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Cuffless technique enables continuous blood pressure (BP) measurement in an unobtrusive manner, and thus has the potential to revolutionize the conventional cuff-based approaches. This study extends the pulse transit time (PTT) based cuffless BP measurement method by introducing a new indicator - the photoplethysmogram (PPG) intensity ratio (PIR). The performance of the models with PTT and PIR was comprehensively evaluated in comparison with six models that are based on sole PTT. The validation conducted on 33 subjects with and without hypertension, at rest and under various maneuvers with induced BP changes, and over an extended calibration interval, respectively. The results showed that, comparing to the PTT models, the proposed methods achieved better accuracy on each subject group at rest state and over 24 hours calibration interval. Although the BP estimation errors under dynamic maneuvers and over extended calibration interval were significantly increased for all methods, the proposed methods still outperformed the compared methods in the latter situation. These findings suggest that additional BP-related indicator other than PTT has added value for improving the accuracy of cuffless BP measurement. This study also offers insights into future research in cuffless BP measurement for tracking dynamic BP changes and over extended periods of time.

Cuffless technology for blood pressure (BP) measurement offers great potential for unobtrusive monitoring of hypertension. However, the accuracy is still a challenging issue probably owning to the inadequacy of existing noninvasive BP indicators in tracking BP changes, i.e., either the poor trackability of the indicators or the lack of relationship to map the indicators to BP. To figure out the covariation of BP-related noninvasive indicators and BP, we propose to analyze the coherence of intra-arterial systolic BP (SBP) and a selected group of noninvasive indicators, including the mostly used pulse transit time (PTT), photoplethysmogram intensity ratio (PIR) and RR interval (RRI) of electrocardiogram (ECG), in both time domain, with singular spectrum analysis (SSA), and frequency domain, with cross-spectral analysis. Through SSA the SBP and the indicators are decomposed into fast oscillations superimposed on a slow time-varying component. It is found that the fast variation components oscillate at similar frequencies for the SBP and the indicators, while that their slow variation components are out of phase synchronization. Cross-spectra between SBP and the indicators further illustrate stronger coherence correlation at high frequencies (HF, 0.15-0.40 Hz) (PTT: 0.54±0.30, PIR: 0.73±0.25, RRI: 0.63±0.25) than at low frequencies (LF, 0.04-0.15 Hz) (PTT: 0.24±0.19, PIR: 0.37±0.23, RRI: 0.33±0.23). The results suggest that the widely used indicators are poor to track the LF component of BP. Our study reveals the importance of exploring LF-related BP indicators as well as new models to integrate LF and HF information for improvement of cuffless BP measurement accuracy.

This study evaluated the association between carotid intima-media thickness (IMT) and 24 h ambulatory blood pressure variability (BPV) in 150 subjects. The subjects were divided into different age groups and gender groups. We found that for the subjects aged less than 45 years, 24 h and daytime diastolic BPV were associated with the increased IMT (r = 0.525, P = 0.018; r = 0.507, P = 0.022). For the middle aged people (46-55 years), daytime (r = 0.377, P = 0.014) and 24 h systolic BPV (r = 0.366, P = 0.017) were more related to the increases in IMT than 24 h diastolic BPV (r = 0.320, P = 0.039). However, no association between carotid IMT and BPV was found in the elderly (>55 years). In addition, the relationships between carotid IMT and BPV were more obvious in males than females. 24 h systolic BPV (P = 0.008) is the independent factor to evaluate the increased carotid IMT for males, but not for females. The findings in our study indicated that age and sex had influences on progression of carotid IMT. We conclude that the relationship between carotid IMT and ambulatory BPV can be modified by age and sex, thus, the regression model using BPV to evaluate the arteriosclerotic progression should take age and sex into account.

Pulse transit time (PTT) has been widely studied as an index of blood pressure (BP) changes. In recent years, some prototypes of PTT-based wearable BP measurement devices have been developed, which can relieve users from the discomfort caused by the inflating cuff used in auscultatory and oscillometric BP measurement techniques. However, in the common practice for PTT detection, multi-site sensor implementation on human body is required, making it difficult for the integration of wearable devices. Since multi-wavelength (MW) photoplethysmogram (PPG) signals carry blood pulsation information of different blood vessels embedded in different skin depths, the time difference between different wavelength PPG signals collected at the same body site can be treated as a special PTT on a short length of blood vessels beneath the skin. In this work, the time difference between MW PPG, denoted as PTT&#95;MW, was explored to track BP changes as a substitute of infrared (IR) PTT&#95;EP. (PTT&#95;EP is the time interval between electrocardiogram (ECG) and IR PPG.) Ten healthy adult subjects participated in the experiment, and their continuous BP, ECG and fingertip MW PPG signals generated from blue, green, yellow and IR light were recorded after 2-minute static handgrip exercise at 33% maximal voluntary contraction. The results showed that the correlation between Systolic BP (SBP) and IR-Blue PTT&#95;MW (|r|= 0.52) was comparable to the correlation between SBP and IR PTT&#95;EP (|r|= 0.59). Moreover, we optimized the wavelength combination of PTT&#95;MWs for each subject and found the average value of optimal correlation between SBP and PTT&#95;MW reached 0.76, which was significantly (p<;0.01) higher than the correlation between IR PTT&#95;EP and SBP. This study reveals that the time difference between MW PPG can be potentially used as PTT for cuffless BP measurement with its unique advantage in simple sensor implementation at only one body site.

Carotid intima-media thickness (IMT) has been one widely used index of early carotid atherosclerosis. We speculated that the influence of blood pressure variability (BPV) on early carotid atherosclerosis may be varied by the location of the carotid artery and diabetes history. Thus, the goal of this study was to evaluate the effects of BPV on early arteriosclerosis progression in different segments of the carotid artery for hypertension with and without diabetes.A total of 148 hypertension patients who underwent 24 hours ambulatory blood pressure (BP) monitoring and carotid ultrasonography were enrolled in this study. Of them, 84 subjects were without diabetes, and 64 subjects were with diabetes. Short-term BPV during daytime, nighttime, and over 24 hours were evaluated through standard deviation (SD) and average real variability (ARV). We measured carotid IMT at left and right common carotid artery (CCA), carotid bulb, and the origin of the internal carotid artery (ICA). The associations between segment-specific measurements of carotid IMT and 24 hours ambulatory BPV were analyzed.We found that IMT at the common carotid artery (CCA-IMT) and IMT at the internal carotid artery (ICA-IMT) were more closely associated with BPV than was carotid bulb IMT. In addition, for all subjects, BPV was clearly associated with left CCA-IMT but not with right CCA-IMT. Furthermore, in diabetes patients, nighttime systolic BPV was independently related to mean CCA-IMT (P < 0.01) and mean bulb IMT (P < 0.01). In contrast, in nondiabetes patients, daytime and 24 hours systolic BPV was positively associated with mean CCA-IMT (P < 0.05), but not independent after adjusting for baseline characteristics such as age and sex.The findings of our study indicate a segment-specific association between carotid IMT and 24 hours ambulatory BPV, and the associations also vary according to the diabetes history. We conclude that BPV plays a distinct role in early carotid arteriosclerosis progression within different segments of the carotid artery, especially for the hypertensions with and without diabetes., Competing Interests: The authors have no conflicts of interest to disclose.

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.

Current markers for heart failure (HF) diagnosis and prognosis are mainly for the evaluation of cardiac functions. Since previous studies have reported that HF patients demonstrated abnormal vascular responses to external stimuli, it is speculated that vascular tone, a measure of activation level of vascular wall, may be able to reflect these abnormalities to assist HF detection. Nevertheless, vascular tone is difficult to be objectively quantified using existing tools. In this study, a vascular tone index was estimated from noninvasive blood pressure and pulse transit time measurements using system identification technique. This method was evaluated in 35 subjects (10 healthy, 13 with HF risk factors and 12 HF patients) in a regular maximal exercise test. It was found that the vascular tone index significantly increased by 24.4 ± 26.6% (p < 0.01) during maximal exercise in the healthy subjects. Moreover, the response was gradually attenuated in the risk-factor and HF groups (15.8 ± 36.5 and 0.9 ± 17.9%, respectively). The results reveal the association between the vascular tone response to maximal exercise and HF disease or risks. To conclude, the proposed method provides a quantitative characterization of vascular tone which may be a useful indicator of the pathological changes of the arteries or the heart.

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.

24-h blood pressure (BP) has significant prognostic value for cardiovascular risk screening, but the present BP devices are mainly cuff-based, which are unsuitable for long-term BP measurement, especially during nighttime. In this paper, we developed an armband wearable pulse transit time (PTT) system for 24-h cuff-less BP measurement and evaluated it in an unattended out-of-laboratory setting. Ten healthy young subjects participated in this ambulatory study, where PTT was measured at 30-min interval by this wearable system and the reference BP was measured by a standard oscillometric ambulatory BP monitor. Due to the misalignment of BP and PTT on their recording time caused by the different measurement principles of the two BP devices, a new estimation method has been proposed: transients in PTT were removed from the raw data by defined criteria, and then evenly interpolated, low-pass filtered, and resampled to synchronize at the time when BP was recorded. The results show that with the proposed method, the correlation between PTT and systolic BP (SBP) during nighttime with dynamic range of 21.8 ± 14.2 mmHg has improved from -0.50 ± 0.24 to -0.62 ± 0.20 , and the difference between the estimated and reference SBP has improved from 0.7 ± 10.7 to 2.8 ± 8.2 mmHg with root mean square error reduced from 10.7 to 8.7 mmHg. In addition, the correlation between a very low frequency component of SBP and PTT obtained from the proposed method during nighttime is -0.80 ± 0.10 and the difference is 2.4 ± 5.7 mmHg for a dynamic BP range of 13.5 ± 8.0 mmHg. It is therefore concluded from this study that the proposed wearable system has great potential to be used for overnight SBP monitoring, especially to measure the averaged SBP over a long period.

Pulse transit time (PTT) is a cardiovascular parameter of emerging interest due to its potential to estimate blood pressure (BP) continuously and without a cuff. Both linear and nonlinear equations have been used in the estimation of BP based on PTT. This study, however, demonstrates that there is a hysteresis phenomenon between BP and PTT during and after dynamic exercise. A total of 46 subjects including 16 healthy subjects, 13 subjects with one or more cardiovascular risk factors, and 17 patients with cardiovascular disease underwent graded exercise stress test. PTT was measured from electrocardiogram and photoplethysmogram of the left index finger of the subject, i.e., a pathway that includes predominately aorta, brachial, and radial arteries. The results of this study showed that, for the same systolic BP (SBP), PTT measured during exercise was significantly larger than PTT measured during recovery for all subject groups. This hysteresis was further quantified as both normalized area bounded by the SBP-PTT relationship (AreaN) and SBP difference at PTT during peak exercise plus 20 ms (ΔSBP20). Significant attenuation of both AreaN (p <; 0.05) and ΔSBP20 (p <; 0.01) is observed in cardiovascular patients compared with healthy subjects, independent of resting BP. Since the SBP-PTT relationship are determined by the mechanical properties of arterial wall, which is predominately mediated by the sympathetic nervous system through altered vascular smooth muscle (VSM) tone during exercise, results of this study are consistent with the previous findings of autonomic nervous dysfunction in cardiovascular patients. We further conclude that VSM tone has a nonnegligible influence on the BP-PTT relationship and thus should be considered in the PTT-based BP estimation.

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.

Background: Carotid arterial stiffness measured by techniques of speckle tracking echocardiography is helpful to assess vascular wall deformation. We conducted a study to investigate the relationship between vascular deformation of the carotid artery and ischemic stroke in the elderly., Methods: We recruited 89 consecutive individuals aged ≥60 years (mean age = 72±6 years; 31 men) from a community health survey program. Ten (11%) had a history of ischemic stroke. Carotid B-mode images were acquired using a high-resolution vascular probe equipped on an echocardiographic system. Circumferential strain (CS) and strain rate (CSR) were obtained by speckle tracking techniques with a region of interest covering the entire depth of the common carotid arterial wall., Results: Both CS and CSR were significantly correlated with beta index and distensibility but not with carotid intima-medial thickness and pulse wave velocity. In the comparison between patients with or without history of stroke, carotid CS (1.46% ± 0.54% vs. 2.75% ± 1.23%; P = 0.002) and CSR (0.30±0.13 1/s vs. 0.47±0.18 1/s; P = 0.007) were significantly lower in patients with stroke. Multivariable analysis showed that both carotid CS and CSR were independent factors associated with previous strokes., Conclusions: Carotid wall deformation indices are useful for assessment of local carotid arterial stiffness. CS and CSR of carotid artery measured by speckle tracking techniques were associated with previous ischemic stroke in the elderly.

Pulse arrival time (PAT) is comprised of the vascular transit time (TT) through the arterial system and the pre-ejection period (PEP) in the heart. It has been used to predict arterial blood pressure (BP) without using a cuff. The aim of this study was to investigate the effects of including the PEP on the accuracy of cuffless systolic BP (SBP) estimation using the PAT technique in post-exercise recovery. Experiments were conducted on 22 normotensive participants. PAT, TT and PEP were determined from simultaneous measurements of the electrocardiogram, photoplethysmogram and impedance cardiogram. Moderate exercise induced significant (p < 0.05) increases in SBP and heart rate and significant (p < 0.05) decreases in PEP and PAT. Diastolic blood pressure and TT only varied insignificantly (p > 0.05). SBP was moderately correlated with PEP (r = -0.61) and PAT (r = -0.81). PAT and PEP were moderately correlated (r = 0.67). When SBP was estimated using least-squares methods, the differences between the measured and predicted SBP using PEP, PAT and TT were 0.0 ± 6.6, 0.0 ± 4.9 and 0.0 ± 9.3 mmHg, respectively. The findings suggested that PAT gives the best SBP prediction and PEP has some potential to predict blood pressure. The inclusion of PEP in the PAT measurement is necessary to facilitate accurate cuffless blood pressure prediction after exercise.

Pulse transit time (PTT) is a potential parameter for cuffless blood pressure (BP) estimation. Since exercise induces changes in arterial properties that can influence the relationship between BP and PTT, we investigate whether PTT can be used to estimate BP after successive bouts of exercise. PTT-foot, PTT-peak (time intervals from the peak of electrocardiogram R-wave to the foot and peak of photoplethysmogram, respectively) and BP of 41 normotensive subjects (aged 25 +/- 4 years) were measured in the first test. A repeatability test was then conducted on 14 subjects after 6 months. Each test included two periods of running on the treadmill at 10 and 8 km/h (with a rest in between). In both tests, systolic BP (SBP) was closely correlated with PTT-foot and PTT-peak. For each subject, the best fit linear relationships between SBP and PTTs were determined over all phases of each test. The differences between the linear fits and measured data were greater after the second period of running for all subjects in both tests. This implied that the relationships started to change after the second period of running. When SBP in the repeatability test was predicted using the linear regression coefficients from the first test, the linear fit after the first period of exercise was still better than after the second. The repeated observations in both tests suggest that PTT is a potential parameter for cuffless BP estimation after one period of exercise, but would need re-calibration (relationship between BP and PTTs) for measurements after successive phases of exercise.

In the present study, we investigated the relationship between blood pressure (BP) and pulse transit time (PTT) and evaluated the accuracy of the PTT-based cuffless BP estimation on 14 normotensive subjects. Least-squares regression was used to estimate BP in the first test and a repeatability test carried out half year later. BP in the repeatability test was also estimated using the regression coefficients in the first test. The results illustrated that in the first and repeatability tests (1) arterial BP increased and PTT decreased acutely after the exercises and (2) systolic BP was highly correlated with PTT. In the repeatability test, the estimation differences from the references were 0.0 +/- 5.3 mmHg and 0.0 +/- 2.9 mmHg for systolic and diastolic BPs respectively using least-squares regression. However, the estimation differences increased to 1.4 +/- 10.2 mmHg and 2.1 +/- 7.3 mmHg for systolic and diastolic BPs, respectively when the regression coefficients in the first test were used for prediction. In summary, reasonable BP estimations were given in the first and repeatability tests but not using the regression coefficients obtained 6 months ago for some subjects.

The second heart sound (S2) is triggered by an aortic valve closure as a result of the ventricular-arterial interaction of the cardiovascular system. The objective of this paper is to investigate the timing of S2 in response to the changes in hemodynamic parameters and its relation to aortic blood pressure (BP). An improved model of the left ventricular-arterial interaction was proposed based on the combination of the newly established pressure source model of the ventricle and the nonlinear pressure-dependent compliance model of the arterial system. The time delay from the onset of left ventricular pressure rise to the onset of S2 (RS2) was used to measure the timing of S2. The results revealed that RS2 bears a strong negative correlation with both systolic blood pressure and diastolic blood pressure under the effect of changing peripheral resistance, heart rate, and contractility. The results were further validated by a series of measurements of 16 normal subjects submitted to dynamic exercise. This study helps understand the relationship between the timing of S2 and aortic BP under various physiological and pathological conditions.

Pulse arrival time (PAT) has been proposed for measuring blood pressure (BP) noninvasively and continuously. A challenge of the PAT-based BP measurement technique is to calibrate it individually. The objective of this study is to examine a previously proposed model-based calibration method utilizing hydrostatic pressure for BP estimation. A preliminary experiment has been conducted on eight subjects aged from 23 to 36. Each subject was asked to raise their right arms to five different heights (H). At each height, PAT and brachial BP were measured from the elevated arm and the resting arm respectively. The data recorded at each height were used to calibrate a subject-dependent coefficient b which was then used to estimate his/her brachial SBP before and after exercise. It was found that the estimation results were influenced by H and k, which is a constant time interval subtracted from PAT. In this study, the estimation errors were found to be more sensitive to H than to k for -30< or =H< or =30 cm and 40< or =k< or =70 ms.

Previous studies have shown that it is possible to estimate pulmonary and systemic blood pressure using the spectral information of the second heart sound. A mathematical model for the vibration of the closed aortic valve is proposed in the paper with the introduction of the nonlinear elasticity of the aortic wall tissue. Based on the parametric analysis, the effect of the aortic blood pressure at the moment of valve closure on vibration of aortic valve and produced sound is examined. The simulation results show that the increasing aortic pressure results in an increase in frequency and amplitude of produced sound. The results of this study also suggest that it is the increasing resonant frequency of the blood column induced by elevated distending pressure that plays significant role in the process. The application of the modeling study could be extended to interpret the relations of the second heart sound to pulmonary blood pressure.

The onset of second heart sound is triggered by the closure of aortic valve due to the interaction of left ventricle and arterial system. Noninvasive experiments found that RS(2) defined by the time delay from the peak of ECG R wave to the onset of the second heart sound had a close inverse correlation with arterial systolic blood pressure. However, no theoretical study has been carried out to investigate the underline connections between them. A modified model of heart-arterial system is proposed in the present study. In this model the heart is described as a pressure source depending on time, ventricular volume, outflow, and heart rate, and the arterial system as a nonlinear system incorporating a pressure-dependent compliance. Simulation results show that the modified model is able to reflect the cardiovascular function qualitatively. The results also demonstrate that RS(2) is inversely correlated with aortic blood pressure under the effect of changing peripheral resistance, heart rate and contractility. The present study gives insight into the significant functional relations between the parameters characterizing the cardiovascular system and hemodynamics characteristics and provides an interpretation of the experimental observation on the relationship between RS(2) and aortic blood pressure.

Continuous hemodynamic monitoring in a wearable means can play a crucial role in managing hypertension and preventing catastrophic cardiovascular events. In this study, we have described the fully wearable tonometric device, referred to as flexible adaptive sensing tonometry (FAST), which is capable of continuous and accurate monitoring of hemodynamic parameters within the medical-grade precision. In particular, the FAST system integrates a 1 × 8 unit array of highly sensitive and highly flexible iontronic sensing (FITS) with 1 mm spatial resolution and a closed-loop motion system. The flexible tonometric architecture has been used to determine the radial arterial position with high sensitivity and high conformability, which simplifies the biaxial searching process of the traditional applanation tonometry into a highly efficient uniaxial applanation while keeping the medical-precision assessments. Importantly, a self-calibration algorithm can be automatically implemented during the applanation process, from which the intra-arterial blood pressure wave can be continuously predicted within the medical-grade precision, and subsequently, multi-parametric hemodynamic analysis can be performed in real-time. Experimental validations on health volunteers have demonstrated that the FAST measurements are all within the required accuracy of the clinical standards for continuous pulse wave assessments, blood pressure monitoring as well as other key hemodynamic parameter evaluations. Therefore, the FAST system, by integrating the flexible iontronic sensing array, provides a real-time, medical-grade hemodynamic monitoring solution in a continuously wearable manner, from which remote patient-centered monitoring can be delivered with both medical precision and convenience. [ABSTRACT FROM AUTHOR]

Objective: Hypertension refers to the persistent elevation of blood pressure above the established normal range, resulting in increased pressure exerted by blood on the walls of blood vessels during its circulation. Recent studies have identified significant associations between obesity and lipid-related indices, as well as hypertension. Nevertheless, these studies have yet to comprehensively examine the correlation between the two variables. Our objective is to identify the fat and lipid-related indices that have the strongest correlation with hypertension. Method: There was a total of 9488 elderly and middle-aged Chinese citizens who participated in this investigation. The participants in this research were separated into distinct gender cohorts. The participants were classified into normal and hypertensive categories according to their gender, with hypertension defined as a blood pressure level of 140/90 mmHg or higher, or a history of hypertension. Through the utilization of binary logistic regression analyses and the receiver operator curve (ROC), the optimal among fourteen indicators associated with obesity and lipids were identified. Results: After adjusting for variables, statistical analysis showed that all 14 measures of obesity and lipid were risk factors for hypertension. The receiver operating characteristic (ROC) curve analysis reveals that the Chinese visceral adiposity index (CVAI) has the highest degree of relationship to hypertension. Simultaneously, a statistically significant association between hypertension and these 14 variables was observed in both males and females. Conclusion: There was a significant independent association between various parameters related to obesity and lipid-related index and the presence of hypertension, indicating that these factors can be considered risk factors for hypertension. CVAI and WHtR (waist height ratio) can be used to screen the high-risk groups of hypertensions in middle-aged and elderly people in China, and then take individualized health care measures to reduce the harm of hypertension. [ABSTRACT FROM AUTHOR]

Cuffless blood pressure monitoring is critical for the prevention and early diagnosis of a wide variety of cardiovascular diseases. However, cuffless blood pressure estimation devices suitable for home healthcare applications still suffer from numerous technological limitations. In this paper, we propose a novel method to continuously estimate blood pressure from the pulse morphology of the photoplethysmographic signals, acquired by a commercial oximeter. We conducted cold-pressor tests for 70 healthy subjects, simultaneously acquiring the photoplethysmograms from the oximeter and the continuous blood pressure from a commercial sphygmomanometer as a reference. The shape of each pulse was extracted, normalized, and regressed with the reference blood pressure using support vector machines. The performance of the regression model for each subject was evaluated using 10-fold cross-validation. Results showed that the predicted values from the regression model were highly correlated with the reference measurements from the commercial device. The mean correlation coefficients were 0.748, 0.754, and 0.775 for systolic, diastolic, and mean blood pressures, respectively. The mean errors were 0.043 mmHg, 0.011 mmHg, and 0.008 mmHg, with standard deviations of 5.001 mmHg, 3.689 mmHg, and 4.140 mmHg for systolic, diastolic, and mean blood pressures, respectively. These results suggest high feasibility of the proposed method to be employed in wearable medical and home healthcare devices.

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 prevalence of hypertension has made blood pressure (BP) measurement one of the most wanted functions in wearable devices for convenient and frequent self-assessment of health conditions. The widely adopted principle for cuffless BP monitoring is based on arterial pulse transit time (PTT), which is measured with electrocardiography and photoplethysmography (PPG). To achieve cuffless BP monitoring with more compact wearable electronics, we have previously conceived a multi-wavelength PPG (MWPPG) strategy to perform BP estimation from arteriolar PTT, requiring only a single sensing node. However, challenges remain in decoding the compounded MWPPG signals consisting of both heterogeneous physiological information and motion artifact (MA). In this work, we proposed an improved MWPPG algorithm based on principal component analysis (PCA) which matches the statistical decomposition results with the arterial pulse and capillary pulse. The arteriolar PTT is calculated accordingly as the phase shift based on the entire waveforms, instead of local peak lag time, to enhance the feature robustness. Meanwhile, the PCA-derived MA component is employed to identify and exclude the MA-contaminated segments. To evaluate the new algorithm, we performed a comparative experiment (N = 22) with a cuffless MWPPG measurement device and used double-tube auscultatory BP measurement as a reference. The results demonstrate the accuracy improvement enabled by the PCA-based operations on MWPPG signals, yielding errors of 1.44 ± 6.89 mmHg for systolic blood pressure and −1.00 ± 6.71 mm Hg for diastolic blood pressure. In conclusion, the proposed PCA-based method can improve the performance of MWPPG in wearable medical devices for cuffless BP measurement. [ABSTRACT FROM AUTHOR]