Understanding blood pressure and hypertension

Measuring blood pressure

Blood pressure (also known as arterial blood pressure) is the force at which blood is pumped against the walls of the arteries. The standard unit for measuring blood pressure is millimeters of mercury (mmHg). The pressure measured when the left ventricle of the heart contracts is known as the systolic pressure. The pressure measured when the left ventricle of the heart relaxes is known as the diastolic pressure. The diastolic pressure indicates the minimum amount of pressure exerted against the vessel walls at all times.

Systole (heart contraction) and diastole (heart relaxation) together make up the cardiac cycle. The difference between systolic and diastolic pressure is the pulse pressure. BP is recorded as a fraction, with the systolic reading serving as the numerator (top) and the diastolic reading serving as the denominator (bottom) (e.g., 130/80).

Factors that may influence blood pressure

Learning Objective: Describe the factors that may influence blood pressure.

Factors that determine blood pressure include the following:

• Blood volume
• Peripheral resistance created by blood viscosity (the thickness of the blood)
• Vessel elasticity
• Condition of the heart muscle and arterial walls

Volume is the amount of blood in the arteries. An increased blood volume raises BP, and a decreased blood volume lowers BP. With extensive bleeding, or hemorrhage, the blood volume drops, and so does the BP.

The peripheral resistance of blood vessels refers to the lumen (the diameter of the vessel) and the amount of blood flowing through it. The smaller the lumen, the greater the resistance to blood flow. BP is higher with a small or reduced-size lumen and lower with a large lumen. Vessels affected by fatty cholesterol deposits (atherosclerotic plaque) become narrower over time. This results in smaller vessel lumens and, therefore, higher blood pressure.

Vessel elasticity is the ability of an artery to expand and contract to supply the body with a steady flow of blood. With advancing age, certain lifestyle factors, or the presence of arteriosclerosis, vessel elasticity may decrease. This causes the arterial walls to become firm and resistant, increasing the BP. The condition of the myocardium is a primary determinant of the volume of blood flowing through the body. A strong, forceful contraction empties the heart and tends to keep the BP within normal limits. If the myocardium becomes weak, pressure in the vessels begins to increase in an attempt to maintain an adequate level of circulating blood to meet the oxygen and nutrient needs of the body.

Stages of hypertension

Normal	Less than 120/80 mmHg
Elevated	Systolic between 120-129 and diastolic less than 80 mmHg
Stage 1	Systolic between 130-139 or diastolic between 80-89 mmHg
Stage 2	Systolic at least 140 or diastolic at least 90 mmHg
Hypertensive crisis	Systolic over 180 and/or diastolic over 120 mmHg

Exam tip: systolic and diastolic readings don’t always land in the same category. When they disagree, classify by whichever reading falls in the higher category - for example, 135/92 mmHg is Stage 2, since the diastolic value of 92 meets the Stage 2 threshold even though the systolic value of 135 is only Stage 1.

Example: Classifying a reading

A patient’s BP is recorded as 150/94 mmHg. How is this classified?

• The systolic reading (150) falls in the Stage 2 range (at least 140).
• The diastolic reading (94) also falls in the Stage 2 range (at least 90).
• Both readings point to the same category, so the reading is Stage 2.

Answer: Stage 2 hypertension.

Hypotension is an abnormally low blood pressure, which may be caused by emotional or traumatic shock, hemorrhage, central nervous system (CNS) disorders, and chronic wasting diseases. Persistent readings of 90/60 mm Hg or lower usually are considered hypotensive. Orthostatic (postural) hypotension can cause patients to experience vertigo or syncope. Some medications can cause hypotension.

Evaluating the blood pressure

The stages table above reflects the American Heart Association (AHA) categories used for diagnosis and treatment planning. The goal of the AHA recommendations is to reduce the number of people who die each year from hypertension-related illnesses, such as coronary artery disease, heart attack, heart failure, kidney disease, and stroke.

Hypertension can occur in children or adults, but individuals of African American descent, middle-aged and older adults, patients with diabetes mellitus, and those with kidney disease are at greatest risk. Hypertension has been called the silent killer because it frequently has no symptoms. Individuals may go for long periods without knowing they have a problem. Hypertension often is discovered during treatment for another problem.

Signs and symptoms of hypertension

• Blurred vision
• Angina
• Vertigo
• Dyspnea
• Fatigue
• Headache
• Flushing
• Nosebleeds (epistaxis)

Essential hypertension is the most common type of hypertension. It is idiopathic but is associated with obesity, a high blood level of sodium, elevated cholesterol levels, family history, and race (African Americans, Native Americans, Mexican Americans, Native Hawaiians, and some Asian Americans).

When there is a concern about a patient’s BP, the individual is often asked to track it. These readings should be taken about the same time of day and by the same person using the same-size cuff and the same arm. Secondary hypertension is caused by another underlying pathologic condition, such as renal disease, complications of pregnancy, endocrine imbalance, or brain injury.

Temporary elevations in BP may occur with stress, pain, exercise, exhaustion, or “white coat syndrome” (BP that’s elevated in the medical environment but normal elsewhere).

Exam tip: a misleading BP reading is often a cuff or technique problem rather than a true change in the patient’s BP. Using the wrong cuff size or checking only one arm can produce inconsistent results - always check the BP in both arms with a properly sized cuff, and if the two readings differ, use the higher one for diagnosis.

If a patient’s BP is persistently in the Elevated or Stage 1 range at two or more office visits over time, essential hypertension is diagnosed. If the patient’s BP is elevated initially, it should be checked again after the patient has been allowed to sit comfortably for at least 2 minutes.

Metabolic syndrome

Metabolic syndrome occurs when a patient has at least three of the five following conditions:

• Abdominal obesity
• Elevated blood pressure
• Elevated fasting plasma glucose
• High serum triglycerides
• Low high-density lipoprotein (HDL) levels

Metabolic syndrome is associated with an increased risk of developing cardiovascular disease and type 2 diabetes. It is estimated that one-quarter of adults in the United States have metabolic syndrome.

Treatment guidelines for hypertension have four basic aspects:

1. Individuals with Elevated BP should be encouraged to make lifestyle changes before they need treatment: limiting salt, eating a diet rich in potassium, calcium, magnesium, and protein, reducing saturated fat, restricting alcohol, exercising regularly, and losing weight if necessary. Losing just 10% of body weight often lowers BP.
2. In people older than 50, the systolic reading matters more than the diastolic reading; treatment is indicated at a systolic pressure of 140 mm Hg or higher regardless of the diastolic value, since earlier treatment reduces later cardiac and kidney disease.
3. Most patients need two or more medications, typically a diuretic plus an antihypertensive, to reach a goal below 130/80 mm Hg.
4. A patient-centered approach keeps patients motivated and compliant. The medical assistant supports this through ongoing education and community resources such as dietitian referrals.