Continuous Blood Pressure Monitoring Research Articles

Continuous Non-Invasive Blood Pressure Monitoring: A Methodological Review on Measurement Techniques

Continuous measurement of blood pressure is crucial to the assessment of many medical conditions. However, the current clinical gold standard involving an arterial catheter, occluding cuff, and other invasive procedures are performed in hospital settings while home-based devices can provide only intermittent measurement and are not as reliable. Therefore, there is a significant need for continuous non-invasive blood pressure (cNIBP) monitoring in the daily life. Pulse transit time (PTT)/pulse arrival time (PAT) - based blood pressure measurement has proven its potential to address this need. In this article, we present state-of-the-art devices and recent literature related to measurement technologies used in PTT/PAT - based methods for cNIBP monitoring. Various physiological signals which could be used to enable cNIBP in the home setting are categorized into two groups (i.e., proximal waveforms and distal waveforms) and are thoroughly discussed and compared. Given insightful analysis of these waveforms, we highlight their combinations to derive PTT/PAT values for BP measurement then discuss challenges presented from the cuffless and PTT/PAT - based nature of these devices. Finally, we conclude with future directions needed for home-based cNIBP adaptation and present societal broader impacts.

Continuous Blood Pressure Measurement Platform: A Wearable System Based on Multidimensional Perception Data

The mobile crowd sensing technology in the environment integrating human, machines and things is an emerging direction in social computing. In kinematics research, continuous blood pressure monitoring and calibration are the basis for revealing the correlation between athlete motor function and blood pressure. At the same time, in the field of medical research, hypertension can be more easily controlled, thus improving the effectiveness of hypertension treatment. This paper presents the design principle of a human-machine fusion system based on CrowdOS, a mobile crowd sensing platform. The system innovatively establishes the correlation between blood pressure and exercise, improves the accuracy of cuffless blood pressure measurement, and verifies the feasibility of calibrating continuous cuffless blood pressure measurement based on exercise information. Using our system and electronic cuff sphygmomanometer, we measured 65 groups of data in walking, running, sitting and climbing stairs, each group lasting about 10 minutes. Based on these data, we established a regression analysis model for blood pressure measurement calibration. The accuracy of blood pressure calibration was improved from the original systolic root mean square error of 13.43mmHg and diastolic root mean square error of 8.35mmHg to 9.76mmHg and 5.56mmHg. The design method proposed in this paper provides a feasible solution for continuous cuffless blood pressure measurement and calibration, and shows broad application prospects in the fields of athlete scientific training and medical care.

Accurate Fiducial Point Detection Using Haar Wavelet for Beat-by-Beat Blood Pressure Estimation.

Pulse Arrival Time (PAT) derived from Electrocardiogram (ECG) and Photoplethysmogram (PPG) for cuff-less Blood Pressure (BP) measurement has been a contemporary and widely accepted technique. However, the features extracted for it are conventionally from an isolated pulse of ECG and PPG signals. As a result, the estimated BP is intermittent. Objective: This paper presents feature extraction from each beat of ECG and PPG signals to make BP measurements uninterrupted. These features are extracted by employing Haar transformation to adaptively attenuate measurement noise and improve the fiducial point detection precision. Method: the use of only PAT feature as an independent variable leads to an inaccurate estimation of either Systolic Blood Pressure (SBP) or Diastolic Blood Pressure (DBP) or both. We propose the extraction of supplementary features that are highly correlated to physiological parameters. Concurrent data was collected as per the Association for the Advancement of Medical Instrumentation (AAMI) guidelines from 171 human subjects belonging to diverse age groups. An Adaptive Window Wavelet Transformation (AWWT) technique based on Haar wavelet transformation has been introduced to segregate pulses. Further, an algorithm based on log-linear regression analysis is developed to process extracted features from each beat to calculate BP. Results: The mean error of 0.43 and 0.20 mmHg, mean absolute error of 4.6 and 2.3 mmHg, and Standard deviation of 6.13 and 3.06 mmHg is achieved for SBP and DBP respectively. Conclusions: The features extracted are highly precise and evaluated BP values are as per the AAMI standards. Clinical Impact: This continuous real-time BP monitoring technique can be useful in the treatment of hypertensive and potential-hypertensive subjects.

The Autonomic Regulation of Circulation and Adverse Events in Hypertensive Patients during Follow-Up Study.

Purpose Comprehensive study of autonomic regulation assessed during follow-up could provide new detailed information about the risks stratification for hypertensive patients. Therefore, we investigated the associations of these indices with death, stroke, and revascularization during the follow-up observation of 55 patients. Methods All patients were with target organ damage, and 27 of them had associated clinical conditions (ACC). Mean age of patients with and without ACC was 62.6 ± 4.2 and 51.9 ± 9.9 (mean ± SD) years, respectively. Follow-up was from 66 to 95 months. At entry, autonomic regulation was assessed by the tilt test, Valsalva maneuver, hand-grip test, and cold-stress vasoconstriction. Hemodynamic parameters were measured by continuous blood pressure monitoring, occlusion plethysmography, and electrocardiography. Re-examination of patients was carried out by questioning and physical and laboratory examination. Results We found that fatal outcomes were associated with a lower Valsalva index (1.34 ± 0.16 vs. 1.69 ± 0.37, P < 0.05) and depressed cold vasoconstriction (0.20 ± 0.02 vs. 0.39 ± 0.16%, P < 0.05) and depressed cold vasoconstriction (0.20 ± 0.02 vs. 0.39 ± 0.16%, P < 0.05) and depressed cold vasoconstriction (0.20 ± 0.02 vs. 0.39 ± 0.16%, P < 0.05) and depressed cold vasoconstriction (0.20 ± 0.02 vs. 0.39 ± 0.16%, P < 0.05) and depressed cold vasoconstriction (0.20 ± 0.02 vs. 0.39 ± 0.16%, P < 0.05) and depressed cold vasoconstriction (0.20 ± 0.02 vs. 0.39 ± 0.16%, P < 0.05) and depressed cold vasoconstriction (0.20 ± 0.02 vs. 0.39 ± 0.16%, Conclusions This study shows that such autonomic regulation indices as Valsalva index, blood pressure dynamics in the tilt test, cold-stress vasomotor reactivity, and BPV are important for prognosis of hypertension course.

Non-Invasive Continuous Blood-Pressure Monitoring Models Based on Photoplethysmography and Electrocardiography.

Blood pressure is an extremely important blood hemodynamic parameter. The pulse wave contains abundant blood-pressure information, and the convenience and non-invasivity of its measurement make it ideal for non-invasive continuous monitoring of blood pressure. Based on combined photoplethysmography and electrocardiogram signals, this study aimed to extract the waveform information, introduce individual characteristics, and construct systolic and diastolic blood-pressure (SBP and DBP) estimation models using the back-propagation error (BP) neural network. During the model construction process, the mean impact value method was employed to investigate the impact of each feature on the model output and reduce feature redundancy. Moreover, the multiple population genetic algorithm was applied to optimize the BP neural network and determine the initial weights and threshold of the network. Finally, the models were integrated for further optimization to generate the final individualized continuous blood-pressure monitoring models. The results showed that the predicted values of the model in this study correlated significantly with the measured values of the electronic sphygmomanometer. The estimation errors of the model met the Association for the Advancement of Medical Instrumentation (AAMI) criteria (the SBP error was 2.5909 ± 3.4148 mmHg, and the DBP error was 2.6890 ± 3.3117 mmHg) and the Grade A British Hypertension Society criteria.

Comparison of a noninvasive 3D force sensor-based method and the invasive arterial cannula in postsurgery intensive care patients: a pilot study

Improvement in sensing technologies is leading to new, accurate noninvasive monitoring devices. However, noninvasive continuous blood pressure (BP) monitoring still faces many challenges, such as: patient's movement, device accuracy and consistency. In this study, the accuracy of a novel noninvasive BP measuring system based on a three-axis force sensor is compared with the invasive arterial cannula taking 21 simultaneous measurements mostly on elderly, postsurgical participants. For the simultaneously recorded invasive and noninvasive signals, the similarity was high, the average correlation was 0.9001 ± 0.0588. The average differences (±SD) for simultaneously recorded systolic, diastolic and mean arterial pressures were: -9.53 ± 4.69, -0.26 ± 3.06 and 1.25 ± 2.26 mmHg, respectively. The results of diastolic and mean arterial pressure satisfy the criteria set by the Association for the Advancement of Medical Instrumentation. These results suggest that this noninvasive system could be a useful tool in continuous noninvasive BP monitoring, but still requires development.

Blind, Cuff-less, Calibration-Free and Continuous Blood Pressure Estimation using Optimized Inductive Group Method of Data Handling

Traditionally, blood pressure (BP) is measured by cuff-based instruments, which is inconvenient and does not allow continuous measurement. In fact, continuous blood pressure monitoring is precious for gaining information about the health conditions of people. In this paper, an algorithm is developed using a modified group method of data handling technique to estimate systolic BP (SBP) and diastolic BP (DBP) by only photo-plethysmogram (PPG) signal in a continuous manner. The estimation does not require to calibration and is done without any knowledge about significant features, and features are selected based on their competency. The Multi-parameter Intelligent Monitoring in Intensive Care dataset is used for training the system, and the hold-out validation is used in 7 runs by assuming 70% of the samples as a train set. Moreover, a designed hardware device is used for recording data on 25 subjects for testing the trained model on the real-world. As the state-of-the-art, four popular regression algorithms, including support vector machine, adaptive boosting, decision tree and random forest, are trained with conventional features, which use an electrocardiogram (ECG) and PPG signals simultaneously and compared with the proposed system. The root means square error (RMSE) and the mean absolute error (MAE) of the proposed algorithm is 3.47 ± 1.31 and 2.40 ± 1.01 mmHg for SBP and 4.67 ± 1.44 and 3.33 ± 1.61 mmHg for DBP respectively. Also, the RMSE of the proposed algorithm on recorded data by hardware device is 3.2 ± 0.7 and 4.4 ± 1.0 mmHg, and the MAE is 2.2 ± 0.7 and 2.9 ± 1.2 mmHg for SBP and DBP, respectively. The proposed algorithm is not dependent on synchronization of ECG and PPG, and it is promising compared to the state-of-the-art, especially in recorded data by new hardware.

Anesthetic management of modified electroconvulsive therapy for a patient with coronary aneurysms: a case report

BackgroundModified electroconvulsive therapy (m-ECT) is utilized worldwide as an effective treatment for drug-resistant psychiatric disorders. However, during m-ECT, treatment of hypotension and hypertension in response to rapid hemodynamic changes is required. We used noninvasive continuous blood pressure monitoring system for continuous hemodynamic measurement during m-ECT.Case presentationThe patient was a 77-year-old man with depression complicated by coronary artery aneurysms (CAAs). We managed general anesthesia during m-ECT by using the ClearSight™ system (Edwards Lifesciences Corp, Irvine, CA, USA) for hemodynamic measurement. As a result, we performed a total of 10 m-ECTs. No rupture of CAAs or myocardial ischemia occurred and depressive symptoms improved.ConclusionWe successfully managed the anesthesia in m-ECT for a depressed patient with CAAs without complications by using the ClearSight™ system, which was used for the effective management of circulatory fluctuations.

Harnessing technology and molecular analysis to understand the development of cardiovascular diseases in Asia: a prospective cohort study (SingHEART)

BackgroundCardiovascular disease (CVD) imposes much mortality and morbidity worldwide. The use of “deep learning”, advancements in genomics, metabolomics, proteomics and devices like wearables have the potential to unearth new insights in the field of cardiology. Currently, in Asia, there are no studies that combine the use of conventional clinical information with these advanced technologies. We aim to harness these new technologies to understand the development of cardiovascular disease in Asia.MethodsSingapore is a multi-ethnic country in Asia with well-represented diverse ethnicities including Chinese, Malays and Indians. The SingHEART study is the first technology driven multi-ethnic prospective population-based study of healthy Asians. Healthy male and female subjects aged 21–69 years old without any prior cardiovascular disease or diabetes mellitus will be recruited from the general population. All subjects are consented to undergo a detailed on-line questionnaire, basic blood investigations, resting and continuous electrocardiogram and blood pressure monitoring, activity and sleep tracking, calcium score, cardiac magnetic resonance imaging, whole genome sequencing and lipidomic analysis. Outcomes studied will include mortality and cause of mortality, myocardial infarction, stroke, malignancy, heart failure, and the development of co-morbidities.DiscussionAn initial target of 2500 patients has been set. From October 2015 to May 2017, an initial 683 subjects have been recruited and have completed the initial work-up the SingHEART project is the first contemporary population-based study in Asia that will include whole genome sequencing and deep phenotyping: including advanced imaging and wearable data, to better understand the development of cardiovascular disease across different ethnic groups in Asia.

The Peripheral Perfusion Index tracks systemic haemodynamics during general anaesthesia.

Stable intraoperative haemodynamics are associated with improved outcome and even short periods of instability are associated with an increased risk of complications. During anaesthesia intermittent non-invasive blood pressure and heart rate remains the cornerstone of haemodynamic monitoring. Continuous monitoring of systemic blood pressure or even-flow requires invasive or advanced modalities creating a barrier for obtaining important real-time haemodynamic insight. The Peripheral Perfusion Index (PPI) is obtained continuously and non-invasively by standard photoplethysmography. We hypothesized that changes in indices of systemic blood flow during general anaesthesia would be reflected in the PPI. PPI, stroke volume (SV), cardiac output (CO) and mean arterial pressure (MAP) were evaluated in 20 patients. During general anaesthesia but before start of surgery relative changes of SV, CO and MAP were compared to the relative changes of PPI induced by head-up (HUT) and head-down tilt (HDT). Furthermore, the effect of phenylephrine (PE) during HUT on these parameters was investigated. ∆PPI correlated significantly (p < 0.001) with ∆SV (r = 0.9), ∆CO (r = 0.9), and ∆MAP (r = 0.9). HUT following induction of anaesthesia resulted in a decrease in PPI of 41% (25-52) [median (IQR)], SV 27% (23-31), CO 27% (25-35), and MAP28% (22-35). HDT led to an increase in PPI of 203% (120-375), SV of 29% (21-41), CO 22% (16-34), and MAP47% (42-60). After stabilizing a second HUT decreased PPI 59% (49-76), SV 33% (28-37), CO 31% (28-36), and MAP34% (26-38). Restoration of preload with PE increased PPI by 607% (218-1078), SV by 96% (82-116), CO by 65% (56-99), and MAP by 114% (83-147). During general anaesthesia changes in PPI tracked changes in systemic haemodynamics.

RISK OF HYPOTENSION IN PREGNANT LADIES UNDERGOING SPINAL ANESTHESIA INDUCED CESAREAN SECTION DELIVERIES.

Background; Cesarean section, one of most commonly performed surgical procedure, is associated with significant increase in maternal morbidities as well as mortalities. Objective: To determine frequency of hypotension in normotensive and preeclemptia patients undergoing spinal anaesthesia induced cesarean section. Material and Methods; Spinal anaesthesia was employed following standard technique after aspiration of free flow of CSF from needle in all four quadrants. After induction of spinal anaesthesia continuous monitoring of heart rate, oxygen situation and blood pressure was done immediately and at regular intervals of 5,10,15,20,.25 and 30 minutes to diagnose hypotension. Results; Mean gestational age of our study cases was noted to be 39.23 ± 2.16 weeks and 101 (69.2%) had gestational age more than 38 weeks. Mean age of our study cases was 27.49 ± 2.93 years. Diabetes was presented in 19 (13 %) of our study cases. Status of blood pressure in pregnancy was also noted, 73 (50%) were normotensive and 73 (50%) were pre-eclamptic patients. Mean body mass index of our study cases was 26.23 ± 1.92 kg/m 2 and obesity was present in 43 (29.5 %) of our study cases. Of these 146 study cases, 44 (30.1 %) had elective cesarean section and 102 (69.9%) had emergency cesarean section. Hypotension was noted in 74 (50.7%) of our study cases. Hypotension was 35.6 % in normotensive cases while 65.8% among pre-eclamptic patients. Conclusion; Frequency of hypotension among women undergoing cesarean section with spinal anesthesia was high and hypotension was significantly more prevalent among women with the history of pre-eclampsia. Hypotension was significantly associated with age, residential status, monthly family income, diabetes, obesity and type of Cesarean section. Keywords; cesarean section, hypotension, spinal anesthesia DOI : 10.7176/JMPB/61-06 Publication date: November 30 th 2019

Non-invasive continuous blood pressure monitoring systems: current and proposed technology issues and challenges.

High blood pressure (BP) or hypertension is the single most crucial adjustable risk factor for cardiovascular diseases (CVDs) and monitoring the arterial blood pressure (ABP) is an efficient way to detect and control the prevalence of the cardiovascular health of patients. Therefore, monitoring the regulation of BP during patients' daily life plays a critical role in the ambulatory setting and the latest mobile health technology. In recent years, many studies have been conducted to explore the feasibility and performance of such techniques in the health care system. The ultimate aim of these studies is to find and develop an alternative to conventional BP monitoring by using cuff-less, easy-to-use, fast, and cost-effective devices for controlling and lowering the physical harm of CVDs to the human body. However, most of the current studies are at the prototype phase and face a range of issues and challenges to meet clinical standards. This review focuses on the description and analysis of the latest continuous and cuff-less methods along with their key challenges and barriers. Particularly, most advanced and standard technologies including pulse transit time (PTT), ultrasound, pulse arrival time (PAT), and machine learning are investigated. The accuracy, portability, and comfort of use of these technologies, and the ability to integrate to the wearable healthcare system are discussed. Finally, the future directions for further study are suggested.

Multi-Site Photoplethysmography Technology for Blood Pressure Assessment: Challenges and Recommendations.

Hypertension is one of the most prevalent diseases and is often called the “silent killer” because there are usually no early symptoms. Hypertension is also associated with multiple morbidities, including chronic kidney disease and cardiovascular disease. Early detection and intervention are therefore important. The current routine method for diagnosing hypertension is done using a sphygmomanometer, which can only provide intermittent blood pressure readings and can be confounded by various factors, such as white coat hypertension, time of day, exercise, or stress. Consequently, there is an increasing need for a non-invasive, cuff-less, and continuous blood pressure monitoring device. Multi-site photoplethysmography (PPG) is a promising new technology that can measure a range of features of the pulse, including the pulse transit time of the arterial pulse wave, which can be used to continuously estimate arterial blood pressure. This is achieved by detecting the pulse wave at one body site location and measuring the time it takes for it to reach a second, distal location. The purpose of this review is to analyze the current research in multi-site PPG for blood pressure assessment and provide recommendations to guide future research. In a systematic search of the literature from January 2010 to January 2019, we found 13 papers that proposed novel methods using various two-channel PPG systems and signal processing techniques to acquire blood pressure using multi-site PPG that offered promising results. However, we also found a general lack of validation in terms of sample size and diversity of populations.

Estimation of arterial pressure from pletismography data

Continuous blood pressure monitoring is important for the prevention and early diagnosis of cardiovascular diseases, the number of which is growing worldwide. A method for measuring blood pressure (BP) based on a plethysmography signal is one of many simple methods for non-invasive monitoring of blood pressure. The article presents a comparative analysis of blood pressure signals and plethysmograms (PG) synchronized in time, as well as their spectral features. A certain temporal structural similarity of the BP and PG signals (correspondence of time intervals, amplitudes) with a simultaneous time shift of the PG signal was revealed. It is shown how adequately one can judge blood pressure, having only the captured PG data. As the time intervals, the minute sequence of cardiac cycles was chosen. It is noted that with appropriate calibration of PG signals, it is possible to estimate the average blood pressure value for several cardiac cycles. The results obtained can be used in the diagnosis of various pathologies.

Analysis of Pulse Arrival Time as an Indicator of Blood Pressure in a Large Surgical Biosignal Database: Recommendations for Developing Ubiquitous Blood Pressure Monitoring Methods.

As non-invasive continuous blood pressure monitoring (NCBPM) has gained wide attraction in the recent decades, many pulse arrival time (PAT) or pulse transit time (PTT) based blood pressure (BP) estimation studies have been conducted. However, most of the studies have used small homogeneous subject pools to generate models of BP based on particular interventions for induced hemodynamic change. In this study, a large open biosignal database from a diverse group of 2309 surgical patients was analyzed to assess the efficacy of PAT, PTT, and confounding factors on the estimation of BP. After pre-processing the dataset, a total of 6,777,308 data pairs of BP and temporal features between electrocardiogram (ECG) and photoplethysmogram (PPG) were extracted and analyzed. Correlation analysis revealed that PAT or PTT extracted from the intersecting-tangent (IT) point of PPG showed the highest mean correlation to BP. The mean correlation between PAT and systolic blood pressure (SBP) was −0.37 and the mean correlation between PAT and diastolic blood pressure (DBP) was −0.30, outperforming the correlation between BP and PTT at −0.12 for SBP and −0.11 for DBP. A linear model of BP with a simple calibration method using PAT as a predictor was developed which satisfied international standards for automatic oscillometric BP monitors in the case of DBP, however, SBP could not be predicted to a satisfactory level due to higher errors. Furthermore, multivariate regression analyses showed that many confounding factors considered in previous studies had inconsistent effects on the degree of correlation between PAT and BP.

Episodic stimulation of central chemoreceptor neurons elicits disordered breathing and autonomic dysfunction in volume overload heart failure.

Enhanced central chemoreflex (CC) gain is observed in volume overload heart failure (HF) and is correlated with autonomic dysfunction and breathing disorders. The aim of this study was to determine the role of the CC in the development of respiratory and autonomic dysfunction in HF. Volume overload was surgically created to induce HF in male Sprague-Dawley rats. Radiotelemetry transmitters were implanted for continuous monitoring of blood pressure and heart rate. After recovering from surgery, conscious unrestrained rats were exposed to episodic hypercapnic stimulation [EHS; 10 cycles/5 min, inspiratory fraction of carbon dioxide () 7%] in a whole body plethysmograph for recording of cardiorespiratory function. To determine the contribution of CC to cardiorespiratory variables, selective ablation of chemoreceptor neurons within the retrotrapezoid nucleus (RTN) was performed via injection of saporin toxin conjugated to substance P (SSP-SAP). Vehicle-treated rats (HF+Veh and Sham+Veh) were used as controls for SSP-SAP experiments. Sixty minutes post-EHS, minute ventilation was depressed in sham animals relative to HF animals (ΔV̇e: −5.55 ± 2.10 vs. 1.24 ± 1.35 mL/min 100 g, P < 0.05; Sham+Veh vs. HF+Veh). Furthermore, EHS resulted in autonomic imbalance, cardiorespiratory entrainment, and ventilatory disturbances in HF+Veh but not Sham+Veh rats, and these effects were significantly attenuated by SSP-SAP treatment. Also, the apnea-hypopnea index (AHI) was significantly lower in HF+SSP-SAP rats compared with HF+Veh rats (AHI: 5.5 ± 0.8 vs. 14.4 ± 1.3 events/h, HF+SSP-SAP vs. HF+Veh, respectively, P < 0.05). Finally, EHS-induced respiratory-cardiovascular coupling in HF rats depends on RTN chemoreceptor neurons because it was reduced by SSP-SAP treatment. Overall, EHS triggers ventilatory plasticity and elicits cardiorespiratory abnormalities in HF that are largely dependent on RTN chemoreceptor neurons.

Relationship between mechanisms of blood pressure change and facial skin temperature distribution

Hypertension causes cerebrovascular and cardiovascular diseases. To help prevent this, early detection requires continuous monitoring of blood pressure in daily life, which must be measured without contact. We previously proposed a noncontact technique for measuring blood pressure in which we evaluated the relationship between the variation in blood pressure caused by the cardiac-dominant pattern and facial skin temperature distribution using independent component analysis and multiple regression analysis. The mechanism of blood pressure change is roughly classified into cardiac-dominant patterns and vascular-dominant patterns. An elucidation of the relationship between these patterns and facial skin temperature distribution is the objective of this study. Two tests resulting in cardiac-dominant and vascular-dominant patterns were conducted. These common and different features related to each mechanism of BP change in each subject were then evaluated. The results of the tests show that similar features were extracted from the nasal region and contrasting feature quantities were extracted from the other facial regions. Hence, individual models were constructed for estimating blood pressure using the common features related to both mechanisms. A high coefficient of determination was obtained from these models, suggesting that models for estimating blood pressure caused by both mechanisms can be constructed using the proposed approach.

Inflight leg cuff test does not identify the risk for orthostatic hypotension after long-duration spaceflight

Landing day symptoms from orthostatic hypotension after prolonged spaceflight can be debilitating, but severity of these symptoms can be unpredictable and highly individual. We tested the hypothesis that an impaired baroreflex response to an inflight leg cuff test could predict orthostatic intolerance on return to Earth. Eight male astronauts (44 ± 7 years of age (mean ± SD); mean mission length: 167 ± 12 days) participated in a standardized supine-to-sit-to-stand test (5 min–30s–3 min) pre- and postflight, and a 3 min thigh cuff occlusion test pre- and inflight with continuous monitoring of heart rate and arterial blood pressure. The arterial baroreflex was not changed inflight as shown by similar reductions in mean arterial pressure (MAP) response to leg cuff deflation (preflight −19 ± 2 mmHg vs. inflight −18 ± 5 mmHg). With the sit/stand test, the nadir of MAP was lower postflight (−17 ± 9 mmHg) than preflight (−11 ± 6 mmHg, p < 0.05). A greater increase in heart rate (25 ± 7; 16 ± 3 bpm) and decrease in stroke volume (−24 ± 11; −6 ± 4 mL) occurred with sit/stand postflight than leg cuffs inflight (p < 0.001). Inflight testing was influenced by elevated cardiac output resulting in a smaller drop in total peripheral resistance. Two of eight subjects exhibited orthostatic hypotension during the postflight stand test; their responses were not predicted by the inflight leg cuff deflation test. These results suggest that the baroreflex response examined by inflight leg cuff deflation was not a reliable indicator of postflight stand responses.

Cuffless Blood Pressure Monitoring from an Array of Wrist Bio-Impedance Sensors Using Subject-Specific Regression Models: Proof of Concept.

Continuous and beat-to-beat monitoring of blood pressure (BP), compared to office-based BP measurement, provides significant advantages in predicting future cardiovascular disease. Traditional BP measurement methods are based on a cuff, which is bulky, obtrusive and not applicable to continuous monitoring. Measurement of pulse transit time (PTT) is one of the prominent cuffless methods for continuous BP monitoring. PTT is the time taken by the pressure pulse to travel between two points in an arterial vessel, which is correlated with the BP. In this paper, we present a new cuffless BP method using an array of wrist-worn bio-impedance sensors placed on the radial and the ulnar arteries of the wrist to monitor the arterial pressure pulse from the blood volume changes at each sensor site. BP is accurately estimated by using AdaBoost regression model based on selected arterial pressure pulse features such as transit time, amplitude and slope of the pressure pulse, which are dependent on the cardiac activity and the vascular properties of the wrist arteries. A separate model is developed for each subject based on calibration data to capture the individual variations of BP parameters. In this pilot study, data was collected from 10 healthy participants with age ranges from 18 to 30 years after exercising using our custom low-noise bio-impedance sensing hardware. Post-exercise BP was accurately estimated with an average correlation coefficient and root mean square error (RMSE) of 0.77 and 2.6 mmHg for the diastolic BP and 0.86 and 3.4 mmHg for the systolic BP.

Agreement and Precision of a Novel Smartphone Application (OPTIBP) For Continuous Blood Pressure Monitoring

Agreement and Precision of a Novel Smartphone Application (OPTIBP) For Continuous Blood Pressure Monitoring