Blood Vessels

Blood Circulation

Once it leaves the heart, blood flows through two circulatory systems: the pulmonary and the systemic ( Fig. 16.2 ). The pulmonary circulation routes blood through the lungs, where it is oxygenated before returning to the left atrium and ventricle of the heart. Venous blood arrives at the right atrium via the superior and inferior vena cavae and moves through the tricuspid valve to the right ventricle. During systole, deoxygenated blood is ejected through the pulmonic valve into the pulmonary artery; it then travels through the pulmonary arteries, arterioles, and capillaries until it reaches the alveoli, where gas exchange occurs.

Oxygenated blood of the systemic circulation returns to the heart and enters the systemic circulation through the pulmonary veins into the left atrium and then through the mitral valve into the left ventricle. The left ventricle contracts, forcing a volume of blood with each beat (stroke volume) through the aortic valve into the aorta where it is distributed systemically through the arteries and capillaries. In the capillary bed, oxygen is provided to the tissues of the body; the now-deoxygenated blood is carbon dioxide–rich. It passes into the venous system and returns to the heart via the superior and inferior vena cavae and into the right atrium ( Fig. 16.3 ).

The structure of the arteries and veins reflects their function. The arteries are thicker with a greater smooth muscle layer and less ability to stretch and expand (distension) from internal pressure. They are subjected to much more pressure than the veins. The veins are more distensible than the arteries ( Fig. 16.4 ). Venous return occurs at a lower pressure than blood flow through the arteries, and veins contain valves to keep blood flowing in one direction. If circulatory volume increases significantly, the veins can expand and act as a repository for the extra volume.

Arterial Pulse and Pressure

The palpable and sometimes visible arterial pulses are the result of ventricular systole, which produces a pressure wave throughout the arterial system (arterial pulse). It takes barely 0.2 second for the impact of this wave to be felt in the dorsalis pedis artery within the foot. The arterial blood pressure is the force exerted against the wall of an artery as the bolus of blood exits the heart’s left ventricle with contraction.

The pulse usually is felt as a forceful wave that is smooth and more rapid on the ascending part of the wave; whereas it becomes domed, less steep, and slower on the descending part ( Fig. 16.5 ). Because the carotid arteries are the most accessible of the arteries closest to the heart, they have the most definitive pulse for evaluation of cardiac function.

The following variables contribute to the characteristics of the pulses:

• Volume of blood ejected (stroke volume)

• Distensibility of the aorta and large arteries

• Obstruction of blood flow (e.g., narrowing of aortic valve [stenosis] or aorta [coarctation], vasculitis—blood vessel inflammation with narrowing—or PAD)

• Peripheral artery resistance

• Viscosity of the blood

Jugular Venous Pulse and Pressure

The jugular veins, which empty directly into the superior vena cava, reflect the activity of the right side of the heart and offer clues to its competency. The level at which the jugular venous pulse is visible gives an indication of right atrial pressure.

The external jugular veins are more superficial and more visible bilaterally above the clavicle, close to the insertion of the sternocleidomastoid muscles. The larger internal jugular veins run deep to the sternocleidomastoids, near the carotid arteries, and are less accessible to visual inspection ( Fig. 16.6 ).

The activity of the right side of the heart is transmitted back through the jugular veins as a pulse ^a that has five identifiable components—three peaks and two descending slopes ( Fig. 16.7 ):

a Although often referred to as a pulse, this is not the same as an arterial pulse because it is reflected back from the right heart rather than pushed forward by the left heart. Unlike arterial pulses, it cannot be palpated, only visualized.

a wave	The upward a wave, the first and most prominent component, is the result of a brief backflow of blood to the vena cava during right atrial contraction. This peaks slightly before the first heart sound (S1).
c wave	The upward c wave is a transmitted impulse from the vigorous backward push produced by closure of the tricuspid valve during right ventricular systole.
v wave	The upward v wave is caused by the increasing volume and concomitant increasing pressure in the right atrium. It occurs after the c wave, late in ventricular systole.
x slope	The downward x slope is caused by passive atrial filling. This ends with the initiation of the v wave.
y slope	The y slope following the v wave reflects the open tricuspid valve and the rapid filling of the right ventricle.

Infants and Children

At birth the cutting of the umbilical cord, through which oxygen has been provided in utero, requires the infant to begin breathing. The onset of respiration expands the lungs and carries air to the alveoli. Pulmonary vascular resistance drops, allowing blood to flow more freely to the lungs. Systemic vascular resistance increases. The ductus arteriosus closes, usually within the first 12–14 hours of life. Once pulmonary vascular resistance is lower than systemic resistance, blood flows into the pulmonary arteries rather than across the interatrial foramen ovale. The interatrial foramen ovale is functionally closed by the shifting pressures between the right and left sides of the heart.

Pregnant Patients

During pregnancy, the systemic vascular resistance decreases and peripheral vasodilation occurs, often resulting in palmar erythema and spider telangiectasias. The systolic blood pressure decreases slightly. There is a greater decrease in the diastolic pressure. The lowest levels occur in the second trimester and then rise but still remain below blood pressure readings before pregnancy. Maternal position affects blood pressure. Lower blood pressure can be noted when the patient is supine during the third trimester. This lower pressure is secondary to venous compression of the vena cava and impaired venous return. Blood in the lower extremities tends to pool in later pregnancy—except when the patient is in the lateral recumbent position—as a result of compression of the pelvic veins and inferior vena cava by the enlarged uterus. The compression may result in an increase in dependent edema, varicosities of the legs and vulva, and hemorrhoids.

Older Adults

Calcification and plaque buildup in the walls of the arteries can cause stiffness as well as dilation of the aorta, aortic branches, and carotid arteries. The arterial walls lose elasticity and vasomotor tone and are less distensible. The resulting increased peripheral vascular resistance may lead to elevated blood pressure, especially systolic.

History of Present Illness

Past Medical History

• Cardiac surgery or hospitalization for cardiac evaluation, congenital heart defect, vascular surgery or percutaneous interventions

• Chronic illness: hypertension and studies to define its cause, bleeding or clotting disorder, hyperlipidemia, diabetes, chronic kidney disease, thyroid dysfunction, stroke, vasculitis, thrombosis, transient ischemic attacks, coronary artery disease, atrial fibrillation or other type of dysrhythmia

Family History

Family members with risk factors, morbidity, and mortality related to cardiovascular system; hypertension, dyslipidemia, diabetes, heart disease, thrombosis, varicose veins, venous insufficiency, peripheral vascular disease, abdominal aortic aneurysms, ages at time of illness or death

Personal and Social History

• Employment: physical demands; environmental hazards such as heat, chemicals, dust; sources of emotional stress

• Tobacco: type (cigarettes, cigars, pipe, chewing tobacco, marijuana, vaping, snuff); duration of use; amount; efforts to quit and methods used; age started and, perhaps, stopped; pack-years (Number of years smoking × Number of packs per day)

• Nutritional status

• Usual diet: proportion of fat, food preferences, history of dieting

• Weight: loss or gain, amount and rate, expected or unexpected

• Exercise: type, amount, frequency, intensity

• Use of alcohol: amount consumed, frequency, duration of current intake

• Use of illicit drugs: intravenous drug use, cocaine