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A Sphygmomanometer, blood pressure meter, or blood pressure gage is a device used to measure blood 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. There are 3 types of sphygmomanometers. It is the Aneroid sphygmomanometer, Mercury sphygmomanometer and Digital Sphygmomanometer. Figure 1 below shows an examples SphygmomanometersNames of the parts of aneroid sphygmomanometer

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1)   Aneroid Manometer gauge

2)   Bladder Hose (or Tube)

3)   Air Release valve

4)   Inflation bulb

5)   End Valve

6)   Artery Indicator Label

7)   Cuff

8)   Gauge holder

9)   Range marking

10)        Index marking

11)        Velcro

12)        Cuff size


Names of the parts of the mercury sphygmomanometer

The only difference between an aneroid and mercury sphygmomanometer is that, the measuring unit for the mercury sphygmomanometer is a Mercury manometerIn the figure above, where the arm is placed in and provides the blood pressure readings without needing someone to operate the cuff or listen to the blood flow sounds. The blood pressure readings are displayed on a digital screen.


1.   Function

It can be separated into a four-step functional process Fig 5.


1)   Normal blood flow

2)   After cuff pressure increase à Blood occlusion

3)   First sound after releasing cuff pressure à Systolic

4)   No sound while cuff pressure released à DiastolicBasically, there are two numbers in a blood pressure measurement, it is systolic and the diastolic. An example reading of a blood pressure measurement is about 120/80. To measure the blood pressure, a doctor or nurse will put the cuff around the arm and will pump it using the inflation bulb (for an aneroid and mercury sphygmomanometer). The cuff will be wrapped around the upper arm with the cuff’s lower edge one inch above the antecubital fossa Fig 6.  For a digital sphygmomanometer is automated with a press of a button the cuff is automatically inflated. The reason why this is done, is because to cut off the blood flow usually the brachial artery by the pressure of the cuff. After that press the stethoscope over the brachial artery just below the cuff Fig 6.

 After rapid inflation of the cuff, the pressure is then released by deflating the cuff which can be done by turning the air release valve. This will slowly release the air from the cuff out at a moderate rate (3mm/sec). Now listen with the stethoscope and observe the aneroid dial or the mercury gauge. When the cuff pressure is equivalent to the arterial systolic pressure, blood begins to flow past they cuff which creates audible sounds also known as Korotkoff sounds. Therefore, the first Korotkoff sound heard is the systolic pressure of the patient. The blood will continue flowing until cuff pressure falls below the arterial diastolic pressure. When the Korotkoff sound disappears, it will be recorded as the diastolic pressure for the patient. For example, 120/80 (systolic/diastolic).  

However, in a digital sphygmomanometer, when the cuff is fully inflated no blood flows through the artery. As the cuff is deflated below systolic pressure, the reducing pressure exerted on the artery allows blood to flow through it which will send a vibration through the artery wall which can be detected. When cuff pressure falls below diastolic pressure, blood flows smoothly without any vibration in the artery wall. The vibrations are transferred from the arterial wall through the air in the cuff into a transducer in the monitor which then coverts the measurements into electrical signals. Figure 7 explains the circuitry that enables the digital sphygmomanometer to function as it is.1.   Applications These are some of the reasons why the sphygmomanometer is applied for:-      To measure BP-      To measure the difference in BP in limbs-      To demonstrate postural hypotension. As discussed earlier there are different sphygmomanometers. However, each of the sphygmomanometers have its own restrictions. All three types of sphygmomanometers are used in Hospitals, Clinics, Ambulances, personal use etc. Usually in Hospitals and clinics, an aneroid or mercury sphygmomanometer is used because it is much accurate than the digital sphygmomanometer. Sometimes, doctors & nurses use digital sphygmomanometer first and then use the aneroid or mercury sphygmomanometer to validate the results.   Part B: Hazard Report 1.   Problem Statement Some of the problems faced in use of sphygmomanometers are,  –      Skills of the user who uses the sphygmomanometer-      The variability of blood pressure –      How accurate the device is, which includes limitations and applications –      Difficulty in measuring for different age groups. (Ex. Elderly, patients with large arm etc)  2.   Discussions related to problem Sometimes when the user is using the aneroid or mercury sphygmomanometer, they need to listen and identify the Korotkoff sounds properly. But sometimes There are a lot of errors dude to the user having poor hearing, difficulty in identifying the Korotkoff sounds and lack of concentration. Most of the serious errors are usually wrong interpretation of the Korotkoff sounds and realising the diastolic pressure. The users can also give wrong diagnosis to healthy patients by recording wrong readings of blood pressure.  Aneroid sphygmomanometers easily lose calibration. So, mercury sphygmomanometers are recommended for use and it is considered as gold standard. However, mercury sphygmomanometers are defective because of poor maintenance. Mercury may leak from the gauge which causes underestimation of pressure and cause poisoning if contacted. The interior of the glass tube which holds the mercury might become dirty due to the oxidation of mercury which causes mercury to adhere to tube which results in overestimation of blood pressure. The air vent can be blocked which will block air entry when pressure released leading to overestimation. Inflation-deflation system has problems due to error in control valve which will cause leakage making it difficult to control the release of pressure. Leading to underestimation and overestimation of systolic and diastolic pressure respectively.  3.   Recommendations  –      Oxidised mercury à may be cleaned by filtering or be replaced, the glass tube may be cleaned easily by a pipe cleaner and spirit.-      Leakage à Cleaning the filter or replacing the control valve, may also be caused by perished or punctured rubber tubing, which must be replaced.-      If aneroid sphygmomanometers are used, they must be checked over the entire pressure range against an accurate mercury manometer every three to six months depending on use.-      Use larger cuffs for patients will large arm.-      Don’t place cuff over clothing. –      Users must be well trained and be focussed when using a sphygmomanometer to prevent wrong diagnosis. –      For paediatric patients, use age, sex and height to interpret blood pressure findings.

–      regular inspection, cleaning, testing, replacement of worn parts to prevent faults from occurring, and record?keeping. Maintenance also includes calibration at regular intervals for digital sphygmomanometers.  

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