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1. ESTIMATION OF ARTERIAL PARAMETERS FROM NONINVASIVELY MEASURED ARTERIAL PULSE SIGNALS: VIBRATION-MODEL-BASED ANALYSIS

   Md Mahfuzur Rahman, Najmin Ara ( November 2020 , IMECE2020)

   null (Ed.)

   With the goal of achieving consistence in interpretation of an arterial pulse signal between its vibration model and its hemodynamic relations and improving its physiological implications in our previous study, this paper presents an improved vibration-model-based analysis for estimation of arterial parameters: elasticity (E), viscosity (), and radius (r0) at diastolic blood pressure (DBP) of the arterial wall, from a noninvasively measured arterial pulse signal. The arterial wall is modeled as a unit-mass vibration model, and its spring stiffness (K) and damping coefficient (D) are related to arterial parameters. Key features of a measured pulse signal and its first-order and second-order derivatives are utilized to estimate the values of K and D. These key features are then utilized in hemodynamic relations, where their interpretation is consistent with the vibration model, to estimate the value of r0 from K and D. Consequently, E, , and pulse wave velocity (PWV) are also estimated from K and D. The improved vibration-model-based analysis was conducted on pulse signals of a few healthy subjects measured under two conditions: at-rest and immediately post-exercise. With E, r0, and PWV at-rest as baseline, their changes immediately post-exercise were found to be consistent with the related findings in the literature. Thus, this improved vibration-model-based analysis is validated and contributes to estimation of arterial parameters with better physiological implications, as compared with its previous counterpart. 

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2. Alterations of biaxial viscoelastic properties of the right ventricle in pulmonary hypertension development in rest and acute stress conditions

   https://doi.org/10.3389/fbioe.2023.1182703  

   Liu, Wenqiang ; LeBar, Kristen ; Roth, Kellan ; Pang, Jassia ; Ayers, Jessica ; Chicco, Adam J. ; Puttlitz, Christian M. ; Wang, Zhijie ( May 2023 , Frontiers in Bioengineering and Biotechnology)

   Baek, Seungik (Ed.)

   Introduction:The right ventricle (RV) mechanical property is an important determinant of its function. However, compared to its elasticity, RV viscoelasticity is much less studied, and it remains unclear how pulmonary hypertension (PH) alters RV viscoelasticity. Our goal was to characterize the changes in RV free wall (RVFW) anisotropic viscoelastic properties with PH development and at varied heart rates.

   Methods:PH was induced in rats by monocrotaline treatment, and the RV function was quantified by echocardiography. After euthanasia, equibiaxial stress relaxation tests were performed on RVFWs from healthy and PH rats at various strain-rates and strain levels, which recapitulate physiological deformations at varied heart rates (at rest and under acute stress) and diastole phases (at early and late filling), respectively.

   Results and Discussion:We observed that PH increased RVFW viscoelasticity in both longitudinal (outflow tract) and circumferential directions. The tissue anisotropy was pronounced for the diseased RVs, not healthy RVs. We also examined the relative change of viscosity to elasticity by the damping capacity (ratio of dissipated energy to total energy), and we found that PH decreased RVFW damping capacity in both directions. The RV viscoelasticity was also differently altered from resting to acute stress conditions between the groups—the damping capacity was decreased only in the circumferential direction for healthy RVs, but it was reduced in both directions for diseased RVs. Lastly, we found some correlations between the damping capacity and RV function indices and there was no correlation between elasticity or viscosity and RV function. Thus, the RV damping capacity may be a better indicator of RV function than elasticity or viscosity alone. These novel findings on RV dynamic mechanical properties offer deeper insights into the role of RV biomechanics in the adaptation of RV to chronic pressure overload and acute stress.

    

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3. 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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4. Pulse Wave Velocity And Transmission at the Carotid Artery and the Ascending Aorta

   https://doi.org/10.1115/IMECE2021-69412  

   Smith, Sara M. ; Marin, Justine ; Adams, Amari ; West, Keith ; Hao, Zhili ( November 2021 , Proceedings of the ASME 2021 International Mechanical Engineering Congress & Exposition)

   With consideration of a full set of mechanical properties: elasticity, viscosity, and axial and circumferential initial tensions, and radial and axial motion of the arterial wall, this paper presents a theoretical study of pulse wave propagation in arteries and evaluates pulse wave velocity and transmission at the carotid artery (CA) and the ascending aorta (AA). The arterial wall is treated as an initially-tensioned, isotropic, thin-walled membrane, and the flowing blood in the artery is treated as an incompressible Newtonian fluid. Pulse wave propagation in arteries is formulated as a combination of the governing equations of radial and axial motion of the arterial wall, the governing equations of flowing blood in the artery, and the interface conditions that relate the arterial wall variables to the flowing blood variables. We conduct a free wave propagation analysis of the problem and derive a frequency equation. The solution to the frequency equation indicates two waves: Young wave and Lamb wave, propagating in the arterial tree. With the related values at the CA and the AA, we evaluate the influence of arterial wall properties on their wave velocity and transmission, and find the opposite effects of axial and circumferential initial tensions on transmission of both waves. Physiological implications of such influence are discussed. 

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5. 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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