A Virtual Instrument for Automated Measurement of Arterial Compliance

Abstract: Vascular stiffness is an indicator of cardiovascular health, with carotid artery stiffness having established correlation to coronary heart disease and utility in cardiovascular diagnosis and screening. State of art equipment for stiffness evaluation are expensive, require expertise to operate and not amenable for field deployment. In this context, we developed ARTerial Stiffness Evaluation for Noninvasive Screening (ARTSENS), a device for image free, noninvasive, automated evaluation of vascular stiffness amenable for field use. ARTSENS has a frugal hardware design, utilizing a single ultrasound transducer to interrogate the carotid artery, integrated with robust algorithms that extract arterial dimensions and compute clinically accepted measures of arterial stiffness. The ability of ARTSENS to measure vascular stiffness in vivo was validated by performing measurements on 125 subjects. The accuracy of results was verified with the state-of-the-art ultrasound imaging-based echo-tracking system. The relation between arterial stiffness measurements performed in sitting posture for ARTSENS measurement and sitting/supine postures for imaging system was also investigated to examine feasibility of performing ARTSENS measurements in the sitting posture for field deployment. This paper verified the feasibility of the novel ARTSENS device in performing accurate in vivo measurements of arterial stiffness. As a portable device that performs automated measurement of carotid artery stiffness with minimal operator input, ARTSENS has strong potential for use in large-scale screening.

Abstract: Evaluation of arterial compliance is very significant in early detection of coronary heart disease. Here we present an imageless portable system for automated estimation of local arterial compliance, designed to be operated by a general medical practitioner with no prior knowledge of ultrasonography. An algorithm for automatic detection and tracking of the arterial wall locations has been developed to minimize the operator expertise required for measurement. The performance of the automated algorithm was thoroughly characterized using a simulation platform developed for the purpose. Measurements performed on a few human volunteers by untrained personnel clearly illustrated the practical utility of the automatic algorithm during in-vivo tests. The proposed system could be used for developing an inexpensive cardiovascular screening device for large scale deployment in primary health care centers.

Abstract: Evaluation of arterial compliance is significant in cardiovascular diagnosis for early detection of coronary heart disease. We present ARTSENS, an image-free system for non-invasive evaluation of arterial compliance in-vivo. The system utilizes a single element ultrasound probe with intelligent measurement algorithms to ensure accurate evaluation of local arterial compliance without an image. The ability of the system to detect artery anatomy and measure compliance was verified by in-vivo measurements conducted on 106 subjects. The accuracy of compliance estimates were evaluated by comparison with a state of art imaging system. The measurements made using ARTSENS showed strong correlation with those made using the imaging system. The ability of ARTSENS to detect age-related trends in arterial compliance was also investigated.

Abstract: Over past few years, we are developing a system for facilitating large scale screening of patients for cardiovascular risk - ARTSENS. ARTSENS is an image-free device that uses a single element ultrasound transducer to obtain non-invasive measurements of arterial stiffness (AS) in a fully automated manner. AS is directly proportional to end-diastolic lumen diameter (�� �� ). Multi- layered structure of the arterial walls and indistinct characteristics of intima-lumen interface (ILI) makes it quite difficult to accurately estimate �� �� in A-Mode radio-frequency (RF) frames obtained from ARTSENS. In this paper, we propose a few methods based on fitting simple mathematical models to the echoes from arterial walls, followed by a novel method to fuse the information from curve fitting error and distension curve to arrive at an accurate measure of �� ��. To bring down the curve fitting time and facilitate processing on low-end processors, a novel approach using the autocorrelation of echoes from opposite walls of the artery has been discussed. The methods were analyzed for their comparative accuracy against reference �� �� obtained from 85 human volunteers using Hitachi-Aloka eTRACKING system. �� �� from all reported methods show strong and statistically significant positive correlation with eTRACKING and mean error of less than 7 % could be achieved. As expected, �� �� from all methods show significant positive correlation with age.

Abstract: Objective: We propose a calibration-free method and system for cuffless blood pressure (BP) measurement from superficial arteries. A prototype device with bi-modal probe arrangement was designed and developed to estimate carotid BP – an indicator of central aortic pressure. Methods: Mathematical models relating BP parameters of an arterial segment to its dimensions and local pulse wave velocity (PWV) are introduced. A bi-modal probe utilizing ultrasound and photoplethysmograph sensors was developed and used to measure diameter values and local PWV from the carotid artery. Carotid BP was estimated using the measured physiological parameters without any subject- or population-specific calibration procedures. The proposed cuffless BP estimation method and system were tested for accuracy, usability, and for potential utility in hypertension screening, on a total of 83 subjects. Results: The prototype device demonstrated its capability of detecting beat-by-beat arterial dimensions and local PWV simultaneously. Carotid diastolic BP (DBP) and systolic BP (SBP) were estimated over multiple cardiac cycles in real-time. The absolute error in carotid DBP was Conclusion: The feasibility of calibration-free, cuffless BP measurement at an arterial site of interest was demonstrated with a level of acceptable accuracy. The study also demonstrated the potential utility of the proposed method and system in hypertension screening and local evaluation of arterial stiffness indices. Significance: Novel approach for calibration-free cuffless BP estimation; a potential tool for local BP measurement and hypertension screening.

Abstract: Background and Purpose—Studies of the association between arterial stiffness and atherosclerosis are contradictory. We studied stiffness of the aorta and the common carotid artery in relation to se...

Abstract: Investigation of arterial stiffness, especially of the large arteries, has gathered pace in recent years with the development of readily available noninvasive assessment techniques. These include the measurement of pulse wave velocity, the use of ultrasound to relate the change in diameter or area of an artery to distending pressure, and analysis of arterial waveforms obtained by applanation tonometry. Here, we describe each of these techniques and their limitations and discuss how the measured parameters relate to established cardiovascular risk factors and clinical outcome. We also consider which techniques might be most appropriate for wider clinical application. Finally, the effects of current and future cardiovascular drugs on arterial stiffness are also discussed, as is the relationship between arterial elasticity and endothelial function.

Abstract: Background—Common carotid intima-media thickness (IMT) and distensibility are markers of structural and functional vessel wall properties. Both parameters have been found in population-based studies to be associated with cardiovascular risk factors and prevalent cardiovascular disease. We investigated cross-sectionally whether IMT and distensibility are associated with cardiovascular risk in patients who already have vascular disease or atherosclerotic risk factors and evaluated the diagnostic ability of IMT and distensibility to discriminate between low- and high-risk patients. Methods and Results—IMT and distensibility (change of diameter) of the left and right common carotid arteries were measured in the first 570 patients (537 for distensibility) enrolled in the Second Manifestations of ARTerial disease (SMART) study, a cohort study among patients with a manifestation of vascular disease or cardiovascular risk factors. Three risk scores were used to classify each patient’s vascular risk. Areas under t...

Abstract: The Doppler technique has traditionally been the method used to extract motion information from ultrasonic echoes reflected by moving tissues. The Doppler technique has been around for a long time, and has been extensively reviewed and analyzed in the literature. Recently, time-domain methodologies for estimating tissue motion have gained in popularity. Time-domain methods have advantages over Doppler methods in many applications, and as of yet have not been comprehensively reviewed. An overview of time-domain techniques that have appeared in the literature over the past few years is presented. Their potential advantages over Doppler are examined, and the individual techniques are compared. >

Abstract: 1. Repeatability of measurements of arterial compliance and flow-mediated dilation of the brachial artery has been infrequently reported, despite increasing use in interventional and risk-factor modification studies. Furthermore, little is known about the interrelationships of the various indices. The purposes of this study were to determine the repeatability and interrelationships of a range of arterial indices.2. Fifty healthy volunteers, 20 men and 30 women, aged 20-70 (mean 46.5) years, were studied on two occasions, using an identical protocol, at a mean interval of 2.5 weeks. Tonometry, ultrasound and Doppler technique were used to measure the following: carotid wall intima-media thickness (IMT), total systemic artery compliance (SAC), arterial pulse wave velocity [PWV aorto-femoral (A-F), and femoral-dorsalis pedis (F-D)], carotid distensibility coefficient (DC) and carotid augmentation index (AI). Brachial flow-mediated dilation was measured in 30 subjects with analysis of diameter change for 4 min post ischaemia.3. There were no systematic differences over the observed range of measurements for any of the reported parameters. Coefficients of variation were as follows: IMT 2.8%, SAC 9.2%, PWV(A-F) 3.2%, PWV(F-D) 5.0%, DC 10.0%, AI 1.3%. Brachial flow-mediated dilation curves were not different between visits; changes were maximum 60-s post ischaemia. All indices of arterial compliance were significantly correlated with age. The three different indices of central arterial compliance [SAC, PWV(A-F) and AI] were significantly correlated with carotid intima-media thickness.4. Under controlled experimental conditions there was good repeatability of measurements of indices between sessions of both intrinsic and functional arterial mechanical properties (central and carotid arterial compliance, intima-media thickness and brachial flow-mediated dilation). Sample size tables for clinical trials using these indices are presented.