Use of Relaxation Time as a Marker for Arterial

Distensibility

C.C. Winchester, N.-Y. Chou, and L.W. WinchesterUniversity of Mary Washington, Fredericksburg, VA, USA

CW Optics, Inc., Seaford, VA, USA

EMBS 2008

Patent Pending

Arterial Distensibility and Cardiovascular Disease

• Distensibility: arterial distension/pulse pressure• Associated with a number of cardiovascular

risk factors• Early detection

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Current Methods of Assessing Arterial Distensibility

• Ankle Brachial Index (ABI)

• Intima-Media Thickness (IMT)• Flow-Mediated Dilation (FMD)

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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

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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

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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

xxxx ttBAtY /exp)( 0

Y delay time

A constant

B maximum time delay before raising the arm

t0 time where subject raised right arm

τx relaxation 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: undetermined

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• r: radius; 4.46 mm (Betik et al.)

• v: velocity

• 1: control; before raising the arm

• 2: after raising the arm

Constant Flow

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222

211 rvrvFlow

Betik, A.C., V.B. Luckham, and R.L. Hughson. Flow-mediated dilation in human brachial artery after different circulatory occlusion conditions. Am J Physiol Heart Circ Physiol 286: H442-H448, 2004.

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.

21 V

L

V

LT

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Comparison with FMD

•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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Betik, A.C., V.B. Luckham, and R.L. Hughson. Flow-mediated dilation in human brachial artery after different circulatory occlusion conditions. Am J Physiol Heart Circ Physiol 286: H442-H448, 2004.

Pyke, K.E., E.M. Dwyer, and M.E. Tschakovsky. Impact of controlling shear rate on flow-mediated dilation responses in the brachial artery of humans. J Appl Physiol 97: 499-508, 2004.

Stoner, L., M. Sabatier, K. Edge, and K. McCully. Relationship between blood velocity and conduit artery diameter and the effects of smoking on vascular responsiveness. J Appl Physiol 96: 2139-2145, 2004.

Clinical Applications/Future Work

• The extent of which venous emptying stimulates arterial dilation

• In-office measurements• 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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