The Changes of Cardiovascular Neurotransmitter Levels under Low-Intensity Focused Ultrasound Stimulation of the Vagus Nerve.

BACKGROUND: Our previous study has shown that stimulation of the vagus nerve with low-intensity focused ultrasound could modulate blood pressure (BP), but the underlying mechanisms remain unclear. This study investigated the changes of cardiovascular neurotransmitter levels to indirectly evaluate the responses of the autonomic nervous system and renin-angiotensin system under low-intensity focused ultrasound stimulation (FUS) of the vagus nerve. METHODS: Cardiovascular neurotransmitter levels of epinephrine (EPI), norepinephrine (NE), and angiotensin II (ANGII) were measured and compared before and after the FUS in seven spontaneously hypertensive rats; and were also measured and compared between a target stimulation group (FUS, n = 6) and non-target stimulation group (Control, n = 5) after stimulation to exclude the influence of potential confounding factors. RESULTS: The t-test results showed that the levels of EPI, NE, and ANGII were significantly decreased (P < 0.05) after stimulation compared to before stimulation. Additionally, the levels of NE and EPI were significantly lower (P < 0.05) in the FUS group than in the Control group after stimulation, indicating that the activities of the sympathetic nervous system and renin-angiotensin system of the vagus nerve might be inhibited by FUS of the vagus nerve. CONCLUSION: These findings reveal the mechanism of BP lowing in response to FUS of the vagus nerve.Clinical Relevance-This study revealed the mechanism of BP lowering in response to focused ultrasound stimulation of the vagus nerve through analyzing the changes of cardiovascular neurotransmitter levels.

Filtering-induced changes of pulse transmit time across different ages: a neglected concern in photoplethysmography-based cuffless blood pressure measurement.

Background: Pulse transit time (PTT) is a key parameter in cuffless blood pressure measurement based on photoplethysmography (PPG) signals. In wearable PPG sensors, raw PPG signals are filtered, which can change the timing of PPG waveform feature points, leading to inaccurate PTT estimation. There is a lack of comprehensive investigation of filtering-induced PTT changes in subjects with different ages. Objective: This study aimed to quantitatively investigate the effects of aging and PTT definition on the infinite impulse response (IIR) filtering-induced PTT changes. Methods: One hundred healthy subjects in five different ranges of age (i.e., 20-29, 30-39, 40-49, 50-59, and over 60 years old, 20 subjects in each) were recruited. Electrocardiogram (ECG) and PPG signals were recorded simultaneously for 120 s. PTT was calculated from the R wave of ECG and PPG waveform features. Eight PTT definitions were developed from different PPG waveform feature points. The raw PPG signals were preprocessed then further low-pass filtered. The difference between PTTs derived from preprocessed and filtered PPG signals, and the relative difference, were calculated and compared among five age groups and eight PTT definitions using the analysis of variance (ANOVA) or Scheirer-Ray-Hare test with post hoc analysis. Linear regression analysis was used to investigate the relationship between age and filtering-induced PTT changes. Results: Filtering-induced PTT difference and the relative difference were significantly influenced by age and PTT definition (p < 0.001 for both). Aging effect on filtering-induced PTT changes was consecutive with a monotonous trend under all PTT definitions. The age groups with maximum and minimum filtering-induced PTT changes depended on the definition. In all subjects, the PTT defined by maximum peak of PPG had the minimum filtering-induced PTT changes (mean: 16.16 ms and 5.65% for PTT difference and relative difference). The changes of PTT defined by maximum first PPG derivative had the strongest linear relationship with age (R-squared: 0.47 and 0.46 for PTT difference relative difference). Conclusion: The filtering-induced PTT changes are significantly influenced by age and PTT definition. These factors deserve further consideration to improve the accuracy of PPG-based cuffless blood pressure measurement using wearable sensors.

Age-Related Changes in Blood Volume Pulse Wave at Fingers and Ears.

OBJECTIVE: The decline in vascular elasticity with aging can be manifested in the shape of pulse wave. The study investigated the pulse wave features that are sensitive to age and the pattern of these features change with increasing age were examined. METHODS: Five features were proposed and extracted from the photoplethysmography (PPG)-based pulse wave or its first derivative wave. The correlation between these PPG features and ages was studied in 100 healthy subjects with a wide range of ages (20-71 years). Piecewise regression coefficients were calculated to examine the rates of change of the PPG features with age at different age stages. RESULTS: The proposed PPG features obtained from the finger showed a strong and significant correlation with age (with r = 0.76 - 0.77, p < 0.01), indicating higher sensitivity to age changes compared to the PPG features reported in previous studies (with r = 0.66 - 0.75). The correlation remained significant even after correcting for other clinical variables. The rate of change of the PPG feature values was found to be significantly faster in subjects aged ≥40 years compared to those aged < 40 years in the healthy population. This rate of change was similar to the age-related progression of arterial stiffness evaluated by pulse wave velocity (PWV), which is considered a gold standard for evaluating vascular stiffness. CONCLUSIONS: The proposed PPG features showed a high correlation with chronological age in healthy subjects and exhibited a similar age-related change trend as PWV. SIGNIFICANCE: With the convenience of PPG measures, the proposed age-related features have the potential to be used as biomarkers for vascular aging and estimating the risk of cardiovascular disease.

Autonomic modulation by low-intensity focused ultrasound stimulation of the vagus nerve.

Objective.Our previous study has shown that low-intensity focused ultrasound stimulation (FUS) of the vagus nerve could modulate blood pressure (BP), but its underlying mechanisms remain unclear. We hypothesized that low-intensity FUS of the vagus nerve would regulate autonomic function and thus BP.Approach.17 anesthetized spontaneously hypertensive rats were treated with low-intensity FUS of the left vagus nerve for 15 min each trial. Continuous BP, heart rate, respiration rate (RR), and core body temperature were simultaneously recorded to evaluate the effects on BP and other physiological parameters. Heart rate variability (HRV), systolic BP variability, and baroreflex sensitivity were computed to evaluate the autonomic modulation function. A Control-sham group without stimulation and another Control-FUS group with non-target stimulation were also examined to exclude the influence of potential confounding factors on autonomic modulation.Main results.A prolonged significant decrease in BP, pulse pressure, RR, the normalized low-frequency power of HRV, and the low-to-high frequency power ratio of HRV were found after the low-intensity FUS of the left vagus nerve in comparison with the baseline and those of the control groups, demonstrating that activities of the sympathetic nervous system were inhibited. The prolonged significant increase of the normalized high-frequency power of HRV suggested the activation of parasympathetic activity.Significance.Low-intensity FUS of the left vagus nerve effectively improved the autonomic function by activating parasympathetic efferent and inhibiting sympathetic efferent, which contributes to BP reduction. The findings shed light on the hypotensive mechanism underlying FUS.

A Pilot Study of Thermal Effect of Low-intensity Focused Ultrasound on Blood Pressure Modulation.

Our recent study showed that low-intensity focused ultrasound stimulation (FUS) of the vagus nerve is capable of lowering blood pressure (BP). However, it remains unknown that what is the underlying mechanisms of BP modulation with FUS. In our preliminary experiments, we noticed that there was temperature elevation accompanied the FUS. Thus, to verify whether the thermal effect of ultrasound contributes in the BP-lowering effect, this study compared the BP response under the FUS (with thermal effect and mechanical effect) and the alternative heating source treatment (AHST) (with thermal effect only) of left vagus nerve. Six Sprague Dawley rats were randomly divided into two groups (FUS, n=3 and AHST, n=3). In vivo temperature measurements were conducted to evaluate the heating performance of the FUS and the AHST. Blood pressure (BP) waveform was continuously recorded from the right common artery and was used for analyzing systolic BP (SBP), diastolic BP (DBP), mean BP (MBP), and heart rate (HR). The results showed that the SBP, DBP, MBP and HR decreased during the 15-min FUS. However, most of the SBP, DBP, MBP and HR increased during the 15-min AHST, which had the approximate temperature elevation of the FUS. Thus, the thermal effect of ultrasound probably does not contribute in the BP-lowering effect induced by low-intensity FUS of the vagus nerve.

Blood Pressure Modulation With Low-Intensity Focused Ultrasound Stimulation to the Vagus Nerve: A Pilot Animal Study.

OBJECTIVE: For hypertensive individuals, their blood pressure (BP) is often managed by taking medications. However, antihypertensive drugs might cause adverse effects such as congestive heart failure and are ineffective in significant numbers of the hypertensive population. As an alternative method for hypertension management, non-drug devices-based neuromodulation approaches such as functional electrical stimulation (FES) have been proposed. The FES approach requires the implantation of a stimulator into the body. One recently emerging technique, called low-intensity focused ultrasound stimulation (FUS), has been proposed to non-invasively modulate neural activities. In this pilot study, the feasibility of adopting low-intensity FUS neuromodulation for BP regulation was investigated using animal models. METHODS: A FUS system was developed for BP modulation in rabbits. For each rabbit, the low-intensity FUS with different acoustic intensities was used to stimulate its exposed left vagus nerve, and the BP waveform was synchronously recorded in its right common carotid artery. The effects of the different FUS intensities on systolic blood pressure (SBP), diastolic blood pressure (DBP), mean blood pressure (MAP), and heart rate (HR) were extensively examined from the BP recordings. RESULTS: The results demonstrated that the proposed FUS method could successfully induce changes in SBP, DBP, MAP, and HR values. When increasing acoustic intensities, the values of SBP, DBP, and MAP would tend to decrease more substantially. CONCLUSION: The findings of this study suggested that BP could be modulated through the FUS, which might provide a new way for non-invasive and non-drug management of hypertension.

Investigating the physiological mechanisms of the photoplethysmogram features for blood pressure estimation.

OBJECTIVE: Photoplethysmogram (PPG) signals have been widely used to estimate blood pressure (BP) cufflessly and continuously. A number of different PPG features have been proposed and extracted from PPG signals with the aim of accurately estimating BP. However, the underlying physiological mechanisms of PPG-based BP estimation still remain unclear, particularly those corresponding to various PPG features. In this study, the physiological mechanisms of PPG features for BP estimation were investigated, which may provide further insight. APPROACH: Experiments with cold stimuli and an exercise trial were designed to change the total peripheral vascular resistance (TPR) and cardiac output (CO), respectively. Instantaneous BP and continuous PPG signals from 12 healthy subjects were recorded throughout the experiments. A total of 65 PPG features were extracted from the original, the first derivative, and the second derivative waves of PPG. The significance of the change of PPG features in the cold stimuli phase and in the early exercise recovery period was compared with that in the baseline phase. MAIN RESULTS: Intensity-specific PPG features changed significantly (p < 0.05) in the cold stimuli phase compared with the baseline phase, demonstrating that they were TPR-correlated. Time-specific PPG features changed significantly (p < 0.05) in the early exercise recovery period compared with the baseline phase, suggesting they were CO-correlated. Most of the PPG features associated with slope and area changed obviously both in the cold stimuli phase and in the early exercise recovery period, indicating that they should be TPR-correlated and CO-correlated. SIGNIFICANCE: The findings of this study explained the intrinsic physiological mechanisms underlying PPG features used for BP estimation, and provided insights for exploring more diagnostic applications of the PPG features.

A Characteristic Filtering Method for Pulse Wave Signal Quality Assessment.

Pulse wave is an important physiological signal widely used in clinic. In practical applications, the pulse wave recordings are easily corrupted by different interferences. Sometimes, it is very difficult to eliminate the noise by commonly used filtering methods. In this study, we proposed a filtering method based on the characteristics of pulse wave recordings to remove the noisy outliers. Firstly, five characteristics, short-term energy (SE), ascending intensity difference (AID), descending intensity difference (DID), ascending time difference (ATD), and descending time difference (DTD), were chosen as metrics and calculated from cardiac pulse wave. Then the median lines of the five metrics were obtained using a median filter, respectively. An acceptable value range around the median line of each metric was set based on histogram distribution analysis and was used to examine pulse wave recordings cardiac-cycle-by-cycle. For each cardiac cycle, when one or more of its five characteristic values exceed(s) the acceptable range, the pulse wave recording segment was discarded from further analysis. With this proposed method, the noisy outliers could be efficiently identified from the pulse wave recordings. This suggests that the proposed preprocessing method would be useful in improving the assessment performance of pulse-wave-based clinical applications. Additionally, the method might also be extended used in other physiological signals pre-processing, such as ECG, blood pressure wave, etc.

Reply to Comment on 'New photoplethysmogram indicators for improving cuffless and continuous blood pressure estimation accuracy'.

OBJECTIVE: This article was written by the invitation of the editorial board of Physiological Measurement. It is a Reply to the Comment regarding our recently published paper entitled 'New photoplethysmogram indicators for improving cuffless and continuous blood pressure estimation accuracy' (Lin et al 2018 Physiol. Meas. 29 025005). APPROACH: We appreciate van Helmond and Joseph's (2018 Physiol. Meas. 098001) interests and comments on our previous paper. In the Comment, they discussed in detail the physiology underlying the pulse arrive time (PAT)-based methods for blood pressure (BP) measurement, and concluded that there are inherent physiological reasons precluding the development of an accurate continuous cuffless BP measurement using PAT-based methods. We could agree with the comments of van Helmond and Joseph about the physiology underlying PAT-based methods for BP measurement. It may be difficult to minimize the confounding effects of physiological factors such as pre-ejection period and smooth muscle tone, etc. However, in this Reply, we discuss some potential solutions to deal with these problems from an engineering point of view. MAIN RESULTS: When heart rate, more photoplethysmogram (PPG) features, PAT, robust machine learning models, and other techniques were adopted for BP estimation, it is promising for improving the accuracy of BP estimation to an acceptable range that can meet professional standards (e.g. Advancement of Medical Instrumentation (AAMI) standard, British Hypertension Society (BHS) protocol). SIGNIFICANCE: PAT- and/or PPG-based methods may be a promising technique for continuous and unobtrusive blood pressure measurement.

New photoplethysmogram indicators for improving cuffless and continuous blood pressure estimation accuracy.

OBJECTIVE: The accuracy of cuffless and continuous blood pressure (BP) estimation has been improved, but it is still unsatisfactory for clinical uses. This study was designed to further increase BP estimation accuracy. APPROACH: In this study, a number of new indicators were extracted from photoplethysmogram (PPG) recordings and a linear regression method was used to construct BP estimation models based on the PPG indicators and pulse transit time (PTT). The performance of the BP estimation models was evaluated by the PPG recordings from 22 subjects when they performed mental arithmetic stress and Valsalva's manoeuvre tasks that could induce BP fluctuations. MAIN RESULTS: Our results showed that the best PPG-based BP estimation model could achieve a decrease of 0.31 ± 0.08 mmHg in systolic BP (SBP) and 0.33 ± 0.01 mmHg in diastolic BP (DBP) on estimation errors of grand absolute mean (GAM) and standard deviation (GSD) in comparison to the previously reported PPG-based methods. The best estimation model based on the combination of PPG and PPT could achieve a decrease (GAM & GSD) of 0.81 ± 0.95 mmHg in SBP and 0.75 ± 0.54 mmHg in DBP in comparison to the PPT-based methods. SIGNIFICANCE: The findings suggest that the newly proposed PPG indicators would be promising for improving the accuracy of continuous and cuffless BP estimation.

Arylurea Derivatives: A Class of Potential Cancer Targeting Agents.

Arylurea derivatives, an important class of small molecules, have received considerable attention in recent years due to their wide range of biological applications. Various molecular targeted agents with arylurea scaffold as potential enzyme/receptor inhibitors were constructed with the successful development of sorafenib and regorafenib. This review focuses on those arylureas possessing anti-cancer activities from 2010 to date. According to their different mechanisms of action, these arylureas are divided into the following six categories: (1) Ras/Raf/MEK/ERK signaling pathway inhibitors; (2) tumor angiogenesis inhibitors, their targets include Vascular Endothelial Growth Factor Receptors (VEGFRs), Fibroblast Growth Factor Receptors (FGFRs), Platelet-Derived Growth Factor Receptors (PDGFRs), Epidermal Growth Factor Receptors (EGFRs), Insulin-Like Growth Factor 1 Receptor (IGF-1R), Fmslike Tyrosine Kinase 3 (FLT3), c-Kit, MET, and Smoothened (Smo); (3) PI3K/AKT/mTOR signaling pathway inhibitors; (4) cell cycle inhibitors, their targets include Checkpoint Kinases (Chks), Cyclin- Dependent Kinases (CDKs), Aurora, SUMO activating enzyme 1 (SUMO E1), tubulin, and DNA; (5) tumor differentiation, migration, and invasion inhibitors, their targets include Matrix Metalloproteinases (MMPs), LIM kinase (Limk), Nicotinamide Phosphoribosyltransferase (Nampt), and Histone Deacetylase (HDAC); (6) arylureas from the rational modification of natural products. This review focuses on the Structure-Activity Relationships (SARs) of these arylureas. The structural evolution and current status of some typical anti-cancer agents used in clinic and/or in clinical trials are emphasized.

High in vivo antitumor activity of cobalt oxoisoaporphine complexes by targeting G-quadruplex DNA, telomerase and disrupting mitochondrial functions.

Two G-quadruplex ligands: [Co(H-La)2Cl2] (Co1) and [Co(Lb)2][CoCl4]⋅2H2O (Co2) have been synthesized and characterized. Two cobalt oxoisoaporphine complexes exhibited selective cytotoxicity to SK-OV-3/DDP cells than for HL-7702 cells. Cytotoxic mechanism studies indicated that both Co1 and Co2 were telomerase inhibitor targeting c-myc, telomere, and bcl-2 G4s, and triggering cell senescence and apoptosis, which caused S phase arrest. They also induced mitochondrial dysfunction. The better antitumor activity of Co2, which should be correlated with a moiety of 2-[5-(2-pyridinyl)-1H-pyrrol-2-yl]pyridine in the Lb. Importantly, Co2 at high doses showed at least the same level of tumor growth inhibition efficacy compared to that of cisplatin, and better in vivo safety profile.

Correlation between beat-to-beat blood pressure variability and arterial stiffness in healthy adults in the cold pressor test.

Blood pressure variability has a great effect on the progression of arterial stiffness, which has increasingly become a hot research topic recently. In this study, beat-to-beat recordings of blood pressure (BP), heart rate, cardiac output, total peripheral resistance, and left ventricular ejection time during the cold pressor test (CPT) were analyzed together. We recruited 101 young Chinese subjects (aged 21-33) with no known history of high BP into the study. We found that the mean level of beat-to-beat BP and the average real variability and successive variation of beat-to-beat diastolic BP variability in the CPT showed significant correlations with pulse wave velocity (PWV) (r = 0.22-0.34, P < 0.05). In addition, we also found correlations between beat-to-beat heart rate and heart rate variability indices and PWV in each phase of the CPT. At the same time, the standard deviation of the R-R intervals and square root of the mean squared difference of successive R-R intervals in the cold stimulus phase also showed significant correlations with PWV (r = 0.23-0.24, P < 0.05). In conclusion, the level and variability of beat-to-beat BP have a strong influence on arterial stiffness.

Cuffless and Continuous Blood Pressure Estimation from the Heart Sound Signals.

Cardiovascular disease, like hypertension, is one of the top killers of human life and early detection of cardiovascular disease is of great importance. However, traditional medical devices are often bulky and expensive, and unsuitable for home healthcare. In this paper, we proposed an easy and inexpensive technique to estimate continuous blood pressure from the heart sound signals acquired by the microphone of a smartphone. A cold-pressor experiment was performed in 32 healthy subjects, with a smartphone to acquire heart sound signals and with a commercial device to measure continuous blood pressure. The Fourier spectrum of the second heart sound and the blood pressure were regressed using a support vector machine, and the accuracy of the regression was evaluated using 10-fold cross-validation. Statistical analysis showed that the mean correlation coefficients between the predicted values from the regression model and the measured values from the commercial device were 0.707, 0.712, and 0.748 for systolic, diastolic, and mean blood pressure, respectively, and that the mean errors were less than 5 mmHg, with standard deviations less than 8 mmHg. These results suggest that this technique is of potential use for cuffless and continuous blood pressure monitoring and it has promising application in home healthcare services.

The Different Effects of BMI and WC on Organ Damage in Patients from a Cardiac Rehabilitation Program after Acute Coronary Syndrome.

One of the purposes of cardiac rehabilitation (CR) after acute coronary syndrome (ACS) is to monitor and control weight of the patient. Our study is to compare the different obesity indexes, body mass index (BMI), and waist circumference (WC), through one well-designed CR program (CRP) with ACS in Guangzhou city of Guangdong Province, China, in order to identify different effects of BMI and WC on organ damage. In our work, sixty-one patients between October 2013 and January 2014 fulfilled our study. We collected the vital signs by medical records, the clinical variables of body-metabolic status by fasting blood test, and the organ damage variables by submaximal exercise treadmill test (ETT) and ultrasonic cardiogram (UCG) both on our inpatient and four-to-five weeks of outpatient part of CRP after ACS. We mainly used two-tailed Pearson's test and liner regression to evaluate the relationship of BMI/WC and organ damage. Our results confirmed that WC could be more accurate than BMI to evaluate the cardiac function through the changes of left ventricular structure on the CRP after ACS cases. It makes sense of early diagnosis, valid evaluation, and proper adjustment to ACS in CRP of the obesity individuals in the future.

Quantification of three-dimensional computed tomography angiography for evaluating coronary luminal stenosis using digital subtraction angiography as the standard of reference.

OBJECTIVE: We sought to evaluate the accuracy of quantitative three-dimensional (3D) CT angiography (CTA) for the assessment of coronary luminal stenosis using digital subtraction angiography (DSA) as the standard of reference. METHOD: Twenty-three patients with 54 lesions were referred for CTA followed by DSA. The CTA scans were performed with 256-slice spiral CT. 3D CTA were reconstructed from two-dimensional CTA imaging sequences in order to extract the following quantitative indices: minimal lumen diameter, percent diameter stenosis (%DS), minimal lumen area, and percent area stenosis (%AS). Correlation and limits of agreement were calculated using Pearson correlation and Bland-Altman analysis, respectively. The diagnostic performance and the diagnostic concordance of 3D CTA-derived anatomic parameters (%DS, %AS) for the detection of severe coronary arterial stenosis (as assessed by DSA) were presented as sensitivity, specificity, diagnostic accuracy, and Kappa statistics. Of which vessels with %DS >50% or with %AS >75% were identified as severe coronary arterial lesions. RESULT: The correlations of the anatomic parameters between 3D CTA and DSA were significant (r = 0.51-0.74, P < 0.001). Bland-Altman analysis confirmed that the mean differences were small (from -1.11 to 27.39%), whereas the limits of agreement were relatively wide (from ±28.07 to ±138.64%). Otherwise, the diagnostic accuracy (74.1% with 58.3% sensitivity and 86.7% specificity for DS%; 74.1% with 45.8% sensitivity and 96.7% specificity for %AS) and the diagnostic concordance (k = 0.46 for DS%; 0.45 for %AS) of 3D CTA-derived anatomic parameters for the detection of severe stenosis were moderate. CONCLUSION: 3D advanced imaging reconstruction technique is a helpful tool to promote the use of CTA as an alternative to assess luminal stenosis in clinical practice.

Time-frequency analysis of heart rate variability during the cold pressor test using a time-varying autoregressive model.

Heart rate variability is a useful clinical tool for autonomic function assessment and cardiovascular disease diagnosis. To investigate the dynamic changes of sympathetic and parasympathetic activities during the cold pressor test, we used a time-varying autoregressive model for the time-frequency analysis of heart rate variability in 101 healthy subjects. We found that there were two sympathetic peaks (or two parasympathetic valleys) when the abrupt changes of temperature (ACT) occurred at the beginning and the end of the cold stimulus and that the sympathetic and parasympathetic activities returned to normal in about the last 2 min of the cold stimulus. These findings suggested that the ACT rather than the low temperature was the major cause of the sympathetic excitation and parasympathetic withdrawal. We also found that the onsets of the sympathetic peaks were 4-26 s prior to the ACT and the returns to normal were 54-57 s after the ACT, which could be interpreted as the feedforward and adaptation of the autonomic regulation process in the human body, respectively. These results might be helpful for understanding the regulatory mechanisms of the autonomic system and its effects on the cardiovascular system.

Extraction of heart rate variability from smartphone photoplethysmograms.

Heart rate variability (HRV) is a useful clinical tool for autonomic function assessment and cardiovascular diseases diagnosis. It is traditionally calculated from a dedicated medical electrocardiograph (ECG). In this paper, we demonstrate that HRV can also be extracted from photoplethysmograms (PPG) obtained by the camera of a smartphone. Sixteen HRV parameters, including time-domain, frequency-domain, and nonlinear parameters, were calculated from PPG captured by a smartphone for 30 healthy subjects and were compared with those derived from ECG. The statistical results showed that 14 parameters (AVNN, SDNN, CV, RMSSD, SDSD, TP, VLF, LF, HF, LF/HF, nLF, nHF, SD1, and SD2) from PPG were highly correlated (r > 0.7, P < 0.001) with those from ECG, and 7 parameters (AVNN, TP, VLF, LF, HF, nLF, and nHF) from PPG were in good agreement with those from ECG within the acceptable limits. In addition, five different algorithms to detect the characteristic points of PPG wave were also investigated: peak point (PP), valley point (VP), maximum first derivative (M1D), maximum second derivative (M2D), and tangent intersection (TI). The results showed that M2D and TI algorithms had the best performance. These results suggest that the smartphone might be used for HRV measurement.

The relationship between the 24 h blood pressure variability and carotid intima-media thickness: a compared study.

Large blood pressure variability (BPV) will not only harm the target organ but also increase the possibility of the cardiovascular events. Since the damage of vascular system always leads to the alteration of the carotid wall, the structure and function of the carotid artery have been extensively examined in previous studies. In this work we conduct a study (60 subjects, aged 33-79) to evaluate the relationship between BPV and carotid intima-media thickness (IMT) in Shenzhen, which is one large city in the southern area of China. In our study, the blood pressure (BP) was collected using the 24 h ambulatory BP monitoring, and the BPV was evaluated using standard deviation (SD), coefficient of variation (CV), and average real variability (ARV) during 24 h, daytime and nighttime. All the IMT measurements are collected by ultrasound. The results show that both the daytime, and 24 h systolic BPV evaluated by three indices are positively associated with IMT. Among them, daytime systolic BPV evaluated with ARV is the best variable to represent the increasing of carotid IMT. In addition, after adjusting by age, sex, smoking, hypertension, and mean BP and PP values, 24 h diastolic BPV evaluated with SD also presents the favorable performance.

A stochastic filtering approach to recover strain images from quasi-static ultrasound elastography.

BACKGROUND: Model-based reconstruction algorithms have shown potentials over conventional strain-based methods in quasi-static elastographic image by using realistic finite element (FE) or bio-mechanical model constraints. However, it is still difficult to properly handle the discrepancies between the model constraint and ultrasound data, and the measurement noise. METHODS: In this paper, we explore the usage of Kalman filtering algorithm for the estimation of strain imaging in quasi-static ultrasound elastography. The proposed strategy formulates the displacement distribution through biomechanical models, and the ultrasound-derived measurements through observation equations. Through this filtering strategy, the discrepancies are quantitatively modelled as one Gaussian white noise, and the measurement noise of ultrasound data is modelled as another independent Gaussian white noise. The optimal estimation of kinematic functions, i.e. the full displacement and velocity field, are computed through this Kalman filter. Then the strain images can be easily calculated from the estimated displacement field. RESULTS: The accuracy and robustness of our proposed framework is first evaluated in synthetic data in controlled conditions, and the performance of this framework is then evaluated in the real data collected from elastography phantoms and patients with favourable results. CONCLUSIONS: The potential of our algorithm is to provide the distribution of mechanically meaningful strain under a proper biomechanical model constraint. We address the model-data discrepancy and measurement noise by introducing process noise and measurement noise in our framework, and then the mechanically meaningful strain is estimated through the Kalman filter in the minimum mean square error (MMSE) sense.