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Cardiovascular Physiology Concepts

Richard E. Klabunde, PhD

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Cardiovascular Physiology Concepts textbook cover

Click here for information on Cardiovascular Physiology Concepts, 2nd edition, a textbook published by Lippincott Williams & Wilkins (2012)


Cardiovascular Physiology Concepts textbook cover

Click here for information on Normal and Abnormal Blood Pressure, a textbook published by Richard E. Klabunde (2013)


 


Hypertension - Introduction

 

High blood pressure, termed "hypertension," is a condition that afflicts almost 1 billion people worldwide and is a leading cause of morbidity and mortality. More than 20% of Americans are hypertensive, and one-third of these Americans are not even aware they are hypertensive. Therefore, this disease is sometimes called the "silent killer." This disease is usually asymptomatic until the damaging effects of hypertension (such as stroke, myocardial infarction, renal dysfunction, visual problems, etc.) are observed. Hypertension is a major risk factor for coronary artery disease, myocardial infarction ("heart attacks") and stroke.

Definition of Hypertension (pre-2017 Guidelines)

Arterial blood pressure is "normal" when the systolic pressure is 90-119 mmHg and the diastolic pressure is 60-79 mmHg. Blood pressures <90/60 mmHg are considered abnormally low (hypotension). When the arterial pressure is ≥120/80 mmHg, a person is said to have "elevated" pressure or hypertension. Mean arterial pressure is also elevated in hypertension, but it is not usually measured in people. In past years, the diastolic value was emphasized in assessing hypertension. However, elevations in systolic pressure ("systolic hypertension") are also associated with increased incidence of coronary and cerebrovascular disease (e.g., stroke). Therefore, we now recognize that both systolic and diastolic pressure values are important risk factors.

Until November 2017, the classification of hypertension followed the guidelines found in the JNC 7 Report and JNC 8 Report as shown in the following table:

Blood Pressure Categories in Adults (Pre-2017)
Category

Systolic
(mmHg)

  Diastolic
(mmHg)
Normal < 120 and < 80
Prehypertension 120 139 or 80  89
Hypertension      
   Stage 1 140 159 or 90  99
   Stage 2 ≥ 160 or  > 100

 

 

 

 

 

 

 

 

 

Although the above table is found in most current textbooks, a signicant change in this classification system occurred in November 2017 as described below.

Definition of Hypertension (Current Guidelines)

Several leading physician organizations, including the American Heart Association and the American College of Cardiology, published new guidelines in November 2017 for defining and treating hypertension. Based upon large-scale clinical studies, the following definitions are now applied to adults:

Blood Pressure Categories in Adults (Current Guidelines)
Category

Systolic
(mmHg)

  Diastolic
(mmHg)
Normal < 120 and < 80
Elevated 120 129 and < 80
Hypertension      
   Stage 1 130 139 or 80  89
   Stage 2 ≥ 140 or  ≥ 90

 

 

 

 

 

 

 

 

 

The current guidelines lower the threshold for Stage 1 hypertension by 10 mmHg compared to JNC 7 & 8, which is a significant reduction. This dramatically increases the number of people considered hypertensive and therefore should be treated by lifestyle modification and drugs.

Two Classes of Hypertension

In 90-95% of patients presenting with hypertension, the cause is unknown.  This condition is called primary (or essential) hypertension.  The remaining 5-10% of hypertensive patients have hypertension that results secondarily from renal disease, endocrine disorders, or other identifiable causes. This form of hypertension is called secondary hypertension.

Hemodynamic Basis of Hypertension

Regardless of the origin of hypertension, the actual increase in arterial blood pressure is caused by either an increase in systemic vascular resistance (SVR) or an increase in cardiac output (CO). The former is determined by the vascular tone (i.e., state of constriction) of systemic resistance vessels, whereas the latter is determined by heart rate and stroke volume.  Therefore, in order to understand how arterial blood pressure can become elevated, it is necessary to understand the mechanisms that regulate both SVR and CO.

Treatment of Hypertension

Most people diagnosed with hypertension are treated with antihypertensive medications in addition to lifestyle modification (diet, exercise, stress reduction, etc). In most forms of hypertension, the hypertensive state is maintained by an elevation in blood volume, which in turn increases cardiac output by the Frank-Starling relationshipVasodilator drugs, which decrease systemic vascular resistance, are commonly used to treat hypertension. Included in these drugs are alpha-adrenoceptor antagonists (alpha-blockers), direct-acting vasodilators, calcium-channel blockersangiotensin-converting enzyme inhibitors and angiotensin receptor blockers. The latter two groups are most commonly used. Diuretic drugs, which enhance the removal of sodium and water by the kidneys and thereby decrease blood volume, are very effective in the treatment of hypertension. Hypertension is sometimes treated with drugs that decrease cardiac output. These cardioinhibitory drugs either block beta-adrenoceptors on the heart (i.e., beta-blockers) or L-type calcium channels (i.e., calcium-channel blockers), which decreases cardiac output by decreasing heart rate and contractility (inotropy). A complete list of drugs used to treat hypertension can be found by clicking here.

Go to:  primary hypertension

Revised 11/17/2017

 

 

 

DISCLAIMER: These materials are for educational purposes only, and are not a source of medical decision-making advice.