Blood Pressure

Table of Contents

• Updated
• Resources
  • Wikipedia
  • Advocacy, Charities
• Pressure
  • Circulation
  • Pressure
  • Normal?
• Measurement Methods
  • Introduction
  • Ausculatory
  • Oscillometric
    • Method and history
    • Automated
• Home Use Devices in Canada
  • Basic Features
  • Displays
  • Cuffs
    • Construction
    • Fastening
  • Options
  • Retail Market
  • Standards
    • Regulatory & Product Rating
    • Margin of error
  • Manufacturer Manuals
  • Electromagnetic Fields

Updated

This post was first published in 2023 as part of a longer post. It was edited to focus on blood pressure and republished in 2025. It is related to posts on hypertension, sodium in food, cooking and nutrition. I became interested in these topics in 2011 after recovering from a stroke that was attributed to hypertension. I have used a few home blood pressure monitors.

Resources

Wikipedia

Wikipedia entries provide information on the science and the medical views of subjects:

• Standard Atmosphere; Atmospheric Pressure;
• Pulse;
• Pressure Measurement (Manometers); mmHg – Millimeters of Mercury;
• Blood pressure;
• Stethoscope; Sphygmomanometer (devices used by medical professionals to measure blood pressure);
• Blood Pressure Measurement; Ambulatory blood pressure monitoring.

Advocacy, Charities

The American Heart Association (AHA):

• Understanding Blood Pressure Readings – web page;
• published medical scientific journal Hypertension.
• diet guides and cookbooks. The AHA sells a Low-Salt Cookbook, first published in 1990. The 2011 4th edition is the most modern, and is currently for sale on the internet at the AHA website;

Hypertension Canada:

• 2020-22 Guidelines Highlights;
• Diagnosis & Assessment Guidelines.

Pressure

Circulation

The noises of the heartbeat, the flow of blood through blood vessels, and the detectable pulse in blood vessels have been known for a very long time. Humans do not have a sense to detect when their blood pressure is not normal or healthy.

Medical science, in the 19th and 20th centuries, credited the idea that blood circulated through the body by vessels from and to the heart to William Harvey, in 1628. This theory was accepted as a better idea than the idea of “humours” postulated by classical and medieval Greek, Roman, Arabic, and middle Eastern writers.

Pressure

The measurement of blood pressure was identified by medical and scientific persons at the end of the 19th century. The Wikipedia entry Sphygnomanometer summarizes of the inventions of mercury column devices, the inflatable brachial cuff and the uses of the inventions for the ausculatory method of determining blood pressure. It notes that the devices, concepts and method were accepted in medical research and clinical practice without fully explaining how the measurement of blood pressure became a standard diagnostic procedure.

The Wikipedia entry for Blood Pressure notes, as of late 2023 “Blood pressure is one of the vital signs … that healthcare professionals use in evaluating a patient’s health.”

Systolic pressure is the maximum pressure during one heartbeat. Diastolic pressure is the minimum pressure between two heartbeats. The units of measurement are millimeters of mercury (abbreviated mmHg), derived from the original mercury column sphygnomanometer.

Normal?

According to advocacy groups, including the American Heart Association (“AHA”) and medical charities, and members of the health care communities, the normal blood pressure of a “normal healthy” adult is 120 mmHg systolic and 80 mmHg diastolic, written as 120/80 (spoken as “120 over 80”).

The AHA’s online pamphlet Understanding Blood Pressure Readings classifies of 5 bands of BP readings. Hypertension can be described(by the AHA stage 2, above) as a medical condition in which the blood pressure in the arteries is persistently elevated – systolic blood pressure is elevated (>140 mmHg) with a normal diastolic blood pressure. Isolated systolic hypertension may present a health concern. Where elevated readings (>140/>90) appear twice, a medical doctor can diagnose hypertension.

Wikipedia, in the Hypertension entry, places normal in a range:

Blood pressure is classified by two measurements, the systolic and diastolic pressures, which are the maximum and minimum pressures, respectively. For most adults, normal blood pressure at rest is within the range of 100–130 millimeters mercury (mmHg) systolic and 60–80 mmHg diastolic. For most adults, high blood pressure is present if the resting blood pressure is persistently at or above 130/80 or 140/90 mmHg. … Ambulatory blood pressure monitoring over a 24-hour period appears more accurate than office-based blood pressure measurement.

Wikipedia, September 2022, Hypertension

The position is more complex and subtle:

“… the average blood pressure, age standardized, since 1975 to the present, at approx. 127/79 in men and 122/77 in women, although these average data mask significantly diverging regional trends.”

… in many older people, systolic blood pressure often exceeds the normal adult range”.

Wikipedia, September 2022, Blood Pressure

Blood pressure is variable, and is affected by physiological, environmental and psychological factors. :

Blood pressure fluctuates from minute to minute and normally shows a circadian rhythm over a 24-hour period, with highest readings in the early morning and evenings and lowest readings at night. Loss of the normal fall in blood pressure at night is associated with a greater future risk of cardiovascular disease and there is evidence that night-time blood pressure is a stronger predictor of cardiovascular events than day-time blood pressure. Blood pressure varies over longer time periods (months to years) and this variability predicts adverse outcomes. Blood pressure also changes in response to temperature, noise, emotional stress, consumption of food or liquid, dietary factors, physical activity, changes in posture (such as standing-up), drugs, and disease. The variability in blood pressure and the better predictive value of ambulatory blood pressure measurements has led some authorities, such as the National Institute for Health and Care Excellence (NICE) in the UK, to advocate for the use of ambulatory blood pressure as the preferred method for diagnosis of hypertension

Wikipedia, September 2022, Blood Pressure

Hypertension is defined:

Hypertension … is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high blood pressure, however, is a major risk factor for stroke, coronary artery disease, heart failure, atrial fibrillation, peripheral arterial disease, vision loss, chronic kidney disease, and dementia. Hypertension is a major cause of premature death worldwide.

High blood pressure is classified as primary (essential) hypertension or secondary hypertension. About 90–95% of cases are primary, defined as high blood pressure due to nonspecific lifestyle and genetic factors. Lifestyle factors that increase the risk include excess salt in the diet, excess body weight, smoking, and alcohol use. The remaining 5–10% of cases are categorized as secondary high blood pressure, defined as high blood pressure due to an identifiable cause, such as chronic kidney disease, narrowing of the kidney arteries, an endocrine disorder, or the use of birth control pills.

Wikipedia, September 2022, Hypertension

Health care professionals recognize 2 notable categories of blood pressure readings being elevated without actual hypertension:

• white coat hypertension, the effect of being monitored in a clinical setting, and
• labile hypertension.

Measurement Methods

Introduction

The “non-invasive” methods (blood vessels are not pierced or penetrated) for the measurement of pressure are: ausculatory and oscillometric . Both methods, as of the late 20th century, measure the air pressure in an airtight bladder contained in inflatable cuffs, held in a fixed position against the body.

Since the early 20th century, the flow of blood in a major artery – usually the brachial artery in an upper arm – has been been restricted with an inflatable cuff device. A cuff is wide enough to apply pressure without bruising or injury to the limb, and applied above the elbow. The pressure in the cuff is the measure of blood pressure.

Ausculatory

Ausculatory blood pressure measurement started after the stethoscope and the sphygnomanometer were invented and came into use in the 19th century.. The ausculatory method was administered by trained professionals – medical doctors and nurses. In the 20th century medical offices, clinics and hospitals were equipped with aneroid sphygnomanometers. The devices are or were regularly calibrated to the ambient air pressure for proper use.

The steps of the process:

• inflating the cuff while listening to the pulse in the artery with a stethoscope and stopping when the beating was no longer audible,
• recording the highest pressure in the cuff as the systolic pressure,
• releasing pressure gradually, and
• recording the lower pressure in the cuff when the beat resumed as the diastolic pressure.

Oscillometric

Method and history

Oscillometric blood pressure cuffs and meters do not rely on human hearing to detect the sounds in the artery. Oscillations, caused by the pulsing of blood though an artery near the skin are detected and counted while the pressure in the cuff is used to measure blood pressure.

The oscillometric method is used in automated devices that inflate the cuff, detect when blood flow through the limb has paused, take readings, release the cuff, record and display blood pressure and pulse. It is analogous to a health care worker’s using a stethoscope and an aneroid sphygnomanometer.

Oscillations in the circulatory system were noted in medical literature as early as 1876. The oscillometric method is dependent on the development of transducers and monitors by the electronic industry. The idea of using compressed air in hose to trigger a switch had been used commercially to design devices that could monitor traffic in the 20th century. Automobile service stations used devices made up of a hose, a pressure switch and a bell to alert staff that vehicle had entered the lot and was in a position to purchase gasoline. Such devices are still on the market in the early 21st century to monitor entry to some properties.

The first commercial oscillometric blood pressure monitor was patented in the USA in 1976. With an electronic sensor, this kind of monitor could detect oscillations in the cuff. A sensor could detect the pressure applied by the cuff when the oscillations of the artery in the limb to which the cuff was applied had stopped.

Automated

No manufacturers explain how an oscillometric, automated monitor reads blood pressure or calculates other numbers. The authors of a paper in the Journal of Human Hypertension, (available in Springer Nature‘s unlocked service) explain:

… With every arterial pulse wave there is a small rise and fall in the volume of the limb, which in turn causes an increase and then a decrease in the pressure within the encircling cuff, which can be detected using a solid-state transducer. When the cuff encircling a limb is inflated with [a] electronic pump … the rising pressure in the cuff eventually stops arterial blood flowing into the underlying limb and pulsation ceases. This is detected by the machine which continues to inflate the cuff for a second or two more to ensure that the limb flow has stopped completely. At this point, inflation stops, and a valve opens allowing the pressure in the cuff to reduce slowly … The pressure within the cuff is monitored carefully by the machine. At first it only detects the pulseless reduction in pressure. As the pressure in the cuff falls to below the pressure of the peak of the arterial pulse, the machine begins to detect a small pressure wave which reflects the difference between the pressure in the cuff and that in the artery. With further cuff deflation these pressure differences become greater until the cuff begins to fall away from the limb and less of the volume pulsation is detected. The machine therefore records within it a series of pulse waves, which are initially flat, then very slight, then increase to a peak and then diminish until they are hardly detected.

….

Automated oscillometric machines differ with respect to their algorithms, transducers, inflation and deflation rates, cuff sizes and materials, all of which may affect the estimation of BP. These may result in significant differences in estimations of systolic and diastolic BP compared with auscultatory readings in the same patient. Some machines may be accurate in one subject group but not necessarily in others e.g. in obese or pregnant subjects.

Phillip Lewis on behalf of the British and Irish Hypertension Society’s Blood Pressure Measurement Working Party “Oscillometric measurement of blood pressure: a simplified explanation. A technical note …” , J Hum Hypertens 33, 349–351 (2019)

Automated oscillometric monitors are less time consuming for health care providers. Such devices are used by health care professionals in medical settings including hospitals, clinics and private medical offices/clinics. The devices built to professional standards are relatively accurate and reliable.

A type of automated meter is by professionals for ambulatory measurement.

Home Use Devices in Canada

Basic Features

A home blood pressure measurement device is an automated device which has these basic components:

1. a cuff; with a hose; and
2. an operating unit containing the pump that inflates the cuff, sensors, controls, processors and an LCD display.

A patient must install the cuff, take the reading and record the result. The display area of a operating unit has an icon(s) or area that flashes as the cuff inflates, and deflates. When the cuff has been is deflated and the reading is complete the device displays the systolic reading, the diastolic reading, the pulse (in beats per minute), and other data.

Home use devices deliver acceptably accurate readings, if:

• the device is working and operated correctly,
• the cuff is applied properly,
• the patient has been inactive, is warm and comfortable and seated, sitting with the correct posture.

Displays

The displays on the operating units are monochrome LCD displays that display icons and numerals. There are icons that flash as the cuff deflates and/or as the pump inflates the cuff and the cuff deflates. Conventionally these are triangles pointing up or down. An icon flashes when a heartbeat or pulse is detected, according the design decisions of the manufacturer Conventionally the icon is heart shaped.

Numerals are displayed digitally. When the cuff is being inflated or deflated, the pressure in the cuff changes every few seconds. When the cuff has been deflated the device displays the systolic pressure, diastolic pressure and beat per minute as counted by the device using its algorithms.

Some devices will display an icon for “irregular heartbeat”. The irregular heart beat icon can be triggered by movement,or when the cuff is not attached properly, or coughs or sneezes.

Most devices will display error codes when the machine fails to generate the expected readings, including codes for”movement error”.

Cuffs

Construction

A cuff is basically a package of fabric. It might be flat, but is flexible and its used after being pulled into a cyclindrical shape. The exterior is made of a durable material, which holds an inflatable, airtight, interior bladder. The top of the cuff forms the exterior of the cuff, which is wrapped around a body part – usually the upper arm of an adult. The hose connecting the cuff to the device projects from a fitting on the exterior surface. The fastening device is attached to one end of the cuff also to the exterior of the cuff where the cuff overlaps when the cuff is drawn into a cylinder wrapping the limb. The inflatable cuff is the inner layer of the cuff assembly.

Its outer layer has a fastener sewed into the shell. The hose fitting is on the outside so that it will be on the outside of the cuff as it is inflated.

Some home devices use a flexible internal plastic shell which pulls the cuff into a curve around the limb where the cuff is applied. This makes the cuff easier to fit on an arm, and easier to fasten. The shell places enough pressure on the cuff to ensure the cuff contacts the arm.

Fastening

The adhesive hook and loop fastener system, known as Velcro is used in devices built in and after the late 20th century. The hook fabric and the loop fabric are both on the outside of the cuff. The a short section of hooked fabric is at the end of the loop and press into the longer section of loop fabric to close the cuff and hold it in place to focus the pressure on the limb. It is necessary have the cuff contacting the limb, and to close and fasten the cuff.It is not necessary to pull the cuff tight. The cuff will tighten when it is inflated.

Some cuffs, such as the BIOS Diagnostic Easy-Fit BD41RC cuff ¹the cuff does not have a BOA mark and is not held out as a genuine BOA product are assembled into cylinders is secured with devices that use ratcheting dials and wire, like those ²genuine BOA systems are made or licensed by the US firm Boa Technology, Inc. that secure some sporting footwear. It is necessary to press and turn the dial to hold the cuff in contact with the limb and engage the ratcheting mechanism.

Options

Some devices may have a Bluetooth radio to upload data to another device, or other data collection and transmission functions. These features may have value to some users who want to make a more durable record than the limited memory space of the monitor device. However it is unlikely that users will be able to send reading from home devices to medical professionals, who normally would not spend time going through that data or want to store it.

Retail Market

Home monitors are sold as retail consumer products, without prescriptions in the retail sections of pharmacies’ (UK “chemists’) or “drug stores'”. In Victoria, British Columbia, many such stores are part of retail store chains. The chains include London Drugs, Shoppers Drug Mart, Pharmasave, and Rexall. Chain stores and other retain drug stores acquire monitors from wholesale distributors. The brands available include national and international brands and store brands, including :

• Omron an international brand used by the Japanese firm Omron based in Mukō, a city in the Kyoto urban area in the Kyoto prefecture in Japan, manufactured in Vietnam;
• BIOS Diagnostic, a brand used by the Canadian firm Thermor Limited (based in Newmarket, Ontario) for blood pressure monitors and medical electronics. Thermor uses BIOS brands for devices used for personal care including BIOS Medical and BIOS Weather. Thermor was founded as Taylor Instrument Companies of Canada, founded in Toronto,. Ontario before 1939³not to be confused with other brands, companies or business names named “Taylor” including the modern USA firms (1) Taylor Technologies associated with maintaining swimming pools, or (2) Taylor USA, which distributes scales, thermometers and other measuring devices.. The BIOS web presence of Thermor is at the BIOS Medical site . BIOS brand blood pressure monitors are manufactured in China;
• Be Better, a store brand sold in Rexall pharmacies in Canada, manufactured by or for Thermor Limited in China.

Standards

Regulatory & Product Rating

The Canadian federal government and provincial governments do not legislate how home monitors are supposed to be built. The Canadian federal department of health has a list of approved standards, including standards for electromedical devices, a requires persons operating some facilities to hold federal licences. The standards are those of national and international agencies including the Canadian Standards Group (CSA), and the International Electrotechnical Commission (IEC). Many CSA standards are republications of IEC standards. Standard 60601-1, and amendments, addresses General requirements for basic safety and essential performance of electrical medical equipment.

The Canadian advocacy entity Hypertension Canada allowed manufacturers to use Hypertension Canada’s mark on approved devices. As of 2025, the mark indicated that the products was approved.This system replaced a previous system of Gold and Silver marks ⁴At the time “Those with a Gold rating meet the highest and most current international standards, and those with the Silver ratings meet the highest international standards available prior to their most recent updates. (Both Gold and Silver levels are accepted as accurate)”.

Hypertension Canada does not says it has tested samples of rated models. It appears that Hypertension Canada requires manufacturers seeking approval to say that they have processes that manufacture devices that meet the CSA and IEC standards.

Margin of error

Monitors distributed in Canada declare or assert a margin of error in the pressure readings under technical specifications in the manuals packed with the monitors. Examples:

Brand	Model	Term
BIOS	BD410	static accuracy	± 3 mm Hg
Omron	BP7350CAN	accuracy	± 3 mm Hg

Devices from different manufacturers may read and report blood pressure and related facts differently. The differences arise from the way the devices are made and way that users operate the machines. A person (i.e. a patient) may be misinformed, as well as having spent money on a device.

The manual for the BIOS BD410, a good quality oscillometric, automated monitor says: “1.2C Many questions arise when two blood pressure devices are compared in an effort to check accuracy. ….”

Manufacturer Manuals

The manufacturers of home devices distributed in Canada provide instructions to users in manuals on the topics of:

• attaching the cuff,
• posture during readings, and
• the operation of devices.

A manual will suggest the cuff be applied to upper part of the left arm at a distance above the elbow, usually with the inflation tube aligned to the inside of the limb. It may suggest a different place and alignment on the right arm.

A manual will advise taking readings in a quiet place, at the same time, keeping warm, avoiding stress and not taking readings for at least 30 minutes after bathing, consuming alcohol or caffeine, smoking or exercising.

Similar advice can also be found in resources like the Canadian advocacy entity Hypertension Canada’s pamphlet for professionals.

Electromagnetic Fields

The manuals will address some kinds of electrical interference that may affect some operations.

The manual for Omron devices

The manual for the BIOS BD410 recites

1.2B Care of the device

For the prolonged life of your blood pressure monitor, note the following instructions:

…

in the immediate vicinity of mobile phones, microwave appliances or other devices with strong electromagnetic fields may result in impaired functioning.

This does not explain what is the immediate vicinity, or explain what state a smartphone should be in (airplane mode, cellular radio, wifi radio, bluetooth radio on or off, or totally off). It does not address proximity to a wifi router. It does not discuss which appliances have electromagnetic fields. Does a dehumidifier (a device with cooling coils like a refrigerator or air conditioner) have an electromagnetic field?