Estimation of pressure pulse amplification between aorta and brachial artery using stepwise multiple regression models

Emerging Trends in Soft Electronics: Integrating Machine Intelligence with Soft Acoustic/Vibration Sensors

In the last decade, soft acoustic/vibration sensors have gained tremendous research interest due to their unique ability to detect broadband acoustic/vibration stimuli, potentializing futuristic applications including voice biometrics, voice-controlled human-machine-interfaces, electronic skin, and skin-mountable healthcare devices. Importantly, to benefit most from these sensors, it is inevitable to use machine learning (ML) to process their output signals; with ML, a more accurate and efficient interpretation of original data is possible. This paper is dedicated to offering an overview of recent advances empowering the development of soft acoustic/vibration sensors and their signal processing using ML. First, the key performance parameters of the sensors are discussed. Second, popular transduction mechanisms for the sensors are addressed, followed by an in-depth overview of each type, covering materials used, structural designs, and sensing performances. Third, potential applications of the sensors are elaborated and fourth, a thorough discussion on ML is conducted, exploring different types of ML, specific ML algorithms suitable for processing acoustic/vibration signals, and current trends in ML-assisted applications. Finally, the challenges and potential opportunities in soft acoustic/vibration sensor and ML research are revealed to offer new insights into future prospects in these fields.

Estimating Central Pulse Pressure From Blood Flow by Identifying the Main Physical Determinants of Pulse Pressure Amplification

Several studies suggest that central (aortic) blood pressure (cBP) is a better marker of cardiovascular disease risk than peripheral blood pressure (pBP). The morphology of the pBP wave, usually assessed non-invasively in the arm, differs significantly from the cBP wave, whose direct measurement is highly invasive. In particular, pulse pressure, PP (the amplitude of the pressure wave), increases from central to peripheral arteries, leading to the so-called pulse pressure amplification (ΔPP). The main purpose of this study was to develop a methodology for estimating central PP (cPP) from non-invasive measurements of aortic flow and peripheral PP. Our novel approach is based on a comprehensive understanding of the main cardiovascular properties that determine ΔPP along the aortic-brachial arterial path, namely brachial flow wave morphology in late systole, and vessel radius and distance along this arterial path. This understanding was achieved by using a blood flow model which allows for workable analytical solutions in the frequency domain that can be decoupled and simplified for each arterial segment. Results show the ability of our methodology to (i) capture changes in cPP and ΔPP produced by variations in cardiovascular properties and (ii) estimate cPP with mean differences smaller than 3.3 ± 2.8 mmHg on in silico data for different age groups (25-75 years old) and 5.1 ± 6.9 mmHg on in vivo data for normotensive and hypertensive subjects. Our approach could improve cardiovascular function assessment in clinical cohorts for which aortic flow wave data is available.

Vascular Aging and Central Aortic Blood Pressure: From Pathophysiology to Treatment

Large conductive arteries undergo to structural modifications by aging, eventually leading to increased vascular stiffness. As consequence, cardiovascular hemodynamic changes by increasing central blood pressure which may be also associated to the remodelling of peripheral resistance arteries that contribute to increase further the central vascular stiffness and blood pressure. These modifications resemble the ones that has been shown in essential hypertension, thus a condition of "early vascular aging" has been described in hypertensive patients. Since hypertension related target organs, particularly the heart, face aortic blood pressure rather than brachial blood pressure, it has been recently suggested that central blood pressure and other parameters of large arteries' stiffness, including pulse wave velocity (PWV), may better correlate with subclinical organ damage and might be useful to assess the cardiovascular risk of patients beyond the traditional risk factors. Different devices have been validated to measure central blood pressure and PWV, and are currently available for clinical use. The increasing application of these tools in clinical practice could improve the management of hypertensive patients by better defining the cardiovascular risk and address the antihypertensive therapy.

Central blood pressure for the management of hypertension: Is it a practical clinical tool in current practice?

Since noninvasive central blood pressure (BP) measuring devices are readily available, central BP has gained growing attention regarding its clinical application in the management of hypertension. The disagreement between central and peripheral BP has long been recognized. Some previous studies showed that noninvasive central BP may be better than the conventional brachial BP in association with target organ damages and long-term cardiovascular outcomes. Recent studies further suggest that the central BP strategy for confirming a diagnosis of hypertension may be more cost-effective than the conventional strategy, and guidance of hypertension management with central BP may result in less use of medications to achieve BP control. Despite the use of central BP being promising, more randomized controlled studies comparing central BP-guided therapeutic strategies with conventional care for cardiovascular events reduction are required because noninvasive central and brachial BP measures are conveniently available. In this brief review, the rationale supporting the utility of central BP in clinical practice and relating challenges are summarized.

2019 Consensus of the Taiwan Hypertension Society and Taiwan Society of Cardiology on the Clinical Application of Central Blood Pressure in the Management of Hypertension

The Taiwan Society of Cardiology (TSOC) and the Taiwan Hypertension Society (THS) have appointed a joint consensus group for the 2019 Consensus of the TSOC and THS on the Clinical Application of Central blood pressure (BP) in the Management of Hypertension with the aim of formulating a management consensus on the clinical application of central BP in the management of hypertension. This consensus document focuses on the clinical application of central BP in the care of patients with hypertension. The major determinants of central BP are increased arterial stiffness and wave reflection, which are also the dominant hemodynamic manifestations of vascular aging. Central BP can be measured noninvasively using various techniques, including with convenient cuff-based oscillometric central BP monitors. Noninvasive central BP is better than conventional brachial BP to assess target organ damage and long-term cardiovascular outcomes. Based on the analysis of long-term events, a central BP threshold of 130/90 mmHg for defining hypertension has been proposed. Recent studies have suggested that a central BP strategy to confirm a diagnosis of hypertension may be more cost-effective than conventional strategies, and that guiding hypertension management with central BP may result in the use of fewer medications to achieve BP control. Although noninvasive measurements of brachial BP are inaccurate and central BP has been shown to carry superior prognostic value beyond brachial BP, the use of central BP should be justified in studies comparing central BP-guided therapeutic strategies with conventional care for cardiovascular events.

Monitoring of the central blood pressure waveform via a conformal ultrasonic device

Continuous monitoring of the central-blood-pressure waveform from deeply embedded vessels, such as the carotid artery and jugular vein, has clinical value for the prediction of all-cause cardiovascular mortality. However, existing non-invasive approaches, including photoplethysmography and tonometry, only enable access to the superficial peripheral vasculature. Although current ultrasonic technologies allow non-invasive deep-tissue observation, unstable coupling with the tissue surface resulting from the bulkiness and rigidity of conventional ultrasound probes introduces usability constraints. Here, we describe the design and operation of an ultrasonic device that is conformal to the skin and capable of capturing blood-pressure waveforms at deeply embedded arterial and venous sites. The wearable device is ultrathin (240 μm) and stretchable (with strains up to 60%), and enables the non-invasive, continuous and accurate monitoring of cardiovascular events from multiple body locations, which should facilitate its use in a variety of clinical environments.

Isolated Systolic Hypertension in Young and Middle-Aged Adults

Young and middle-aged adults (ages ≤50 years) are increasingly prone to stroke, kidney disease, and worsening cardiovascular disease (CVD) mortality. An alarming increase in the prevalence of high blood pressure (BP) may underlie the adverse trend. However, there is often uncertainty in BP management for young and middle-aged adults. Isolated systolic hypertension (ISH) is one such example. Whether ISH in young and middle-aged adults represents "pseudo" or "spurious" hypertension is still being debated. ISH in young and middle-aged adults is a heterogeneous entity; some individuals appear to have increased stroke volume, whereas others have stiffened aortae, or both. One size does not seem to fit all in the clinical management of ISH in young and middle-aged adults. Rather than treating ISH as a monolithic condition, detailed phenotyping of ISH based on (patho)physiology and in the context of individual global cardiovascular risks would seem to be most useful to assess an individual expected net benefit from therapy. This review provides an overview of the current understanding of ISH in young and middle-aged adults, including the prevalence, pathophysiology, and treatment.

How to Measure 24-hour Central Blood Pressure and Its Potential Clinical Implications

The evaluation of 24-hour central blood pressure (24h cBP) combines the cBP non-invasive assessment with the 24-h ambulatory BP measurement. The major strength of the 24-h cBP evaluation is the ability to assess the degree of circadian changes between central and peripheral BP, namely 24-h BP amplification. This allows an accurate quantification of the degree of spatial and temporal BP variability in each single individual. BP amplification depends from a number of factors, such as the interaction between pressure and flow pulsatile motions, vasomotor tone, arterial tapering and other physiological and anthropometrical determinants. The assessment of 24-h BP amplification, a relatively pressure-independent parameter, may be helpful in better refining the risk of organ damage and future CV events over traditional measures of office and 24-h brachial BP. Currently, only few devices enable the assessment of 24-h cBP. These devices are based on peripheral (brachial or radial) BP waveform detection, and reconstruction of central BP waveform through mathematical models. The estimation of 24-h cBP imputed from multivariate regression equations was also proposed. Clinical data are still scarce and, although suggesting a possible superiority of 24-h cBP over brachial BP in the association with markers of organ damage, they are limited by methodological and technical aspects. There is urgent need of a standardized methodology and rigorous validation protocols for the 24-h cBP assessment. The field of 24-h cBP measurement still requires significant advancements of scientific knowledge before its introduction into clinical practice.

Non-invasive aortic systolic pressure and pulse wave velocity estimation in a primary care setting: An in silico study

Everyday clinical cardiovascular evaluation is still largely based on brachial systolic and diastolic pressures. However, several clinical studies have demonstrated the higher diagnostic capacities of the aortic pressure, as well as the need to assess the aortic mechanical properties (e.g., by measuring the aortic pulse wave velocity). In order to fill this gap, we propose to exploit a set of easy-to-obtain physical characteristics to estimate the aortic pressure and pulse wave velocity. To this aim, a large population of virtual subjects is created by a validated mathematical model of the cardiovascular system. Quadratic regressive models are then fitted and statistically selected in order to obtain reliable estimations of the aortic pressure and pulse wave velocity starting from the knowledge of the subject age, height, weight, brachial pressure, photoplethysmographic measures and either electrocardiogram or phonocardiogram. The results are very encouraging and foster clinical studies aiming to apply a similar technique to a real population.

Effect of acute aerobic exercise and histamine receptor blockade on arterial stiffness in African Americans and Caucasians

African Americans (AA) exhibit exaggerated central blood pressure (BP) and arterial stiffness measured by pulse wave velocity (PWV) in response to an acute bout of maximal exercise compared with Caucasians (CA). However, whether potential racial differences exist in central BP, elastic, or muscular arterial distensibility after submaximal aerobic exercise remains unknown. Histamine receptor activation mediates sustained postexercise hyperemia in CA but the effect on arterial stiffness is unknown. This study sought to determine the effects of an acute bout of aerobic exercise on central BP and arterial stiffness and the role of histamine receptors, in AA and CA. Forty-nine (22 AA, 27 CA) young and healthy subjects completed the study. Subjects were randomly assigned to take either histamine receptor antagonist or control placebo. Central blood BP and arterial stiffness measurements were obtained at baseline, and at 30, 60, and 90 min after 45 min of moderate treadmill exercise. AA exhibited greater central diastolic BP, elevated brachial PWV, and local carotid arterial stiffness after an acute bout of submaximal exercise compared with CA, which may contribute to their higher risk of cardiovascular disease. Unexpectedly, histamine receptor blockade did not affect central BP or PWV in AA or CA after exercise, but it may play a role in mediating local carotid arterial stiffness. Furthermore, histamine may mediate postexercise carotid arterial dilation in CA but not in AA. These observations provide evidence that young and healthy AA exhibit an exaggerated hemodynamic response to exercise and attenuated vasodilator response compared with CA.NEW & NOTEWORTHY African Americans are at greater risk for developing cardiovascular disease than Caucasians. We are the first to show that young and healthy African Americans exhibit greater central blood pressure, elevated brachial stiffness, and local carotid arterial stiffness following an acute bout of submaximal exercise compared with Caucasians, which may contribute to their higher risk of cardiovascular disease. Furthermore, African Americans exhibit attenuated vasodilator response compared with Caucasians.

Aortic Pulse Pressure Amplification Imputed From Simple Clinical Measures Adds to the Ability of Brachial Pressure to Predict Survival

BACKGROUND

Although aortic-to-brachial pulse pressure amplification (PPamp) may offer prognostic information beyond brachial blood pressure (BP), this approach is limited in resource-limited settings. We aimed to derive an equation to impute central aortic PP (PPc) from simple clinical measures and assess whether imputed PPamp adds to the ability of brachial BP to predict mortality.

METHODS

An imputation equation for PPc, incorporating brachial PP, age, mean arterial pressure, and pulse rate, was identified from multivariate modeling of the factors associated with radial applanation tonometry-derived (measured) PPc in 1,179 community participants and validated in a clinical sample of 351 patients. We applied the equation to ambulatory awake BP and pulse rate values in a separate group of 4,796 patients referred for ambulatory monitoring and evaluated the impact on all-cause mortality.

RESULTS

Imputed PPc values closely approximated measured PPc (r (2) = 0.96, mean difference ± (2 × SD) = 1.4±6.2mm Hg). In adjusted Cox proportional models including adjustments for awake brachial PP during 47,111 person-years of follow-up, where 648 patients died, hazards ratio for all-cause mortality per SD of awake PPamp was 0.79 (95% confidence interval (CI): 0.68-0.93, P < 0.005). The hazards ratio for brachial PP with (1.49, CI = 1.36-1.64, P < 0.0001) or without (1.46, CI = 1.35-1.59, P < 0.0001) PPamp in the model was similar. Awake PPamp also predicted survival independent of awake brachial systolic BP (P < 0.0001).

CONCLUSIONS

PPc imputed from simple clinical assessments closely approximates measured PPc. PPamp derived from imputed PPc adds to the ability of brachial BP to predict survival. In resource-limited settings, an imputation equation may be employed to approximate aortic BP and enhance risk prediction.

Effect of angiotensin receptor blockade on central aortic systolic blood pressure in hypertensive Asians measured using radial tonometry: an open prospective cohort study

INTRODUCTION

Central aortic systolic pressure (CASP) has been shown to be a stronger predictor of cardiovascular events than brachial blood pressure (BP). Different classes of drugs have differential effects on CASP and brachial BP. This open prospective cohort study aimed to observe changes in CASP (measured using radial tonometry) among hypertensive Asians after 12 weeks of treatment with valsartan, an angiotensin receptor blocker (ARB).

METHODS

Patients with treatment-naïve hypertension or uncontrolled hypertension who were on non-ARB therapy were eligible for inclusion. Patients with uncontrolled BP (i.e. ≥ 140/90 mmHg) received valsartan for 12 weeks. The patients' brachial systolic and diastolic BP (SBP and DBP), and CASP changes were monitored using the BPro® watch.

RESULTS

The mean age of the 44 enrolled patients was 35 years. At baseline, the mean BP and CASP were 150.2/91.4 ± 10.6/9.4 mmHg and 136.3 ± 12.2 mmHg, respectively. Valsartan reduced SBP, DBP and CASP by 14.9 ± 10.7 mmHg, 10.9 ± 8.4 mmHg and 15.3 ± 10.9 mmHg, respectively (all p < 0.001). Every 1.0-mmHg reduction in brachial SBP resulted in a 0.8-mmHg reduction in CASP (p < 0.001). A CASP cut-off of 122.5 mmHg discriminated between controlled and uncontrolled BP (sensitivity 74%, specificity 88%).

CONCLUSION

Using radial tonometry, we demonstrated good correlation between CASP and brachial SBP reductions after 12 weeks of treatment with valsartan in our study cohort. Correlation analysis between CASP and SBP reductions may be useful for demonstrating whether a drug is able to lower CASP beyond lowering SBP.

Central blood pressure: current evidence and clinical importance

Pressure measured with a cuff and sphygmomanometer in the brachial artery is accepted as an important predictor of future cardiovascular risk. However, systolic pressure varies throughout the arterial tree, such that aortic (central) systolic pressure is actually lower than corresponding brachial values, although this difference is highly variable between individuals. Emerging evidence now suggests that central pressure is better related to future cardiovascular events than is brachial pressure. Moreover, anti-hypertensive drugs can exert differential effects on brachial and central pressure. Therefore, basing treatment decisions on central, rather than brachial pressure, is likely to have important implications for the future diagnosis and management of hypertension. Such a paradigm shift will, however, require further, direct evidence that selectively targeting central pressure, brings added benefit, over and above that already provided by brachial artery pressure.

Sex difference in cardiovascular risk: role of pulse pressure amplification

OBJECTIVES

The study was to explore whether the brachial/carotid pulse pressure (B/C-PP) ratio selectively predicts the sex difference in age-related cardiovascular (CV) death.

BACKGROUND

Hypertension and CV complications are more severe in men and post-menopausal women than in pre-menopausal women. C-PP is lower than B-PP, and the B/C-PP ratio is a physiological marker of PP amplification between B and C arteries that tends toward 1.0 with age.

METHODS

The study involved 72,437 men (ages 41.0 ± 11.1 years) and 52,714 women (39.5 ± 11.6 years). C-PP was calculated for each sex by a multiple regression analysis including B-PP, age, height and risk factors, and a method validated beforehand in a subgroup of 834 subjects. During the 12 years of follow-up, 3,028 men and 969 women died.

RESULTS

In the total population, the adjusted hazard ratios (HR) (95% confidence interval [CI]) of B/C-PP ratio were: 1) for all-cause mortality: men, HR: 1.51 (95% CI: 1.47 to 1.56), women; HR: 2.46 (95% CI: 2.27 to 2.67) (p < 0.0001); and 2) for CV mortality: men, HR 1.81 (95% CI: 1.70 to 1.93); women, HR: 4.46 (95% CI: 3.66 to 5.45) (p < 0.0001). The B/C-PP impact on mortality did not significantly increase from younger men to those ≥ 55 years of age, from: HR: 1.44 (95% CI: 1.31 to 1.58) to HR 1.65 (95% CI: 1.48 to 1.84), but increased significantly with age in women: HR: 3.19 (95% CI: 2.08 to 4.89) versus HR: 5.60 (95% CI: 4.17 to 7.50) (p < 0.01). Thus, the mortality impact of B/C-PP ratio was 3-fold higher in women than in men ≥ 55 years old.

CONCLUSIONS

PP amplification is highly predictive of differences in CV risk between men and women. In post-menopausal women, the attenuation of PP amplification, mainly related to increased aortic stiffness, contributes to the significant increase in CV risk.

Noninvasive evaluation of coronary distensibility in older adults: a feasibility study with MR angiography

PURPOSE

To assess the feasibility of using magnetic resonance (MR) angiography to noninvasively measure the coronary distensibility index (CDI) in older adults.

MATERIALS AND METHODS

This study was approved by the institutional review board and was compliant with HIPAA. Informed consent was obtained from all participants. Three-dimensional MR angiography was performed in 23 patients with type 2 diabetes mellitus (DM) (mean age, 72.9 years ± 5.8 [standard deviation]; age range, 65-84 years; 12 men, 11 women) and 50 healthy aging control subjects (mean age, 73.1 years ± 5.6; age range, 64-84 years; 28 men, 22 women). Imaging data were acquired in the rest periods of cardiac motion identified during end systole and middiastole. For imaging data with different acquisition windows, cross-sectional coronary planes were reconstructed and matched for the same anatomy according to coronary landmarks. The CDI, defined as [(lumen area at systole--lumen area at diastole)/(lumen area at diastole × pulse pressure)] × 1000, was compared between patients with DM and control subjects by using the Student t test. With the same protocol, CDIs were calculated in 10 randomly selected subjects by two independent readers. In addition, MR angiography (in systole and diastole) was repeated in those 10 subjects after repositioning.

RESULTS

CDIs were measured in 43 coronary segments of patients with DM and in 124 coronary segments of control subjects. The mean CDI in patients with DM was significantly lower than that in control subjects (2.79 mm Hg(-1) ± 2.12 vs 9.14 mm Hg(-1) ± 5.87, respectively; P < .001). CDI measurements showed good intraobserver (r = 0.914), interobserver (r = 0.820), and imaging-repeat imaging agreements (r = 0.811).

CONCLUSION

Coronary MR angiography is a reproducible and repeatable noninvasive method for detecting significant differences in coronary distensibility between patients with DM and healthy aging control subjects.

Pulse pressure amplification a mechanical biomarker of cardiovascular risk

OBJECTIVES

The aim of this study was to determine whether the carotid/brachial (C/B) ratio is an independent predictor of cardiovascular (CV) risk.

BACKGROUND

Brachial and carotid pulse pressure (PP) are independent predictors of CV risk, mainly in elderly patients. Because PP is physiologically lower at the brachial than at the carotid arterial site, PP amplification is represented by the C/B ratio and could independently predict CV risk.

METHODS

In a Paris population (n = 834), brachial and carotid PP were measured from sphygmomanometry and pulse wave analysis. With stepwise multiple regression, carotid PP was calculated from a nomogram including age, sex, body height, brachial PP, and plasma glucose. This model was applied to 125,151 subjects, followed for 12 years, during which 3,997 deaths occurred (735 of CV origin). With Cox regression analysis, multi-adjusted hazard ratios (HRs) were calculated for 1 SD increase of brachial PP, calculated carotid PP, and C/B ratio.

RESULTS

Brachial PP was significantly associated with both CV and all-cause mortality (HR: 1.16, 95% confidence interval [CI]: 1.13 to 1.19, and HR: 1.13, 95% CI: 1.10 to 1.17, respectively). Calculated carotid PP predicted a similar risk (HR: 1.21, 95% CI: 1.15 to 1.28, and HR: 1.18, 95% CI: 1.12 to 1.25, respectively). Finally, the C/B ratio was a strong risk predictor (HR: 1.22, 95% CI: 1.12 to 1.32, and HR: 1.41, 95% CI: 1.14 to 1.73, respectively). Addition of drug treatment and other confounding variables did not statistically modify the results.

CONCLUSIONS

Brachial PP, calculated carotid PP, and C/B PP amplification all predict CV mortality. In contrast to brachial and carotid PP, the C/B ratio is less dependent on blood pressure calibration and thus can be directly applicable to large population studies.

Central pressure: variability and impact of cardiovascular risk factors: the Anglo-Cardiff Collaborative Trial II

Pulse pressure varies throughout the arterial tree, resulting in a gradient between central and peripheral pressure. Factors such as age, heart rate, and height influence this gradient. However, the relative impact of cardiovascular risk factors and atheromatous disease on central pressure and the normal variation in central pressure in healthy individuals are unclear. Seated peripheral (brachial) and central (aortic) blood pressures were assessed, and the ratio between aortic and brachial pulse pressure (pulse pressure ratio, ie, 1/amplification) was calculated in healthy individuals, diabetic subjects, patients with cardiovascular disease, and in individuals with only 1 of the following: hypertension, hypercholesterolemia, or smoking. The age range was 18 to 101 years, and data from 10 613 individuals were analyzed. Compared with healthy individuals, pulse pressure ratio was significantly increased (ie, central systolic pressure was relatively higher) in individuals with risk factors or disease (P<0.01 for all of the comparisons). Although aging was associated with an increased pulse pressure ratio, there was still an average+/-SD difference between brachial and aortic systolic pressure of 11+/-4 and 8+/-3 mm Hg for men and women aged >80 years, respectively. Finally, stratifying individuals by brachial pressure revealed considerable overlap in aortic pressure, such that >70% of individuals with high-normal brachial pressure had similar aortic pressures as those with stage 1 hypertension. These data demonstrate that cardiovascular risk factors affect the pulse pressure ratio, and that central pressure cannot be reliably inferred from peripheral pressure. However, assessment of central pressure may improve the identification and management of patients with elevated cardiovascular risk.