Repeatability Study of Local Vascular Stiffness Measurement Using Carotid Surface Acceleration Plethysmogram.

We have developed an accelerometric system with a custom-designed patch probe and signal acquisition hardware to acquire the carotid wall displacement from the soft tissue surface for arterial stiffness evaluation. A subject-specific calibration model was developed to estimate the morphology of accurate carotid diameter waveform, using a standard ultrasound B-mode imaging system as the reference. Following the one-time calibration, the accelerometric system continuously acquired a non-invasive carotid lumen diameter waveform. The capability of the accelerometric system to measure the carotid stiffness index (ß) in-vivo was experimentally validated by performing measurements on 8 normotensive subjects in the supine position. The repeatability and reproducibility of the results were investigated and were found to be comparable to those provided by ultrasound imaging systems. Further, the variation of arterial stiffness index measurements on different days was studied to verify the ability of the system to give a stable measure of stiffness. The accuracy of the observed results was confirmed with the state-of-art B-mode ultrasound imaging system. The results were found to be stable over a day, indicating the utility of the system for a reliable measure of non-invasive carotid arterial stiffness.

Local Pulse Wave Velocity: Theory, Methods, Advancements, and Clinical Applications.

Local pulse wave velocity (PWV) is evolving as one of the important determinants of arterial hemodynamics, localized vessel stiffening associated with several pathologies, and a host of other cardiovascular events. Although PWV was introduced over a century ago, only in recent decades, due to various technological advancements, has emphasis been directed toward its measurement from a single arterial section or from piecewise segments of a target arterial section. This emerging worldwide trend in the exploration of instrumental solutions for local PWV measurement has produced several invasive and noninvasive methods. As of yet, however, a univocal opinion on the ideal measurement method has not emerged. Neither have there been extensive comparative studies on the accuracy of the available methods. Recognizing this reality, makes apparent the need to establish guideline-recommended standards for the measurement methods and reference values, without which clinical application cannot be pursued. This paper enumerates all major local PWV measurement methods while pinpointing their salient methodological considerations and emphasizing the necessity of global standardization. Further, a summary of the advancements in measuring modalities and clinical applications is provided. Additionally, a detailed discussion on the minimally explored concept of incremental local PWV is presented along with suggestions of future research questions.

Continuous Assessment of Carotid Diameter using an Accelerometer Patch Probe for Ambulatory Arterial Stiffness Monitoring.

We present a system with an accelerometer patch probe design for non-invasive evaluation of carotid arterial stiffness. The proposed system could continuously measure the acceleration signal derived due to the propagation of blood pulse wave through the left carotid artery, double integrating and scaling it to estimate the accelerometer-derived carotid wall displacement. This functional principle was proved by comparing the accelerometer-derived carotid wall displacement with the carotid distension signal from the reference system ARTSENS® (ARTerial Stiffness Evaluation for Noninvasive Screening device) for all the recruited human subjects. Assuming the relationship to be linear, a one-time subject-specific calibration was performed with the simultaneously acquired reference distension signal and the accelerometer-derived carotid displacement signals on its anachrotic limbs data points (at systolic phases) for each subject. This calibration equation was tested with latterly acquired accelerometer signals and results in the measurement of accelerometer-derived carotid distension and lumen-diameter values. The ability of the accelerometer system to measure real-time carotid distension and lumen diameter in a repeatable beat-by-beat manner for arterial stiffness index evaluation was validated in-vivo. The accuracy of the obtained results was studied with our clinically validated reference system. The experimental validation study results exhibit the feasibility of using the developed accelerometer system for continuous carotid distension and lumen diameter measurements, whereby the estimation of carotid arterial stiffness.

Image-Free Technique for Flow Mediated Dilation Using ARTSENS® Pen.

Flow mediated dilation (FMD) is a clinically accepted non-invasive tool for assessing endothelial dysfunction. FMD is conventionally performed with B-mode ultrasound systems that involve recording of the image sequences as DICOM files or video-graphic files and processing them offline. Sometimes the examinations may have to be rejected due to poor or unstable image sequences resulting non-reliable diameter estimates. We had earlier developed and extensively validated an image-free ultrasound technology, ARTSENS®, for the measurement of carotid artery wall dynamics and arterial stiffness metrics. In this work, we evaluate the feasibility of using the technology for continuous real-time diameter measurement of the brachial artery and thereby FMD. To investigate the performance of the ARTSENS® device an in-vivo study was conducted on 5 subjects as pilot. As a reference the measurements were also performed by a B-mode imaging system with a help of a commercially available clinically validated offline FMD analysis tool. The brachial artery diameter and FMD measurements performed by the ARTSENS® device were consistent with the earlier reported literature. The beat-to-beat repeatability of the baseline diameter measurements was acceptable with a CoV <; 4% for all the subjects. The diameter measurements performed by the two devices exhibited a significant correlation (r-square = 0.81, p <; 0.05). The RMSE for the diameter and FMD% measurements was 0.32 mm and 0.63% respectively, illustrating the measurement accuracy. The study demonstrated that the ARTSENS® can be reliably employed for performing FMD measurements and assessing endothelial dysfunction. This would help realize a field deployable solution for real-time automated FMD measurement and consequently for the acceleration of large population studies in this research area.