OSCILLOMETRIC NONINVASIVE BLOOD PRESSURE MEASUREMENTS: THE INFLUENCE OF EXTERNAL ARTIFACTS

1
OSCILLOMETRIC NONINVASIVE BLOOD PRESSURE
MEASUREMENTS THE INFLUENCE OF EXTERNAL
ARTIFACTS

• V. Jazbinsek, J. Luznik, S. Mieke and Z.
  Trontelj
• Institute of Mathematics, Physics and Mechanics,
  University of Ljubljana, Ljubljana, Slovenia
• Physikalisch-Technische Bundesanstalt, Berlin,
  Germany

2
Introduction

• Non-invasive blood pressure (NIBP) measuring
  devices are based on recording the arterial
  pressure pulsations in an inflated cuff wrapped
  around a limb during the cuff pressure deflation.
  
• The recorded NIBP data contains the pressure
  pulses in the cuff, called oscillometric pulses,
  superimposed on the cuff pressure deflation.

3
Objective

• to separate the deflation and external artifacts
  from the pressure pulses and to obtain the
  typical shapes of pressures changes in the cuff
  due to those artifacts

4
Measurements

• EU-project Simulator for NIBP
• Compressor for the cuff inflation and a sensor
  for pressure detection, built in a PC (LODE, NL)
• 25 healthy volunteers took part in this research

5
Measurement

• Measured data Arterial pressure pulses, called
  oscillometric pulses, superimposed on the cuff
  pressure deflation.
• Filtered pulsesDeflation can be removed from
  data by the digital high pass filtering.
  Subtraction of negative envelope (curve defined
  by blue dots) leads to
• Oscillometric pulsesThe waveform describing the
  pulse amplitudes (red dots) as a function of the
  cuff pressure is a base for automated
  determination of the systolic and diastolic
  pressures.

6
Data presentation

• Segmentation of data (red) into pulses (blue
  vert. lines)

• The deflation signal is calculated by the
  interpolation of data between subsequent segment
  borders (green)

• Subtraction of deflation from the measured data
  to obtain only pulses with positive deflections
  (oscillometric pulses - black)

7
Extraction of tapping artifact
Mesurements tapping on the cuff with a plastic
tube every 2 s Segmentation of artefact was
obtained from filtered data (band pass 2.5-250
HZ) by selecting 0.7 s time interval around the
artefact peak.
8
Typical shapes of high frequency artifacts
Averaging of tapping artifacts
9
Projection into normalized heart beat view
reference waveform
10
Subtraction of reference waveform

• 3rd recording
• Subtracted reference using waveform optimization
  (WO)
• Subtracted reference using single beat
  optimization (SBO)

11
Extraction of fist closing artifact
Mesurements fist closing every 5 s
12
Typical shapes of low frequency artifacts
13
Conclusion I

• High frequency artifacts (tapping, vibrations)
  can be exctracted by applying digital fitering

14
Conclusion II

• Low frequency artifacts (moving) extraction
  require
• Transformation into heartbeat view to obtain the
  reference signal.
• Reference can be applied as a template to extract
  a normal oscillometric waveform used for
  automated determination of systolic and diastolic
  pressures.
• Subtraction of normalized oscillometric waveform
  from contaminated data.
• Averaging of extracted artifacts to obtain
  typical shape.