy level? Ability to perform activities?
• Assess edema: swelling in feet, legs, or hands? Weight gain?
• Assess paresthesia: numbness, tingling, or abnormal sensations in extremities?
• Ask about childhood diseases: rheumatic fever or scarlet fever?
• Assess modifiable risk factors: diet, exercise, smoking, and stressors.
• Ask about family history: cardiovascular disorders in family?

Physical Examination

• Bradycardia, tachycardia, hypotension, and hypertension may indicate cardiovascular problems.
• Crackles and wheezes may indicate left-sided heart failure.
• Jugular vein distention and edema may indicate right-sided heart failure.
• Heart sounds, such as S3 and S4, may indicate heart failure or other cardiac issues.
• Murmurs may indicate valvular disease.
• Skin discoloration may indicate tissue hypoxia or blood flow problems.
• Normal blood pressure is considered less than 120/80 mm Hg.
• Compare readings in both arms, and report differences to the health-care provider (HCP).

Accurate Blood Pressure Measurements

• The patient should avoid exercise, caffeine, and smoking for 30 minutes before the blood pressure (BP) measurement.
• The patient should void before taking the BP measurement.
• Use the auscultatory method with a properly calibrated and validated BP instrument.
• Seat the patient quietly for at least 5 minutes in a chair (not on an examination table) with feet on the floor and arm supported at heart level before the BP measurement.
• Use the appropriate-sized cuff so that the cuff bladder encircles at least 80% of arm when placed 1 inch above the antecubital fossa.
• Ask the patient to remain still and quiet during BP measurement, as motion alters reading.
• Determine the patient’s baseline blood pressure by inflating cuff and noting the reading when the radial pulse is no longer felt. When taking BP, inflate the cuff to 20 numbers above the obtained baseline reading. (Overinflation may cause inaccurate reading.)
• During BP measurement, deflate the cuff slowly at rate of 2 mm Hg/second.
• Take at least two BP measurements and average them.
• Systolic BP is the first of two or more sounds heard and that diastolic BP is the final sound before the disappearance of sounds.
• Provide patients, verbally and in writing, with their specific BP reading.

Orthostatic Blood Pressure

• In response to the drop in blood pressure, the pulse increases 15 to 20 beats per minute to maintain cardiac output.
• Orthostatic hypotension (postural hypotension) is a drop in systolic blood pressure greater than 15 mm Hg, a drop or slight increase in diastolic blood pressure greater than 10 mm Hg, and an increase in heart rate greater than 20 beats per minute in response to the drop in blood pressure.
• It indicates a problem that should be investigated by the HCP.
• The patient often reports lightheadedness or syncope because the drop in blood pressure decreases the amount of oxygen-rich blood traveling to the brain.
• Factors that may cause orthostatic hypotension include deficient fluid volume, diuretics, analgesics, or pain.
• Anticipate orthostatic hypotension with position changes to reduce risk of falls

Pulses

• Auscultate the apical pulse for 1 minute to identify rate and regularity.
• Normal heart rate is 60 to 100 beats per minute.
• The heart rate is often slower, around 50 beats per minute in athletic people.
• Compare the apical rate with the radial rate for equality.
• Fewer radial beats than apical beats indicate a pulse deficit.
• Palpate arterial pulses bilaterally for volume and pressure quality and compare for equality and described on a four-point scale: 0 absent; 1+ weak, thready; 2+ normal; and 3+ bounding.
• A normal vessel feels soft and springy; a sclerotic vessel feels stiff.
• A vibration is felt, called a thrill in abnormal vessels.
• Humming is heard because of turbulent blood flow through the vessel, called a bruit when auscultating an abnormal vessel.

Respirations

• Observe the rate and ease of respirations and auscultate breath sounds.
• Note sputum characteristics such as amount, color, and consistency.
• Pink, frothy sputum indicates acute heart failure.

Inspection

• Note shortness of breath when the patient speaks or moves.
• Note the patient’s oxygenation status through skin, mucous membrane, lip, and nailbed color.
• Pallor may indicate anemia or lack of arterial blood flow.
• Distention of the internal and external jugular neck veins indicates an increase in the venous volume, often caused by right-sided heart failure.
• A capillary refill time is normally 3 seconds or less
• Capillary refill time briefly squeeze the patient’s nailbed
• Clubbing of the nailbeds occurs from oxygen deficiency

Learning Tip Ps of peripheral vascular disease:

• Pain
• Paresthesia (decreased sensation)
• Pallor
• Pulselessness
• Paralysis
• Poikilothermia (assumes temperature of the environment)

Palpation

• An enlarged heart may shift the PMI to the left of the midclavicular line.
• Palpate the temperature of the extremities bilaterally for comparison to determine sufficient arterial blood flow.
• If the finger imprint or indentation remains, the edema is pitting

Auscultation

• Normal heart sounds are produced by the closing of the heart valves.
• Erb’s point is where S2 is best heard.
• S1 is heard at the beginning of systole as “lub” when the tricuspid and mitral (AV) valves close.
• S2 is heard at the start of diastole as “dub” when the aortic and pulmonic semilunar valves close.
• With the bell of the stethoscope placed at the apex, a third heart sound (S3) or a fourth heart sound (S4) may be heard.
• The S3 heart sound is normal for younger adults sounds like a gallop and is a low-pitched sound heard early in diastole.
• The S4 heart sound is also a low-pitched sound, similar to a gallop but heard late in diastole.

Learning Tip:

• This sentence can help you remember the heart’s auscultation points:
• All (aortic)
• People (pulmonic)
• Eat (Erb’s point)
• Three (tricuspid)
• Meals (mitral)
• Murmurs are caused by a narrowed valve opening or a valve that does not close tightly and is a prolonged, swishing sound that ranges in intensity from faint to very loud.
• A pericardial friction rub occurs from inflammation of the pericardium and has a grating sound that occurs when the pericardial surfaces rub together during a heartbeat.

Diagnostic Tests

• Diagnostic test results are combined with the health history and physical data collection to diagnose disorders and plan care for the patient.
• Additional tests can identify genetic and inflammation factors contributing to cardiovascular risk to develop a preventive plan of care for the patient.