Novel Methods for Pulse Wave Velocity Measurement

J. Med. Biol. Eng. (2015) 35:555–565 DOI 10.1007/s40846-015-0086-8 REVIEW ARTICLE Novel Methods for Pulse Wave Velocity Measurement Tânia Pereira1 • Carlos Correia1 • João Cardoso1 Received: 26 June 2015 / Accepted: 14 September 2015 / Published online: 14 October 2015 Ó The Author(s) 2015. This article is published with open access at Springerlink.com Abstract The great incidence of cardiovascular (CV) diseases in the world spurs the search for new solutions to enable an early detection of pathological processes and provides more precise diagnosis based in multi-parameters assessment. The pulse wave velocity (PWV) is considered one of the most important clinical parameters for evaluate the CV risk, vascular adaptation, and therapeutic efficacy. Several studies were dedicated to find the relationship between PWV measurement and pathological status in different diseases, and proved the relevance of this parameter. The commercial devices dedicate to PWV estimation make a regional assessment (measured between two vessels), however a local measurement is more precise evaluation of artery condition, taking into account the differences in the structure of arteries. Moreover, the current devices present some limitations due to the contact nature. Emerging trends in CV monitoring are moving away from more invasive technologies to non-invasive and non-contact solutions. The great challenge is to explore the new instrumental solutions that allow the PWV assessment with fewer approximations for an accurately evaluation and relatively inexpensive techniques in order to be used in the clinical routine. Keywords Pulse wave velocity
Arterial stiffness
Commercial devices
Non-invasive methods
Measurement methods & Tânia Pereira 1 Physics Department, Instrumentation Center, University of Coimbra, Rua Larga, 3004-516 Coimbra, Portugal 1 Introduction Cardiovascular diseases (CVDs) are a group of disorders that includes several heart diseases of circulatory system [1]. The World Health Organization refers the CVDs as the worldwide leading cause of death, resulting in a number of annually deceased people higher than from any other cause [1]. The improvements of diagnostics, treatments, medications, and surgical techniques were responsible for a significant decrease in total CVD mortality over the past few decades [1, 2]. Nonetheless, it is estimated that 17 million people died from CVD in 2011, which represents approximately 30 % of the global deaths, and approximately 23 million by 2030, to remain the single leading cause of death [3]. The great incidence of CVDs in the world spurred the search for new solutions to enable an early detection of pathological processes, to monitor the vital signals continuously, and to provide a more precise diagnosis based in multi-parameters assessment [4]. An accurate assessment of the CV system changes and the identification of risk factors is of utmost importance to avoid hospitalization and to reduce CVD morbidity and mortality rates [5]. The early detection based in multi-parameters of pathological condition is the key to the patient survival. Current CV risk evaluation systems are based on clinical judgment and traditional vital signals measurement, including heart rate, respiratory rate, blood pressure (BP), temperature and pulse oximetry. However, these vital signals are not sufficient to predict and evaluate the CVDs risk [1]. The appropriate management of classical risk factors such as (age, gender, smoking habits, hypertension, body mass index) and biological analysis (cholesterol, glucose, triglycerides, potassium, sodium) together with new biomarkers [pulse wave velocity (PWV), augmentation index] may represent a better method for more accurate diagnosis [6, 7]. 123 556 Biomarkers are characteristics that are measured and evaluated as indicators of normal stages or pathogenic processes and responses to therapeutic interventions [8]. Efforts to identified new biomarkers have largely focused on the use of new measurements [9]. PWV is an emerging biomarker useful for CV risk stratification of patients, assessment of BP [10], vascular stiffness and for therapeutic effects and efficacy in clinical studies [11–13]. The arterial stiffness is the first vessels modification, responsible for several pathological processes, which can lead to CVDs. For this reason, the arterial elastic properties are used for risk stratification purposes in several populations. Recently, the European Society of Cardiology guidelines for the management of arterial hypertension suggested the measurement of PWV, considered the gold standard method for assessing arterial stiffness, as a tool to evaluate the arterial system damage, vascular adaptation, and therapeutic efficacy [6]. Another important application of PWV measurement is the indirect estimation of BP. It has been demonstrated that PWV is inversely related with BP and have been reported to be suitable for indirect BP measurements [14]. Important part of research studies in PWV was focused in the correlation between PWV and BP and on the development of a cuff-less continuous BP monitoring device [15–17]. Several models were proposed for BP estimation based in the PWV measurement [18], and they were based in the arterial wall mechanics and wave propagation in the arteries [18–20]. However, major progress on the algorithms to determine the BP using the PWV measurement is still required, like the calibration of pulse transit time (PTT, in units of ms) to BP (in units of mmHg) [21]. Apart from invasive methods, the PWV can also be measured using non-invasive, reproducible and relatively inexpensive techniques [7]. Many different waves have been used to determine the PWV, such as pressure wave, distension wave or flow wave. Commercial devices dedicate to PWV measurements make a regional assessment, i.e., the PWV is measured between two vessels. However the advantages of a local measurement are evident and some solutions are being exploited that enable this measurement in a short vessel segment. There is an ever-increasing need and demand for novel and more efficient diagnostic tools to early detect CVDs. The great challenge is to explore new sensors and configurations that allow the PWV assessment with fewer approximations, leading to an accurate evaluation, and to develop relatively inexpensive techniques in order to be considered an interesting clinical solution. This paper aims to review the most relevant studies on PWV and introduce the discussion of advantages, disadvantages and applications of biomedical instrumentation for local versus regional PWV measurements. 123 T. Pereira et al. 2 Pulse Wave Velocity: Regional Versus Local PWV is defined as the velocity at which the pressure waves, generated by the systolic contraction of the heart, propagate along the arterial tree. The evaluation of PWV provides complementary information about the elastic properties of arterial system. The higher PW (...truncated)