On-Device, Continuous, Cuffless, and Accelerometer-Based Blood Pressure Monitoring.

Due to the global hypertension epidemic, a convenient, miniaturized, and cuff-less blood pressure (BP) monitoring device is desirable. During the past several years, we have attested various studies to acquire BP indirectly via pulse transit time (PTT) obtained from electrocardiogram (ECG) and photoplethysmogram (PPG). Towards this end, some progress has been achieved but the prospect of designing a device that requires neither a pressure cuff nor cross-body contact of ECG electrodes has been uncharted. In this paper, we present two approaches to determine PTT which open the door to convenient, non-invasive, and cuff-less wearables for continuous BP monitoring at home settings. The first device was designed with contact-electrode ECG and PPG sensors, located on the bicep and the ear; while the second one, which is a wrist-worn device, consisted of a non-contact ECG circuit and a piezoelectric pulse sensor. Results indicated that our novel designs enable next-generation devices, providing essential continuous BP monitoring off-the-clinic for hypertension patients as well as healthy people.

Continuous blood pressure (BP) monitoring in daily life is needed to enable early detection of hypertension and improve its control. Although pulse transit time (PTT)-based BP estimation represents a promising approach, it still lacks of performance in systolic blood pressure (SBP) estimation and its use in daily life is limited owing to the requirement of bulky systems for measurement of PTT. This study aims at developing a wearable system providing continuous PTT measurement and enhanced SBP estimation for continuous BP monitoring. A single chest-worn device was developed, which measures the photoplethysmogram and seismocardiogram simultaneously, and thereby obtains PTT by time difference between two signals. A multivariate model using the seismocardiogram amplitude (SA) in conjunction with PTT was proposed for SBP estimation, and validated against 30 healthy males (31.47 ± 7.23 years old). Performance of the proposed model was compared with that of conventional univariate models using PTT or pulse arrival time in two types of BP interventions, and for the verification of real use in daily life, performance assessment with calibration and BP monitoring in daily life were conducted. The results suggested that the proposed model (1) outperformed the conventional models, (2) showed potential to be generalized with just a simple calibration, and (3) demonstrated the potential of continuous BP monitoring in daily life. In conclusion, the presented system provides an improved performance of continuous BP monitoring by using a combination of PTT and SA with a convenient and compact single chest-worn device, and thus, it can contribute to mobile healthcare services.

Continuous blood pressure (BP) monitoring has a significant meaning to the prevention and early diagnosis of cardiovascular disease. However, existing continuous BP monitoring approaches, especially cuff-less BP monitoring approaches, are all contraptions which complex and huge computation required. For example, for the most sophisticated cuff-less BP monitoring method using pulse transit time (PTT), the simultaneous record of photoplethysmography (PPG) signal and electrocardiography (ECG) are required, and various measurement of characteristic points are needed. These issues hindered widely application of cuff less BP measurement in the wearable devices. In this study, a novel BP estimation method using single PPG signal feature was proposed and its performance in BP estimation was also tested. The results showed that the new approach proposed in this study has a mean error -0.91 ± 3.84 mmHg for SBP estimation and -0.36 ± 3.36 mmHg for DBP estimation respectively. This approach performed better than the traditional PTT based BP estimation, which mean error for SBP estimation was -0.31 ± 4.78 mmHg, and for DBP estimation was -0.18 ± 4.32 mmHg. Further investigation revealed that this new BP estimation approach only required measurement of one characteristic point, reducing much computation when implementing. These results demonstrated that this new approach might be more suitable implemented in the wearable BP monitoring devices.

Recently, pulse wave velocity (PWV), or its reciprocal pulse transit time (PTT), has been intensively investigated as a promising technique for continuous, cuffless, and noninvasive blood pressure (BP) monitoring. BP is mathematically derived through PTT, or the “time delay” in propagation of pressure waves in the vascular system, which can be easily derived from two pulse signals, including electrocardiography (ECG) and pulse plethysmography (PPG) signals, together with adequate calibration procedure. Practical steps in applying this method as well as mathematical models in estimating BP were reviewed; while limitations of this approach, such as the need for individual calibration and the need for a reasonably stable condition were discussed. The future of this technology can be potentially used in, but not limited to, continuous BP monitoring, BP change tracker, and trigger for absolute BP measurement. Furthermore, with machine learning, the initially extract surrogate cardiovascular indexes from physiological signals can be used to train and adapt to the model to further improve the accuracy of BP prediction.

Objective: Continuous cuffless blood pressure (BP) monitoring research has emerged as blood pressure is one of the dynamic parameters which reflects cardiac arrhythmias and rheological disorders without the drawbacks of current techniques. All the existing measurement techniques are cuff-based with drawbacks such as being discontinuous in nature, being uncomfortable for the patient, etc. Therefore, the goal is to develop an algorithm to estimate BP accurately using the pulse transit time (PTT), photoplethysmogram intensity ratio (PIR) and Womersley number (α) in a noninvasive way. Approach: The PTT technique holds the promise of real-time, cuffless, continuous BP monitoring in clinical settings. However, the non-Newtonian fluid nature of blood is considered insignificant in the conventional PTT model-based BP modeling. In the proposed work, α, representing viscous effects, along with PTT and PIR, is included in the algorithm since it is also one of the parameters that affects the BP. Main results: The proposed algorithm is evaluated with 42 healthy and 39 diseased subjects and compared with the other conventional techniques to evaluate the importance of viscous effects in BP, using performance metrics like mean ± standard deviation, and 95% confidence interval for bias and limits of agreement; a better estimate is achieved with the proposed algorithm. Significance: The proposed algorithm reflects the influences of vasomotor tone and baroflex as well, which makes it suitable for the assessment of BP in both healthy and diseased subjects, with improved accuracy than the current measurement techniques.

Continuous blood pressure monitoring is essential in the management of patients in critical conditions, as well as those under anesthesia. However, continuous blood pressure monitoring requires insertion of a catheter into the radial artery. Thus, continuous noninvasive arterial blood pressure monitoring would be ideal. We designed and built a continuous noninvasive arterial blood pressure monitoring device with a pressure sensor diaphragm using microelectromechanical system technology, a square with 4 mm sides that were 0.4 mm thick. Comparisons between a continuous noninvasive arterial blood pressure monitoring device and a sphygmomanometer were carried out on 92 volunteers, and comparisons between noninvasive and invasive blood pressure monitoring were performed on three patients perioperatively at Fukushima Medical University Hospital. In the comparisons of arterial blood pressure measurements between a sphygmomanometer and our device, the differences became gradually greater over time after starting continuous monitoring in conscious participants. In the comparisons of arterial blood pressure measurements between the invasive and noninvasive methods in unconscious subjects under general anesthesia, the results of noninvasive monitoring were consistent with those of invasive arterial blood pressure monitoring. Continuous noninvasive arterial monitoring with a pressure sensor diaphragm using microelectromechanical system technology is a possible alternative to conventional invasive arterial pressure monitoring by an arterial catheter.

Continuous noninvasive cuffless blood pressure (BP) monitoring is essential for early detection and treatment of hypertension. In this paper, we provide an overview of the recent advancements in cuffless BP sensors. These include contact wearable sensors such as electrocardiography (ECG), photoplethysmography (PPG), contact non-wearable sensors such as ballistocardiography (BCG), and contactless sensors such as video plethysmography (VPG). These sensors employ different measuring mechanisms such as pulse arrival time (PAT), pulse transit time (PTT), and pulse wave analysis (PWA) to estimate BP. However, challenges exist in the effective use and interpretation of signal features to obtain clinically reliable BP measurements. The correlations between signal features and BP are obtained by mechanism-driven models which use physiological principles to identify mathematical correlations, and data-driven models which use machine learning algorithms to analyze observational data to identify multidimensional correlations. On the one hand, applying mechanism-driven models to non-linear scenarios and incomplete or noisy data is challenging On the other hand, data-driven models require a large amount of data in order to prevent physically inconsistent predictions, resulting in poor generalization. From this perspective, this paper proposes to combine the strengths of mechanism-driven and data-driven approaches to obtain a more comprehensive approach, the physiology-informed machine-learning approach, with the goal of enhancing the accuracy, interpretability, and scalability of continuous cuffless BP monitoring. This holds promise for personalized clinical applications and the advancement of hypertension management.

IntroductionThe intra-arterial catheter (invasive method) is the clinical and reference standard for continuous blood pressure (BP) monitoring. Continuous noninvasive blood pressure (CNBP) monitoring methods, for example applanation tonometry, volume clamp, and cuffless BP monitoring devices are gaining popularity. This review clarified the evidence on the accuracy of CNBP monitoring devices, which could potentially replace invasive monitoring in clinical care.MethodsA systematic search was carried out to look for systematic reviews with the following elements:Population: patients needing continuous BP monitoring;Intervention: CNBP monitoring devices;Comparator: intra-arterial BP monitoring; andOutcomes: accuracy of BP monitoring.The databases searched included PubMed (MEDLINE), Epistemonikos, and the Cochrane Database of Systematic Reviews. Two reviewers independently reviewed the search results and shortlisted relevant articles for retrieval of full texts. Included reviews were critically appraised with the AMSTAR 2 instrument and the findings were summarized in a narrative synthesis.ResultsThree systematic reviews with meta-analyses of fairly good quality were included. The included primary studies were conducted in perioperative or critical care settings. Subgroup analyses by CNBP monitoring method were included in each meta-analysis. The findings from the systematic reviews were consistent. On average, CNBP devices consistently measured lower systolic BPs than the invasive method (mean difference <0) and measured higher diastolic BPs and mean arterial pressures than the invasive method (mean difference >0), with wide ranging 95 percent limits of agreement. It was evident from subgroup analyses that the measurements obtained from different CNBP methods varied significantly.ConclusionsThis rapid review found the accuracy of CNBP monitoring devices to be suboptimal in comparison with invasive monitoring. CNBP devices should not be routinely used but may be considered when there is difficult arterial access, or in patients who do not require arterial puncture for other purposes.

Utility of pulse transit time in the detection of high blood pressure in patients admitted in a sleep unit

Funding AcknowledgementsType of funding sources: None.IntroductionTranscatheter atrial fibrillation (AF) ablation is in most centres commonly carried out with continuous invasive radial arterial blood pressure (BP) monitoring. Novel devices enable continuous non-invasive BP monitoring, with acceptable agreement and optimal safety profile when compared to standard of care invasive BP monitoring, leading to improved patient comfort in the electrophysiology lab.PurposeAim of the study was to assess in terms of procedural efficiency continuous non-invasive BP monitoring during transcatheter atrial fibrillation ablation.MethodsWe prospectively enrolled 42 consecutive patients (age 61±9 years, 80% male) undergoing transcatheter AF ablation (60% paroxysmal, 40% persistent) at our centre undergoing AF ablation with continuous BP measurement using a non-invasive finger volume clamp device. We then compared them with an historical cohort of 42 consecutive patients undergoing AF ablation (62% paroxysmal, 38% persistent) with standard of care invasive BP monitoring with a radial cannula. We compared the two groups in terms of total procedural duration (in and out from the EP lab).ResultsMean total procedural duration was 165,29±54,95 minutes in the non-invasive group and 196,55±46,67 minutes in the invasive group (P=0,006).ConclusionIn patients undergoing AF ablation, non-invasive finger volume-clamp continuous BP monitoring allowed for a significant reduction of total procedural duration when compared to standard of care invasive BP monitoring. Larger studies are needed to confirm these results.Non-invasive BP monitoringProcedural duration comparison boxplot

Continuous blood pressure (BP) monitoring in a noninvasive and unobtrusive way can significantly improve the awareness, control and treatment rate of prevalent hypertension. Pulse transit time (PTT) has become increasingly popular in recent years for continuous BP measurement without a cuff. However, the accuracy issue of PTT-based method remains to be solved for clinical application. Some previous studies have attempted to estimate BP with only PTT by using linear regression, which is susceptible to arterial regulation and may not reflect the actual relationship between PTT and BP. Furthermore, PTT does not contain all the information of BP variation, thereby resulting in unsatisfactory accuracy. In this paper we establish a cuffless BP estimation model from a physiological perspective by utilizing PTT and photoplethysmogram (PPG) intensity ratio (PIR), an indicator we have recently proposed for evaluation of the change in arterial diameter and the low frequency variation of BP, with the consideration that PIR can track changes in mean BP (MBP) and arterial diameter change. The performance of the proposed BP model was evaluated by comparing the estimated BP with Finapres BP as reference on 10 healthy subjects. The results showed that the mean ± standard deviation (SD) of the estimation error for systolic and diastolic BP were −0.41 ± 5.15 and −0.84 ± 4.05 mmHg, and mean absolute difference (MAD) were 4.18 and 3.43 mmHg, respectively. Furthermore, the proposed modeling method was superior to one contrast PTT-based method, demonstrating the proposed model would be promising for reliable continuous cuffless BP measurement.

Continuous blood pressure (BP) monitoring is essential for cardiovascular health, yet current BP sensors face cuff‐dependent limitations. Cuff‐free alternatives still suffer from discomfort and discontinuous measurement. Here a wearable hyperspectral photoplethysmography (HS‐PPG) is reported for continuous and nonconscious BP monitoring. The HS‐PPG module integrates an ultrathin and high‐resolution double‐folded solid immersion grating microspectrometer (DFSIG‐µSPEC) with a white light LED. DFSIG‐µSPEC shows an average spectral resolution of 3.4 nm for 550–800 nm in the operational range. The HS‐PPG module has a compact physical dimension of 8 mm × 16 mm × 24 mm, suitable for wrist‐wearable configuration. The PPG waveforms contain 50 spectral bands, achieving precise measurement of arteriolar pulse transit time (aPTT). The diastolic and systolic BPs are precisely estimated with R‐values of 0.92 and 0.96, and mean absolute differences (MAD) of 1.20 and 0.40 mmHg with the 2‐element Windkessel model, respectively. Further, the BP is continuously measured with heart rate (HR) and respiratory exchange ratio (RER) with exercise‐induced hypertension. Continuous monitoring of systolic blood pressure (SBP) exhibits immediate responses during hemodynamic changes, with the physiological parameters of SBP, HR, and RER during exercise and recovery. The wearable HS‐PPG clearly supports the strong potential for high‐fidelity continuous BP monitoring.

Blood pressure (BP), the pressure exerted by circulating blood upon the walls of blood vessels, is an important physiological parameter and can provide some information for personal healthcare. There are two ways to measure blood pressure of human being, invasive and noninvasive methods. Invasive method can measure BP continuously and accurately, however, it is inconvenient to operate and may cause infection. Although traditional noninvasive methods such as Korotkoff and Oscillometric are easy to obtain BP value, they all need a cuff and not very convenient. Therefore, in this paper, we implement a cuff-less continuous blood pressure monitoring device, which is consisted of two acquisition nodes and an Android smart-phone. The data can be transmitted by a Bluetooth module in the system. The pulse transit time (PTT) can be obtained by using the ECG and pulse wave signals, which were synchronously acquired by our designed system, for estimating blood pressure. Our proposed method can be used for non-constrained and continuous blood pressure monitoring.

The assessment of dynamic features of blood pressure, which represent a response of cardiovascular control mechanisms to environmental stimulations and to daily life challenges, not only offers important insights into cardiovascular regulation patterns but also carries clinically relevant information. Availability of tools for continuous blood pressure monitoring represents a key step to make such an assessment possible, but its implementation in daily practice requires noninvasive, simple and minimally intrusive methods. These methods are expected to overcome the well-known limitations characterizing the conventional approach to blood pressure measurement based on discontinuous blood pressure readings obtained through repeated arm cuff inflations. In such a perspective, techniques able to provide continuous blood pressure monitoring without the need of a cuff inflation would be welcome.

There is an unmet need for cuff-less blood pressure (BP) monitoring especially, in personal healthcare applications. The pulse arrival time (PAT) approach might offer a suitable solution to enable comfortable BP monitoring even at beat-level. However, the methodology is based on hemodynamic surrogate measures, which are sensitive to patient activities such as posture changes, not necessarily related to blood pressure variations. In this paper, we analyze the impact of posture on the PAT measure and related hemodynamic parameters such as the pre-ejection period in well-defined procedures. Additionally, the PAT of a monitored subject is investigated in an unsupervised scenario illustrating the complexity of such a measurement. Our results show the failure of blood pressure inference based on simple calibration strategies using the PAT measure only. We discuss opportunities to compensate for the observed effects towards the realization of wearable cuff-less blood pressure monitoring. These findings emphasize the importance of accessing context information in personal healthcare applications, where vital sign monitoring is typically unsupervised.