Blood pressure (BP) is the force of blood flow pushing against the walls of the blood vessels.
High Blood Pressure, or hypertension, is when the force of blood against the arterial walls is greater than it should be; eventually, long-term force against the artery walls increases a person's risk for health problems, including heart attack and stroke.
According to the Center for Disease Control (CDC), high blood pressure is a common and potentially dangerous condition. About 75 million people in the US—or 1 in 3 US adults—have high blood pressure. An even more terrifying fact is that only about half of the people with high blood pressure have the condition under control.
Low Blood Pressure, or hypotension, is when the force of blood pushing against the walls of the arteries is lower than it should be. Low blood pressure is only a concern if a person experiences signs or symptoms or is associated with a serious medical condition, such as heart disease.
Many people think blood pressure and heart rate, also called pulse, go hand-in-hand. After all, these two vital signs are often measured at the same time at the doctor’s office. Vital signs are clinical measurements that indicate the state of a person’s bodily functions, specifically, BP, pulse, temperature, and respiratory rate.
Each of these vital signs measure distinctly different components of the heart and body systems. As mentioned, the blood pressure is the force of blood circulating through the arteries, while the pulse is the number of times the heart beats per minute (bpm).
The BP and pulse often rise and fall simultaneously; however, if the heart rate increases this does not mean the blood pressure increases or vice versa.
During exercise, for example, the heart speeds up to provide more blood to the muscles. It may be possible for the pulse rate to double safely, while the blood pressure responds by increasing a nominal amount. Even though the heart is beating more a minute, healthy blood vessels get larger (dilate) to accommodate the increase in blood to flow.
On the other hand, when faced with fear the hormone epinephrine, also known as adrenaline, is released into the circulatory system causing both the blood pressure and pulse rate to rise.
The body’s nervous system helps regulate the blood pressure by using sensors in the walls of the arteries that send signals to the vessels, the heart, and the kidneys—causing them to raise or lower the blood pressure.
The aorta and carotid arteries have important stretch sensors called baroreceptors. These are the most sensitive receptors of the circulatory system, which allows for immediate correction of abnormal arterial pressure.
A BP reading is determined by both the amount of blood the heart pumps and the amount of resistance to the blood flow in the arteries.
Constricted arteries will cause an increase in resistance to the blood flow; therefore, the more narrow the arteries the higher a person's blood pressure.
Blood pressure doesn’t stay the same throughout the day—it decreases during sleep and increases upon awakening. Blood pressure also increases during activity, anxiety, and excitement.
Blood pressure is an easy measurement that is done at a doctor’s office, at home, or at a pharmacy. Often, home readings and measurements at the pharmacy are taken with a mechanical blood pressure monitor.
Some doctors may prefer to take a manual blood pressure (BP) with a sphygmomanometer. This technique is known as the auscultatory method.
Basic steps for taking a manual blood pressure are as follows:
Two numbers are heard and measured when taking a blood pressure:
The tapping sounds heard with the stethoscope when taking a blood pressure are universally known as Korotkoff sounds, or K-Sounds.
However, the exact physical basis for the mechanism producing these sounds is poorly understood.
Classification of blood pressure sounds are as follows:
Over the years K-4 and K-5 have both been used as the diastolic blood pressure. The Journal of the American Society of Hypertension (2015), explains there is some evidence that the muffling in K-4 may be a more accurate end-point than K-5 in children, pregnancy, and exercise.
Some people may not have a distinct fifth sound, therefore, the muffling sound of K-4 is heard all the way to 0 mmHg. When this is heard, K-4 is noted as the diastolic pressure.
Some practitioners often take note of all three numbers such as in the example below.
Blood pressure guidelines exist, but what is optimal, or healthy, varies from person to person—keep this in mind when reviewing table 1.
Table 1. Blood Pressure Guidelines.
|BP Category||Systolic (upper #)||Diastolic (lower #)|
|Prehypertension (Normal)||120 - 139||80 - 89|
|Hypertension (Stage 1)||140 - 159||90 - 99|
|Hypertension (Stage 2)||160⥸||100⥸|
A person's age and health condition determine their particular "optimal" blood pressure reading.
The Eighth Joint National Committee (JNC 8) released target blood pressure recommendations (see table 2).
Table 2. Target Blood Pressure.
|Age and Health Condition||Target|
|30 – 59||140/90|
|People with diabetes or people with non-diabetic chronic kidney disease||140/90|
Published guidelines on the treatment of hypertension since 2013 can be found here.
The exact cause of hypertension is not known; however, several conditions and risk factors may have a role in the development, including:
Many people with hypertension have zero signs or symptoms, even when the blood pressure measurement reaches high levels. Often, prolonged hypertension is called the “silent killer.”
People presenting with high blood pressure may have shortness of breath, headaches, facial flushing, or nosebleeds. These clinical manifestations are not distinctive or inclusive and usually don’t occur until the blood pressure has reached a life-threatening stage.
Development of hypotension most commonly occurs in two different scenarios.
In a functional, healthy nervous system and circulatory system the body is extremely sensitive and responsive to changes. Therefore, the body rapidly adjusts to ensure enough blood and oxygen are available to the brain and other essential organs.
With most forms of hypotension, the body can’t bring the blood pressure back to normal or can’t do it quick enough. Some people have a normally low blood pressure—all the time—and they have no symptoms. In other people, certain conditions can cause an abnormally low blood pressure that results in less blood and oxygen to the body’s organs.
Risk factors for the development of low blood pressure may include:
Many of the signs and symptoms of hypotension are related to the cause and not the effects of hypotension.
Orthostatic hypotension, neurally mediated hypotension (NMH), postprandial hypotension, and severe hypotension (discussed in untreated complications) are three types of hypotension.
Blood pressure is customarily taken during a routine doctor’s appointment. The following table is a replication of the 2015 US Preventative Services Task Force (USPSTF) clinical guidelines for blood pressure screening (see table 3).
Table 3. USPSTF Screening for High Blood Pressure in Adults: Clinical Summary.
|Factors||Suggestions and Advice|
|Population||Adults aged ≥18 y without known hypertension|
|Recommendation||Screen for high blood pressure; obtain measurements outside of the clinical setting for diagnostic confirmation.|
|Risk Assessment||Persons at increased risk for high blood pressure are those who have high-normal blood pressure (130–139/85–89 mmHg), those who are overweight or obese, and African Americans.|
|Screening Tests||Office measurement of blood pressure is done with a manual or automated sphygmomanometer. Proper protocol is to use the mean of 2 measurements taken while the patient is seated, allow for ≥5 min between entry into the office and blood pressure measurement, use an appropriately sized arm cuff, and place the patient’s arm at the level of the right atrium. Multiple measurements over time have better positive predictive value than a single measurement.Ambulatory and home blood pressure monitoring can be used to confirm a diagnosis of hypertension after initial screening.|
|Screening Interval||Adults aged ≥40 y and persons at increased risk for high blood pressure should be screened annually. Adults aged 18 to 39 y with normal blood pressure (<130/85 mmHg) who do not have other risk factors should be rescreened every 3 to 5 y.|
|Treatment and Interventions||For non-black people, initial treatment consists of a calcium-channel blocker, angiotensin-receptor blocker, angiotensin-converting enzyme inhibitor, or a thiazide diuretic. For black people, initial treatment is a calcium-channel blocker or a thiazide diuretic. Initial or add-on treatments for people with chronic kidney disease consists of either an angiotensin-receptor blocker or an angiotensin-converting enzyme inhibitor, but not both.|
High blood pressure in children is a growing health concern that is often overlooked. Children 3 years and older will ordinarily have a blood pressure check during their yearly check-up.
Normal blood pressure readings for children and adolescents are based on sex, age, and height—prehypertension is defined as a blood pressure in at least the 90th percentile, but less than the 95th percentile, for sex, age, and height, or a measurement of 120/80 mmHg or higher.
The National Institute of Health provides details of blood pressure levels based on age and height percentiles of boys and girls in this table. Under JNC 8, in all cases, target blood pressure levels should be reached within 30 days of starting any treatment.
Lifestyle changes are an enormous part of managing proper blood pressure levels, whether the person has hypertension or hypotension.
Hypertension is more likely to cause complications than hypotension, both, however, need to be taken seriously.
Excessive pressure on the arteries, if left uncontrolled, can lead to:
A hypertensive urgency is defined as a severe increase in blood pressure marked by systolic greater than 220 mmHg or diastolic greater than 120 with no evidence of organ damage.
A hypertensive emergency occurs when hypertension results in organ damage. Systems most affected include the central nervous system, the cardiovascular system, and the renal system.
If the blood pressure is sufficiently low, syncope and seizures can occur.
To healthcare providers the word shock implies a collapse of the cardiovascular system from a possibility of several reasons. Shock related to hypotension occurs when not enough oxygenated blood is flowing to the body’s major organs, including the brain. Signs and symptoms of shock vary, depending on the cause.
Typical characteristics include:
In vasodilatory shock, blood vessels suddenly relax causing an extreme drop in blood pressure. A person will feel warm and have flushed skin at first, then they become diaphoretic and weak. As shock worsens, the person cannot sit up without passing out, and if not treated, the person will lose consciousness. As with any medical emergency, a person needs treatment right away. If a person has signs or symptoms of a hypotensive or hypertensive urgency or emergency, call emergency services immediately.
Written by Sarah Gehrke, MSN, RN and last updated 2017-30-21
Last reviewed by Michael A. Tomeo MD on 2017-30-21