Radial pulse transit time is an index of arterial stiffness

Thermoforming 2D films into 3D electronics for high-performance, customizable tactile sensing

The demand for tactile sensors in robotics, virtual reality, and health care highlights the need for high performance and customizability. Despite advances in vision-based technologies, tactile sensing remains crucial for precise interaction and subtle pressure detection. In this work, we present a design and fabrication method of customizable tactile sensors based on thermoformed three-dimensional electronics. This approach enables ultrawide modulus tunability (10 pascals to 1 megapascal) and superior mechanical properties, including negligible hysteresis and high creep resistance. These features allow the sensor to detect a broad spectrum of pressures, from acoustic waves to body weight, with high performance. The proposed sensors have high sensitivity (up to 5884 per kilopascal), high linearity (R2 = 0.999), low hysteresis (<0.5%), and fast response (0.1 milliseconds). We demonstrate applications in human-computer interaction and health care, showcasing their potential in various fields. This platform provides a scalable solution for fabricating versatile, high-performance tactile sensors.

Regional Variation in Pulse Transit Time in the Upper Limb Arteries During Hypotensive and Non-hypotensive Lower Body Negative Pressure

PURPOSE

Pulse transit time (PTT) is crucial in developing non-invasive cuffless blood pressure (BP) measurement devices. Sympathetic activation, due to its effect on PTT, can lead to erroneous estimation of BP. Sympathetic activation might affect the PTT differentially depending on the site where PTT is measured in the upper limb. This study aimed to decipher regional variation in PTT in response to sympathetic activation in three segments of the upper limb arteries. Exposure to graded lower body negative pressure (LBNP) at hypotensive (-30 mmHg and -40 mmHg) and non-hypotensive (-10 mmHg and -20 mmHg) levels has been used to produce sympathetic activation.

METHODS

This was a pilot study. Ten healthy subjects were recruited for the study, and recordings were done. Carotid, brachial, and radial pulse waveforms were recorded simultaneously by tonometry, and the finger pulse waveform was recorded by photoplethysmography (PPG). LBNP was applied at -10 mmHg, -20 mmHg, -30 mmHg, and -40 mmHg for two minutes. Carotid-brachial PTT (cbPTT), brachial-radial PTT (brPTT), and radial-finger PTT (rfPTT) were calculated.

RESULTS

cbPTT did not show any significant change, whereas both brPTT (0.02679±0.00635 sec at baseline vs. 0.02027±0.00662 sec at hypotensive LBNP; p=0.0386) and rfPTT (0.00908±0.00350 sec at baseline vs. 0.00585±0.00211 sec at hypotensive LBNP; p=0.003) showed a significant decrease in response to hypotensive LBNP. rfPTT (0.00908±0.00350 at baseline vs. 0.00534±0.00249s at non-hypotensive LBNP; p=0.0257) also showed a significant decline in response to non-hypotensive LBNP as well.

CONCLUSION

The current study reveals that in upper limb arteries, PTT response to LBNP shows regional variation with an accentuation of response from proximal to distal segments.

Multi-Level High Entropy-Dissipative Structure Enables Efficient Self-Decoupling of Triple Signals

The theory of high entropy-dissipative structure is confined to high-entropy alloys and their oxide materials under harsh conditions, but it is very difficult to obtain high entropy-dissipative structure for smart sensors based on polymers and metal oxides under mild conditions. Moreover, multiple signal coupling effect heavily hinder the sensor applications, and current multimodal integrated devices can solve two signal-decoupling, but need very complicated process way. In this work, new synthesis concept is the first time to fabricate high entropy-dissipative conductive layer of smart sensors with triple-signal response and self-decoupling ability within poly-pyrrole/zinc oxide (PPy/ZnO) system. The sensor (SPZ20) amplifies pressure (17.54%/kPa) and gas (0.37%/ppm), reduces humidity (0.41%/% RH) and temperature (0.12%/°C) signals, simultaneously achieving the triple self-decoupling effect of pressure and gas in the complex temperature-humidity field because of the enlarged pressure-contact area, enhanced gas-responsive sites, altered vapor path and its own heat insulation function. Additionally, it inherits the strong robustness (500 rubbing, washing, and heating or freezing cycles) and endurance (10 000 photo-purification cycles) of traditional high-entropy materials for information transmission and smart alarms in emergencies or harsh environments. This work gives a new insight into the multiple-signal response and smart flexible electronic design from natural fibers.

A Novel Photo-electro-mechano Sensing Array for the Visualization and Estimation of Tonoarteriogram

Existing cuffless blood pressure (BP) monitoring technologies commonly rely on single-site measurements with unimodal sensor configurations, thereby constraining the precision and visualization of the two-dimensional data. Building upon our previous observations regarding the significant influence of measurement sites on BP evaluation, and leveraging the widely acknowledged utility of electrocardiography (ECG) in BP assessment, in this study, we develop a multimodal photo-electro-mechano tonoarteriographic (TAG) imaging system, enabling continuous visualization of local BP variation and estimation of central BP. The system integrates a 3×3 photoplethysmography (PPG) sensor array, one-lead ECG, and a 2×2 pressure sensor array, allowing to collect simultaneously 15 channel physiological signals. The proposed system was tested with 20 subjects and the experimental results reveal noticeable variations in local pulse transit time (PTT)/BP across different anatomical structures at the measurement site. To further improve the system performance, we designed and tested a flexible 2×4 ultrasound sensor array and demonstrated its feasibility to augment the system's capability for central BP estimation. In summary, the proposed system can not only estimate continuously central BP but also visualize the two-dimensional local BP/PTT variation at the measurement site, holding potential to support clinical decision-making and offering geographic-dependent information for micro-circulation investigations.

Investigating the relationship between early cardiovascular disease markers and loneliness in young adults

Loneliness is recognised as a risk factor for cardiovascular disease development. However, it is unclear whether loneliness itself or other closely related mental health symptoms, such as depression and social anxiety, are associated with the development of cardiovascular disease. In the present study, we examined the relationship between loneliness and several early cardiovascular disease markers in young adults, after controlling for depression and social anxiety. Sixty-six young adults (18-35 years old, Mage = 22.70; 75.8% females) completed psychological questionnaires and took part in several physiological tests assessing cardiovascular health (e.g., vascular function). Results revealed higher loneliness was significantly associated with shorter pulse transit time (β = - 0.70, p = 0.002; shorter pulse transit time is a subclinical marker for arterial stiffness). Additionally, results show that while loneliness and depression were both related to vascular dysfunction in young adults, the underlining physiological mechanisms through which they affect vascular function may be different. Specifically, higher loneliness was associated with increased arterial stiffness, whereas depression was associated with increased endothelial dysfunction (β = - 0.43, p = 0.04). Our findings indicate that presence of loneliness and depression in young adults may be accompanied by early indicators of poor cardiovascular health, such as arterial stiffness and endothelial dysfunction. Results from the study further support the link between loneliness and cardiovascular disease development.

Single measurement estimation of central blood pressure using an arterial transfer function

BACKGROUND

Central blood pressure (BP) better reflects the loading conditions on the major organs and is more closely correlated with future cardiovascular events. The increased invasiveness and risk of infection prevents the routine measurement of central BP. Arterial transfer functions can provide central BP estimates from clinically available peripheral measurements. However, current methods are either generalized, potentially lacking the ability to adapt to inter and intra subject variability, or individualized based on additional, clinically unavailable, pulse transit time measurements. This work proposes a novel, self-contained method for individualizing an arterial transfer function from a single peripheral pressure measurement, capable of accurately estimating central BP in a range of hemodynamic conditions.

METHODS

Pulse wave analysis of femoral BP waves was employed to formulate initial approximations of central BP and arterial inlet flow waveforms, to serve as objective functions for the identification of all model parameters. Root mean squared error (RMSE), and systolic and pulse pressure errors were assessed with respect to invasive aortic BP measurements in a seven (7) porcine endotoxin experiments. Systolic and pulse pressure errors were analysed using Bland-Altman analysis. Method accuracy is also compared with an idealized transfer function, derived using the measured aortic-femoral pulse transit time and minimizing the RMSE of model output pressure with respect to reference aortic pressure, a generalized transfer function model, and invasive femoral pressure measurements.

RESULTS

Mean bias and limits of agreement (95% CI) for the proposed method were 1.0(-4.6, 6.7)mmHg and -1.0(-6.6, 4.6)mmHg for systolic and pulse pressure, respectively, compared to 3.6(-0.9, 8.2)mmHg and 2.7(-1.8, 7.3)mmHg for the generalized transfer function model. Mean bias and limits of agreement for femoral pressure measurements were -6.4(-15.0, 2.3)mmHg and -9.4(-18.1, -0.8)mmHg, for systolic and pulse pressure, respectively. The pooled mean and standard deviation of the RMSE produced by the single measurement method, relative to reference aortic pressure, was 4.3(1.1)mmHg, consistent with estimates produced by the idealized transfer function, 3.9(1.2)mmHg, and improving of the generalized transfer function, 4.6(1.4)mmHg.

CONCLUSIONS

The proposed single measurement method provides accurate central BP estimates from routinely available peripheral pressure measurements, and nothing else. The method allows for the individualization of transfer functions on a per patient basis to better capture changes in patient condition during the progression of disease and subsequent treatment, at no additional clinical cost.

Wrist pulse signal based vascular age calculation using mixed Gaussian model and support vector regression

Purpose

Vascular age (VA) is the direct index to reflect vascular aging, so it plays a particular role in public health. How to obtain VA conveniently and cheaply has always been a research hotspot. This study proposes a new method to evaluate VA with wrist pulse signal.

Methods

Firstly, we fit the pulse signal by mixed Gaussian model (MGM) to extract the shape features, and adopt principal component analysis (PCA) to optimize the dimension of the shape features. Secondly, the principal components and chronological age (CA) are respectively taken as the independent variables and dependent variable to establish support vector regression (SVR) model. Thirdly, the principal components are fed into the SVR model to predicted the vascular aging of each subject. The predicted value is regarded as the description of VA. Finally, we compare the correlation coefficients of VA with pulse width (PW), inflection point area ratio (IPA), Ratio b/a (RBA), augmentation index (AIx), diastolic augmentation index (DAI) and pulse transit time (PTT) with those of CA with these six indices.

Results

Compared with the CA, the VA is closer to PW (r = 0.539, P < 0.001 to r = 0.589, P < 0.001 in men; r = 0.325, P < 0.001 to r = 0.400, P < 0.001 in women), IPA (r =  - 0.446, P < 0.001 to r =  - 0.534, P < 0.001 in men; r =  - 0.623, P < 0.001 to r =  - 0.660, P < 0.001 in women), RBA (r = 0.328, P < 0.001 to r = 0.371, P < 0.001 in women), AIx (r = 0.659, P < 0.001 to r = 0.738, P < 0.001 in men; r = 0.547, P < 0.001 to r = 0.573, P < 0.001 in women), DAI (r = 0.517, P < 0.001 to r = 0.532, P < 0.001 in men; r = 0.507, P < 0.001 to r = 0.570, P < 0.001 in women) and PTT (r = 0.526, P < 0.001 to r = 0.659, P < 0.001 in men; r = 0.577, P < 0.001 to r = 0.814, P < 0.001 in women).

Conclusion

The VA is more representative of vascular aging than CA. The method presented in this study provides a new way to directly and objectively assess vascular aging in public health.

Vascular age acquired from the pulse signal: A new index to screen early vascular aging

BACKGROUND

Chronological age (CA) has been adopted as an important independent risk factor in cardiovascular risk assessment. However, different individuals with same CA may have distinct actual vascular aging due to various lifestyles. Therefore, it is difficult to fully describe the difference of actual vascular aging by CA.

OBJECTIVE

This study proposes a new index vascular age (VA) to avoid the limitations of CA.

METHOD

In this work, VA refers to the sum of CA and lifestyle impact (Age_LI). Firstly, we take the pulse signal features and CA as independent variables and dependent variable respectively, and adopt cross validation to train Support Vector Regression model. Then we acquire the predicted chronological age (PA) of all subjects with the model. Secondly, we obtain the function model between CA and PA, and calculate the expectation of PA (ePA) for each subject. Simultaneously, we take the difference between PA and ePA as the estimated value of Age_LI to further calculate VA. Finally, in order to evaluate the effectiveness of VA, we compare the correlations between CA, PA, VA and 8 objective indices such as augmentation index, pulse transit time, diastolic augmentation index, etc. RESULTS: In general, VA and PA are closer to these 8 objective indices than CA. Moreover, VA is also superior to PA in vascular aging evaluation.

CONCLUSION

The VA suggested in this study emphasizes the difference of vascular aging in same CA group, which can better reflect the actual vascular aging than CA and PA.

A Novel Clustering-Based Algorithm for Continuous and Noninvasive Cuff-Less Blood Pressure Estimation

Extensive research has been performed on continuous and noninvasive cuff-less blood pressure (BP) measurement using artificial intelligence algorithms. This approach involves extracting certain features from physiological signals, such as ECG, PPG, ICG, and BCG, as independent variables and extracting features from arterial blood pressure (ABP) signals as dependent variables and then using machine-learning algorithms to develop a blood pressure estimation model based on these data. The greatest challenge of this field is the insufficient accuracy of estimation models. This paper proposes a novel blood pressure estimation method with a clustering step for accuracy improvement. The proposed method involves extracting pulse transit time (PTT), PPG intensity ratio (PIR), and heart rate (HR) features from electrocardiogram (ECG) and photoplethysmogram (PPG) signals as the inputs of clustering and regression, extracting systolic blood pressure (SBP) and diastolic blood pressure (DBP) features from ABP signals as dependent variables, and finally developing regression models by applying gradient boosting regression (GBR), random forest regression (RFR), and multilayer perceptron regression (MLP) on each cluster. The method was implemented using the MIMIC-II data set with the silhouette criterion used to determine the optimal number of clusters. The results showed that because of the inconsistency, high dispersion, and multitrend behavior of the extracted features vectors, the accuracy can be significantly improved by running a clustering algorithm and then developing a regression model on each cluster and finally weighted averaging of the results based on the error of each cluster. When implemented with 5 clusters and GBR, this approach yielded an MAE of 2.56 for SBP estimates and 2.23 for DBP estimates, which were significantly better than the best results without clustering (DBP: 6.27, SBP: 6.36).

The key role of pulse wave transit time to predict blood pressure variation during anaesthesia induction

OBJECTIVE

To establish the relationship between pulse wave transit time (PWTT) before anaesthesia induction and blood pressure variability (BPV) during anaesthesia induction.

METHODS

This prospective observational cohort study enrolled consecutive patients that underwent elective surgery. Invasive arterial pressure, electrocardiography, pulse oximetry, heart rate and bispectral index were monitored. PWTT and BPV were measured with special software. Anaesthesia was induced with propofol, sufentanil and rocuronium.

RESULTS

A total of 54 patients were included in this study. There was no correlation between BPV and the dose of propofol, sufentanil and rocuronium during anaesthesia induction. Bivariate linear regression analysis demonstrated that PWTT (r = -0.54), age (r = 0.34) and systolic blood pressure (r = 0.31) significantly correlated with systolic blood pressure variability (SBPV). Only PWTT (r = -0.38) was significantly correlated with diastolic blood pressure variability (DBPV). Patients were stratified into high PWTT and low PWTT groups according to the mean PWTT value (96.8 ± 17.2 ms). Compared with the high PWTT group, the SBPV of the low PWTT group increased significantly by 3.4%. The DBPV of the low PWTT group increased significantly by 2.1% compared with the high PWTT group.

CONCLUSIONS

PWTT, assessed before anaesthesia induction, may be an effective predictor of haemodynamic fluctuations during anaesthesia induction.

Wave reflection: More than a round trip

Reflected pressure waves are key to the understanding of vascular ageing, a prominent factor in major cardiovascular events. Several different metrics have been proposed to index the effect of wave reflection on the pressure waveform and thereby serve as an indicator of vascular ageing. The extent to which these indices are influenced by factors other than vascular health remains a matter of concern. In this paper, we use transmission-line theory to derive a mathematical model for the reflection time (T_refl), and the augmentation index (AI), assuming a general extended model of the arterial system. Then, we test the proposed model against values reported in the literature. Finally, we discuss insights from the model to common observations in the literature such as age-related "shift" in the reflection site, the variation of AI with heart rate, and the flattening of T_refl in older participants.

Noninvasive Measurement of Time-Varying Arterial Wall Elastance Using a Single-Frequency Vibration Approach

The arterial wall elastance is an important indicator of arterial stiffness and a kind of manifestation associated with vessel-related disease. The time-varying arterial wall elastances can be measured using a multiple-frequency vibration approach according to the Voigt and Maxwell model. However, such a method needs extensive calculation time and its operating steps are very complex. Thus, the aim of this study is to propose a simple and easy method for assessing the time-varying arterial wall elastances with the single-frequency vibration approach. This method was developed according to the simplified Voigt and Maxwell model. Thus, the arterial wall elastance measured using this method was compared with the elastance measured using the multiple-frequency vibration approach. In the single-frequency vibration approach, a moving probe of a vibrator was induced with a radial displacement of 0.15 mm and a 40 Hz frequency. The tip of the probe directly contacted the wall of a superficial radial artery, resulting in the arterial wall moving 0.15 mm radially. A force sensor attached to the probe was used to detect the reactive force exerted by the radial arterial wall. According to Voigt and Maxwell model, the wall elastance (E_single) was calculated from the ratio of the measured reactive force to the peak deflection of the displacement. The wall elastances (E_multiple) measured by the multiple-frequency vibration approach were used as the reference to validate the performance of the single-frequency approach. Twenty-eight healthy subjects were recruited in the study. Individual wall elastances of the radial artery were determined with the multiple-frequency and the single-frequency approaches at room temperature (25 °C), after 5 min of cold stress (4 °C), and after 5 min of hot stress (42 °C). We found that the time-varying E_single curves were very close to the time-varying E_multiple curves. Meanwhile, there was a regression line (E_single = 0.019 + 0.91 E_multiple, standard error of the estimate (SEE) = 0.0295, p < 0.0001) with a high correlation coefficient (0.995) between E_single and E_multiple. Furthermore, from the Bland-Altman plot, good precision and agreement between the two approaches were demonstrated. In summary, the proposed approach with a single-frequency vibrator and a force sensor showed its feasibility for measuring time-varying wall elastances.

Wearable skin-like optoelectronic systems with suppression of motion artifacts for cuff-less continuous blood pressure monitor

According to the statistics of the World Health Organization, an estimated 17.9 million people die from cardiovascular diseases each year, representing 31% of all global deaths. Continuous non-invasive arterial pressure (CNAP) is essential for the management of cardiovascular diseases. However, it is difficult to achieve long-term CNAP monitoring with the daily use of current devices due to irritation of the skin as well as the lack of motion artifacts suppression. Here, we report a high-performance skin-like optoelectronic system integrated with ultra-thin flexible circuits to monitor CNAP. We introduce a theoretical model via the virtual work principle for predicting the precise blood pressure and suppressing motion artifacts, and propose optical difference in the frequency domain for stable optical measurements in terms of skin-like devices. We compare the results with the blood pressure acquired by invasive (intra-arterial) blood pressure monitoring for >1500 min in total on 44 subjects in an intensive care unit. The maximum absolute errors of diastolic and systolic blood pressure were ±7/±10 mm Hg, respectively, in immobilized, and ±10/±14 mm Hg, respectively, in walking scenarios. These strategies provide advanced blood pressure monitoring techniques, which would directly address an unmet clinical need or daily use for a highly vulnerable population.

Estimation of echocardiogram parameters with the aid of impedance cardiography and artificial neural networks

The advent of cardiovascular diseases as a disease of mass catastrophy, in recent years is alarming. It is expected to spread as an epidemic by 2030. Present methods of determining the health of one's heart include doppler based echocardiogram, MDCT (Multi Detector Computed Tomography), among various other invasive and non-invasive hemodynamic monitoring techniques. These methods require expert supervision and costly clinical set-ups, and cannot be employed by a common individual to perform a self diagnosis of one's cardiac health, unassisted. In this work, the authors propose a novel methodology using impedance cardiography (ICG), for the determination of a person's cardio-vascular health. The recorded ICG signal helps in extraction of features which are used for estimating parameters for cardiac health monitoring. The proposed methodology with the aid of artificial neural network is able to determine Stroke Volume (SV), Left Ventricular End Systolic Volume (LVESV), Left Ventricular End Diastolic Volume (LVEDV), Left Ventricular Ejection Fraction (LVEF), Iso Volumetric Contraction Time (IVCT), Iso Volumetric Relaxation Time (IVRT), Left Ventricular Ejection Time (LVET), Total Systolic Time (TST), Total Diastolic Time (TDT), and Myocardial Performance Index (MPI), with error margins of ±8.9%, ±3.8%, ±1.4%, ±7.8%, ±16.0%, ±9.0%, ±9.7%, ±6.9%, ±6.2%, and ±0.9%, respectively. The proposed methodology could be used in screening of precursors to cardiac ailments, and to keep a check on the cardio-vascular health.

Innovative Multi-Site Photoplethysmography Analysis for Quantifying Pulse Amplitude and Timing Variability Characteristics in Peripheral Arterial Disease

Photoplethysmography (PPG) is a simple-to-perform vascular optics measurement technique that can detect blood volume changes in the microvascular bed of tissue. Beat-to-beat analysis of the PPG waveform enables the study of the variability of pulse features, such as the amplitude and the pulse arrival time (PAT), and when quantified in the time and frequency domains, has considerable potential to shed light on perfusion changes associated with peripheral arterial disease (PAD). In this pilot study, innovative multi-site bilateral finger and toe PPG recordings from 43 healthy control subjects and 31 PAD subjects were compared (recordings each at least five minutes, collected in a warm temperature-controlled room). Beat-to-beat normalized amplitude variability and PAT variability were then quantified in the time-domain using two simple statistical measures and in the frequency-domain bilaterally using magnitude squared coherence (MSC). Significantly reduced normalized amplitude variability (healthy control 0.0384 (interquartile range 0.0217–0.0744) vs. PAD 0.0160 (0.0080–0.0338) (p < 0.0001)) and significantly increased PAT variability (healthy control 0.0063 (0.0052–0.0086) vs. PAD 0.0093 (0.0078–0.0144) (p < 0.0001)) was demonstrated for the toe site in PAD using the time-domain analysis. Frequency-domain analysis demonstrated significantly lower MSC values across a range of frequency bands for PAD patients. These changes suggest a loss of right-to-left body side coherence and cardiovascular control in PAD. This study has also demonstrated the feasibility of using these measurement and analysis methods in studies investigating multi-site PPG variability for a wide range of cardiac and vascular patient groups.

Pulse wave response characteristics for thickness and hardness of the cover layer in pulse sensors to measure radial artery pulse

Background

Piezo-resistive pressure sensors are widely used for measuring pulse waves of the radial artery. Pulse sensors are generally fabricated with a cover layer because pressure sensors without a cover layer are fragile when they come into direct contact with the skin near the radial artery. However, no study has evaluated the dynamic pulse wave response of pulse sensors depending on the thickness and hardness of the cover layer. This study analyzed the dynamic pulse wave response according to the thickness and hardness of the cover layer and suggests an appropriate thickness and hardness for the design of pulse sensors with semiconductor device-based pressure sensors.

Methods

Pulse sensors with 6 different cover layers with various thicknesses (0.8 mm, 1 mm, 2 mm) and hardnesses (Shore type A; 30, 43, 49, 71) were fabricated. Experiments for evaluating the dynamic pulse responses of the fabricated sensors were performed using a pulse simulator to transmit the same pulse wave to each of the sensors. To evaluate the dynamic responses of the fabricated pulse sensors, experiments with the pulse sensors were conducted using a simulator that artificially generated a constant pulse wave. The pulse wave simulator consisted of a motorized cam device that generated the artificial radial pulse waveform by adjusting the stroke of the cylindrical air pump and an air tube that conveyed the pulse to the artificial wrist.

Results

The amplitude of the measured pulse pressure decreased with increasing thickness and hardness of the cover layer. Normalized waveform analysis showed that the thickness rather than the hardness of the cover layer contributed more to waveform distortion. Analysis of the channel distribution of the pulse sensor with respect to the applied constant dynamic pressure showed that the material of the cover layer had a large effect.

Conclusions

In this study, in-line array pulse sensors with various cover layers were fabricated, the dynamic pulse wave responses according to the thickness and the hardness of the cover layer were analyzed, and an appropriate thickness and hardness for the cover layer were suggested. The dynamic pulse wave responses of pulse sensors revealed in this study will contribute to the fabrication of improved pulse sensors and pulse wave analyses.

"Sleep disordered breathing and ECG R-wave to radial artery pulse delay, The Multi-Ethnic Study of Atherosclerosis"

BACKGROUND

Electrocardiography R-wave to radial artery pulse delay (RRD) represents pulse transit time inclusive of pre-ejection period (PEP) and arterial pulse propagation time. RRD is proposed to largely reflect arterial stiffness when PEP is accounted for (shorter RRD = higher arterial stiffness). Sleep disordered breathing (SDB) causes intermittent hypoxemia and sympathetic activation, which negatively influences vascular function. We aimed to examine the association of measures of SDB with RRD.

METHODS

Our sample consisted of participants in the Multi-Ethnic Study of Atherosclerosis without prevalent cardiovascular disease who underwent a daytime arterial elasticity exam, cardiac magnetic resonance imaging (MRI), and overnight polysomnography. SDB measures of interest included apnea hypopnea index (AHI) and oxygen desaturation index (ODI) (N = 1173). RRD was regressed on each measure of SDB separately, with adjustment for other cardiovascular risk factors as well as for correlates of the PEP, another component of RRD, by including cardiac MRI measures of contractility and preload.

RESULTS

In multivariate analysis, among measures of SDB, ODI, a marker of intermittent hypoxemia, was inversely associated with RRD (β = -60.2 msec per SD [15.5/hr], p = 0.04). No significant association was found with AHI. In gender stratified analyses, ODI and AHI were predictive of RRD in men only (β = -111.3 msec per SD [15.5/hr], p = 0.01 and β = -100.3 msec per SD [16.1/hr], p = 0.02 respectively).

CONCLUSION

Severity of SDB as measured by ODI was associated with RRD, a marker of arterial stiffness. Thus, association of RRD with measures of SDB appears to be gender-dependent.

Increased pulse wave transit time after percutaneous coronary intervention procedure in CAD patients

Pulse wave transit time (PWTT) has been widely used as an index in assessing arterial stiffness. Percutaneous coronary intervention (PCI) is usually applied to the treatment of coronary artery disease (CAD). Research on the changes in PWTT caused by PCI is helpful for understanding the impact of the PCI procedure. In addition, effects of stent sites and access sites on the changes in PWTT have not been explored. Consequently, this study aimed to provide this information. The results showed that PWTT significantly increased after PCI (p < 0.01) while the standard deviation (SD) of PWTT time series had no statistically significant changes (p = 0.60) between before and after PCI. Significantly increased PWTT was found in the radial access group (p < 0.01), while there were no significant changes in the femoral access group (p > 0.4). Additionally, PWTT in the left anterior descending (LAD) group significantly increased after PCI (p < 0.01), but the increase that was found in the right coronary artery (RCA) group was not significant (p > 0.1). Our study indicates that arterial elasticity and left ventricular functions can benefit from a successful PCI procedure, and the increase of peripheral PWTT after PCI can help to better understand the effectiveness of the procedure.

Estimation of Pulse Transit Time From Radial Pressure Waveform Alone by Artificial Neural Network

OBJECTIVE

To validate the feasibility of the estimation of pulse transit time (PTT) by artificial neural network (ANN) from radial pressure waveform alone.

METHODS

A cascade ANN with ten-fold cross validation was applied to invasively and simultaneously recorded aortic and radial pressure waveforms during rest and nitroglycerin infusion () for the estimation of mean and beat-to-beat PTT. The results of the ANN models were compared to a multiple linear regression (LR) model when the features of radial arterial pressure waveform in time and frequency domains were used as the predictors of the models.

RESULTS

For the estimation of mean PTT and beat-to-beat PTT by ANN ( ), the correlation coefficient between the and the measured PTT () (mean: ; beat-to-beat: ) is higher than that between the PTT estimated by LR ( ) and (mean: ; beat-to-beat: ). The standard deviation (SD) of the difference between the and ( ; beat-to-beat: ) is significantly less than that between the and (; beat-to-beat: 10 ms), but no significant difference exists between their mean ( ). The lack of frequency features of radial pressure waveform caused obvious reduction in the correlation coefficient and SD of the difference between the and . The performance of the ANN was improved by increasing the sample number but not by increasing the neuron number.

CONCLUSION

ANN is a potential method of PTT estimation from a single pressure measurement at radial artery.

SIMULATION ANALYSIS OF BLOOD FLOW IN ARTERIES OF THE HUMAN ARM

Arteries in the upper limb play important roles in the circulation system of the human body. In particular, the radial artery has received considerable attention in traditional Chinese medicine for thousands of years. Here, a 3D model for the arm arteries has been created uncomplicated, in a Chinese adult's left hand, from the magnetic resonance imaging data, using professional modeling software to restore the basic structure of the arm artery in human body, before being imported to Ansys software for simulation. Blood model has been only simulated, and using the blood density of constant parameter and viscosity using the Carreau fluid model, and using viscous-laminar model of Fluent to obtain the velocity profile, static pressure and shear stress in the brachial, interosseous, ulnar, radial and palmar arch arteries. In particular, the brachial and bifurcations have the high pressure and velocity profiles. The simulation results obtained here are also validated by those published in the literature and proved the ulnar artery prevails over the radial artery as a blood supplier to the vessels in the wrist and hand.

A multi-layer monitoring system for clinical management of Congestive Heart Failure

BACKGROUND

Congestive Heart Failure (CHF) is a serious cardiac condition that brings high risks of urgent hospitalization and death. Remote monitoring systems are well-suited to managing patients suffering from CHF, and can reduce deaths and re-hospitalizations, as shown by the literature, including multiple systematic reviews.

METHODS

The monitoring system proposed in this paper aims at helping CHF stakeholders make appropriate decisions in managing the disease and preventing cardiac events, such as decompensation, which can lead to hospitalization or death. Monitoring activities are stratified into three layers: scheduled visits to a hospital following up on a cardiac event, home monitoring visits by nurses, and patient's self-monitoring performed at home using specialized equipment. Appropriate hardware, desktop and mobile software applications were developed to enable a patient's monitoring by all stakeholders. For the first two layers, we designed and implemented a Decision Support System (DSS) using machine learning (Random Forest algorithm) to predict the number of decompensations per year and to assess the heart failure severity based on a variety of clinical data. For the third layer, custom-designed sensors (the Blue Scale system) for electrocardiogram (EKG), pulse transit times, bio-impedance and weight allowed frequent collection of CHF-related data in the comfort of the patient's home. We also performed a short-term Heart Rate Variability (HRV) analysis on electrocardiograms self-acquired by 15 healthy volunteers and compared the obtained parameters with those of 15 CHF patients from PhysioNet's PhysioBank archives.

RESULTS

We report numerical performances of the DSS, calculated as multiclass accuracy, sensitivity and specificity in a 10-fold cross-validation. The obtained average accuracies are: 71.9% in predicting the number of decompensations and 81.3% in severity assessment. The most serious class in severity assessment is detected with good sensitivity and specificity (0.87 / 0.95), while, in predicting decompensation, high specificity combined with good sensitivity prevents false alarms. The HRV parameters extracted from the self-measured EKG using the Blue Scale system of sensors are comparable with those reported in the literature about healthy people.

CONCLUSIONS

The performance of DSSs trained with new patients confirmed the results of previous work, and emphasizes the strong correlation between some CHF markers, such as brain natriuretic peptide (BNP) and ejection fraction (EF), with the outputs of interest. Comparing HRV parameters from healthy volunteers with HRV parameters obtained from PhysioBank archives, we confirm the literature that considers the HRV a promising method for distinguishing healthy from CHF patients.

Pulse transit time measured by photoplethysmography improves the accuracy of heart rate as a surrogate measure of cardiac output, stroke volume and oxygen uptake in response to graded exercise

Heart rate (HR) is a valuable and widespread measure for physical training programs, although its description of conditioning is limited to the cardiac response to exercise. More comprehensive measures of exercise adaptation include cardiac output (Q̇), stroke volume (SV) and oxygen uptake (V̇O2), but these physiological parameters can be measured only with cumbersome equipment installed in clinical settings. In this work, we explore the ability of pulse transit time (PTT) to represent a valuable pairing with HR for indirectly estimating Q̇, SV and V̇O2 non-invasively. PTT was measured as the time interval between the peak of the electrocardiographic (ECG) R-wave and the onset of the photoplethysmography (PPG) waveform at the periphery (i.e. fingertip) with a portable sensor. Fifteen healthy young subjects underwent a graded incremental cycling protocol after which HR and PTT were correlated with Q̇, SV and V̇O2 using linear mixed models. The addition of PTT significantly improved the modeling of Q̇, SV and V̇O2 at the individual level ([Formula: see text] for SV, 0.548 for Q̇, and 0.771 for V̇O2) compared to predictive models based solely on HR ([Formula: see text] for SV, 0.503 for Q̇, and 0.745 for V̇O2). While challenges in sensitivity and artifact rejection exist, combining PTT with HR holds potential for development of novel wearable sensors that provide exercise assessment largely superior to HR monitors.

The relationship between heart-carotid pulse transit time and carotid intima-media thickness in hypertensive patients

The study aimed to investigate the relationship between heart-carotid pulse transit time and carotid intima-media thickness (CIMT) in hypertensive patients, and whether including the pre-ejection period (PEP) in heart-carotid pulse transit time would affect this correlation. A total of 62 hypertensive patients were included in this study. They were divided into the normal CIMT group (n=33, CIMT⩽0.8 mm) and the thickened CIMT group (n=29, CIMT>0.8 mm). The noninvasive ultrasound method was used to measure CIMT, electrocardiogram R-wave-based heart-carotid pulse transit time (rcPTT) and PEP. Aortic valve-carotid artery pulse transit time (acPTT) was calculated by subtracting PEP from rcPTT. Simple linear analysis showed that CIMT was negatively associated with rcPTT and acPTT (r=-0.57, P<0.0001; r=-0.41, P=0.016) in the normal CIMT group as well as in the thickened CIMT group (r=-0.50, P=0.0053; r=-0.59, P=0.001). These relationships were eliminated in the normal CIMT group after adjusting for age, gender, smoking behaviour, systolic blood pressure, diastolic blood pressure and cholesterol levels. However, rcPTT and acPTT still showed significant correlations with CIMT in the thickened CIMT group. In conclusion, rcPTT and acPTT were associated with CIMT, independent of well-known clinical confounders in thickened CIMT hypertensive patients. Therefore, rcPTT and acPTT might be useful markers for atherosclerosis evaluation.

[Alterations in arterial compliance of dyslipidemic patients]

INTRODUCTION

We studied the alteration on the distensibility of the arterial walls caused by dyslipidemia LDLc dependent, along the decades of life, by means of a study of the radial artery pulse wave.

METHODS

We made an analysis of the radial artery pulse wave records acquired by means a movement displacement sensor, placed on radial palpation area. We recruited 100 dyslipidemic men without other cardiovascular risk factors, between the 3rd and the 6th decade. We identified the reflected wave in the records and we computed the augmentation index in order to quantify its amplitude and position. This index is useful to assess the endothelial dysfunction. Besides, we defined a velocity coefficient as the ratio between the size of the individuals and the delay time between the peak of the systolic wave and the arrival of the reflected wave. Results were compared against those obtained in a group of 161 healthy volunteers.

RESULTS

We found that dyslipidemic patients presented augmentation index values similar to controls until the fourth decade, increasing thereafter with significant differences only in the 6th decade. No significant differences were found in the velocity index in any of the ages studied.

CONCLUSIONS

We conclude that alterations produced by dyslipidemia take decades to manifest, and they begin affecting the mechanism of vasodilation of distal arteries with highest proportion of smooth muscle, without altering the proximal conduit arteries with more elastin content.

A NEW METHOD FOR DETERMINING SUBENDOCARDIAL VIABILITY RATIO FROM RADIAL ARTERY PRESSURE WAVES

Aortic subendocardial viability ratio (SEVR), an index of myocardial oxygen demand relative to supply, has been used for the early detection of hemodynamic changes. We aimed to validate a new method for determining SEVR directly from radial pressures. Hemodynamic parameters were measured in 231 outpatients (108 males and 123 females) for physical examination, aged from 20–77 years (45.9 ± 17.3 years), including 210 healthy and 21 hypertensive subjects. Aortic SEVR was obtained using a validated device (SphygmoCor; AtCor Medical, Sydney, Australia), and radial SEVR was obtained using a portable vascular testing device (IIM-2010A; Institute and Intelligent of Machines, Hefei, China). Radial SEVR was strongly related to aortic SEVR (r = 0.824, p < 0.01), with approximately 15.7% lower value. Aortic and radial SEVR had similar independent predictors, including diastolic time fraction (DTF), systolic blood pressure, diastolic blood pressure, age, and height. DTF exerted the most influence on both of them. In healthy subjects, there were significant changes in aortic and radial SEVR between age groups in both males and females (p < 0.05 for both ). Changes in aortic and radial SEVR with aging were parallel though the differences between them increased. These results suggested that the simple and easily obtainable radial SEVR could provide equivalent information to aortic SEVR, and has potential for the primary prevention of cardiovascular disease in health screening.

A NEW APPROACH FOR ASSESSMENT OF PULSE WAVE VELOCITY AT RADIAL ARTERY IN YOUNG AND MIDDLE-AGED HEALTHY HUMANS

Pulse wave velocity (PWV), based on two-site measurement, is a well-known predictor of arterial stiffness. Interest focused increasingly on simplifying the PWV measurement results in attempts at determining it at a single site. We aimed to validate a new tonometric method (IIM-2010A) for assessment of PWV at radial artery in healthy subjects <65 years of age. PWV measurements were performed in 46 healthy adults (25 men and 21 women) aged 21–65 years (39.6 ± 15.5 years) using Complior device and IIM-2010A respectively. In a subgroup of 21 humans, the measurements were repeated after 1 week using IIM-2010A with the same protocol. There was a strong correlation between PWV obtained by IIM-2010A and PWV obtained by Complior, as well as between pulse transit time (PTT) measurements (r = 0.79 and r = 0.85, respectively, P < 0.01 for both). Although PTT was significantly lower measured by IIM-2010A, no significant difference was found in PWV. The mean difference of PWV with SD was -0.1 ± 1.2 m/s between two repeated measurements at intervals of 1 week. Bland–Altman's plot indicated no trend for the reproducibility of measurements to vary with their underlying mean value. Intraclass correlation coefficient (= 0.87) confirmed this excellent week-to-week reproducibility of PWV. The method provides a simple, easily-obtainable, and reproducible measurement of PWV in young and middle-aged subjects, and has potential to detect premature arterial aging for the management of primary prevention.