Blood Pressure

Table of Contents

Updates

This post was first published in 2023 as part of a longer post. It has been edited to focus on blood pressure and republished in 2025

Resources

Wikipedia

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

Advocacy, Charities

The American Heart Association (AHA):

Hypertension Canada:

Circulation & 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. 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 as possible and desirable in the 18th century. By the early decades of the 20th century, measurement of blood pressure was 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. The normal blood pressure, according to older medical literature and most blood pressure monitor manufacturers, of a healthy adult is 120 mmHg systolic and 80 mmHg diastolic, written as 120/80 (spoken as “120 over 80”). Normal is complicated:

“… 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”.

….

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

Measurement is complicated by environmental and psychological factors. Health care professionals recognize white coat hypertension which is studied in reference to the effect of being monitored in a clinical setting and labile hypertension. Labile means changeable and connotes unstable.

Readings play a major role in the diagnosis and treatment of hypertension. 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. This is called elevated or prehypertension in some material. Where elevated readings (>140/>90) appear twice, a medical doctor can diagnose hypertension.

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.

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

Measurement Methods

Health care professionals have used two main main methods of measurement of blood pressure – termed “non-invasive”, because blood vessels are not pierced or penetrated – ausculatory and oscillometric . Both methods, as of the late 20th century, have monitored the air pressure in an airtight bladder contained in inflatable cuffs, held in a fixed position against the body by a fabric shell of the cuff, closed with a fastener.

Ausculatory blood pressure measurement started in the 19th century. The ausculatory method was administered by trained professionals in medical facilities. Medical doctors and nursed used the method to gather data. The stethoscope and the sphygnomanometer were invented and came into use. 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 ausculatory method involved (and still involves, when used):

  1. listening to the the artery – usually the brachial artery, a major artery in the upper arm – with a stethoscope applied to the inside of the limb above the elbow, to detect when blood is flowing,
  2. restricting the flow until the sound was not detected, then releasing it, and
  3. using a sphygnomanometer to measure the pressure in cuff used to restrict the flow in the artery.

Since the early 20th century, for the ausculatory method, the flow in the artery has been been restricted with an inflatable cuff device – at one time a manually inflated pneumatic device. It was wide enough to apply pressure without bruising or injury to the limb, and applied above the elbow. The pressure in the cuff was a measure of the blood pressure. The steps of the process:

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

Oscillations in the circulatory system were noted in medical literature as early as 1876. The oscillometic method was 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.

Oscillometric blood pressure cuffs and meters do not rely on human hearing to detect the sounds in the artery. These devices 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.

The oscillometric method is very accurate. It can be administered without a stethoscope and by automated devices. Its accuracy is subject to the hardware and to electronic and software settings. It has changed the idea of a normal measurement.The standards of normal pressure and unhealthy hypertension are being redefined according to statistical analysis of sample groups of readings among patients with different characteristics.

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. With the oscillometric method the 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 to measure blood pressure in automated devices used in

  1. most medical care facilities and some diagnostic settings, and
  2. for home use for patients to monitor and report blood pressure.

Automated Measurement

Automation

Automated monitor methods are less expensive and time consuming for health care providers. In theory, automated device are self-calibrating, and deliver acceptably accurate readings every time they are used, if:

  • the device is working as the manufacturer says,
  • the cuff is applied properly,
  • the patient is properly seated, has been inactive, and is warm and comfortable.

Automated devices are used in hospitals, clinics and medical offices.

Most home devices are automated. A home device would have these components:

  1. a cuff; with a hose; and
  2. a device containing the pump and various sensors, with an LCD display.

A patient must install the cuff, take the reading and record the result.

Automated meters are also used in ambulatory measurement. These devices are not similar to consumer home use devices.

Home Device Standards- Canada

The Canadian advocacy entity Hypertension Canada allowed manufacturers to use its Gold and Silver marks on product packages at one time, based on whether the manufacturers have standards on tests reported by the manufacturers1“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)”. As of 2025, the rating was simply approved or not approved. The rating process is not transparent. It appears that Hypertension Canada requires manufacturers seeking approval to say that they have processes that meet standards. Ratings made the devices more marketable.

Devices are complicated. The manuals can be confusing. The manuals and support services for these devices, like those of smart phones and laptop computers have fine print that may conceal important limitations. For instance, 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?

Cuffs

The adhesive hook and loop fastener system, known as Velcro is used in devices built in and after the late 20th century. The airtight inflatable cuff is the inner layer of a cuff assembly. Its outer layer has a fastener sewed the outside.

Many home devices use a flexible internal plastic shell between the inner cuff and the outlayer. The shell curves around the limb where the cuff is applied. This makes the cuff easier to fit on an arm, and easier to fasten. It is possible. perhaps easy, to install the cuff incorrectly, leading to incorrect readings.

Manufacturer Training

The manufacturers of home devices do not train home uses directly. They provide detailed instructions to users on 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 ot exercising. Similar advice can also be found in resources like the Canadian advocacy entity Hypertension Canada’s pamphlet for professionals. These instructions are important to get accurate readings.

The display area has an area that flashes as the cuff inflates, and as the cuff deflates. This area may give the systolic reading when the device stops. A separate heartbeat symbol flashes when oscillations are detected as the cuff is inflated, and as the cuff is deflated and the reading is taken, according the design decisions of the manufacturer. Some devices will display icons for “movement error” and irregular heartbeat”. The irregular heart beat icon can be triggered by movement,or when the cuff is not attached properly, or coughs or sneezes.

Feature Envy

Home devices may have several features. Some may have a Bluetooth radio to upload data to another device, or other data collection and transmission functions.

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