Assessment of peripheral Vascular System
and Lymphatic System
Anatomy overview
The vascular system serves several purposes:
Ø To provide conduits for blood to travel from the heart to
nourish the various tissues of the body
Ø To carry cellular wastes to the excretory organs
Ø To allow lymphatic flow to drain tissue fluid back into the circulation
Ø To return blood to the heart for recirculation
This system of conduits depends on an efficient heart and patent blood vessels to regulate and maintain systemic and regional blood flow and temperature.
The vascular system consists of the vessels of the body.
Vessels are tubes for transporting fluid, such as the blood or lymph.
Function – transporting the blood or lymph :
v Delivery of oxygen to the tissues
v Delivery of nutrients to the tissues
v Elimination of carbon dioxide from cells
v Elimination of waste products from cellular metabolism
The vascular system is divided into the arterial system and the venous system. In the arterial system, blood moves from the larger conduits to a network of smaller blood vessels. In the venous system, blood travels from the capillaries to the venules and to the larger system of veins, eventually returning in the venae cavae to the heart for recirculation.
ARTERIAL SYSTEM
■ Structure
The high-pressure blood vessels of the arterial vascular system may be classified according to their size and wall structure. The large arteries, such as the aorta and femoral arteries, follow relatively straight routes and have few branches.
Smaller arteries, such as the internal iliac and mesenteric arteries, divide from larger ones and have multiple branches.
Arteries may branch into arterioles or anastomose with other arteries. The arterioles branch into terminal arterioles, which join with capillaries and ultimately with venules to form the capillary network. The exchange of nutrients across the capillary membrane occurs primarily by three processes: osmosis, filtration, and diffusion.
■ Function
The arterial system delivers blood to various tissues for nourishment. At the tissue level, nutrients, chemicals, and body defense substances are distributed and exchanged for cellular waste products, depending on the needs of the particular tissue. The arteries transport the cellular wastes to the excretory organs (e.g., kidneys and lungs) to be reprocessed or removed. The arteries also contribute to temperature regulation in the tissues. Blood can be either directed toward the skin to promote heat loss or diverted away from the skin to conserve heat.
■ Blood Pressure
Blood pressure is the force of blood exerted against the vessel walls. Pressure in the larger arterial blood vessels is greater (about 80 to
■ INDIRECT MEASUREMENT OF BLOOD PRESSURE
The blood pressure in the arterial system is determined primarily by the quantity of blood flow or cardiac output (CO), as well as by the resistance in the arterioles:
Blood pressure = Cardiac output x Peripheral vascular resistance
Any factor that increases CO or total peripheral vascular resistance increases blood pressure. In general, blood pressure is maintained at a relatively constant level; therefore an increase or decrease in total peripheral vascular resistance is associated with a decrease or an increase in CO, respectively.
Three mechanisms mediate and regulate blood pressure:
Ø The autonomic nervous system, which excites or inhibits sympathetic nervous system activity in response to impulses from chemoreceptors and baroreceptors
Ø The kidneys, which sense a change in blood flow and activate the renin-angiotensin-aldosterone mechanism
Ø The endocrine system, which releases various hormones (e.g., catecholamine, kinins, serotonin, and histamine) to stimulate the sympathetic nervous system at the tissue level
Systolic blood pressure represents the amount of pressure/force generated by the left ventricle to distribute blood into the aorta with each contraction of the heart; diastolic blood pressure represents the amount of pressure/force sustained by the arteries during the relaxation phase of the heart. In the adult, systolic pressure is normally 90 to
Systolic pressure is affected by a number of factors, including CO. When CO decreases, systolic pressure also decreases. Diastolic pressure is primarily determined by the amount of vasoconstriction in the periphery. An increase in peripheral vascular resistance increases diastolic pressure and cardiac workload.
REGULATION OF BLOOD PRESSURE
The autonomic nervous system (ANS) and the renal system are primarily responsible for regulating blood pressure. External factors can also affect blood pressure.
Autonomic nervous system. Blood pressure is regulated by balancing the sympathetic and parasympathetic nervous systems of the autonomic nervous system. Changes in sympathetic and parasympathetic activity are responses to messages sent by the sensory receptors in the various tissues of the body. These receptors, including the baroreceptors, chemoreceptors, and stretch receptors, respond differently to the biochemical and physiologic changes of the body.
Baroreceptors in the arch of the aorta and at the origin of the internal carotid arteries are stimulated when the arterial walls are stretched by an increased blood pressure. Impulses from these baroreceptors inhibit the vasomotor center, which is located in the pons and the medulla. Inhibition of this center results in a drop in blood pressure.
Several 1- to 2-mm collections of tissue have been identified in the bifurcations of the carotid arteries and along the aortic arch. These carotid and aortic bodies contain specialized chemoreceptors that are sensitive primarily to hypoxemia (a decrease in the partial pressure of arterial oxygen [Pao2]). When stimulated, the carotid chemoreceptors send impulses along Hering’s nerves, and the aortic chemoreceptors send impulses along the vagus nerves to activate a vasoconstrictor response.
The chemoreceptors are also stimulated by hypercapnia (an increase in partial pressure of arterial carbon dioxide [Paco2]) and acidosis. However, the direct effect of carbon dioxide on the central nervous system is 10 times stronger than the effect it produces by stimulating the chemoreceptors.
Stretch receptors found in the venae cavae and the right atrium are sensitive to pressure or volume changes. When a client is hypovolemic, the stretch receptors in the blood vessels sense a reduced volume or pressure and send fewer impulses to the central nervous system. This reaction stimulates the sympathetic nervous system to increase heart rate and constrict the peripheral blood vessels.
Renal system. The renal system also helps to regulate cardiovascular activity. When renal blood flow or pressure decreases, the kidneys retain sodium and water. Blood pressure tends to rise because of fluid retention and because of activation of the renin-angiotensin-aldosterone mechanism. Vascular volume is also regulated by the release of antidi-uretic hormone (vasopressin) from the posterior pituitary gland.
External factors. Other factors can influence the activity of the cardiovascular system. Emotional behaviors (e.g., excitement, pain, anger) stimulate the sympathetic nervous system to increase blood pressure and heart rate. Increased physical activity such as exercise increases blood pressure and pulse rate. Body temperature can affect the metabolic needs of the tissues, thereby influencing the delivery of blood. In hypothermia, tissues require fewer nutrients and blood pressure sure falls. In hyperthermia, the metabolic requirement of the tissues is greater, and blood pressure and pulse rate rise.
VENOUS SYSTEM
■ Structure
The venous system is composed of a series of veins that are located adjacent to the arterial system. A second superficial venous circulation runs parallel to the subcutaneous tissue of the extremity. These two venous systems are connected by communicating veins that provide a means for blood to travel from the superficial veins to the deep veins. Blood flow is directed toward the deep venous circulation.
The venules collect blood from the capillaries and the terminal arterioles. White blood cells also enter and exit the body tissues at the venules.
Venules branch into veins, which are low-pressure blood vessels. Veins have the ability to accommodate large shifts in volume with minimal changes in venous pressure. This flexibility allows the venous system to accommodate the administration of intravenous (IV) fluids and blood transfusions, blood loss, and dehydration. All veins in the superficial and deep venous systems in the legs (except the smallest and the largest veins) have valves that direct blood flow back to the heart; this prevents retrograde flow (backflow).
■ Function
The primary function of the venous system is to complete the circulation of blood by returning blood from the capillaries to the right side of the heart. The venous system also acts as a reservoir for a large portion of the blood volume. In contrast to the arterial system, which consists of a high-pressure, continuous flow system through relatively rigid conduits, the venous system consists of a low-pressure, intermittent flow system through collapsible tubes that work against the effects of gravity.
Gravity exerts an increase in hydrostatic pressure (capillary blood pressure) when the client is in an upright position, which delays venous return. Hydrostatic pressure is lessened when the client is lying down, and thus there is less hindrance of venous return to the heart.
Cardiovascular Changes Associated with Aging
A number of physiologic changes in the cardiovascular system occur with advancing age. Many of these changes result in a loss of cardiac reserve. Thus these changes are usually not evident when the older adult is resting. They become apparent only when the person is physically or emotionally stressed and the heart cannot meet the increased metabolic demands of the body.
LYMPHATICS
n A completely separate vascular system.
n It retrieves excess fluid from the tissue spaces and returns it to the blood stream.
Lymphatic ducts and drainage patterns
Functions of the lymphatic system:
à To converse fluid and plasma proteins that leak out of the capillaries.
à To form the major part of the immune system that defends body against infection.
à To absorb lipids from the intestinal tract.
Lymphoid tissue:
Lymph nodes:
§ Filter the fluid before it comes back to the bloodstream
§ Filter out microorganisms
Tonsils:
§ Pharyngeal (adenoid)
§
§ Lingual
Spleen
Peyer’s patches (Lymphoid tissue in intestines)
Tymus gland
Bone marrow
ASSESSMENT TECHNIQUES
Taking client’s complaints and history
n Ask: “Any leg pain (cramps)? Where?”
n Detail: pain type, onset (gradual/sudden), aggravating/ relieving factors (activity, walking, dangling, rubbing), associated signs (skin changes, sexual malfunction), relation to time of day, claudication distance.
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History
The nurse obtains a thorough history, which includes demographic data, personal and family history, diet, socioeconomic status, and a functional assessment. The focus of the history is on obtaining information relative to client’s risk factors and symptoms of cardiovascular disease.
■ DEMOGRAPHIC DATA
Demographic data include the client’s age, sex, and ethnic origin. The incidence of conditions such as coronary artery disease (CAD) and valvular disease increases with age (AHA, 1998). The incidence of CAD also varies with the client’s sex. Women who are premenopausal have a lower incidence of CAD than do men.
CULTURAL CONSIDERATIONS
Information about the client’s ethnic or cultural background is important because some disease conditions may be more prevalent in specific ethnic groups. For example, African Americans and Mexican Americans have a higher incidence of hypertension than do Caucasians (AHA, 1998). The nurse should be aware that some clients may refer to their hypertension as “high blood.”
Age, sex, ethnic background, and family history of cardiovascular disease are considered nonmodifiable or uncontrollable risk factors for cardiovascular disease. Modifiable risk factors (e.g., high blood pressure and excessive blood cholesterol), if controlled, can reduce the risk of heart disease.
PERSONAL AND FAMILY HISTORY
The nurse reviews the client’s history, noting any major illnesses such as diabetes mellitus, renal disease, anemia, high blood pressure, stroke, bleeding disorders, connective tissue diseases, chronic pulmonary diseases, heart disease, and thrombophlebitis. These conditions can influence the client’s cardiovascular status.
The nurse asks about previous treatment for cardiovascular disease, identifies previous diagnostic procedures (e.g., electrocardiography and cardiac catheterization), and requests information about any medical or invasive treatment of cardiovascular disease. It is important for the nurse to ask specifically about recurrent tonsillitis, streptococcal infections, and rheumatic fever, because these conditions may lead to valvular abnormalities of the heart. In addition, the nurse inquires about any known congenital heart defects. Many clients with congenital heart problems are living into adulthood because of improved treatment and surgical modalities.
Clients are asked in detail about their medication history, beginning with any current or recent use of prescription or over-the-counter (OTC) medications or herbal/natural products (e.g., ginseng). The nurse inquires about known sensitivities to any drug and the nature of the reaction (e.g., nausea, rash). Clients should be asked whether they have recently used cocaine or any IV “street” drugs, because they may be associated with chest pain or endocarditis.
The nurse also asks female clients whether they are taking oral contraceptives or an estrogen replacement. There is an increased incidence of myocardial infarction (MI) and stroke in women over the age of 35 who take oral contraceptives, but only if they smoke, have diabetes, or have hypertension
The nurse reviews the family history and obtains information about the age, health status, and cause of death of immediate family members. A family history of hypertension, obesity, diabetes, or sudden cardiac death is especially significant.
DIET HISTORY
A diet history includes the client’s recall of food and fluid intake during a 24-hour period, self-imposed or medically prescribed dietary restrictions or supplementations, and the amount and type of alcohol consumption.
The dietitian reviews the type of foods selected by the client for the amount of sodium, sugar, cholesterol, fiber, and fat. The nurse or dietitian also explores the client’s attitude toward food, knowledge level of essential and nonessential dietary elements, and willingness to make changes in the diet. Cultural beliefs and economic status can influence the choice of food items and therefore must be reviewed. Family members or significant others who are responsible for shopping and cooking are included in this discussion.
SOCIOECONOMIC STATUS
The social history includes information about the client’s domestic situation, such as marital status, number of children, household members, living environment, and occupation. The nurse also identifies support systems. It is especially important to explore the possibility that the client might have difficulty paying for medications or treatment.
The nurse asks about the client’s occupation, including the type of work performed and the requirements of the specific job. For instance, does the job involve lifting of heavy objects? Is the job emotionally stressful? What does a day’s work entail? Does the client’s job require him or her to be outside in extreme weather conditions?
MODIFIABLE RISK FACTORS
Personal habits that are risk factors for heart disease include cigarette smoking, physical inactivity, obesity, and type A behavior. These factors are considered modifiable or controllable risk factors. The nurse inquires about each of the following modifiable risk factors.
Cigarette Smoking
Cigarette smoking is a major risk factor for cardiovascular disease, specifically CAD and peripheral vascular disease (PVD) (AHA, 1998). According to the U.S. Department of Health and Human Services (DHHS), cigarette smoking is directly responsible for 21% of all deaths from CAD. Three compounds in cigarette smoke have been implicated in the development of CAD: tar, nicotine, and carbon monoxide.
The risks to the cardiovascular system from cigarette smoking appear to be dose related, noncumulative, and transient. The smoking history should include the number of cigarettes smoked daily, the duration of the smoking habit, and the age of the client when smoking started. A person who smokes fewer than 4 cigarettes per day has twice the risk of cardiovascular disease of a person who does not smoke; a person who smokes more than 20 cigarettes per day has four times the risk. Typically, the nurse records the smoking history in pack-years, which is the number of packs per day multiplied by the number of years the client has smoked.
The nurse should inquire about the client’s desire to quit, past attempts to quit, and the methods used. The nurse may ascertaiicotine dependence by asking questions such as the following:
• How soon after you wake up in the morning do you smoke?
• Do you find it difficult not to smoke in places where smoking is prohibited?
• Do you smoke when you are ill?
Three to four years after a client has stopped smoking, his or her cardiovascular risk appears to be similar to that of a person who has never smoked. The nurse asks clients who do not currently smoke whether they have ever smoked and when they quit.
Physical Inactivity
A sedentary lifestyle is also considered a significant risk factor in the development of heart disease. Regular physical activity promotes cardiovascular fitness and produces beneficial changes in blood pressure and levels of blood lipids and clotting factors.
Unfortunately, few people in the
The nurse questions clients concerning the type of exercise in which they engage, the period for which they have participated in the exercise, and the frequency and intensity of the exercise.
Obesity
Approximately 104 million Americans adults are overweight when defined as a body mass index (BMI) of 25 to 30. Another 42 million Americans are obese, which is defined as a BMI greater than 30 (AHA, 1998). Obesity in the American population has increased 36% in the last 30 years; it is particularly a problem for African-American females, Mexican Americans, and native Hawaiians (AHA, 1998).
Obesity is associated with hypertension, hyperlipidemia, and diabetes; all are known contributors to cardiovascular disease.
The nurse weighs the client, calculates the BMI, and examines the pattern of obesity, also known as the waist-hip ratio. Chapter 61 describes these assessments in detail.
Type A Personality
Researchers have identified that people with type A personalities are more vulnerable to the development of heart disease. Type A personalities are highly competitive, overly concerned about meeting deadlines, and are often hostile or angry. The nurse might ask the client: “Have you ever experienced road rage?” or “How do you respond when you have to wait for an appointment?” The chronic anger and hostility displayed by type A people appear to be most closely associated with cardiovascular disease. The constant arousal of the sympathetic nervous system as a result of anger may influence blood pressure, serum fatty acids and lipids, and clotting mechanisms. The nurse observes the client and determines his or her response to stressful situations.
Objective data
Preparation:
n Environment
n Should be warm (about 22°C) and draftless to prevent vasodilatation or vasoconstriction.
n Privacy
n Make sure the female’s breasts and client’s genitals remain draped.
n Order of exam
n Begin with observations peripherally and move toward the heart.
1. Pulse and blood pressure
2. Extremities – peripheral vascular assessment
3. Neck vessels
4. Precordium – (portion of body over heart and thorax)
n Equipment needed:
n Tourniquet or blood pressure cuff
n Stethoscope
n Paper tape measure
n Doppler ultrasonic stethoscope
Arteries accessible to examination on hand
Arteries accessible to examination on leg
Veins accessible to examination
v Jugular veins
v Veins in the arm:
Ø Superficial – in the subQ tissue, responsible for most of the venous return
Ø Deep
v Veins in the leg:
Ø Deep veins: femoral, popliteal; responsible for most of the venous return
Ø Superficial: great and small saphenous
Ø Perforators: connecting veins that join the two sets. They have one-way valves ► blood ► into the deep veins.
Groups of peripheral lymph nodes:
1. Auricular: anterior and posterior
2. Sublingual.
3. Submandibular.
4. Cervical: anterior and posterior.
5. Supra- and subclavian.
6. Axillary.
7. Epithrochlear.
8. Inguinal.
9. Popliteal.
Assesment:
n Inspection and palpation
n Amount in each group
n Size
n Shape
n Consistency
n Movable/connected with surrounding tissues
n Pain/tenderness
n Signs of inflammation: swelling and redness above the node
The nurse assesses the client’s hands, arms, feet, and legs for skin changes, vascular changes, clubbing, capillary filling, and edema. Skin mobility and turgor are affected by the fluid status of the client. Dehydration and aging reduce skin turgor, and edema decreases skin mobility. Vascular changes in an affected extremity may include paresthesia, muscle fatigue and discomfort, numbness, pain, coolness, and loss of hair distribution from a reduced blood supply.
Clubbing of the fingers and toes results from chronic oxygen deprivation in these tissue beds. Clubbing is characteristic in clients with advanced chronic pulmonary disease, congenital heart defects, and cor pulmonale. Clubbing can be identified by assessing the angle of the nail bed. The angle of the normal nail bed is 160 degrees. With clubbing, this angle increases to greater than 180 degrees, and the base of the nail becomes spongy.
Capillary filling of the fingers and the toes is an indicator of peripheral circulation. Pressing or blanching the nail bed of a finger or a toe produces a whitening effect; when pressure is released, a brisk return of color should occur. If color returns within 3 seconds, peripheral circulation is considered intact. If the capillary refill time exceeds 3 seconds, the lack of circulation may be due to arterial insufficiency from atherosclerosis or spasm. Older adults typically have a prolonged capillary refill. Rubor (dusky redness) that replaces pallor in a dependent foot suggests arterial insufficiency.
Peripheral edema is a common finding in clients with cardiovascular problems. The location of edema helps the nurse to determine its potential cause. Bilateral edema of the legs may be seen in clients with heart failure or chronic venous insufficiency. Abdominal and leg edema can be seen in clients with heart disease and cirrhosis of the liver. Localized edema in one extremity may be the result of venous obstruction (thrombosis) or lymphatic blockage of the extremity (lymph-edema). Edema may also be noted in dependent areas, such as the sacrum, when a client is confined to bed.
The nurse documents the location of edema as precisely as possible (e.g., midtibial or sacral) and the number of centimeters from an anatomic landmark. Although some health care severe (or 1 + , 2+, 3 + , or 4+), there is no universal scale. In addition, these values are not precise and are subjective. Instead of using a grading scale, the nurse determines whether the edema is pitting (the skin can be indented) or nonpitting, the depth of the pit (in millimeters), and the amount of time the pit lasts (in seconds).
BLOOD PRESSURE
Arterial blood pressure is measured indirectly by sphygmomanometry.
Normal blood pressure in adults older than 45 years of age ranges from 90 to
A blood pressure less than 90/60 mm Hg may be inadequate for providing proper and sufficient nutrition to body cells. In certain circumstances, such as shock and hypotension, the Korotkoff sounds are less audible or are absent. In these cases the nurse might palpate the blood pressure, use an ultrasonic device (Doppler device), or obtain a direct measurement by arterial catheter. When blood pressure is palpated, the diastolic pressure is usually not obtainable.
Postural Blood Pressure
Clients may report dizziness or lightheadedness when they move from a flat, supine position to a sitting or a standing position at the edge of the bed. Normally these symptoms are transient and pass quickly; pronounced symptoms may be due to orthostatic (postural) hypotension. Postural hypotension occurs when blood pressure is not adequately maintained while moving from a lying to a sitting or standing position. It is defined as a decrease of more than
To detect orthostatic changes in blood pressure, the nurse first measures the blood pressure when the client is supine. After remaining supine for at least 3 minutes, the client changes position to sitting or standing. Normally systolic pressure drops slightly or remains unchanged as the client rises, whereas diastolic pressure rises slightly. After the position change, a time delay of 1 to 5 minutes should be permitted before auscultating blood pressure and palpating the radial pulse. The cuff should remain in the proper position on the client’s arm. The nurse observes and records any signs or symptoms of distress. If the client is unable to tolerate the position change, he or she is returned to the previous position of comfort.
Paradoxical Blood Pressure
Paradoxical blood pressure is defined as an exaggerated decrease in systolic pressure by more than
decrease slightly. However, the decreased fluid volume in the ventricles resulting from these pathologic conditions produces an exaggerated or marked reduction in cardiac output.
Hepatojugular reflux is determined by locating the internal jugular vein after positioning the client with the head of the bed elevated to 45 degrees. The nurse compresses the right upper abdomen for 30 to 40 seconds. Sudden distention of the neck veins after abdominal compression is usually indicative of right-sided heart failure.
Pulse Pressure
The difference between the systolic and diastolic values is referred to as pulse pressure. A normal pulse pressure for an adult is 30 to
Proportional pulse pressure = (Systolic blood pressure – Diastolic blood pressure)/ Systolic blood pressure
A proportional pulse pressure less than 25% usually indicates a cardiac index of less than 2.2, as well as a critically low cardiac output (Stevenson & Braunwald, 1998). Narrowed pulse pressure is rarely normal and results from increased peripheral vascular resistance or decreased stroke volume in clients with heart failure, hypovolemia, or shock. Narrowed pulse pressure can also be seen in clients who have mitral stenosis or regurgitation. An increased pulse pressure may be seen in clients with slow heart rates, aortic regurgitation, atherosclerosis, hypertension, and aging.
Ankle Brachial Index
The ankle brachial index (ABI) can be used to assess the vascular status of the lower extremities. The nurse applies a blood pressure cuff to the lower extremities just above the malleoli and measures the systolic pressure by Doppler ultrasound at both the dorsalis pedis and posterior tibial pulses. The higher of these two pressures is then divided by the higher of the two brachial pulses to obtain the ankle brachial index:
Normal values for ABI are 1 or higher, because blood pressure in the legs is usually higher than blood pressure in the arms. ABI values less than 0.80 usually indicate moderate vascular disease, whereas values less than 0.50 indicate severe vascular compromise.
VENOUS AND ARTERIAL PULSATIONS
Venous Pulsations
The nurse observes the venous pulsations in the neck to assess the adequacy of blood volume and central venous pressure (CVP). The nurse can assess jugular venous pressure (JVP) to estimate the filling volume and pressure on the right side of the heart . The right internal jugular vein is usually used to estimate JVP.
Arterial Pulsations
Assessment of arterial pulsations gives the nurse information about vascular integrity and circulation.
For clients with suspected or actual vascular disease, all major peripheral pulses, including the temporal, carotid, brachial, radial, ulnar, femoral, popliteal, posterior tibial, and dorsalis pedis pulses, need to be assessed for presence or absence, amplitude, contour, rhythm, rate, and equality. The nurse examines the peripheral arteries in a head-to-toe approach with a side-to-side comparison.
A hypokinetic pulse is a weak pulsation indicative of a narrow pulse pressure. It is seen in clients with hypovolemia, aortic stenosis, and decreased cardiac output.
A hyperkinetic pulse is a large, “bounding” pulse caused by an increased ejection of blood. It is seen in clients with a high cardiac output (with exercise or thyrotoxicosis) and in those with increased sympathetic system activity (with pain, fever, or anxiety).
In pulsus alternans, a weak pulse alternates with a strong pulse despite a regular heart rhythm. It is seen in clients with severely depressed cardiac function. Clients may be asked to hold their breath to exclude any false readings. The nurse may palpate the brachial or radial arteries to assess this condition, but it is more accurately assessed by auscultation of blood pressure.
Auscultation of the major arteries (e.g., carotid and aorta) is necessary to assess for bruits. Bruits are swishing sounds that may develop iarrowed arteries and are usually associated with atherosclerotic disease. The nurse can assess for the absence or presence of bruits by placing the bell of the stethoscope over the skin of the carotid artery while the client holds his or her breath. Normally there are no sounds if the artery has uninterrupted blood flow. A bruit may develop when the internal diameter of the vessel is narrowed by 50% or more, but this does not indicate the severity of disease in the arteries. Severity is determined by Doppler flow studies and arteriography.
