Sphygmomanometer
Overview
 
A sphygmomanometer or blood pressure meter is a device used to measure blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...

, comprising an inflatable cuff
Cuff
A cuff is an extra layer of fabric at the lower edge of the sleeve of a garment covering the arms. In US usage the word may also refer to the end of the leg of a pair of trousers...

 to restrict blood flow, and a mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just starting, and at what pressure it is unimpeded. Manual sphygmomanometers are used in conjunction with a stethoscope
Stethoscope
The stethoscope is an acoustic medical device for auscultation, or listening to the internal sounds of an animal body. It is often used to listen to lung and heart sounds. It is also used to listen to intestines and blood flow in arteries and veins...

.

The word comes from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 sphygmós (pulse), plus the scientific term manometer (pressure meter).
Encyclopedia
A sphygmomanometer or blood pressure meter is a device used to measure blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...

, comprising an inflatable cuff
Cuff
A cuff is an extra layer of fabric at the lower edge of the sleeve of a garment covering the arms. In US usage the word may also refer to the end of the leg of a pair of trousers...

 to restrict blood flow, and a mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just starting, and at what pressure it is unimpeded. Manual sphygmomanometers are used in conjunction with a stethoscope
Stethoscope
The stethoscope is an acoustic medical device for auscultation, or listening to the internal sounds of an animal body. It is often used to listen to lung and heart sounds. It is also used to listen to intestines and blood flow in arteries and veins...

.

The word comes from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 sphygmós (pulse), plus the scientific term manometer (pressure meter). The device was invented by Samuel Siegfried Karl Ritter von Basch in 1881. Scipione Riva-Rocci
Scipione Riva-Rocci
Scipione Riva-Rocci was an Italian internist and pediatrician who was a native of Almese. He earned his medical degree in 1888 from the University of Turin, and from 1900 until 1928 was director of the hospital in Varese.He developed an easy to use version of the sphygmomanometer...

 introduced a more easily used version in 1896. In 1901, Harvey Cushing modernized the device and popularized it within the medical community.

A sphygmomanometer consists of an inflatable cuff, a measuring unit (the mercury manometer, or aneroid gauge), and inflation bulb and valve, for manual instruments.

Operation

In humans, the cuff is normally placed smoothly and snugly around an upper arm
Arm
In human anatomy, the arm is the part of the upper limb between the shoulder and the elbow joints. In other animals, the term arm can also be used for analogous structures, such as one of the paired forelimbs of a four-legged animal or the arms of cephalopods...

, at roughly the same vertical height as the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

 while the subject is seated with the arm supported. Other sites of placement depend on species, and may include the tongue, flipper, tail or teat. It is essential that the correct size of cuff is selected for the patient. Too small a cuff results in too high a pressure, while too large a cuff results in too low a pressure. The cuff is inflated until the artery
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....

 is completely occluded
Vascular occlusion
Vascular occlusion is a sudden blockage of a blood vessel, usually with a clot. It differs from thrombosis in that it can be used to describe any form of blockage, not just one formed by a clot. When it occurs in a major vein, it can, in some cases, cause deep vein thrombosis. The condition is...

. Listening with a stethoscope
Stethoscope
The stethoscope is an acoustic medical device for auscultation, or listening to the internal sounds of an animal body. It is often used to listen to lung and heart sounds. It is also used to listen to intestines and blood flow in arteries and veins...

 to the brachial artery
Brachial artery
The brachial artery is the major blood vessel of the arm.It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa at the elbow. It then divides into the radial and ulnar arteries...

 at the elbow, the examiner slowly releases the pressure in the cuff. As the pressure in the cuffs falls, a "whooshing" or pounding sound is heard (see Korotkoff sounds
Korotkoff sounds
Korotkoff are the sounds that medical personnel listen for when they are taking blood pressure using a non-invasive procedure. They are named after Dr. Nikolai Korotkoff, a Russian physician who described them in 1905, when he was working at the Imperial Medical Academy in St...

) when blood flow first starts again in the artery. The pressure at which this sound began is noted and recorded as the systolic blood pressure. The cuff pressure is further released until the sound can no longer be heard. This is recorded as the diastolic blood pressure. In noisy environments where auscultation is impossible (such as the scenes often encountered in emergency medicine
Emergency medicine
Emergency medicine is a medical specialty in which physicians care for patients with acute illnesses or injuries which require immediate medical attention. While not usually providing long-term or continuing care, emergency medicine physicians diagnose a variety of illnesses and undertake acute...

), systolic blood pressure alone may be read by releasing the pressure until a radial pulse is palpated (felt). In veterinary medicine, auscultation is rarely of use, and palpation or visualization of pulse distal to the sphygmomanometer is used to detect systolic pressure.

Significance

By observing the mercury in the column while releasing the air pressure with a control valve, one can read the values of the blood pressure in mm Hg. The peak pressure in the arteries during the cardiac cycle
Cardiac cycle
The cardiac cycle is a term referring to all or any of the events related to the flow or blood pressure that occurs from the beginning of one heartbeat to the beginning of the next. The frequency of the cardiac cycle is described by the heart rate. Each beat of the heart involves five major stages...

 is the systolic pressure, and the lowest pressure (at the resting phase of the cardiac cycle) is the diastolic pressure. A stethoscope is used in the auscultatory method. Systolic pressure (first phase) is identified with the first of the continuous Korotkoff sounds. Diastolic is identified at the moment the Korotkoff sounds disappear (fifth phase).

Measurement of the blood pressure is carried out in the diagnosis and treatment of hypertension
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...

 (high blood pressure), and in many other healthcare scenarios.

Types

There are three types of sphygmomanometers:
  • Digital
    Digital
    A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...

     with manual or automatic inflation. These are electronic, easy to operate, and practical in noisy environments. They measure mean arterial pressure
    Mean arterial pressure
    The mean arterial pressure is a term used in medicine to describe an average blood pressure in an individual. It is defined as the average arterial pressure during a single cardiac cycle.-Calculation:...

     (MAP) and use oscillometric detection to calculate systolic and diastolic values. In this sense, they do not actually measure the blood pressure, but rather derive the readings. Digital oscillometric monitors are also confronted with "special conditions" for which they are not designed to be used: arteriosclerosis
    Arteriosclerosis
    Arteriosclerosis refers to a stiffening of arteries.Arteriosclerosis is a general term describing any hardening of medium or large arteries It should not be confused with "arteriolosclerosis" or "atherosclerosis".Also known by the name "myoconditis" which is...

    ; arrhythmia; preeclampsia; pulsus alternans
    Pulsus alternans
    Pulsus alternans is a physical finding with arterial pulse waveform showing alternating strong and weak beats. It is almost always indicative of left ventricular systolic impairment, and carries a poor prognosis.-Pathophysiology:...

    ; and pulsus paradoxus
    Pulsus paradoxus
    In medicine, a pulsus paradoxus , also paradoxic pulse or paradoxical pulse, is defined as an exaggeration of the normal variation during the inspiratory phase of respiration, in which the blood pressure declines as one inhales and increases as one exhales...

    . In a recent study of non-invasive blood pressure measuring devices a digital cuff device (Omron R3) was found to be more accurate than the mercury manometer and stethoscope (traditionally used for blood pressure measurement) when compared to intra-arterial measurement. While the oscillometric wrist cuff device was shown to overestimate high diastolic pressure and underestimate high systolic pressure the report concluded that it measured "arterial blood pressure with great accuracy and reproducibility".
  • Digital portable finger
    Finger
    A finger is a limb of the human body and a type of digit, an organ of manipulation and sensation found in the hands of humans and other primates....

     blood pressure monitors with automatic inflation. These are more portable and easy to operate, although less accurate. They are the smallest blood pressure monitors.
  • Manual. Ideally operated by a trained person, mercury manometers are considered to be the gold standard
    Gold standard (test)
    In medicine and statistics, gold standard test refers to a diagnostic test or benchmark that is the best available under reasonable conditions. It does not have to be necessarily the best possible test for the condition in absolute terms...

     and cannot be decalibrated , they are consistently accurate. Due to their accuracy, they are often required in clinical trial
    Clinical trial
    Clinical trials are a set of procedures in medical research and drug development that are conducted to allow safety and efficacy data to be collected for health interventions...

    s of pharmaceuticals and for clinical evaluations of determining blood pressure for high risk patients including pregnant women. Aneroid
    Aneroid
    Aneroid may mean*The village of Aneroid, Saskatchewan*"without fluid", particularly in reference to barometers...

    , (mechanical types with a dial) are in common use but they require regular calibration checks, unlike a mercury manometer. The prime reason for such maintenance is their susceptibility to bumps which can alter their accuracy. Wall mounted and mobile aneroids avoid this shortcoming. The aneroid sphygmomanometer should be checked for accuracy (usually every 6 months)by using a mercury manometer, as the gold standard. The unit of measurement of blood pressure is millimeters of mercury (mmHg) and are usually given as an even number. Manual sphygmomanometers require a stethoscope for auscultation
    Auscultation
    Auscultation is the term for listening to the internal sounds of the body, usually using a stethoscope...

    . Although it is possible to obtain a basic reading through palpation, this only yields the systolic number.
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