Central Waveform Research Articles

Predialysis central arterial waveform and blood pressure changes during hemodialysis

To investigate the predictive value of the central arterial waveform for intradialytic blood pressure (BP) change, a total of 152 hemodialysis patients (mean age 68 years) on a thrice-weekly hemodialysis schedule were enrolled, and at both the first and second session of the week, BP and central arterial waveform were measured every 30 min during hemodialysis. In both sessions, a 1-standard deviation increase in baseline subendocardial viability ratio (SEVR), an index of subendocardial perfusion, as well as in baseline systolic BP (SBP) was an independent predictor of maximum SBP decrease ≥ 30 mmHg during hemodialysis. When divided into four groups based on the respective median level of SEVR in the SBP ≥ median and SBP < median groups, intradialytic SBP change was different among the subgroups. Multiple logistic regression analysis revealed that, compared with the SBP < median; low SEVR group, the SBP < median; high SEVR group had lower risk, and the SBP ≥ median; low SEVR group had higher risk of SBP decrease ≥ 30 mmHg, but the risk did not differ from that in the SBP ≥ median; high SEVR group. Predialysis subendocardial perfusion evaluated by SEVR was associated with the maximum intradialytic BP decrease, and evaluation of the central arterial waveform could be used as complementary screening for intradialytic BP change.

Multifaced risk factors and clinical impact of a deep Y descent in patients with heart failure irrespective of RV-PA coupling

BackgroundA deep Y descent in the jugular venous pulse (JVP) is associated with diseases such as a decrease in right ventricular (RV) preload reserve. The present study investigated the relationship between RV-pulmonary arterial (PA) coupling and a deep Y descent, examined risk factors for a deep Y descent and clarified whether a deep Y descent was an independent risk factor for cardiac events irrespective of RV-PA coupling in patients with heart failure (HF). MethodsWe enrolled 350 patients with HF who underwent echocardiography and JVP examination. A deep Y descent was identified by a deeper ‘Y’ descent than ‘X’ descent in the JVP waveform. We defined cardiac events of HF as follows: sudden death, death from HF, the emergent infusion of loop diuretics, or hospitalization for decompensated HF. Results and ConclusionsA deep Y descent and cardiac events were observed in 129 and 83 patients, respectively. The prevalence of a deep Y descent increased with decreases in the tricuspid annular plane systolic excursion (TAPSE)/systolic pulmonary arterial pressure (SPAP) ratio. Not only the TAPSE/SPAP ratio (odds ratio,0.756 per0.1 mm/mmHg, 95 %confidence interval [CI], 0.660–0.866, p < 0.001), but also age, atrial fibrillation, and the use of beta-blockers were independent factors for a deep Y descent in multivariate logistic model. Multivariate Cox hazard model demonstrated that a deep Y descent was for cardiac events in patients with HF (Hazard ratio,2.682, 95 %CI, 1.599–4.497, p < 0.001) irrespective of the TAPSE/SPAP ratio. The development of therapeutic strategies based on central venous waveform may be needed for patients with HF.

Multicenter randomized controlled trial of exercise in aortic dissection survivors: rationale, design, and initial hemodynamic data

Aims: There are currently no evidence-based guidelines for exercise after thoracic aortic dissection (TAD), leading to highly variable recommendations that frequently lead patients to restrict their physical activities. This multicenter randomized controlled trial was intended to evaluate the safety and efficacy of a moderate intensity guided exercise program for TAD survivors. Methods: Participants were eligible if they had a Type A or Type B dissection at least 90 days before enrollment and could attend two in-person study visits. The guided exercise circuit consisted of six aerobic, isotonic, or isometric exercises that participants continued at home with virtual follow-up sessions. The primary endpoint is the change in the composite anxiety and depression PROMIS-29 T-score at 12 months. Secondary endpoints include changes in grip strength, weight, 24-h ambulatory blood pressure, and arterial biomechanical properties measured by central arterial waveform analysis. Results: Preliminary analysis of the first 81 enrolled participants demonstrated that the guided exercise circuit was completed safely and was not associated with severe hypertension, injury, or adverse cardiovascular events. At enrollment, adverse central waveform or ABPM characteristics were prevalent and were significantly associated with exertional hypertension. Conclusions: Guided exercise is safe for aortic dissection survivors. Follow-up of enrolled participants will conclude in October 2024.

Increased arterial stiffness in patients with ischemia and no obstructive coronary artery disease

Abstract Introduction Recent studies have shown that patients with angina pectoris and no obstructive coronary artery disease are a heterogeneous population with an elevated risk of major adverse cardiovascular events. The current literature lacks evidence regarding the possible association between arterial stiffness and coronary microvascular dysfunction (CMD). Purpose The aim of this study is to determine whether arterial stiffness is increased among patients with CMD compared to hypertensive control group. Methods We examined 25 patients [10 female, 40%, mean age: 60.7±9.6 years, mean office blood pressure (BP) : 141/88±17/9 mmHg] and 35 CMD patients (22 female, 63%, mean age : 62.4±4.9 years, average office BP: 129/79±15/10 mmHg). In the group of patients with chronic angina, CMD was defined by a standardized systematic protocol in which coronary flow reserve (CFR) and index of microvascular resistance (IMR) were measured in the left anterior descending coronary artery using a temperature/pressure sensor-tipped guidewire. In addition, in all participants, arterial stiffness was assessed using aortic augmentation index (AIx), derived from the analysis of central pulse waveforms, recorded by applanation tonometry directly from the radial artery. Results In the CMD group, mean CFR and IMR were 1.3±0.9 and 45.7±35, respectively. Out of the 35 CMD patients with abnormal CFR 12 of them (34%) had a normal value of IMR, indicating functional microvascular dysfunction. On the other hand, 23 patients (66%) had an abnormal IMR, indicating structural microvascular dysfunction. In CMD group compared to asymptomatic controls, AIx was found significantly higher (35.6±10.5 vs 25.1±12.1%, p=0.03). This difference in AIx between groups was found to be statistically significant after adjustment for age, gender and levels of BP (p&amp;lt;0.05). Moreover, no significant differences were found in body mass index, renal function, history of dyslipidemia, diabetes mellitus and smoking status between the two groups (p=NS for all). Conclusion CMD patients are characterized by increased arterial stiffness in comparison with asymptomatic controls, independently of demographic and hemodynamic confounders. These results indicate that impairment of the microvasculature is associated with large artery stiffening. Thus, potential clinical benefit could be derived from specific therapies targeting AIx in patients with CMD.

Central Venous Waveform Patterns in the Fontan Circulation Independently Contribute to the Prediction of Composite Survival.

It is well appreciated that the Fontan circulation perturbs central venous hemodynamics, with elevated pressure being the clearest change associated with Fontan comorbidities, such as Fontan-associated liver disease (FALD) and protein-losing enteropathy (PLE). Our group has better quantity of these venous perturbations through single- and multi-location analyses of flow waveforms obtained from magnetic resonance imaging of Fontan patients. Here, we determine if such analyses, which yield principal components (PC) that describe flow features, are associated with Fontan survival. Patients with a Fontan circulation (N = 140) that underwent free-breathing and mechanically ventilated cardiac MRI were included in this study. Standard volumetric and functional hemodynamics, as well as flow analysis principal components, were subjected to univariate and bivariate Cox regression analyses to determine composite clinical outcome, including plastic bronchitis, PLE, and referral and receipt of transplant. Unsurprisingly, ventricular function measures of ejection fraction (EF; HR = 0.88, p < 0.0001), indexed end-systolic volume (ESVi; HR 1.02, p < 0.0001), and indexed end-diastolic volume (EDVi; HR = 1.02, p = 0.0007) were found as specific predictors of clinical events, with specificities uniformly > 0.75. Additionally a feature of IVC flow (PC2) indicating increased flow in systole was found as a highly sensitive predictor (HR = 0.851, p = 0.027, sensitivity 0.93). In bivariate prediction, combinations of ventricular function (EF, ESVi, EDVi) with this IVC flow feature yielded best overall prediction of composite outcome. This suggests that central venous waveform analysis relays additional information about Fontan patient survival and that coupling sensitive and specific measures in bivariate analysis is a useful approach for obtaining superior prediction of survival.

Abstract P230: Central Artery Pulsatile Hemodynamics Are Associated With Cerebral Total, Periventricular, And Deep White Matter Lesions: Role Of Reservoir-excess Pressure Components.

Introduction: Accumulating evidence suggests that increased central, rather than peripheral, blood pressure (BP) may be a better predictor of cardiovascular risk. The shape of the central BP waveform is determined by ventricular-arterial interactions that can be quantified via novel hemodynamic analyses, from which some parameters have been implicated in the development of cardiac, vascular, and renal dysfunction. Comparatively, the potential effect of central pulsatile hemodynamics on brain structure has been understudied. Thus, we sought to determine the association of novel central hemodynamic parameters with cerebral white matter lesions. Methods: Central BP waveforms were measured in 130 healthy adults (age 63±6y; 58% female) via non-invasive carotid tonometry and modeled using reservoir-excess pressure analysis to separate the central BP waveform into a reservoir (Rp TI ) and excess (Ep TI ) pressure component. Systolic (Sk) and diastolic (Dk) rate constants were estimated from the rate of increase and decrease of the Rp TI component, respectively. Total, periventricular, and deep cerebral white matter lesion volumes (WMLV) were estimated from T2 weighted and FLAIR MRI and adjusted for total intracranial volume. Results: Both Sk and Ep TI were correlated with total (Sk: r = -0.19, p = 0.033; Ep TI : r = 0.21, p = 0.016), periventricular (Sk: r = -0.18, p = 0.037; Ep TI : r = 0.23, p = 0.009), and deep (Sk: r = -0.28, p = 0.002; Ep TI : r = 0.20, p = 0.027) WMLV. The association of Sk with total ( B = -0.032; 95% confidence interval [CI] = -0.054, -0.010; p = 0.0056), periventricular ( B = -0.030; 95%CI = -0.051, -0.009; p = 0.0063), and deep ( B = -0.064; 95%CI = -0.101, -0.028; p &lt;0.001) WMLV remained significant in multivariable analyses adjusting for age, sex, BMI, peripheral pulse pressure, carotid-femoral pulse wave velocity, heart rate, and non-HDL cholesterol. Additionally, the association between Ep TI and deep WMLV persisted in multivariable analysis ( B = 0.158; 95%CI = 0.045, 0.271; p = 0.007). Conclusion: Pulsatile components of central artery hemodynamics are associated with cerebral WMLV independent of traditional cardiovascular risk factors. In particular, Sk may represent a novel biomarker of early central BP-related cerebral white matter damage.

Accuracy of Estimated Central Systolic Blood Pressure and Augmentation Index in Patients With Type 2 Diabetes Mellitus

It has been suggested that transfer functions to estimate central aortic systolic blood pressure (SBP) and central BP waveform parameters (i.e., augmentation index) may be less accurate in patients with type 2 diabetes mellitus (T2DM). However, these observations have not been confirmed in a large sample, which was the aim of this study. Consecutive patients with and without T2DM undergoing coronary angiography at the Royal Hobart Hospital had BP recorded at the ascending aorta and radial artery with a fluid-filled catheter. Radial BP waveforms were processed using the SphygmoCor Cardiovascular Management System (CVMS) transfer function (AtCor, Sydney) to estimate central BP. Two invasive waveform calibration methods were used: 1) aortic mean arterial pressure/diastolic BP (MAP/DBP); and 2) radial SBP and DBP (SBP/DBP). between-group analyses were performed unadjusted and adjusted for age, sex, hypertension, hypercholesterolaemia, body mass index, and coronary artery disease. Data from 64 patients with T2DM (61±11 years, 73% male) and 186 patients without T2DM (62±8 years, 70% male) were analysed. There was no difference in the accuracy of estimated central SBP between groups when compared with invasive aortic SBP from MAP/DBP calibration (T2DM –1.8±6 mmHg vs –1.1±5 mmHg; p=0.37; adjusted p=0.59) or radial SBP/DBP calibration (T2DM –1.2±9 mmHg vs –2.0±9 mmHg; p=0.57; adjusted p=0.66). Augmentation index was not significantly different between patients with and without T2DM 0.8±12% vs 3.7±14%; p=0.13, respectively). Estimated central SBP and augmentation index do not appear to be less accurate in patients with T2DM when waveforms are calibrated with invasive BP.

CORONARY MICROVASCULAR DISEASE IS ASSOCIATED WITH ARTERIAL STIFNESS IN PATIENTS WITH ISCHEMIA AND NO OBSTRUCTIVE CORONARY ARTERIES

Objective: There is a gap in the literature regarding the association between stiffness and myocardial ischemia. Arterial stiffness (AS) is an independent risk factor for cardiovascular disease, directly related to coronary atherosclerosis, an entity with an unfavorable cardiovascular prognosis frequently encountered in patients with hypertension. The aim of this study was to investigate the relationship between AS and Coronary Microvascular Dysfunction (MVD). Design and method: We examined 23 hypertensive patients [10 female, 43%, mean age: 61.5±10.1 years, mean office blood pressure (BP): 147/88±10/9 mmHg] and 28 MVD patients (19 female, 68%, mean age: 58.3±4.6 years, average office BP: 139/81±16/13 mmHg). In the group of patients with angina, MVD was defined by a standardized systematic protocol in which coronary flow reserve (CFR) and index of microvascular resistance (IMR) were measured in the left anterior descending coronary artery using a temperature/pressure sensor-tipped guidewire. MVD patients were classified into 2 groups, structural and functional endotype, based on commonly used cut-offs (impaired CFR &lt; 2.5, increased IMR &gt; 25). In addition, in all participants, arterial stiffness was assessed using the aortic augmentation index (AIx), derived from the analysis of central pulse waveforms, recorded by applanation tonometry directly from the radial artery. Results: In the MVD group, the coronary flow reserve (CFR) was 1.4±0.9 and the index of microvascular resistance (IMR) was 43.9±30 IU. Of the 28 patients with impaired CFR, 8 (28%) had normal IMR consistent with functional CMD endotype, and 20 (71%) had abnormal IMR associated with structural alterations of the microvasculature. AIx was found to be increased in MVD patients compared to hypertensives (35.4±10.8 vs 27.4±12.6%, p = 0.031). This difference in AIx between the CMD and asymptomatic hypertensive controls was found to be statistically significant after adjustment for gender and age (p&lt;0.05). No statistically significant difference was found in body mass index, renal function, history of dyslipidemia, diabetes mellitus, and smoking between groups. Conclusions: Arterial stiffness was found to be increased in patients with MVD compared to asymptomatic hypertensive individuals. These results suggest that therapies targeting vascular stiffening could provide additional clinical benefit in patients with impaired coronary microvasculature.

Coronary microvascular disease is associated with arterial stiffness in patients with ischemia and no obstructive coronary arteries

Abstract Funding Acknowledgements Type of funding sources: None. Introduction Existing data suggest that stable angina pectoris with no obstructive coronary artery disease is associated with increased risks of major adverse cardiovascular events. There is a gap in the current literature regarding the possible association between higher aortic stiffness and myocardial ischemia in this special population. Arterial Stiffness (AS) is an independent risk factor for cardiovascular disease, directly related to increased coronary atherosclerosis, an entity frequently encountered in hypertensive patients. Purpose The aim of this study is to determine whether arterial stiffness is increased in patients with Coronary Microvascular Dysfunction (CMD) compared to hypertensives controls. Methods We examined 21 hypertensive patients [9 female, 39%, mean age: 61.2±9.9 years, mean office blood pressure (BP) : 139/86±18/10 mmHg] and 25 CMD patients (16 female, 64%, mean age : 57.9±4.8 years, average office BP: 127/77±18/10 mmHg). In the group of patients with chronic angina pectoris, CMD was defined by a standardized systematic protocol in which coronary flow reserve (CFR) and index of microvascular resistance (IMR) were measured in the left anterior descending coronary artery using a temperature/pressure sensor-tipped guidewire. CMD patients were classified into 2 groups, structural and functional endotype, based on commonly used cut-offs (impaired CFR &amp;lt; 2.5, increased IMR ≥ 25). Functional CMD was defined as abnormal CFR in combination with normal IMR and structural CMD as abnormal CFR with abnormal IMR. In addition, in all participants, arterial stiffness was assessed using aortic augmentation index (AIx), derived from the analysis of central pulse waveforms, recorded by applanation tonometry directly from the radial artery. Results In CMD group, mean CFR and IMR were 1.6 ± 0.9 and 43.9± 30 IU, respectively. Of the 25 patients with abnormal CFR, 8 (32%) had normal IMR consistent with functional CMD endotype, and 17 (68%) had abnormal IMR consistent with structural endotype. AIx was found increased in CMD patients compared to asymptomatic hypertensives (36.44±11.1 vs 25.4±11.6%, p=0.024). This difference in AIx between the CMD and asymptomatic hypertensive controls was found to be statistically significant after adjustment for gender and age (p&amp;lt;0.05). No statistically significant difference was found in body mass index, renal function, history of dyslipidemia, diabetes mellitus and smoking between the two groups (p=NS). Conclusion Arterial stiffness was found increased in patients with CMD compared to hypertensives. These results suggest that therapies targeting vascular stiffening could provide additional clinical benefit in this special category of patients with impaired coronary microvasculature.

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

Background: Central blood pressure (BP) better reflects the loading conditions on the major organs and is more closely correlated with future cardiovascular events. The increased invasiveness and risk of infection prevents the routine measurement of central BP. Arterial transfer functions can provide central BP estimates from clinically available peripheral measurements. However, current methods are either generalized, potentially lacking the ability to adapt to inter and intra subject variability, or individualized based on additional, clinically unavailable, pulse transit time measurements. This work proposes a novel, self-contained method for individualizing an arterial transfer function from a single peripheral pressure measurement, capable of accurately estimating central BP in a range of hemodynamic conditions. Methods: Pulse wave analysis of femoral BP waves was employed to formulate initial approximations of central BP and arterial inlet flow waveforms, to serve as objective functions for the identification of all model parameters. Root mean squared error (RMSE), and systolic and pulse pressure errors were assessed with respect to invasive aortic BP measurements in a seven (7) porcine endotoxin experiments. Systolic and pulse pressure errors were analysed using Bland-Altman analysis. Method accuracy is also compared with an idealized transfer function, derived using the measured aortic-femoral pulse transit time and minimizing the RMSE of model output pressure with respect to reference aortic pressure, a generalized transfer function model, and invasive femoral pressure measurements. Results: Mean bias and limits of agreement (95% CI) for the proposed method were 1.0(-4.6, 6.7)mmHg and -1.0(-6.6, 4.6)mmHg for systolic and pulse pressure, respectively, compared to 3.6(-0.9, 8.2)mmHg and 2.7(-1.8, 7.3)mmHg for the generalized transfer function model. Mean bias and limits of agreement for femoral pressure measurements were -6.4(-15.0, 2.3)mmHg and -9.4(-18.1, -0.8)mmHg, for systolic and pulse pressure, respectively. The pooled mean and standard deviation of the RMSE produced by the single measurement method, relative to reference aortic pressure, was 4.3(1.1)mmHg, consistent with estimates produced by the idealized transfer function, 3.9(1.2)mmHg, and improving of the generalized transfer function, 4.6(1.4)mmHg. Conclusions: The proposed single measurement method provides accurate central BP estimates from routinely available peripheral pressure measurements, and nothing else. The method allows for the individualization of transfer functions on a per patient basis to better capture changes in patient condition during the progression of disease and subsequent treatment, at no additional clinical cost.

The effect of cardiac properties on arterial pulse waves: An in-silico study.

This study investigated the effects of cardiac properties variability on arterial pulse wave morphology using blood flow modelling and pulse wave analysis. A lumped-parameter model of the left part of the heart was coupled to a one-dimensional model of the arterial network and validated using reference pulse waveforms in turn verified by comparison with in vivo measurements. A sensitivity analysis was performed to assess the effects of variations in cardiac parameters on central and peripheral pulse waveforms. Results showed that left ventricle contractility, stroke volume, cardiac cycle duration, and heart valves impairment are determinants of central waveforms morphology, pulse pressure and its amplification. Contractility of the left atrium has negligible effects on arterial pulse waves. Results also suggested that it might be possible to infer left ventricular dysfunction by analysing the timing of the dicrotic notch and cardiac function by analysing PPG signals. This study has identified cardiac properties that may be extracted from in vivo central and peripheral pulse waves to assess cardiac function.

Central Venous Waveform Analysis and Cardiac Output in a Porcine Model of Endotoxemic Hypotension and Resuscitation.

Cardiac output (CO) is a valuable proxy for perfusion, and governs volume responsiveness during resuscitation from distributive shock. The underappreciated venous system has nuanced physiology that confers valuable hemodynamic information. In this investigation, deconvolution of the central venous waveform by the fast Fourier transformation (FFT) algorithm is performed to assess its ability to constitute a CO surrogate in a porcine model of endotoxemia-induced distributive hypotension and resuscitation. Ten pigs were anesthetized, catheterized, and intubated. A lipopolysaccharides infusion protocol was used to precipitate low systemic vascular resistance hypotension. Four crystalloid boluses (10 cc/kg) were then given in succession, after which heart rate, mean arterial pressure, thermodilution-derived CO, central venous pressure (CVP), and the central venous waveform were collected, the last undergoing fast Fourier transformation analysis. The amplitude of the fundamental frequency of the central venous waveform's cardiac wave (f0-CVP) was obtained. Heart rate, mean arterial pressure, CVP, f0-CVP, and CO were plotted over the course of the boluses to determine whether f0-CVP tracked with CO better than the vital signs, or than CVP itself. Distributive hypotension to a 25% mean arterial pressure decrement was achieved, with decreased systemic vascular resistance (mean 918 ± 227 [SD] dyne/s/cm-5 vs 685 ± 180 dyne/s/cm-5; p = 0.038). Full hemodynamic parameters characterizing this model were reported. Slopes of linear regression lines of heart rate, mean arterial pressure, CVP, f0-CVP, and CO were -2.8, 1.7, 1.8, 0.40, and 0.35, respectively, demonstrating that f0-CVP values closely track with CO over the 4-bolus range. Fast Fourier transformation analysis of the central venous waveform may allow real-time assessment of CO during resuscitation from distributive hypotension, possibly offering a venous-based approach to clinical estimation of volume responsiveness.

Transient Bilateral Central Scotoma on Awakening: A Distinct Phenomenon.

Transient vision loss can be an alarming symptom owing to potentially serious etiologies such as thromboembolism or giant cell arteritis. Transient monocular vision loss (TVML) on awakening has been recently described as a benign phenomenon (Bouffard et al, 2017). Our objective was to describe the unique phenomenon of transient binocular vision loss (TBVL) on awakening. Retrospective observational case series of 5 patients who experienced TBVL on awakening seen in the neuro-ophthalmology clinic at the Mayo Clinic between 2016 and 2020. Patients who described generalized blurred vision and those with monocular transient vision loss were excluded. The median age was 81.4 years (range, 68-92 years), and all were male. Every patient described a stereotyped transient bilateral central scotoma on awakening with slightly irregular borders and mild asymmetry between the 2 eyes lasting between 15 and 90 minutes. Frequency ranged from 3 to 7 times per week, and there was a median of 319 episodes (range, 126-728 episodes) before evaluation in the neuro-ophthalmology clinic. All patients had normal optic nerves, and no plaques were noted in the retinal vessels. All 5 had macular drusen, which were predominantly extrafoveal and mild. Two patients underwent electrophysiology testing, which were both normal on full-field electroretinogram (ERG), but there was blunted central wave forms on multifocal ERG. Two patients underwent dark adaptation testing, which showed both prolong and diminished dark adaptation. Neuroimaging and thromboembolic workup were unrevealing. TBVL is a distinct phenomenon from TMVL on awakening, which has a different demographic and symptomology. The etiology is unclear but seems to be a focal macular process in conjunction with an autoregulatory failure resulting in a supply-demand mismatch during low-light conditions.

Optimized design of an arterial network model reproduces characteristic central and peripheral haemodynamic waveform features of young adults.

The arterial network in healthy young adults is thought to be structured to optimize wave reflection in the arterial system, producing an ascending aortic pressure waveform with three key features: early systolic peak, negative systolic augmentation and diastolic hump. One‐dimensional computer models have provided significant insights into arterial haemodynamics, but no previous models of the young adult have exhibited these three features. Given that this issue was likely to be related to unrepresentative or non‐optimized impedance properties of the model arterial networks, we developed a new ‘YoungAdult’ model that incorporated the following features: (i) a new and more accurate empirical equation for approximating wave speeds, based on area and relative distance to elastic–muscular arterial transition points; (ii) optimally matched arterial junctions; and (iii) an improved arterial network geometry that eliminated ‘within‐segment’ taper (which causes wave reflection in conduit arteries) whilst establishing ‘impedance‐preserving’ taper. These properties of the model led to wave reflection occurring predominantly at distal vascular beds, rather than in conduit arteries. The model predicted all three typical characteristics of an ascending aortic pressure waveform observed in young adults. When compared with non‐invasively acquired pressure and velocity measurements (obtained via tonometry and Doppler ultrasound in seven young adults), the model was also shown to reproduce the typical waveform morphology observed in the radial, brachial, carotid, temporal, femoral and tibial arteries. The YoungAdult model provides support for the concept that the arterial tree impedance in healthy young adults is exquisitely optimized, and it provides an important baseline model for investigating cardiovascular changes in ageing and disease states. Key points The origin of wave reflection in the arterial system is controversial, but reflection properties are likely to give rise to characteristic haemodynamic features in healthy young adults, including an early systolic peak, negative systolic augmentation and diastolic hump in the ascending aortic pressure waveform, and triphasic velocity profiles in peripheral arteries. Although computational modelling provides insights into arterial haemodynamics, no previous models have predicted all these features.An established arterial network model was optimized by incorporating the following features: (i) a more accurate representation of arterial wave speeds; (ii) precisely matched junctions; and (iii) impedance‐preserving tapering, thereby minimizing wave reflection in conduit arteries in the forward direction. Comparison with in vivo data (n = 7 subjects) indicated that the characteristic waveform features in young adults were predicted accurately.Our findings strongly imply that a healthy young arterial system is structured to optimize wave reflection in the main conduit arteries and that reflection of forward waves occurs primarily in the vicinity of vascular beds.

Evaluation of Pulse Contour Markers using an A-Mode Ultrasound: Association with Carotid Stiffness Markers and Ageing.

Vascular ageing is directly associated with the blood vessel wall structural and functional abnormalities. Pulse morphology carries information on these abnormalities, and pulse contour analysis (PCA) identifies key amplitudes and timing information on the pulse waveforms that has a prognostic value towards cardiovascular risk stratification. PCA markers derived from second derivative waveforms represent the accelerative and decelerative phase of an arterial pulse. In this work, second derivative diameter waveforms of central arteries such as carotid artery are obtained using an A-mode ultrasound device. The derived PCA markers (b/a, c/a, d/a, e/a, (b-c-d-e)/a) from diameter waveform is investigated for its association with central stiffness markers and aging. An observational and cross-sectional study on 106 subjects (51 male/55 females) was conducted for this investigation. The highest correlation (r = 0.5, P < 0.001) was observed between c/a and PWV, and the lowest correlation was between c/a and AC. Group average values of PCA markers for each age decade group were correlated strongly (r > 0.9, p < 0.001) with age. A change > 19% was observed between the group average values of PCA markers of the normotensive and hypertensive population. The applicability of aforesaid PCA markers on central pulse waveforms, measured using a noninvasive device in resource-limited field settings, would accelerate such large scale vascular screening that is essential to understanding the cardiovascular risks at a population level. Clinical Relevance- This study provides an investigation into using second derivative diameter waveforms obtained from the carotid artery to find its associations with arterial stiffness and ageing.

Non-Invasive Assessment of Arterial Stiffness: Pulse Wave Velocity, Pulse Wave Analysis and Carotid Cross-Sectional Distensibility: Comparison between Methods.

Background: The stiffening of large elastic arteries is currently estimated in research and clinical practice by propagative and non-propagative models, as well as parameters derived from aortic pulse waveform analysis. Methods: Common carotid compliance and distensibility were measured by simultaneously recording the diameter and pressure changes during the cardiac cycle. The aortic and upper arm arterial distensibility was estimated by measuring carotid–femoral and carotid–radial pulse wave velocity (PWV), respectively. The augmentation index and blood pressure amplification were derived from the analysis of central pulse waveforms, recorded by applanation tonometry directly from the common carotid artery. Results: 75 volunteers were enrolled in this study (50 females, average age 53.5 years). A significant inverse correlation was found between carotid distensibility and carotid–femoral PWV (r = −0.75; p < 0.001), augmentation index (r = −0.63; p < 0.001) and central pulse pressure (r = −0.59; p < 0.001). A strong correlation was found also between the total slope of the diameter/pressure rate carotid curves and aortic distensibility, quantified from the inverse of the square of carotid–femoral PWV (r = 0.67). No correlation was found between carotid distensibility and carotid–radial PWV. Conclusions: This study showed a close correlation between carotid–femoral PWV, evaluating aortic stiffness by using the propagative method, and local carotid cross-sectional distensibility.

Importance of central BP assessment in ISH of the young. Which devices are best suited for practical use?

Isolated systolic hypertension (ISH), defined as brachial systolic blood pressure (bSBP) ≥140 mmHg and diastolic blood pressure (DBP) <90 mmHg, is highly prevalent among young subjects and in the elderly. The prognostic significance of ISH in young individuals remains the object of large debate which might be solved, at least in part, if considering the prognostic role of central BP. For any given value of pBP, the cardiovascular (CV) risk is better defined by central BP (cBP). Young individuals with ISH have long been considered at low CV risk, given the assumption that a "spurious hypertension" phenotype characterized by elevated peripheral (brachial) BP (pBP), normal cBP, and elevated BP amplification was often found in this population. However, this remains to be proven, because many other studies found no differences in BP amplification between ISH and sisto-diastolic hypertension. Despite numerous attempts, methodologies for cBP assessment by non-invasive devices are currently not standardized. As a result, different devices could provide different cBP values despite using the same biological signals. Devices providing accurate estimates of BP amplification as a dimensionless ratio between amplitudes of central and peripheral arterial waveforms might be well suited for clinical purposes in young individuals with ISH. There is urgent need of well-designed prospective studies aiming at longitudinally evaluating the amount of CV risk associated with elevated cBP in young subjects with ISH and their related incremental prognostic value.

Distributed Online Learning for Coexistence in Cognitive Radar Networks

This work addresses the coexistence problem for radar networks. Specifically, we model a network of cooperative, independent, and non-communicating radar nodes which must share resources within the network as well as with non-cooperative nearby emitters. We approach this problem using online Machine Learning (ML) techniques. Online learning approaches are specifically preferred due to the fact that each radar node has no prior knowledge of the environment nor of the positions of the other radar nodes, and due to the sequential nature of the problem. For this task we specifically select the multi-player multi-armed bandit (MMAB) model, which poses the problem as a sequential game, where each radar node in a network makes independent selections of center frequency and waveform with the same goal of improving tracking performance for the network as a whole. For accurate tracking, each radar node communicates observations to a fusion center on set intervals. The fusion center has knowledge of the radar node placement, but cannot communicate to the individual nodes fast enough for waveform control. Every radar node in the network must learn the behavior of the environment, which includes rewards, interferer behavior, and target behavior. Each independent and identical node must choose one of many waveforms to transmit in each Pulse Repetition Interval (PRI) while avoiding <i>collisions</i> with other nodes and interference from the environment. The goal for the network as a whole is to minimize target tracking error, which relies on obtaining high SINR in each time step. Our contributions include a mathematical description of the MMAB framework adapted to the radar network scenario. We conclude with a simulation study of several different network configurations. Experimental results show that iterative, online learning using MMAB outperforms the more traditional sense-and-avoid (SAA) and fixed-allocation approaches.

Significant Wave Height Retrieval Method Based on Spaceborne GNSS Reflectometry

A geophysical model function (GMF) for significant wave height (SWH) retrieval is developed based on the spaceborne Global Navigation Satellite System Reflectometry (GNSS-R) data measured by the Cyclone GNSS (CYGNSS) satellites. The spreading characteristics of delay-Doppler maps (DDMs) generated by receivers onboard satellites are affected by the surface roughness, which is closely related to the SWH. Four GNSS-R observables [i.e., leading edge slope (LES) of normalized integrated delay waveform (NIDW), LES of normalized central delay waveform (NCDW), trailing edge slope (TES) of NCDW, leading edge waveform summation (LEWS) of NCDW] derived from DDM are first used in this letter to retrieve SWH. Collocated ERA5 SWH data are used as the ground truth to develop and evaluate the SWH models based on the four GNSS-R observables. The results show that there is high consistency between the SWH estimates and the ground truth, with a correlation coefficient of 0.88 and a root mean square error (RMSE) of 0.503 m. This letter demonstrates the feasibility of the spaceborne GNSS-R in SWH retrieval.

Research on laser ultrasonic surface defect identification based on a support vector machine.

To solve the problem of difficult quantitative identification of surface defect depth during laser ultrasonic inspection, a support vector machine-based method for quantitative identification of surface rectangular defect depth is proposed. Based on the thermal-elastic mechanism, the finite element model for laser ultrasound inspection of aluminum materials containing surface defects was developed by using the finite element software COMSOL. The interaction process between laser ultrasound and rectangular defects was simulated, and the reflected wave signals corresponding to defects of different depths under pulsed laser irradiation were obtained. Laser ultrasonic detection experiments were conducted for surface defects of different depths, and multiple sets of ultrasonic signal waveform were collected, and several feature vectors such as time-domain peak, center frequency peak, waveform factor and peak factor were extracted by using MATLAB, the quantitative defect depth identification model based on support vector machine was established. The experimental results show that the laser ultrasonic surface defect identification model based on support vector machine can achieve high accuracy prediction of defect depth, the regression coefficient of determination is kept above 0.95, and the average relative error between the true value and the predicted value is kept below 10%, and the prediction accuracy is better than that of the reflection echo method and BP neural network model.