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Research Papers

Pressure Waves as a Noninvasive Tool for Artery Stiffness Estimation

[+] Author and Article Information
E. El-Aklouk

Institute of Biomedical Technologies, Auckland University of Technology, Auckland 1010, New Zealand

A. M. Al-Jumaily

Institute of Biomedical Technologies, Auckland University of Technology, Auckland 1010, New Zealandahmed.al-jumaily@aut.ac.nz

A. Lowe

 Pulsecor Ltd., Auckland 1061, New Zealand

J. Med. Devices 2(2), 021001 (May 08, 2008) (8 pages) doi:10.1115/1.2918739 History: Received August 19, 2007; Revised March 03, 2008; Published May 08, 2008

In hypertension and aging, central elastic arteries become stiffer and hence the central pulse pressure is augmented due to the increase in the pulse wave velocity and the early return of reflected waves to the heart from the periphery. Valuable information on arterial properties, such as stiffness, can be obtained from both central (aortic) and peripheral (radial) pressure wave forms. A feasibility study for the noninvasive estimation of arterial stiffness using pressure waves detected by a pneumatic cuff wrapped around the upper arm is presented. The propagation and reflection of arterial pressure waves (generated by the heart) in the central elastic arteries are simulated using a simplified water hammer acoustic model. Furthermore, a lumped parameter model is used to describe the transmission of the pressure waves from the brachial artery to the cuff external wall. By combining the two models, we were able to simulate the pressure contours in the brachial artery and illustrate how these pressures transmit to the cuff’s external wall. The effects of aortic stiffness are investigated by simulating the model at different values of aortic elastic moduli and observing the pressure augmentation and the timing of feature points. This work was done as part of the development of a noninvasive diagnostic device by Pulsecor Ltd. The model results obtained in this work are in agreement with published experimental results and the device output; hence, the model can be used to develop the device’s stiffness estimation algorithm.

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Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Power function describing the human aorta thickness variation and a linear function describing the thickness variations along the subclavian and brachial arteries

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Figure 2

Power function describing the human aorta radius variations and a linear function describing the human subclavian and brachial artery radius variations

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Figure 3

Pressure wave traveling time versus number of segments

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Figure 4

A schematic figure showing conditions at a bifurcation

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Figure 5

A schematic of the upper arm with a pneumatic cuff wrapped around it

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Figure 6

A schematic diagram showing the propagation and reflection of pressure waves in the system. The red arrows show the waves arriving to the brachial artery.

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Figure 7

Suprasystolic left ventricle wave form used as an input to the ascending aorta

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Figure 8

Model simulation of the strain on the pneumatic cuff outer wall contours at different aortic stiffness values ranging from healthy (75% of average stiffness for young healthy subjects) to diseased (400% the average stiffness for young healthy subjects)

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Figure 9

The effect of variations in aortic stiffness on the brachial AI; the stiffness is relative to a normal value for a healthy young male

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Figure 10

The effect of variations in aortic stiffness on the time lag between the upstroke of the incident wave and the arrival of the reflected wave in both the pressure and strain contours

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Figure 11

Strain contours obtained from the Pulsecor device for three individuals of different age

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Figure 12

A comparison between experimental and model PWV versus aortic stiffness and patient’s age

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