Both structural and functional evaluations of the endothelium exist in order to diagnose cardiovascular disease (CVD) in its asymptomatic stages. Vascular reactivity, a functional evaluation of the endothelium in response to factors such as occlusion, cold, and stress, in addition to plasma markers, is the most widely accepted test and has been found to be a better predictor of the health of the endothelium than structural assessment tools such as coronary calcium scores or carotid intima-media thickness. Among the vascular reactivity assessment techniques available, digital thermal monitoring (DTM) is a noninvasive technique that measures the recovery of fingertip temperature after 2–5 min of brachial occlusion. On release of occlusion, the finger temperature responds to the amount of blood flow rate overshoot referred to as reactive hyperemia (RH), which has been shown to correlate with vascular health. Recent clinical trials have confirmed the potential importance of DTM as an early stage predictor of CVD. Numerical simulations of a finger were carried out to establish the relationship between DTM and RH. The model finger consisted of essential components including bone, tissue, major blood vessels (macrovasculature), skin, and microvasculature. The macrovasculature was represented by a pair of arteries and veins, while the microvasculature was represented by a porous medium. The time-dependent Navier–Stokes and energy equations were numerically solved to describe the temperature distribution in and around the finger. The blood flow waveform postocclusion, an input to the numerical model, was modeled as an instantaneous overshoot in flow rate (RH) followed by an exponential decay back to baseline flow rate. Simulation results were similar to clinically measured fingertip temperature profiles in terms of basic shape, temperature variations, and time delays at time scales associated with both heat conduction and blood perfusion. The DTM parameters currently in clinical use were evaluated and their sensitivity to RH was established. Among the parameters presented, temperature rebound (TR) was shown to have the best correlation with the level of RH with good sensitivity for the range of flow rates studied. It was shown that both TR and the equilibrium start temperature (representing the baseline flow rate) are necessary to identify the amount of RH and, thus, to establish criteria for predicting the state of specific patient’s cardiovascular health.
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Sensitivity of Digital Thermal Monitoring Parameters to Reactive Hyperemia
Mohammad W. Akhtar,
Mohammad W. Akhtar
Department of Mechanical Engineering,
e-mail: mwakhtar3@uh.edu
University of Houston
, Houston, TX 77204
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Ralph W. Metcalfe,
Ralph W. Metcalfe
Department of Mechanical Engineering,
e-mail: metcalfe@uh.edu
University of Houston
, Houston, TX 77204
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Morteza Naghavi
e-mail: mn@vp.org
Morteza Naghavi
Fairway Medical Technologies, Inc.
, 710 N. Post Oak Road, Suite 204, Houston, TX 77024
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Mohammad W. Akhtar
Department of Mechanical Engineering,
University of Houston
, Houston, TX 77204e-mail: mwakhtar3@uh.edu
Stanley J. Kleis
Ralph W. Metcalfe
Department of Mechanical Engineering,
University of Houston
, Houston, TX 77204e-mail: metcalfe@uh.edu
Morteza Naghavi
Fairway Medical Technologies, Inc.
, 710 N. Post Oak Road, Suite 204, Houston, TX 77024e-mail: mn@vp.org
J Biomech Eng. May 2010, 132(5): 051005 (14 pages)
Published Online: March 25, 2010
Article history
Received:
November 17, 2008
Revised:
December 29, 2009
Posted:
January 28, 2010
Published:
March 25, 2010
Online:
March 25, 2010
Citation
Akhtar, M. W., Kleis, S. J., Metcalfe, R. W., and Naghavi, M. (March 25, 2010). "Sensitivity of Digital Thermal Monitoring Parameters to Reactive Hyperemia." ASME. J Biomech Eng. May 2010; 132(5): 051005. https://doi.org/10.1115/1.4001137
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