血壓計原理

Current blood pressure monitors use manual and digital meters, with different trade-offs in accuracy and convenience.

manual

A stethoscope is required for auscultation. Manual meters are best used by a trained practitioner, and while it is possible to obtain a basic reading by palpation alone, this will only produce systolic blood pressure.

  • Mercury sphygmomanometers are considered the gold standard. They indicate pressure as a column of mercury and do not require recalibration. Due to their accuracy, they are frequently used in drug clinical trials and clinical evaluation of high-risk patients, including pregnant women. A commonly used wall-mounted mercury sphygmomanometer is also called a Baumanometer .
  • Aneroid sphygmomanometers (mechanical ones with a dial) are common; unlike mercury manometers, they may require calibration checks. Aneroid sphygmomanometers are considered safer than mercury sphygmomanometers, although cheaper sphygmomanometers are less accurate. A major cause of deviations from calibration is mechanical shock. Aneroids mounted on walls or brackets are less susceptible to this particular problem.

digital

Recent advances in medical technology have paved the way for affordable, easy-to-use digital blood pressure monitors that anyone can use in the comfort of their own home, without the need for specialized knowledge or training.

Digital meters use oscillometric measurements and electronic calculations rather than auscultation. They may use manual or automatic inflation, but both types are electronic, can be operated easily without training, and can be used in noisy environments.

Digital blood pressure monitors use an inflatable balloon cuff, a battery-operated air pump, and a pressure sensor to sense artery wall vibrations to measure arterial blood pressure. This is called the oscillometric method .

They measure systolic and diastolic blood pressure by oscillometric detection, using a deformable membrane, using differential capacitance or differential piezoresistive measurements, and they include a microprocessor. They measure average blood pressure and pulse rate, and obtaining systolic and diastolic blood pressure is less accurate than manual meters, and calibration is an issue. In certain patients, such as those with arteriosclerosis, cardiac arrhythmias, preeclampsia , alternans , and paradoxical pulses , the use of digital oscillometric monitors may not be recommended because their calculations may not be corrected for these conditions. When used by trained personnel, it is best to use an analog sphygmomanometer.

Digital instruments may use cuffs, in order of accuracy and in reverse order of portability and convenience, placed around the upper arm, wrist, or fingers. Recently, a team of researchers at Michigan State University developed a smartphone-based device that uses the oscillometric method to estimate blood pressure. The oscillometric testing methods used give blood pressure readings that differ from those determined by auscultation and vary based on a number of factors such as pulse pressure, heart rate and arterial stiffness, although some instruments are said to also measure arterial stiffness, and some Detect irregular heartbeats.

Measurement technology

Digital blood pressure monitors use an air pump to inflate a cuff around the upper arm or wrist with enough pressure to prevent blood flow in the local aorta. This pressure is then gradually released using a digitally controlled solenoid valve until blood begins to flow through the artery.

The blood pressure measured by the pressure sensor at this time determines the systolic blood pressure. The pulse rate is also sensed at this time. Diastolic blood pressure is determined by measurements taken when blood flow is no longer restricted. This complete measurement cycle is automatically controlled by a microcontroller.

The signal from the pressure sensor is conditioned by an instrumentation amplifier before data conversion by an analog-to-digital converter (ADC). Systolic blood pressure, diastolic blood pressure, and pulse rate are then calculated in the digital domain using algorithms appropriate for the type of monitor and sensor used. The resulting systolic blood pressure, diastolic blood pressure, and pulse rate measurements are displayed on a liquid crystal display (LCD), time-stamped, and stored in non-volatile memory.

operate

Medical student measures brachial artery blood pressure

In humans, the cuff is typically placed smoothly and snugly around the upper arm, at about the same vertical height as the heart, while the subject is seated and supporting the arm. Other placement locations depend on the species and may include flippers or tails. Choosing the correct size cuff for the patient is critical. A cuff that is too small will result in too high a pressure, while a cuff that is too large will result in too low a pressure. For clinical measurements, both arms are typically measured and recorded during the initial consultation to determine if the pressure in one arm is significantly higher than the other. A difference of 10 mm Hg may be a sign of aortic coarctation. If the arms have different readings, the higher reading arm will be used for subsequent readings. The cuff is inflated until the artery is completely occluded.

Using a hand tool, with a stethoscope to the brachial artery, the examiner slowly releases pressure on the cuff at a rate of approximately 2 mm per heart beat. As the pressure in the cuff drops, a "whooshing" or popping sound is heard as blood flow starts flowing again in the artery. The pressure at which this sound begins is recorded and recorded as systolic pressure. Release the cuff pressure further until the sound is no longer heard. This is recorded as diastolic blood pressure. In noisy environments where auscultation is not possible, systolic blood pressure can be read alone by releasing pressure until a radial pulse is palpated. In veterinary medicine, auscultation is rarely useful and palpation or visualization of the pulse distal to the sphygmomanometer is used to detect systolic blood pressure.

Digital instruments use a cuff, which, depending on the instrument, can be placed around the upper arm, wrist, or fingers, and in all cases is raised to the same height as the heart. They inflated the cuff and gradually lowered the pressure in the same way as a manual meter, and measured blood pressure by the oscillometric method.

Review

All comments are moderated before being published

HealthyPIG Magazine

View all
無人機醫療配送:低空經濟下的香港新契機

無人機醫療配送:低空經濟下的香港新契機

  無人機醫療配送:低空經濟下的香港新契機 —— 從健康、醫療金融到商業模式的全球比較與啟示 在香港「低空經濟」監管沙盒下,無人機由數碼港跨海至長洲醫院,約 12 公里航線僅需 18–20 分鐘,相比傳統 45–65 分鐘大幅提速。本文聚焦醫療價值、醫療金融回報與商...
醫管局普通科門診改名「家庭醫學門診」——香港基層醫療新里程?

醫管局普通科門診改名「家庭醫學門診」——香港基層醫療新里程?

  基層醫療 家庭醫學 健康政策 醫管局普通科門診改名「家庭醫學門診」:利與弊、國際比較與香港基層醫療的下一步 醫務衞生局宣佈由 2025 年 10 月 11 日起,將「普通科門診」與「家庭醫學專科門診」統一命名為「家庭醫學門診服務」,74 間普通科門診...
基孔肯雅熱:被伊蚊叮咬後的劇痛病毒 — 病毒、傳播、症狀與防治全解析

基孔肯雅熱:被伊蚊叮咬後的劇痛病毒 — 病毒、傳播、症狀與防治全解析

什麼是基孔肯雅熱? 基孔肯雅熱(Chikungunya Fever)是一種由**基孔肯雅病毒(Chikungunya virus, CHIKV)**引起的急性傳染病,屬於 Togaviridae 家族 Alphavirus 屬。這種病毒最早於 1952 年在坦桑尼亞被發現,其名稱來自當地馬孔德...
登革熱:全球爆發中的熱帶威脅與防護全解析

登革熱:全球爆發中的熱帶威脅與防護全解析

登革熱係乜嘢? 登革熱(Dengue fever)係一種由登革熱病毒(Dengue virus)引起嘅急性傳染病,主要經由伊蚊(Aedes mosquito)叮咬傳播,特別係白紋伊蚊(Aedes albopictus)同埃及伊蚊(Aedes aegypti)。呢啲蚊喺日間最活躍,因此唔似瘧疾嗰...
流感點樣會引致腦病變、心肌炎同休克?——從「感冒」變成致命風暴

流感點樣會引致腦病變、心肌炎同休克?——從「感冒」變成致命風暴

近排有新聞報導,一名原本健康嘅中學生感染乙型流感(Influenza B)之後,出現腦病變、心肌炎同休克,情況危殆。好多家長都會問:「流感唔就係普通感冒?點解可以嚴重到影響腦同心臟?」其實,流感背後嘅機制比我哋想像中複雜得多。 一、流感病毒唔止攻擊呼吸道 流感病毒(包括甲型同乙型)主要透過飛...
牛骨湯食譜大全|Instant Pot 壓力煲 & 傳統老火湯版本

牛骨湯食譜大全|Instant Pot 壓力煲 & 傳統老火湯版本

牛骨湯食譜係香港家庭常見嘅煲湯之一,牛骨湯香濃滋補,配合中藥材更具養生功效。本文介紹肉骨類選擇、牛骨湯建議配搭、常見中藥材分類,以及Instant Pot壓力煲與傳統老火湯版本食譜,並引用科學研究支持。
澳洲飲用水發現「食腦變形蟲」:全球風險與地區對策(含各國/各州實用指南)

澳洲飲用水發現「食腦變形蟲」:全球風險與地區對策(含各國/各州實用指南)

澳洲飲用水發現「食腦變形蟲」:全球風險與地區對策(含各國/各州實用指南) 澳洲飲用水發現「食腦變形蟲」:全球風險與地區對策(含各國/各州實用指南) 重點:事件本身不代表飲水會感染;主要風險來自水經鼻腔進入。 目錄 ...
如何判斷雞翅是否變壞?

如何判斷雞翅是否變壞?

重點摘要 雞翅會變質嗎? 如何判斷雞翅是否變壞? 過期雞翅還能食嗎? 雞翅可存放多久? 如何儲存雞翅? 雞翅可以冷凍嗎? 結論 雞翅會變質嗎? 會。皮脂較多、表面不潔或溫度過高時,細菌繁殖更快。 如何判斷雞翅是否變壞? 外觀:皮色發黃、出黑斑或血水。 觸感:表面黏滑、軟爛。 氣...
如何判斷雞蛋是否變壞?

如何判斷雞蛋是否變壞?

重點摘要 雞蛋會變質嗎? 如何判斷雞蛋是否變壞? 過期雞蛋還能食嗎? 雞蛋可存放多久? 如何儲存雞蛋? 雞蛋可以冷凍嗎? 結論 雞蛋會變質嗎? 會。殼面有微孔,溫差及濕度變化會令細菌入侵。 如何判斷雞蛋是否變壞? 水測:沉底=較新鮮;浮起=多半變壞。 打開觀察:蛋白渾濁水樣、蛋黃...