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Non Invasive BP Measurement. Medical Physics. History of BP Measurement. 1733 Reverend Stephen Hales first to measure BP Measured the height of a column of blood after cannulating the carotid artery in a horse with a brass pipe. . History of BP Measurement.

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Presentation Transcript
history of bp measurement
History of BP Measurement
  • 1733 Reverend Stephen Hales first to measure BP
  • Measured the height of a column of blood after cannulating the carotid artery in a horse with a brass pipe.

Dr Rishi Mehra

history of bp measurement3
History of BP Measurement
  • The brass pipe was attached to a 12 inch glass tube.
  • Tube was connected to the pipe via trachea of a goose!
  • First to observe respiratory variation and pulsatile nature
  • 100 years later, Poiseuille used a mercury manometer, connected to the artery in a dog to measure BP

Dr Rishi Mehra

history of bp measurement4
History of BP Measurement
  • Both of these methods were invasive
  • First attempts at non-invasive BP measurement began in the late 1800’s

Dr Rishi Mehra

history of bp measurement5
History of BP Measurement
  • In late 1890s, Italian physician – Scipione Riva Rocci invented sphygmomanometer
  • Sphygmos = Pulse (Greek)
  • Manometer = Pressure meter

Dr Rishi Mehra

history of bp measurement6
History of BP Measurement
  • Consisted of mercury column manometer
  • Silk covering a rubber sleeve, which is filled with air
  • Squeeze bag to inflate rubber sleeve

Dr Rishi Mehra

history of bp measurement7
History of BP Measurement
  • 10 years later, a Russian surgeon – Nikolai Korotkoff discovered that sounds were present as cuff was deflated
  • Works on principle that normal blood flow is laminar, and hence silent
  • As cuff pressure drops, some blood begins to flow past compressed area of cuff
  • Blood flow is turbulent, non-laminar and audible

Dr Rishi Mehra

history of bp measurement8
History of BP Measurement
  • This method of measuring BP is called the Auscultatory method
  • Roy and Adami (1890) developed oscillometric method
  • With cuff being deflated, onset of oscillations in mercury height were noted
  • Called onset of oscillations = Systolic BP

Dr Rishi Mehra

history of bp measurement9
History of BP Measurement
  • Maximum oscillations = Diastolic (Nb Incorrect)
  • Hence all indirect BP measurement involves use of Riva-Rocci cuff, either via auscultatory measurement or via oscillometric methods.

Dr Rishi Mehra

automated auscultatory method
Automated Auscultatory Method
  • First automated systems used a microphone to replace need for manual auscultation
  • Analysis of sound produced was used to estimate SBP and DBP
  • Problems with this approach

- External noise can lead to artefact

- Difficulty obtaining BP where sounds may be muted eg hypotension

Dr Rishi Mehra

automated auscultatory method11
Automated Auscultatory Method
  • Method used largely in 1960’s
  • Generally found to be unreliable, and often gave wide variations in BP
  • No longer used in isolation, but is incorporated in several systems in conjunction with oscillometric systems.

Dr Rishi Mehra

automated oscillometric method
Automated Oscillometric Method
  • Oscillometric method involves measuring oscillations
  • Oscillations are a result of application of cuff in order to compress artery
  • Principle of measurement involves tranducer
  • Measuring oscillations over time with decreasing cuff pressure enables estimation of BP

Dr Rishi Mehra

automated oscillometric method14
Automated Oscillometric Method
  • Cuff pressure at point of maximum oscillations is taken to be MAP
  • Various methods of estimating systolic and diastolic BP from MAP
  • Auscultatory method = measure SBP and DBP and estimate MAP
  • Oscillometric method = measure MAP and estimate SBP and DBP

Dr Rishi Mehra

sources of error
Sources of error
  • Cuff size

- Oscillations are direct result of BP cuff application - Cuff too small = overestimation of BP - Cuff too large = underestimation of BP

  • Cuff position – Bladder needs to be placed over brachial artery

Dr Rishi Mehra

sources of error16
Sources of error
  • Movement

Dr Rishi Mehra

sources of error17
Sources of error
  • Beat to beat variation- Oscillometric method requires reasonably stable BP during cuff deflation- Required for detecting maximum aplitude of oscillations- If BP varies due to arrhythmia, difficult to estimate BP accurately

Dr Rishi Mehra

sources of error18
Sources of error
  • Beat to beat variation cont…

Dr Rishi Mehra

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