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 EMBS 20087

Data Analysis Savitzky-Golay fourth-order filtering technique Peak detection algorithm Computed time delays EMBS 20088

Both Hands at Heart LevelRight Arm Raised EMBS 20089

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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. EMBS

Subject Characteristics Normotensive –6 female, 4 male –Ages Hypertensive –4 male –3 overweight, 1 with pacemaker EMBS

Computations Delay times were fitted to the equation below Ydelay time Aconstant Bmaximum time delay before raising the arm T 0 time where subject raised arm Τ x relaxation time EMBS

Results Normal τ P : 78.8 ± s Hypertensive τ P : 584 ± 116 s Normal τ V : ± s Hypertensive τ V : unable to determine EMBS

r: radius; 4.46 mm (Betik et al.) v: velocity 1: control; before raising the arm 2: after raising the arm Constant Flow EMBS

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. EMBS

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

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

Acknowledgments CW Optics, Inc Volunteer subjects EMBS