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.

The Association of Dietary Intake with Arterial Stiffness and Vascular Ageing in a Population with Intermediate Cardiovascular Risk-A MARK Study.

The aim of this study was to analyse the association of diet with arterial stiffness and vascular ageing in a Caucasian population with intermediate cardiovascular risk. We recruited 2475 individuals aged 35-75 years with intermediate cardiovascular risk. Brachial-ankle pulse wave velocity (baPWV) was measured using a VaSera VS-1500® device. Vascular ageing was defined in two steps. Step 1: The 20 individuals who presented kidney disease, peripheral arterial disease, or heart failure were classified as early vascular ageing (EVA). Step 2: The individuals with percentiles by age and sex above the 90th percentile of baPWV among the participants of this study were classified as EVA, and the rest of the individuals were classified as non-EVA. The diet of the participants was analysed with two questionnaires: (1) the diet quality index (DQI) questionnaire and (2) the Mediterranean diet (MD) adherence questionnaire. The mean age of the sample was 61.34 ± 7.70 years, and 61.60% were men. Adherence to the MD was 53.30%. The DQI was 54.90%. Of the entire sample, 10.70% (11.15% of the men and 9.95% of the women) were EVA. In the multiple linear regression analysis, for each additional point in the DQI questionnaire, there was a decrease of -0.081 (95%CI (confidence intervals) -0.105--0.028) in baPWV; in the MD adherence questionnaire, there was a decrease of -0.052 (95%CI -0141--0.008). When performing the analysis, separated by sex, the association remained significant in men but not in women. In the logistic regression analysis, there was an increase in MD adherence and a decrease in the probability of presenting EVA, both with the DQI questionnaire (OR (odds ratio) = 0.65; 95%CI 0.50-0.84) and with the MD adherence questionnaire (OR = 0.75; 95%CI 0.58-0.97). In the analysis by sex, the association was only maintained in men (with DQI, OR = 0.54; 95%CI 0.37-0.56) (with MD, OR = 0.72; 95%CI 0.52-0.99). The results of this study suggest that a greater score in the DQI and MD adherence questionnaires is associated with lower arterial stiffness and a lower probability of presenting EVA. In the analysis by sex, this association is only observed in men.

Using compositional analysis to explore the relationship between physical activity and cardiovascular health in children and adolescents with and without type 1 diabetes.

OBJECTIVE: The aim of this study was to use a compositional analysis approach to account for the inherent co-dependencies between behaviors and to explore how daily movement behaviors influence cardiovascular health in children with and without T1D. RESEARCH DESIGN AND METHODS: Augmentation index, pulse wave velocity (PWV) and heart rate variability were measured in 20 children with (11.9 ± 1.6 years) and 17 children without T1D (11.6 ± 2.2 years). Subsequently, physical activity and sleep were assessed at 20 Hz for 28 consecutive days using a wrist-worn accelerometer. Compositional analyses were utilized to explore the relative effects of each movement behavior and the overall movement complex on cardiovascular parameters, with predictive modeling used to explore the effects of reallocating 20 min between behaviors. RESULTS: Arterial stiffness markers were most influenced by the total movement composition, whereas autonomic function was most influenced by sedentary time and sleep relative to all other behaviors. Reallocation of time from moderate-to-vigorous physical activity (MVPA) to any other behavior was predicted to negatively affect all cardiovascular measures, independent of disease status, whereas reallocating time to MVPA was consistently predicted to improve all outcome measures. Additionally, the same intensity of physical activity appeared to be more potent for cardiovascular health in T1D children compared to nondiabetic peers. CONCLUSIONS: Intensity, rather than volume, of physical activity may be key in reducing risk of premature adverse changes in cardiovascular health, whereas increasing time in MVPA could potentially the slow progression of cardiovascular aging in children with diabetes.

Evaluation of the Accuracy of Cuffless Blood Pressure Measurement Devices: Challenges and Proposals.

Several novel cuffless wearable devices and smartphone applications claiming that they can measure blood pressure (BP) are appearing on the market. These technologies are very attractive and promising, with increasing interest among health care professionals for their potential use. Moreover, they are becoming popular among patients with hypertension and healthy people. However, at the present time, there are serious issues about BP measurement accuracy of cuffless devices and the 2021 European Society of Hypertension Guidelines on BP measurement do not recommend them for clinical use. Cuffless devices have special validation issues, which have been recently recognized. It is important to note that the 2018 Universal Standard for the validation of automated BP measurement devices developed by the American Association for the Advancement of Medical Instrumentation, the European Society of Hypertension, and the International Organization for Standardization is inappropriate for the validation of cuffless devices. Unfortunately, there is an increasing number of publications presenting data on the accuracy of novel cuffless BP measurement devices, with inadequate methodology and potentially misleading conclusions. The objective of this review is to facilitate understanding of the capabilities and limitations of emerging cuffless BP measurement devices. First, the potential and the types of these devices are described. Then, the unique challenges in evaluating the BP measurement accuracy of cuffless devices are explained. Studies from the literature and computer simulations are employed to illustrate these challenges. Finally, proposals are given on how to evaluate cuffless devices including presenting and interpreting relevant study results.

Correlation of vascular risk age with pulse wave velocity in young patients with low absolute cardiovascular risk.

OBJECTIVE: The systematic coronary risk evaluation (SCORE) estimates the 10-year risk of fatal cardiovascular disease (CVD), and its application is recommended. The absolute risk of CVD, independent of risk factors, is relatively low in young individuals. Expressing the risk as their "risk age" may aid in understanding the risk. This study aimed to demonstrate a possible correlation between vascular risk age, SCORE risk value, and the level of subclinical atherosclerosis evaluated using a pulse wave velocity (PWV) device. METHODS: This work was designed to be a cross-sectional study. The SCORE 10-year fatal CVD risk and vascular risk age were calculated for patients below the age of 50 years and without any previous diagnosis of atherosclerotic disease or equivalents. The PWV of each patient was measured non-invasively using a PWV device. RESULTS: The study population included a total of 300 patients with a mean age of 35.1±9.5 years. The mean PWV and mean vascular age of the entire study population were 6.3±1.3 m/s and 44.3±5.5 years, respectively, and the median 10-year risk of fatal CVD score was 0.4 (0.04-2.74). There was a positive correlation between PWV and the 10-year risk of fatal CVD (r=0.613; P<0.001) and vascular risk age (r=0.684; P<0.001). CONCLUSION: Despite their young age and low to moderate 10-year risk of fatal CVD (<1%-5%) according to the SCORE chart, patients with a high vascular risk age were found to have high PWV values. These results show that calculations of vascular risk age might be used to assess the risk of fatal CVD in young patients and correlate with subclinical atherosclerosis.

Surrogate based continuous noninvasive blood pressure measurement.

Arterial blood pressure is one of the most often measured vital parameters in clinical practice. State-of-the-art noninvasive ABP measurement technologies have noticeable limitations and are mainly based on uncomfortable techniques of complete or partial arterial occlusion by cuffs. Most commonplace devices provide only intermittent measurements, and continuous systems are bulky and difficult to apply correctly for nonprofessionals. Continuous cuffless ABP measurements are still an unmet clinical need and a topic of ongoing research, with only few commercially available devices. This paper discusses surrogate-based noninvasive blood pressure measurement techniques. It covers measurement methods of continuously and noninvasively inferring BP from surrogate signals without applying external pressures, except for reference or initialization purposes. The BP is estimated by processing signal features, so called surrogates, which are modulated by variations of BP. Discussed techniques include well-known approaches such as pulse transit time and pulse arrival time techniques, pulse wave analysis or combinations thereof. Despite a long research history, these methods have not found widespread use in clinical and ambulatory practice, in part due to technical limitations and the lack of a standardized regulatory framework. This work summarizes findings from an invited workshop of experts in the fields covering clinical expertise, engineering aspects, commercialization and standardization issues. The goal is to provide an application driven outlook, starting with clinical needs, and extending to technical actuality. It provides an outline of recommended research directions and includes a detailed overview of clinical use case scenarios for these technologies, opportunities, and limitations.

A Flexible Pressure Sensor with Ink Printed Porous Graphene for Continuous Cardiovascular Status Monitoring.

Flexible electronics with continuous monitoring ability a extensively preferred in various medical applications. In this work, a flexible pressure sensor based on porous graphene (PG) is proposed for continuous cardiovascular status monitoring. The whole sensor is fabricated in situ by ink printing technology, which grants it the potential for large-scale manufacture. Moreover, to enhance its long-term usage ability, a polyethylene terephthalate/polyethylene vinylacetate (PET/EVA)-laminated film is employed to protect the sensor from unexpected shear forces on the skin surface. The sensor exhibits great sensitivity (53.99/MPa), high resolution (less than 0.3 kPa), wide detecting range (0.3 kPa to 1 MPa), desirable robustness, and excellent repeatability (1000 cycles). With the assistance of the proposed pressure sensor, vital cardiovascular conditions can be accurately monitored, including heart rate, respiration rate, pulse wave velocity, and blood pressure. Compared to other sensors based on self-supporting 2D materials, this sensor can endure more complex environments and has enormous application potential for the medical community.

Radial-digital pulse wave velocity: a noninvasive method for assessing stiffness of small conduit arteries.

Pulse wave velocity (PWV) is used to evaluate regional stiffness of large and medium-sized arteries. Here, we examine the feasibility and reliability of radial-digital PWV (RD-PWV) as a measure of regional stiffness of small conduit arteries and its response to changes in hydrostatic pressure. In 29 healthy subjects, we used Complior Analyse piezoelectric probes to record arterial pulse wave at the radial artery and the tip of the index. We determined transit time by second-derivative and intersecting tangents using the device-embedded algorithms and in-house MATLAB-based analyses of only reliable waves and by numerical simulation using a one-dimensional (1-D) arterial tree model coupled with a heart model. Second-derivative RD-PWV was 4.68 ± 1.18, 4.69 ± 1.21, and 4.32 ± 1.19 m/s for device-embedded, MATLAB-based, and numerical simulation analyses, respectively. Intersecting-tangent RD-PWV was 4.73 ± 1.20, 4.45 ± 1.08, and 4.50 ± 0.84 m/s for device-embedded, MATLAB-based, and numerical simulation analyses, respectively. Intersession coefficients of variation were 7.0% ± 4.9% and 3.2% ± 1.9% (P = 0.04) for device-embedded and MATLAB-based second-derivative algorithms, respectively. In 15 subjects, we examined the response of RD-PWV to changes in local hydrostatic pressure by vertical displacement of the hand. For an increase of 10 mmHg in local hydrostatic pressure, RD-PWV increased by 0.28 m/s (95% confidence interval: 0.16-0.40; P < 0.001). This study shows that RD-PWV can be used for the noninvasive assessment of regional stiffness of small conduit arteries. This finding allows for an integrated approach for assessing arterial stiffness gradient from the aorta to medium-sized arteries and now to small conduit arteries.NEW & NOTEWORTHY The interaction between the stiffness of various arterial segments is important in understanding the behavior of pressure and flow waves along the arterial tree. In this article, we provide a novel and noninvasive method of assessing the regional stiffness of small conduit arteries using the same piezoelectric sensors used for determination of pulse wave velocity over large- and medium-sized arteries. This development allows for an integrated approach for studying arterial stiffness gradient.

Serum Osteocalcin Level is Negatively Associated with Vascular Reactivity Index by Digital Thermal Monitoring in Kidney Transplant Recipients.

BACKGROUND AND OBJECTIVES: Osteocalcin is the most abundant noncollagenous protein in bone matrix, which is considered a marker of bone formation. Previous studies indicate that circulating osteocalcin can be expressed by osteoblasts and even by osteoblast-like cells in vessel walls, and it is often associated with arterial stiffness. Our study aims to examine the potential association between osteocalcin levels and endothelial function among kidney transplant (KT) recipients. MATERIALS AND METHODS: Fasting blood samples were obtained from 68 KT recipients. To measure the endothelial function and vascular reactivity index (VRI), a digital thermal monitoring test (VENDYS) was used. A commercial enzyme-linked immunosorbent assay kit was also utilized to measure serum total osteocalcin levels. In this study, a VRI of less than 1.0 indicated poor vascular reactivity; a VRI of 1.0-2.0 indicated intermediate vascular reactivity; and a VRI of 2.0 or higher indicated good vascular reactivity. RESULTS: Our findings show that 8 KT recipients (11.8%) had poor vascular reactivity (VRI < 1.0), 26 (38.2%) had intermediate vascular reactivity (1.0 ≤ VRI < 2.0), and 34 (50%) had good vascular reactivity. Increased serum osteocalcin levels (p < 0.001) were found to be associated with poor vascular reactivity. Advanced age (r = -0.361, p = 0.002), serum alkaline phosphate level (r = -0.254, p = 0.037), and log-transformed osteocalcin levels (r = - 0.432, p < 0.001) were identified to be negatively correlated with VRI in KT recipients. Multivariable forward stepwise linear regression analysis revealed that the serum level of osteocalcin (ß = -0.391, adjusted R2 change = 0.174; p < 0.001) and advanced age (ß = -0.308, adjusted R2 change = 0.084; p = 0.005) were significantly and independently associated with VRI in KT recipients. CONCLUSIONS: Higher serum osteocalcin level was associated with lower VRI and poorer endothelial dysfunction among KT recipients.

Automated pulse wave velocity assessment using a professional oscillometric office blood pressure monitor.

Carotid-femoral pulse wave velocity (cfPWV) is the gold standard method for assessing arterial stiffness. This study evaluated automated brachial-ankle PWV (baPWV) taken by a professional oscillometric blood pressure monitor (Microlife WatchBP Office Vascular) versus reference cfPWV (Complior device). Subjects recruited from a hypertension outpatient clinic had duplicate baPWV and cfPWV measurements (randomized crossover design) and carotid ultrasonography. Of 102 subjects recruited, 101 had valid baPWV measurements. Four subjects were excluded and 97 were analyzed (age 58.3 ± 11.4 years, men 70%, hypertensives 76%, diabetics 17%, cardiovascular disease 10%, smokers 23%). The mean difference between baPWV (13.1 ± 1.8 m/s) and cfPWV (9.1 ± 1.8 m/s) was 4.0 ± 1.4 m/s (P < .01) with close association between them (r = 0.70, P < .01). baPWV and cfPWV were correlated with age (r 0.54/0.49 respectively), systolic blood pressure (0.45/0.50), carotid intima-media thickness (0.31/0.44), and carotid distensibility coefficient (-0.47/-0.34) (all P < .05; no difference between the two methods, z test). There was reasonable agreement (77%) between the two methods in identifying subjects at the top quartile of their distributions (kappa 0.39, P < .01). The areas under the receiver operating characteristic curves for the identification of carotid plaques were comparable for cfPWV and baPWV (0.79 and 0.74 respectively, P = NS). Automated baPWV measurement by a professional oscillometric blood pressure monitor is feasible and observer-independent. baPWV values differ from those by cfPWV, yet they are closely correlated, have reasonable agreement in detecting increased arterial stiffness and give similar associations with carotid stiffness and atherosclerosis.

Reference values of office central blood pressure, pulse wave velocity, and augmentation index recorded by means of the Mobil-O-Graph PWA monitor.

Assessment of central blood pressure (BP), pulse wave velocity (PWV), and augmentation index (AIx) measurements may improve cardiovascular risk stratification. This study aimed to establish reference office values for central BP, PWV, and AIx by means of a Mobil-O-Graph PWA monitor and to evaluate the impact of cardiovascular risk factors (CVRFs) on these measurements. We cross-sectionally evaluated clinical characteristics, central BP, PWV, AIx, and peripheral BP measurements among 867 apparently healthy individuals (age = 46.0 ± 15.5 years, 39% males) who were free of obesity, hypertension, active smoking, dyslipidemia, and diabetes (CVRF-No) and 5632 individuals (age = 57.0 ± 14.7 years, 44% males) with at least one of these major CVRFs (CVRF-Yes). Reference values for central BP, PWV, and AIx were provided for the CVRF-No and CVRF-Yes groups, stratified by age and sex. PWV and AIx exhibited curvilinear increases with age, and there was an interaction between age and sex for central systolic BP and PWV in both the CVRF-No and CVRF-Yes groups. The results of a multivariable analysis including the whole sample (n = 6499) showed that obesity had a direct association with central BP, while diabetes was directly related to PWV. In addition, alcohol intake was directly associated with central BP, while performance of physical activity was inversely related to AIx. In conclusion, values of office-measured central BP, PWV, and AIx obtained in an apparently healthy population and in a population with CVRFs are now available according to age and sex and may be useful to build thresholds for use in clinical practice.

A Comparative Study of Brachial-Ankle Pulse Wave Velocity and Heart-Finger Pulse Wave Velocity in Korean Adults.

Arterial stiffness is considered an index of vascular aging. The brachial-ankle pulse wave velocity (baPWV) method is widely used because of its proven effectiveness; and the pulse wave velocity measurement method using both electrocardiogram (ECG) and photoplethysmogram (PPG) is actively being studied due to the convenience of measurement and the possibility of miniaturization. The aim of this study was to evaluate and compare the effects of age and gender in Korean adults using both the baPWV method and the PWV method with ECG and finger PPG (heart-finger PWV). The measurements have been carried out for 185 healthy subjects of Korean adults, and the results showed that the baPWV was highly correlated with age in both genders (r = 0.94 for both males and females). However, the correlation values in heart-finger PWV measurement were significantly lower than those of baPWV (r = 0.37 for males and r = 0.71 for females). Although the heart-finger PWV method is suitable for mobile applications because it can be easily miniaturized while maintaining its signal quality, these results show that the heart-finger PWV method is not as effective as baPWV at evaluating the arterial stiffness.

The association between arterial pulse waveform analysis device and in-hospital mortality in high-risk non-cardiac surgeries.

BACKGROUND: Perioperative goal-directed fluid therapy is used for haemodynamic optimization in high-risk surgeries. Cardiac output monitoring can be performed by a specialized pressure transducer for arterial pulse waveform analysis (S-APWA). No study has assessed whether real-world use of S-APWA is associated with post-operative outcomes; therefore, using a Japanese administrative claims database, we retrospectively investigated whether S-APWA use is associated with in-hospital mortality among patients undergoing high-risk surgery under general anaesthesia. METHODS: Adult patients who underwent high-risk surgery under general anaesthesia and arterial catheterization between 2014 and 2016 were divided into S-APWA and conventional arterial pressure transducer groups, then compared regarding baseline factors and outcomes. Logistic regression analysis was performed to compare in-hospital mortality. Subgroup analyses evaluated S-APWA efficacy and outcomes based on the type of surgery and patients' comorbidity. RESULTS: S-APWA was used in 6859 of 23 655 (29.0%) patients; the crude in-hospital mortality rate was 3.5%. Adjusted analysis showed no significant association between S-APWA use and in-hospital mortality rate (adjusted odds ratio [aOR] = 0.91; 95% confidence interval [CI]: 0.76-1.07; P = .25). S-APWA use was associated with significantly lower in-hospital mortality in patients undergoing vascular surgery (aOR = 0.67; 95% CI: 0.49-0.94), and significantly higher in-hospital mortality in patients undergoing lower limb amputation (aOR = 2.63; 95% CI: 1.32-5.22). S-APWA use and in-hospital mortality were not significantly associated with other subgroups. CONCLUSION: S-APWA use was not associated with in-hospital mortality in the entire study population. However, S-APWA was associated with decreased in-hospital mortality among vascular surgery and increased in-hospital mortality among lower limb amputation.

A wireless optical handheld device for carotid waveform measurement and its validation in a clinical study.

OBJECTIVE: Here we introduce Vivio, a wireless optical tonometer, and compare its pulse waveform measurement capabilities to the AtCor SphygmoCor. APPROACH: Pulse waveform data from both devices was captured on a heterogeneous cohort of 29 participants (15 males, 14 females), including 16 healthy individuals free from cardiovascular diseases and 13 patients with one or more cardiovascular diseases. These participants were a subgroup of the Huntington Medical Research Institutes (HMRI) iPhone Heart Study. Main r esults: Carotid pulse waveforms captured by Vivio were comparable to those captured using the AtCor SphygmoCor tonometer. The point-by-point root-mean-square error between averaged waveforms captured by either device on the same participant was 6.3% with a standard deviation of 2%. The harmonic content of the pulse waveforms captured by either device was also similar. Data collected by Vivio displayed good to excellent agreement across a wide range of pulse waveform features such as left ventricular ejection time, reflected wave arrival time, the ratio of systolic to diastolic time intervals, and heart rate. A comparison between augmentation index (AI) measured by Vivio and tonometry showed a correlation of 0.82 (p < 0.01). Bland-Altman analysis of this data yielded a bias of -2.5% and limits of agreement spanning -15.1%-10.1%. SIGNIFICANCE: The Vivio has the potential to enhance the availability of noninvasive pulse waveform data, thereby expanding the tools available for the diagnosis and monitoring of cardiovascular disease. When used in combination with advanced waveform analysis methods, Vivio can impact mobile healthcare resulting in improved patient health, quality of life and the overall reduction of healthcare costs.

Validity of transit time-based blood pressure measurements in patients with and without heart failure or pulmonary arterial hypertension across different breathing maneuvers.

PURPOSE: Pulse transit time (PTT) derived by ECG and plethysmographic signal can be a promising alternative to invasive or oscillometry-based blood pressure (BP) monitoring in sleep laboratories because it does not cause arousals from sleep. Therefore, this study assessed the validity of PTT for BP monitoring under sleep laboratory-like conditions. METHODS: Ten volunteers (55.8 ± 19.6 years), 12 patients with heart failure with reduced ejection fraction (HFrEF; 67.3 ± 8.6 years), and 14 patients with Nizza class I pulmonary arterial hypertension (PAH; 59.5 ± 13.4 years) performed different breathing patterns to simulate nocturnal sleep-disordered breathing (SDB). BP was measured at least every 15 min over 1 h using oscillometry (Task Force Monitor™) and PTT (SOMNOscreen™) devices in free breathing conditions and during SDB simulation (alternating phases of hyperventilation and apneas). RESULTS: One hundred forty-two points of measurements were collected. No difference was found in both mean systolic BP (SBP) and diastolic BP (DBP) between oscillometric PTT-based BP measurements in the whole population and throughout the whole recording (SBP 111.3 ± 15.1 mmHg versus 110.0 ± 14.7 mmHg, p = 0.051; DBP 69.9 ± 12.2 versus 69.9 ± 14.2 mmHg, p = 0.701). Likewise, no significant difference in SBP and DBP was found between the two methods in the subgroups of healthy subjects, HFrEF patients and PAH patients, both in free breathing conditions (p > 0.05) and during SDB simulation (p > 0.05). CONCLUSIONS: When monitoring BP in healthy subjects, and in patients with HFrEF or PAH, PTT provides a BP estimation comparable with oscillometric measurement, though slightly inaccurate, both in the condition of regular and unstable breathing.

Pilot Study to Detect Changes in Blood Flow in the External Auditory Meatus During Hemodialysis.

Blood flow to internal organs is reported to fall during hemodialysis (HD). As such, noninvasive monitoring devices are required to detect changes in perfusion, which could then be used for therapeutic interventions. We report on a pilot study monitoring blood flow in the outer auditory meatus. We measured the maximum pulse wave amplitude and indicators of blood flow by analyzing red and green color changes in the outer auditory meatus from video recordings made using an otoscope fitted with a digital camera during HD treatments. We studied 61 patients, 43 (71.5%) male, mean age 64.9 ± 12.7 years. Weight fell from 72.8 ± 22.5 kg predialysis to 71.5 ± 22.1 kg postdialysis (P < 0.001). BP did not significantly change (predialysis 142 ± 29/67 ± 18 to 143 ± 25/68 ± 17 mm Hg postdialysis). The maximum pulse wave amplitude in the external auditory meatus fell from 0.21 (0.1-0.55) to 0.14 (0.04-0.4) after 90 min, P < 0.001, and remained low thereafter, and the change at the end of the dialysis session was associated with percentage weight loss (r = -0.37, P = 0.003). Green and red pixel values did not change (predialysis 0.339 [0.333-0.345] to 0.302 [0.291-0.33] post, and 0.301 [0.293-0.328] predialysis to 0.339 [0.334-0.347] post, respectively). This pilot study showed that the maximum pulse wave amplitude measured in the external auditory meatus fell during the dialysis session, and that the fall was associated with fluid removal. This could potentially lead to the development of a monitoring device, which could fit in the ear and record during the dialysis session.

Evaluation of transit time-based models in wearable central aortic blood pressure estimation.

Evidence suggests that central aortic blood pressure (CABP) may provide a more accurate prognosis of cardiovascular events than peripheral pressure. The capability of monitoring CABP in a continuous, wearable, unobtrusive way might have a significant impact on hypertension management. The purpose of this study is to experimentally explore whether a wearable device equipped with an electrocardiogram (ECG) and ballistocardiogram (BCG) acquisition system could be used to predict CABP. This is based on state-of-the-art results on the relationship between transit time extracted from these signals and CABP. Ten young, healthy volunteers participated in the study where data-sets were acquired during three hemodynamic interventions, i.e., breath-holding, Valsalva maneuver, and cold pressor. Each data-set included ECG and BCG waveforms acquired by the wearable device and a CABP assessment from a cuff-based device. A total of nine PTT-based models (PBMs) derived from pulse transit time methodology were considered. Each PBM was tested with three alternative feature times extracted from the recorded waveforms PBMs were calibrated with data-sets acquired at baseline state, which were not considered for testing the PBM estimation performance. Four of the nine tested models presented a proper agreement in estimating CABP through the acquired signals, after the calibration procedure with baseline-state data. Results in one of these promising models are the following. Mean estimation error (95% confidence interval), systolic: 0 to 1.7 mmHg, diastolic: 0.4 to 2.3 mmHg, Pearson correlation: 0.82 systolic and 0.78 diastolic (p < 0.001). The proposed methodology may lead to continuous wearable BP monitoring.

Extracting physiological information in experimental biology via Eulerian video magnification.

BACKGROUND: Videographic material of animals can contain inapparent signals, such as color changes or motion that hold information about physiological functions, such as heart and respiration rate, pulse wave velocity, and vocalization. Eulerian video magnification allows the enhancement of such signals to enable their detection. The purpose of this study is to demonstrate how signals relevant to experimental physiology can be extracted from non-contact videographic material of animals. RESULTS: We applied Eulerian video magnification to detect physiological signals in a range of experimental models and in captive and free ranging wildlife. Neotenic Mexican axolotls were studied to demonstrate the extraction of heart rate signal of non-embryonic animals from dedicated videographic material. Heart rate could be acquired both in single and multiple animal setups of leucistic and normally colored animals under different physiological conditions (resting, exercised, or anesthetized) using a wide range of video qualities. Pulse wave velocity could also be measured in the low blood pressure system of the axolotl as well as in the high-pressure system of the human being. Heart rate extraction was also possible from videos of conscious, unconstrained zebrafish and from non-dedicated videographic material of sand lizard and giraffe. This technique also allowed for heart rate detection in embryonic chickens in ovo through the eggshell and in embryonic mice in utero and could be used as a gating signal to acquire two-phase volumetric micro-CT data of the beating embryonic chicken heart. Additionally, Eulerian video magnification was used to demonstrate how vocalization-induced vibrations can be detected in infrasound-producing Asian elephants. CONCLUSIONS: Eulerian video magnification provides a technique to extract inapparent temporal signals from videographic material of animals. This can be applied in experimental and comparative physiology where contact-based recordings (e.g., heart rate) cannot be acquired.

MEMS-Based Sensor for Simultaneous Measurement of Pulse Wave and Respiration Rate.

The continuous measurements of vital signs (body temperature, blood pressure, pulse wave, and respiration rate) are important in many applications across various fields, including healthcare and sports. To realize such measurements, wearable devices that cause minimal discomfort to the wearers are highly desired. Accordingly, a device that can measure multiple vital signs simultaneously using a single sensing element is important in order to reduce the number of devices attached to the wearer's body, thereby reducing user discomfort. Thus, in this study, we propose a device with a microelectromechanical systems (MEMS)-based pressure sensor that can simultaneously measure the blood pulse wave and respiration rate using only one sensing element. In particular, in the proposed device, a thin silicone tube, whose inner pressure can be measured via a piezoresistive cantilever, is attached to the nose pad of a pair of eyeglasses. On wearing the eyeglasses, the tube of sensor device is in contact with the area above the angular artery and nasal cavity of the subject, and thus, both pulse wave and breath of the subject cause the tube's inner pressure to change. We experimentally show that it is possible to extract information related to pulse wave and respiration as the low-frequency and high-frequency components of the sensor signal, respectively.

Non-Invasive Device for Blood Pressure Wave Acquisition by Means of Mechanical Transducer.

Blood pressure wave monitoring provides interesting information about the patient's cardiovascular function. For this reason, this article proposes a non-invasive device capable of capturing the vibrations (pressure waves) produced by the carotid artery by means of a pressure sensor encapsulated in a closed dome filled with air. When the device is placed onto the outer skin of the carotid area, the vibrations of the artery will exert a deformation in the dome, which, in turn, will lead to a pressure increase in its inner air. Then, the sensor inside the dome captures this pressure increase. By combining the blood pressure wave obtained with this device together with the ECG signal, it is possible to help the screening of the cardiovascular system, obtaining parameters such as heart rate variability (HRV) and pulse transit time (PTT). The results show how the pressure wave has been successfully obtained in the carotid artery area, discerning the characteristic points of this signal. The features of this device compare well with previous works by other authors. The main advantages of the proposed device are the reduced size, the cuffless condition, and the potential to be a continuous ambulatory device. These features could be exploited in ambulatory tests.