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1. Relations of Radial Vibration of the Arterial Wall to Pulsatile Parameters in Blood Flow for Extraction of Arterial Indices

   https://doi.org/10.1115/1.4055390  

   Hao, Zhili (February 2023, Journal of Engineering and Science in Medical Diagnostics and Therapy)

   Abstract Given the wide utility of radial vibration of the arterial wall for clinical values, this paper presents a theoretical study on the relations of radial vibration of the arterial wall to pulsatile parameters in blood flow. Pulse wave propagation in an artery is formulated as a combination of the governing equations of blood flow and the arterial wall and no-slip conditions at the blood-wall interface and is analyzed to obtain the wave velocity and the theoretical expressions for blood flow rate and radial wall displacement in terms of pulsatile pressure. With the harmonics of a pulse signal, theoretical relations of radial vibration of the arterial wall to pulsatile parameters in blood flow are derived under two conditions: without and with wave reflection. These theoretical relations identify the assumptions for the simplified relations employed in the utility of radial vibration of the arterial wall for clinical values. With the arterial wall treated as a unit-mass vibration system, these simplified relations are utilized for extraction of arterial indices from radial vibration of the arterial wall. Other applications of such relations for clinical values are discussed, and the interaction between the arterial wall and blood flow is further revealed from the perspective of energy and one-dimensional wave equations. With harmonics and wave reflection considered, the derived theoretical expressions for radial wall vibration, pulsatile parameters in blood flow, and the relations between them provide theoretical guidance for improving their interpretation of clinical values with clearly defined physiological implications and assumptions. 

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2. Measurement of Post-Exercise Response of Local Arterial Parameters Using an Adjustable Microfluidic Tactile Sensor

   https://doi.org/10.1109/EMBC46164.2021.9630432  

   Rahman, Md Mahfuzur; Twiddy, Hannah; Reynolds, Leryn; Hao, Zhili (November 2021, Annual International Conference of the IEEE Engineering in Medicine and Biology Society)

   In this work, we demonstrate an adjustable microfluidic tactile sensor for measurement of post-exercise response of local arterial parameters. The sensor entailed a polydimethylsiloxane (PDMS) microstructure embedded with a 5×1 resistive transducer array. The pulse signal in an artery deflected the microstructure and registered as a resistance change by the transducer aligned at the artery. PDMS layers of different thicknesses were added to adjust the microstructure thickness for achieving good sensor-artery conformity at the radial artery (RA) and the carotid artery (CA). Pulse signals of nine (n=9) young healthy male subjects were measured at-rest and at different times post-exercise, and a medical instrument was used to simultaneously measure their blood pressure and heart rate. Vibration-model-based analysis was conducted on a measured pulse signal to estimate local arterial parameters: elasticity, viscosity, and radius. The arterial elasticity and viscosity increased, and the arterial radius decreased at the two arteries 1min post-exercise, relative to at-rest. The changes in pulse pressure (PP) and mean blood pressure (MAP) between at-rest and 1min post-exercise were not correlated with that of heart rate and arterial parameters. After the large 1min post-exercise response, the arterial parameters and PP all went back to their at-rest values over time post-exercise.Clinical Relevance— The study results show the potential application of an affordable, user-friendly device for a more comprehensive arterial health assessment. 

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3. Radial and axial motion of the initially-tensioned orthotropic arterial wall in arterial pulse wave propagation

   https://doi.org/10.1115/1.4053863  

   Smith, Sara M.; Marin, Justine; Adams, Amari; West, Keith; and Hao, Zhili. (May 2022, Journal of Engineering and Science in Medical Diagnostics and Therapy)

   With the arterial wall modeled as an initially-tensioned thin-walled orthotropic tube, this study aims to analyze radial and axial motion of the arterial wall and thereby reveal the role of axial motion and two initial tensions of the arterial wall in arterial pulse wave propagation. By incorporating related clinical findings into the pulse wave theory in the literature, a theoretical study is conducted on arterial pulse wave propagation with radial and axial wall motion. Since the Young wave is excited by pulsatile pressure and is examined in clinical studies, commonly measured pulsatile parameters in the Young wave are expressed in terms of pulsatile pressure and their values are calculated with the well-established values of circumferential elasticity (E) and initial tension (T0) and assumed values of axial elasticity (Ex) and initial tension (Tx0) at the ascending aorta and the carotid artery. The corresponding values with exclusion of axial wall motion are also calculated. Comparison of the calculated results between inclusion and exclusion of axial wall motion indicates that 1) axial wall motion does not affect radial wall motion and other commonly measured pulsatile parameters, except wall shear stress; 2) axial wall motion is caused by wall shear stress and radial wall displacement gradient with a factor of (Tx0T0), and enables axial power transmission through the arterial wall; and 3) while radial wall motion reflects E and T0, axial wall motion reflects Ex and (Tx0T0). 

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4. A THEORETICAL STUDY OF SENSOR-ARTERY INTERACTION IN NONINVASIVE ARTERIAL PULSE SIGNAL MEASUREMENT USING TACTILE SENSORS

   Roman Carlo B. Roxas, Adam T. (November 2020, IMECE2020)

   null (Ed.)

   This paper presents a theoretical study of sensor-artery interaction in arterial pulse signal measurement using a tactile sensor. A measured pulse signal is a combination of the true pulse signal in an artery, the arterial wall, its overlying tissue, and the sensor, under the influence of hold down pressure exerted on the sensor and motion artifact. The engineering essence of sensor-artery interaction is identified as elastic wave propagation in the overlying tissue and pulse signal transmission into the sensor at the skin surface, and different lumped-element models of sensor-artery interaction are utilized to examine how the involved factors affect a measured pulse signal. Achieving ideal sensor-artery conformity is the key for acquiring a measured pulse signal with minimum distortion. Hold-down pressure, sensor design, and overlying tissue collectively contribute to ideal sensor-artery conformity. Under ideal sensor-artery conformity, both the sensor and overlying tissue cause an increase in the measured stiffness of the arterial wall; damping and inertia of the sensor and overlying tissue also affects a measured pulse signal. The theoretical study shows the need to tailor the sensor design for different arteries and individual, and interpret estimated arterial indices with consideration of individual variations as well as instruments used. 

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5. Elastin haploinsufficiency in mice has divergent effects on arterial remodeling with aging depending on sex

   https://doi.org/10.1152/ajpheart.00517.2020  

   Hawes, Jie Z.; Cocciolone, Austin J.; Cui, Amy H.; Griffin, Diana B.; Staiculescu, Marius Catalin; Mecham, Robert P.; Wagenseil, Jessica E. (December 2020, American Journal of Physiology-Heart and Circulatory Physiology)

   null (Ed.)

   Elastin is a primary structural protein in the arterial wall that contributes to vascular mechanical properties and degrades with aging. Aging is associated with arterial stiffening and an increase in blood pressure. There is evidence that arterial aging follows different timelines with sex. Our objective was to investigate how elastin content affects arterial remodeling in male and female mice with aging. We used male and female wild-type ( Eln +/+ ) and elastin heterozygous ( Eln +/− ) mice at 6, 12, and 24 mo of age and measured their blood pressure and arterial morphology, wall structure, protein content, circumferential stress, stretch ratio, and stiffness. Two arteries were used with varying contents of elastin: the left common carotid and ascending aorta. We show that Eln +/− arteries start at a different homeostatic set point for circumferential wall stress, stretch, and material stiffness but show similar increases with aging to Eln +/+ mice. With aging, structural stiffness is greatly increased, while material stiffness and circumferential stress are only slightly increased, highlighting the importance of maintaining these homeostatic values. Circumferential stretch shows the smallest change with age and may be important for controlling cellular phenotype. Independent sex differences are mostly associated with males being larger than females; however, many of the measured factors show age × sex and/or genotype × sex interactions, indicating that males and females follow different cardiovascular remodeling timelines with aging and are differentially affected by reduced elastin content. NEW & NOTEWORTHY A comprehensive study on arterial mechanical behavior as a function of elastin content, aging, and sex in mice. Elastin haploinsufficient arteries start at a different homeostatic set point for mechanical parameters such as circumferential stress, stretch, and material stiffness. Structural stiffness of the arterial wall greatly increases with aging, as expected, but there are interactions between sex and aging for most of the mechanical parameters that are important to consider in future work. 

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