Accelerometric patch probe for cuffless blood pressure evaluation from carotid local pulse wave velocity: design, development, and in vivo experimental study

Plethysmograph-Based Self-Assessment Device for Carotid-Femoral Pulse Wave Velocity Measurement: A Pilot Usability Study

Arterial stiffness, a proxy of vascular aging is an important marker of cardiovascular events and mortality, independent of traditional risk factors. The aortic or carotid-femoral pulse wave velocity (cf-PWV) is the gold standard for determining arterial stiffness. Measuring arterial stiffness can help identify people who are at risk early on. State-of-the-art devices, majorly employing applanation tonometry at the carotid site, demand extensive skill, are costly, and are not intended for out-of-clinic use. However, a device that is suitable for homecare and primary health settings would facilitate primordial care. To address this gap, we have developed a novel easy-to-use, fully automated, and affordable photoplethysmography-based device for measuring cf-PWV. An in-vivo study on 25 subjects was conducted to investigate the device's usability by comparing self and expert-performed measurements, and by quantifying the user experience (score out of 5). A strong correlation (r = 0.88) and a statistically insignificant bias indicated the measurement reproducibility in self-versus expert-performed measurements. An average usability score of 3.98 ± 0.83 given by the participants showed the convenience and ease of use of the device. The results demonstrate the feasibility and reliability of using the device by inexperienced operators, even when newly introduced. Future clinical studies are in progress to assess the device's accuracy in comparison to gold-standard reference equipment.Clinical Relevance-This pilot study revealed the device's potential to offer a user-friendly solution for home care and other non-hospital settings.

Arterial Wave Separation Analysis and Reflection Wave Transit Time Estimation using a Double Rayleigh Flow Rate Model

Arterial pulse wave separation analysis (WSA) requires simultaneously measured pressure and flow rate waveform from the same arterial site. Modelling approaches to flow rate waveforms offers a methodological and instrumentational advantage. However, current techniques are limited to the aortic site. For non-aortic sites such as carotid artery, modelling methods that were developed for aortic sites are not likely to capture the intrinsic differences in the carotid flow rate. In this work, a double-Rayleigh flow rate model for the carotid artery is developed to separate the forward and backward pressure waves using WSA (DRMWSA). The model parameters are optimally found based on characteristic features - obtained from the pressure waveform. The DRMWSA was validated using a database of 4374 virtual (healthy) subjects, and its performance was compared with actual flow rate based WSA (REFWSA) at the carotid artery. An RMSE < 2 mmHg were obtained for forward and backward pressure waveforms. The reflection quantification indices (ΔPF, ΔPB), (RM, RI) obtained from DRMWSA demonstrated strong and statistically significant correlation (r > 0.96, p < 0.001) and (r > 0.80, p < 0.001) respectively, with insignificant bias (p > 0.05), upon comparing with counterparts in REFWSA. A moderate correlation (r = 0.64, p < 0.001) was obtained for reflection wave transit time between both methods. The proposed method minimises the measurements required for WSA and has the potential to widen the vascular screening procedures incorporating carotid pulse wave dynamics.Clinical Relevance-This methodology quantifies arterial pressure wave reflections in terms of pressure augmentation and reflection transit time. The methodological advantage of using only a single waveform helps easy translation to technological solutions for clinical research.

A Flexible Ultrasound Array for Local Pulse Wave Velocity Monitoring

Pulse wave velocity (PWV) measured at a specific artery location is called local PWV, which provides the elastic characteristics of arteries and indicates the degree of arterial stiffness. However, the large and cumbersome ultrasound probes require an appropriate sensor position and pressure maintenance, introducing usability constraints. In this paper, we developed a light (0.5 g) and thin (400 μm) flexible ultrasound array by encapsulating 1-3 composite piezoelectric transducers with a silicone elastomer. It can capture the distension waveforms of four arterial positions with a spacing of 10 mm and calculate the local PWV by multi-point fitting. This is illustrated by in vivo experiments, where the local PWV value of five normal subjects ranged from 3.07 to 4.82 m/s, in agreement with earlier studies. The beat-to-beat coefficient of variation (CV) is 12.0% ± 3.5%, showing high reliability. High reproducibility is shown by the results of two groups of independent measurements of three subjects (the error between the mean values is less than 0.3 m/s). These properties of the developed flexible ultrasound array enable the bandage-like application of local PWV monitoring to skin surfaces.

A Data-Driven Model with Feedback Calibration Embedded Blood Pressure Estimator Using Reflective Photoplethysmography

Ambulatory blood pressure (BP) monitoring (ABPM) is vital for screening cardiovascular activity. The American College of Cardiology/American Heart Association guideline for the prevention, detection, evaluation, and management of BP in adults recommends measuring BP outside the office setting using daytime ABPM. The recommendation to use night–day BP measurements to confirm hypertension is consistent with the recommendation of several other guidelines. In recent studies, ABPM was used to measure BP at regular intervals, and it reduces the effect of the environment on BP. Out-of-office measurements are highly recommended by almost all hypertension organizations. However, traditional ABPM devices based on the oscillometric technique usually interrupt sleep. For all-day ABPM purposes, a photoplethysmography (PPG)-based wrist-type device has been developed as a convenient tool. This optical, noninvasive device estimates BP using morphological characteristics from PPG waveforms. As measurement can be affected by multiple variables, calibration is necessary to ensure that the calculated BP values are accurate. However, few studies focused on adaptive calibration. A novel adaptive calibration model, which is data-driven and embedded in a wearable device, was proposed. The features from a 15 s PPG waveform and personal information were input for estimation of BP values and our data-driven calibration model. The model had a feedback calibration process using the exponential Gaussian process regression method to calibrate BP values and avoid inter- and intra-subject variability, ensuring accuracy in long-term ABPM. The estimation error of BP (ΔBP = actual BP—estimated BP) of systolic BP was −0.1776 ± 4.7361 mmHg; ≤15 mmHg, 99.225%, and of diastolic BP was −0.3846 ± 6.3688 mmHg; ≤15 mmHg, 98.191%. The success rate was improved, and the results corresponded to the Association for the Advancement of Medical Instrumentation standard and British Hypertension Society Grading criteria for medical regulation. Using machine learning with a feedback calibration model could be used to assess ABPM for clinical purposes.

Evaluation of Vascular Pulse Contour Indices over the Physiological Blood Pressure Ranges in an Anesthetized Porcine Model

A series of physiological measures can be assessed from the arterial pulse waveform, which is beneficial for cardiovascular health diagnosis, monitoring, and decision making. In this work, we have investigated the variations in regional pulse wave velocity (PWVR) and other pulse waveform indexes such as reflected wave transit time (RWTT), augmentation index (Alx), ejection duration index (ED), and subendocardial viability ratio (SEVR) with blood pressure (BP) parameters and heartrate on a vasoconstrictor drug-induced porcine model. Two healthy female (nulliparous and non-pregnant) Sus scrofa swine (~ 80 kg) was used for the experimental study. The measurement system consists of a catheter-based system with two highly accurate pressure catheters placed via the sheath at the femoral and carotid artery for acquiring and recording the pressure waveforms. The pulse waveform indexes were extracted from these recorded waveforms. Results from the pulse contour analysis of these waveforms demonstrated that Phenylephrine, as a post-synaptic alpha-adrenergic receptor agonist that causes vasoconstriction, produced a significant increment in the carotid BP parameters and heartrate. Due to the drug's effect, the PWVR and SEVR were significantly increased, whereas the RWTT, AIx index and ED index significantly decreased.Clinical Relevance- This experimental study provides the usefulness of the pulse contour analysis and estimation of various pulse waveform indexes for cardiovascular health screening and diagnosis.

Estimation of aortic pulse wave velocity based on waveform decomposition of central aortic pressure waveform

Objective.Aortic stiffness is associated with risk of cardiovascular events. Carotid-femoral pulse wave velocity (cfPWV) is the current noninvasive gold standard for assessing aortic stiffness. However, the cfPWV measurement is challenging, requiring simultaneous signals at the carotid and femoral sites.Approach.In this study, the aortic PWV is estimated using a single radial pressure waveform and compared with cfPWV. 111 subjects' aortic PWVs are estimated from the decomposition of the derived central aortic pressure waveform based on three types of reconstructed flow waveform: the peak of triangular flow waveform based on 30% ejection time (Q_30%tri), the peak of triangular flow waveform based on inflection point (Q_tri), and averaged flow waveform (Q_avg). The central aortic pressure waveform is derived from a radial pressure waveform via a validated transfer function.Main results.TheQ_avgis used for estimating aortic PWV without the determination of the peak point of the triangular flow waveforms. The estimated aortic PWV shows good agreement with cfPWV. The mean difference ± SD is 0.29 ± 1.50 m s^-1(r² = 0.29,p< 0.001) for theQ_30%tri; 0.27 ± 1.40 m s^-1(r² = 0.38,p < 0.001) for theQ_tri; 0.23 ± 1.39 m s^-1(r² = 0.40,p < 0.001) for theQ_avg. The correlation between estimated aortic PWV based onQ_30%triand measured cfPWV is weak. The results ofQ_triandQ_avgshow no obvious difference.Significance.The proposed method can be used as a less complex way than conventional measurement of cfPWV to further assess arterial stiffness and predict cardiovascular risks or events.

Wearable Sensing and Telehealth Technology with Potential Applications in the Coronavirus Pandemic

Coronavirus disease 2019 (COVID-19) has emerged as a pandemic with serious clinical manifestations including death. A pandemic at the large-scale like COVID-19 places extraordinary demands on the world's health systems, dramatically devastates vulnerable populations, and critically threatens the global communities in an unprecedented way. While tremendous efforts at the frontline are placed on detecting the virus, providing treatments and developing vaccines, it is also critically important to examine the technologies and systems for tackling disease emergence, arresting its spread and especially the strategy for diseases prevention. The objective of this article is to review enabling technologies and systems with various application scenarios for handling the COVID-19 crisis. The article will focus specifically on 1) wearable devices suitable for monitoring the populations at risk and those in quarantine, both for evaluating the health status of caregivers and management personnel, and for facilitating triage processes for admission to hospitals; 2) unobtrusive sensing systems for detecting the disease and for monitoring patients with relatively mild symptoms whose clinical situation could suddenly worsen in improvised hospitals; and 3) telehealth technologies for the remote monitoring and diagnosis of COVID-19 and related diseases. Finally, further challenges and opportunities for future directions of development are highlighted.

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.