Introduction

Blood pressure (BP) is the pressure exerted by blood on the walls of blood vessels. Blood and blood vessels are components of the circulatory system, functions of which include the supply of energy (e.g., heat), oxygen, and nutrients to tissues. In order to facilitate this, BP exists in all blood vessels, from major arteries and veins to capillaries, and varies throughout the body. For the purpose of this discussion, BP will refer specifically to the brachial (upper arm) arterial pressure.

Blood pressure is a vital sign, and its measurement is a standard clinical procedure. Blood pressure is typically represented with two numbers: systolic blood pressure (SYS) and diastolic blood pressure (DIA). These numbers describe the pulsatile nature of BP – SYS denoting the maximum, and DIA the minimum pressure during a heartbeat. This means that there is a physiological SYS and DIA during each heartbeat. Another measure of BP is the mean arterial pressure (MAP). This is the average BP, and is considered to be the body’s internal measure of BP. These 3 measures of BP are displayed (in traditional units of mmHg – millimeters of mercury) as part of the results for each Pulsewave reading.

Blood Pressure Measurement

Blood pressure can be measured directly from within the artery; however, this invasive technique carries physical risks, and its use is limited to special circumstances. More commonly, BP is measured indirectly and non-invasively. In contrast to direct BP measurement, indirect techniques, such as the auscultatory method, do not measure BP for each heartbeat; rather, they make a single measurement of BP that spans the duration of the reading. These techniques are sensitive to various factors, including the cuff size, cuff placement, body position, and the height of the measurement site with respect to the heart. It is extremely important to adhere to the instructions pertaining to proper BP measurement in order to ensure the most accurate results. 

The auscultatory method is considered the standard for non-invasive BP measurement. Automatic BP measurement devices, such as Pulsewave, gain acceptance by complying with standards that dictate BP measurement accuracy with respect to the auscultatory method. Thus, although the Pulsewave measurement site is at the wrist, the reported BP is that of the upper arm.

Blood Pressure Classification

High BP

Blood pressure can be classified into categories. These categories, which have been defined by guidelines (refer to “Additional Resources” at the end of this article), indicate a degree of risk of cardiovascular complications associated with high BP. Although these guidelines define the classification of BP, it is very important that your physician determine your own classification. This is because the guidelines change over time, and differ depending on geographical region. Furthermore, the degree of risk of cardiovascular complications is dependent not only on your BP, but various other factors as well, such as the existence of other complications (e.g., diabetes) and age. Systolic blood pressure, for instance, typically tends to rise with age.

The following table provides a classification of high BP for adults aged 18 and older based on the guidelines of JNC 7 (refer to “Additional Resources” at the end of this article). These classifications should not be used based on a single Pulsewave reading. The guidelines indicate that the classifications are based on a series of properly measured readings. 

Classification of blood pressure for adults

The classification of high BP is defined in terms of categories of hypertension. Hypertension may be diagnosed by a physician through a series of readings of sustained high BP. The complications associated with hypertension include damage to the heart, brain, blood vessels, kidneys, and eyes.

Low BP

Low BP is defined in terms of hypotension, which is considered to be indicated by SYS < 90 mmHg or DIA < 60 mmHg. The symptoms associated with hypotension include dizziness, weakness, and fainting. In severe cases, hypotension may lead to heart and brain damage due to insufficient tissue oxygenation.

Blood Pressure Variability

First and foremost, BP is pulsatile and naturally varies between a minimum (DIA) and a maximum (SYS) with each heartbeat. Invasive BP measurement techniques show this variation, accentuating the fact that indirect methods of BP measurement produce estimates of BP, and are uncertain in nature. In the long-term, BP naturally tends to increase with age. Hypertension that tends to develop gradually over many years with no identifiable cause is known as primary or essential hypertension. These two extremes, short-term and long-term variations, surround variations that occur on a daily basis. These daily BP fluctuations may have a circadian rhythm that can be diagnostically useful. Typically, the daily minimum BP occurs during sleep and the daily maximum BP occurs during wake.

Various conditions and medications can cause high BP. Sustained high BP that tends to appear suddenly and has an underlying cause is called secondary hypertension. This may be caused by conditions such as kidney problems, or medications such as birth control pills. Similarly, various conditions and medications can cause low BP. This includes conditions such as heart and endocrine problems, and medications such as diuretics. Low BP can also be caused by major internal or external bleeding and severe allergic reactions.

Blood pressure not only varies naturally, but may vary in response to external influences and events that affect our bodies. Diet, exercise, stress, and environmental conditions (e.g., temperature) can cause variations in BP. High and low BP may not necessarily be sustained, and may occur temporarily due to factors such as white-coat syndrome (increases BP) and standing up (decreases BP).

Additional Resources

Introduction:

Hypertension Canada. Blood pressure information [Online]. Available: http://hypertension.ca/en/public . Accessed: 2014-08-27.

Wikipedia. Blood pressure [Online]. Available: http://en.wikipedia.org/wiki/Blood_pressure. Accessed: 2014-08-27.

Wikipedia. Vital signs [Online]. Available: http://en.wikipedia.org/wiki/Vital_signs. Accessed: 2014-08-27.

Blood Pressure Measurement:

Manual, electronic, or automated sphygmomanometers, ANSI/AAMI SP10, 2002.

Non-invasive sphygmomanometers - Part 4: Test procedures to determine the overall system accuracy of automated non-invasive sphygmomanometers, BS EN 1060-4, 2004.

Non-invasive sphygmomanometers - Part 2: Clinical validation of automated measurement type, ANSI/AAMI/ISO 81060-2, 2009.

Wikipedia. Blood pressure measurement [Online]. Available: http://en.wikipedia.org/wiki/Blood_pressure#Measurement. Accessed: 2011-01-20.

Blood Pressure Classification:

A. V. Chobanian et al, “Seventh report of the joint national committee on prevention, detection, evaluation, and treatment of high blood pressure (JNC 7)”, Hypertension, vol. 42, pp. 1206-1252, 2003.

B. Williams et al, “Guidelines for management of hypertension: report of the fourth working party of the British Hypertension Society (BHS-IV)”, Journal of Human Hypertension, vol. 18, pp. 139-185, 2004.

Hypertension Canada. Blood pressure information [Online]. Available: http://hypertension.ca/en/. Accessed: 2014-09-23.

Mayo Clinic. High blood pressure [Online]. Available: http://www.mayoclinic.com/health/high-blood-pressure/DS00100. Accessed: 2011-01-20.

American Heart Association. High blood pressure [Online]. Available: http://www.heart.org/HEARTORG/Conditions/HighBloodPressure/High-Blood-Pressure_UCM_002020_SubHomePage.jsp. Accessed: 2011-01-20.

The task force for the diagnosis and management of syncope of the European Society of Cardiology (ESC), “Guidelines for the diagnosis and management of syncope”, European Heart Journal, vol. 30, pp. 2631-2671, 2009.

Mayo Clinic. Low blood pressure [Online]. Available: http://www.mayoclinic.com/health/low-blood-pressure/DS00590. Accessed: 2011-01-20.

American Heart Association. Low blood pressure [Online]. Available: http://www.heart.org/HEARTORG/Conditions/HighBloodPressure/AboutHighBloodPressure/Low-Blood-Pressure_UCM_301785_Article.jsp. Accessed: 2011-01-20.

Wikipedia. Blood pressure classification [Online]. Available: http://en.wikipedia.org/wiki/Blood_pressure#Classification. Accessed: 2011-01-20.

Blood Pressure Variability:

A. V. Chobanian et al, “Seventh report of the joint national committee on prevention, detection, evaluation, and treatment of high blood pressure (JNC 7)”, Hypertension, vol. 42, pp. 1206-1252, 2003.

Hypertension Canada. Lifestyle choices [Online]. Available: http://hypertension.ca/en/public. Accessed: 2014-09-23.

Mayo Clinic. High blood pressure causes [Online]. Available: http://www.mayoclinic.com/health/high-blood-pressure/DS00100/DSECTION=causes. Accessed: 2011-01-20.

Mayo Clinic. Low blood pressure causes [Online]. Available: http://www.mayoclinic.com/health/low-blood-pressure/DS00590/DSECTION=causes. Accessed: 2011-01-20.

National Heart Lung and Blood Institute. High blood pressure causes [Online]. Available: http://www.nhlbi.nih.gov/health/dci/Diseases/Hbp/HBP_Causes.html. Accessed: 2011-01-20.

National Heart Lung and Blood Institute. Hypotension causes [Online]. Available: http://www.nhlbi.nih.gov/health/dci/Diseases/hyp/hyp_causes.html. Accessed: 2011-01-20.

Wikipedia. Blood pressure [Online]. Available: http://en.wikipedia.org/wiki/Blood_pressure. Accessed: 2011-01-20.