Use of Relaxation Time as a Marker for Arterial Distensibility

1. 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 Patent Pending EMBS 2008

2. Arterial Distensibility and Cardiovascular Disease • Distensibility: arterial distension/pulse pressure • Associated with a number of cardiovascular risk factors • Early detection EMBS 2008 2

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4. Current Methods of Assessing Arterial Distensibility • Ankle Brachial Index (ABI) • Intima-Media Thickness (IMT) • Flow-Mediated Dilation (FMD) EMBS 2008 4

5. 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 2008 5

6. 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 2008 6

7. Data Collection • Sensors connected to storage oscilloscope • Oscilloscope connected to computer • >1kHz acquisition rate EMBS 2008 7

8. Data Analysis • Savitzky-Golay fourth-order filtering technique • Peak detection algorithm • Computed time delays EMBS 2008 8

9. Both Hands at Heart Level Right Arm Raised EMBS 2008 9

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11. 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 2008 11

12. Subject Characteristics • Normotensive • 6 female, 4 male • Ages 19-60 • Hypertensive • 4 male • 3 overweight, 1 with pacemaker EMBS 2008 12

13. Computations • Delay times were fitted to the equation below Y delay time A constant B maximum time delay before raising the arm t0 time where subject raised right arm τx relaxation time EMBS 2008 13

14. Results • NormalτP: 78.8 ± 15.60 s • HypertensiveτP: 584 ± 116 s • Normal τV: 50.45 ± 16.28 s • Hypertensive τV: undetermined EMBS 2008 14

15. Constant Flow • r: radius; 4.46 mm (Betik et al.) • v: velocity • 1: control; before raising the arm • 2: after raising the arm 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. EMBS 2008 15

16. 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 2008 16

17. 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.) 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. EMBS 2008 17

18. 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. EMBS 2008 18

19. Acknowledgments CW Optics, Inc Volunteer subjects EMBS 2008 19