Use of relaxation time as a marker for arterial distensibility
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Use of Relaxation Time as a Marker for Arterial Distensibility. C.C. Winchester, N.-Y. Chou, and L.W. Winchester University of Mary Washington, Fredericksburg, VA, USA CW Optics, Inc., Seaford, VA, USA. EMBS 2008. Arterial Distensibility and Cardiovascular Disease.

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Use of Relaxation Time as a Marker for Arterial Distensibility

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Use of relaxation time as a marker for arterial distensibility

Use of Relaxation Time as a Marker for Arterial Distensibility

C.C. Winchester, N.-Y. Chou, and L.W. Winchester

University of Mary Washington, Fredericksburg, VA, USA

CW Optics, Inc., Seaford, VA, USA

EMBS 2008


Arterial distensibility and cardiovascular disease

Arterial Distensibility and Cardiovascular Disease

  • Distensibility: arterial distension/pulse pressure

  • Associated with a number of cardiovascular risk factors

  • Early detection

EMBS 20082


Use of relaxation time as a marker for arterial distensibility

EMBS 20083


Current methods of assessing arterial distensibility

Current Methods of Assessing Arterial Distensibility

  • Ankle Brachial Index (ABI)

  • Intima-Media Thickness (IMT)

  • Flow-Mediated Dilation (FMD)

EMBS 20084


Arterial relaxation time

Arterial Relaxation Time

  • The time it takes to relax to the baseline diameter

  • Uses timing measurements of the pulse waves to infer the conditions of peripheral arteries

EMBS 20085


Protocol

Protocol

  • Two different sensors, piezoelectric and photoelectric, on each hand

  • Collect baseline data with hands at heart-level

  • Arm raised while data were collected for another 400 s

EMBS 20086


Data collection

Data Collection

  • Sensors connected to storage oscilloscope

  • Oscilloscope connected to computer

  • >1kHz acquisition rate

EMBS 20087


Data analysis

Data Analysis

  • Savitzky-Golay fourth-order filtering technique

  • Peak detection algorithm

  • Computed time delays

EMBS 20088


Use of relaxation time as a marker for arterial distensibility

Both Hands at Heart Level

Right Arm Raised

EMBS 20089


Use of relaxation time as a marker for arterial distensibility

EMBS 200810


Observations

Observations

  • Decreased blood velocity in the right arm and a delay in pulse waveform in that arm as compared to the left arm (control)

  • After sudden dilation, brachial artery relaxes back to its normal condition as indicated by the delay approaching that of the baseline.

EMBS 200811


Subject characteristics

Subject Characteristics

  • Normotensive

    • 6 female, 4 male

    • Ages 19-60

  • Hypertensive

    • 4 male

    • 3 overweight, 1 with pacemaker

EMBS 200812


Computations

Computations

  • Delay times were fitted to the equation below

Ydelay time

Aconstant

Bmaximum time delay before raising the arm

T0time where subject raised arm

Τxrelaxation time

EMBS 200813


Results

Results

  • Normal τP: 78.8 ± 15.60 s

  • Hypertensive τP: 584 ± 116 s

  • Normal τV: 50.45 ± 16.28 s

  • Hypertensive τV: unable to determine

EMBS 200814


Constant flow

Constant Flow

  • r: radius; 4.46 mm (Betik et al.)

  • v: velocity

  • 1: control; before raising the arm

  • 2: after raising the arm

EMBS 200815


Time delay

Time Delay

Using the measured time delay and an estimated length of the brachial artery(35 cm), the relationship between V1 and V2 can be determined.

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Comparison with fmd

Comparison with FMD

  • a dilation of 3% is computed

  • In agreement with values of 3% to 8% obtained from ultrasound measurements (Pyke et al., Betik et al., Stoner et al.)

EMBS 200817


Clinical applications future work

Clinical Applications/Future Work

  • The extent of which venous emptying stimulates arterial dilation

  • Routinely conducted and reviewed in-office measurements

  • Regularly conducted to monitor pre-atherosclerotic patients and other at risk patients

  • Larger study to investigate relaxation time pre-hypertensive subjects

EMBS 200818


Acknowledgments

Acknowledgments

  • CW Optics, Inc

  • Volunteer subjects

EMBS 200819


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