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Jai Ganesh

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Sphygmomanometer

Sphygmomanometer

Gist

A sphygmomanometer is used to indirectly measure arterial blood pressure. Sphygmomanometry is the process of manually measuring one's blood pressure. Aneroid sphygmomanometer with an adult cuff. This is the blood pressure cuff that one would see in the Doctor's office, or in a medical clinical/setting.

A sphygmomanometer is used to measure blood pressure. It is a vital tool for assessing cardiovascular health and is used to detect conditions like hypertension (high blood pressure) or hypotension (low blood pressure).

Summary

A sphygmomanometer is an instrument for measuring blood pressure. It consists of an inflatable rubber cuff, which is wrapped around the upper arm and is connected to an apparatus that records pressure, usually in terms of the height of a column of mercury or on a dial (an aneroid manometer). An arterial blood pressure reading consists of two numbers, which typically may be recorded as x/y. The x is the systolic pressure, and y is the diastolic pressure. Systole refers to the contraction of the ventricles of the heart, when blood is forced from the heart into the pulmonary and systemic arterial circulation, and diastole refers to the resting period, when the ventricles expand and receive another supply of blood from the atria. At each heartbeat, blood pressure is raised to the systolic level, and, between beats, it drops to the diastolic level. As the cuff is inflated with air, a stethoscope is placed against the skin at the crook of the arm. As the air is released, the first sound heard marks the systolic pressure; as the release continues, a dribbling noise is heard. This marks the diastolic pressure, which is dependent on the elasticity of the arteries.

The first clinically applicable sphygmomanometer was invented in 1881 by Austrian physician Karl Samuel Ritter von Basch. Von Basch introduced the aneroid manometer, which uses a round dial that provides a pressure reading. The pressure is indicated by a needle, which is deflected by air from an inflation device (e.g., a diaphragm or Bourdon tube).

Details

A sphygmomanometer, also known as a blood pressure monitor, blood pressure machine, or blood pressure gauge, is a device used to measure blood pressure, composed of an inflatable cuff to collapse and then release the artery under the cuff in a controlled manner,[1] and a mercury or aneroid manometer to measure the pressure. Manual sphygmomanometers are used with a stethoscope when using the auscultatory technique.

A sphygmomanometer consists of an inflatable cuff, a measuring unit (the mercury manometer, or aneroid gauge), and a mechanism for inflation which may be a manually operated bulb and valve or a pump operated electrically.

History

The sphygmomanometer was invented by Samuel Siegfried Karl Ritter von Basch in the year 1881. Scipione Riva-Rocci introduced a more easily-usable version in 1896. In 1901, pioneering neurosurgeon Dr. Harvey Cushing brought an example of Riva-Rocci's device to the US, modernized and popularized it within the medical community. Further improvement came in 1905 when Russian physician Nikolai Korotkov included diastolic blood pressure measurement following his discovery of "Korotkoff sounds". William A. Baum invented the Baumanometer brand in 1916, while working for The Life Extension Institute which performed insurance and employment physicals.

Types

Both manual and digital meters are currently employed, with different trade-offs in accuracy versus convenience.

Manual

A stethoscope is required for auscultation. Manual meters are best used by trained practitioners, and, while it is possible to obtain a basic reading through palpation alone, this yields only the systolic pressure.

* Mercury sphygmomanometers are considered the gold standard. They indicate pressure with a column of mercury, which does not require recalibration. Because of their accuracy, they are often used in clinical trials of drugs and in clinical evaluations of high-risk patients, including pregnant women. A frequently used wall mounted mercury sphygmomanometer is also known as a Baumanometer.
* Aneroid sphygmomanometers (mechanical types with a dial) are in common use; they may require calibration checks, unlike mercury manometers. Aneroid sphygmomanometers are considered safer than mercury sphygmomanometers, although inexpensive ones are less accurate. A major cause of departure from calibration is mechanical jarring. Aneroids mounted on walls or stands are not susceptible to this particular problem.

Digital

Digital meters employ oscillometric measurements and electronic calculations rather than auscultation. They may use manual or automatic inflation, but both types are electronic, easy to operate without training, and can be used in noisy environments. They calculate systolic and diastolic pressures by oscillometric detection, employing either deformable membranes that are measured using differential capacitance, or differential piezoresistance, and they include a microprocessor. They estimate mean arterial blood pressure and measure pulse rate; while systolic and diastolic pressures are obtained less accurately than with manual meters, and calibration is also a concern. Digital oscillometric monitors may not be advisable for some patients, such as those with arteriosclerosis, arrhythmia, preeclampsia, pulsus alternans, and pulsus paradoxus, as their calculations may not be correct for these conditions, and in these cases, an analog sphygmomanometer is preferable when used by a trained person.

Digital instruments may use a cuff placed, in order of accuracy and inverse order of portability and convenience, around the upper arm, the wrist, or a finger. Recently, a group of researchers at Michigan State University developed a smartphone based device that uses oscillometry to estimate blood pressure. The oscillometric method of detection used gives blood pressure readings that differ from those determined by auscultation, and vary according to many factors, such as pulse pressure, heart rate and arterial stiffness, although some instruments are claimed also to measure arterial stiffness, and some can detect irregular heartbeats.

Operation

In humans, the cuff is normally placed smoothly and snugly around an upper arm, at roughly the same vertical height as the heart while the subject is seated with the arm supported. Other sites of placement depend on species and may include the flipper or tail. 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. For clinical measurements it is usual to measure and record both arms in the initial consultation to determine if the pressure is significantly higher in one arm than the other. A difference of 10 mmHg may be a sign of coarctation of the aorta. If the arms read differently, the higher reading arm would be used for later readings. The cuff is inflated until the artery is completely occluded.

With a manual instrument, listening with a stethoscope to the brachial artery, the examiner slowly releases the pressure in the cuff at a rate of approximately 2 mmHg per heart beat. As the pressure in the cuffs falls, a "whooshing" or pounding sound is heard 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), 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.

Digital instruments use a cuff which may be placed, according to the instrument, around the upper arm, wrist, or a finger, in all cases elevated to the same height as the heart. They inflate the cuff and gradually reduce the pressure in the same way as a manual meter, and measure blood pressures by the oscillometric method.

Significance

By observing the mercury in the column, or the aneroid gauge pointer, while releasing the air pressure with a control valve, the operator notes the values of the blood pressure in mmHg. The peak pressure in the arteries during the cardiac cycle is the systolic pressure, and the lowest pressure (at the resting phase of the cardiac cycle) is the diastolic pressure. A stethoscope, applied lightly over the artery being measured, is used in the auscultatory method. Systolic pressure (first phase) is identified with the first of the continuous Korotkoff sounds. Diastolic pressure 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 (high blood pressure), and in many other healthcare scenarios.

Additional Information:

Introduction

A sphygmomanometer is used to indirectly measure arterial blood pressure. Sphygmomanometry is the process of manually measuring one's blood pressure.

The sphygmomanometer consists of  :

* An inflatable arm cuff
* A bulb pump for pumping air into the cuff, and a valve for letting air out of the cuff
* A column of mercury, to display the changing pressure
* A pressure meter/dial (manometer), which measures the air pressure, with the help of the rising mercury

In addition to the sphygmomanometer, a stethoscope is also used to listen to the sounds of blood flowing through the brachial artery.  See the auscultation page for guidelines on proper placement and usage of the stethoscope.

Definitions

Blood Pressure: Pressure exerted on the walls of blood vessels while blood is moving through the body. This is measured in mmHg and displayed as 'systolic blood pressure/diastole blood pressure' (mmHg).

Normal blood pressure values are around 120/80mmHg . If values are below 90/60mmHg, that would be considered low blood pressure (hypotension). Blood pressure values above 140/90 mmHg would be considered high blood pressure, and is classified as hypertension. If it is 180/120mmHg, that is dangerously high and would require medical attention.

* Systole: The contraction phase of the cardiac cycle, when the heart fills with blood.
* Diastole: The relaxation phase of the cardiac cycle, when the heart empties the blood.
* Systolic Pressure: Pressure that is exerted on the arteries as blood is leaving the heart during ventricular systole.
* Diastolic Pressure: Pressure that is exerted on the arteries during ventricular relaxation (diastole).

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