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

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

  • Distensibility: arterial distension/pulse pressure

  • Associated with a number of cardiovascular risk factors

  • Early detection

EMBS 20082


EMBS 20083


Current Methods of Assessing Arterial Distensibility

  • Ankle Brachial Index (ABI)

  • Intima-Media Thickness (IMT)

  • Flow-Mediated Dilation (FMD)

EMBS 20084


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

  • 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

  • Sensors connected to storage oscilloscope

  • Oscilloscope connected to computer

  • >1kHz acquisition rate

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Data Analysis

  • Savitzky-Golay fourth-order filtering technique

  • Peak detection algorithm

  • Computed time delays

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Both Hands at Heart Level

Right Arm Raised

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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.

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Subject Characteristics

  • Normotensive

    • 6 female, 4 male

    • Ages 19-60

  • Hypertensive

    • 4 male

    • 3 overweight, 1 with pacemaker

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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

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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

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Constant Flow

  • r: radius; 4.46 mm (Betik et al.)

  • v: velocity

  • 1: control; before raising the arm

  • 2: after raising the arm

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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

  • 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.)

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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

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Acknowledgments

  • CW Optics, Inc

  • Volunteer subjects

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