Siegfried Wassertheurer

AIT Austrian Institute of Technology, Wien, Vienna, Austria

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Publications (59)147.36 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: In general, higher blood pressure levels and increased central pulsatility are indicators for increased cardiovascular risk. However, in systolic heart failure (SHF), this relationship is reversed. Therefore, the aim of this work is to compare pulsatile hemodynamics between patients with SHF and controls and to clarify the relationships between measures of cardiac and arterial function in the two groups. We used parameters derived from angiography, echocardiography, as well as from pulse wave analysis (PWA) and wave separation analysis (WSA) based on non-invasively assessed pressure and flow waves to quantify cardiac function, aortic stiffness and arterial wave reflection in 61 patients with highly reduced (rEF) and 122 matched control-patients with normal ejection fraction (nEF). Invasively measured pulse wave velocity was comparable between the groups (8.6/8.05m/s rEF/nEF, P=0.24), whereas all measures derived by PWA and WSA were significantly decreased (augmentation index: 18.1/24.8 rEF/nEF, P<0.01; reflection magnitude: 56.3/62.1 rEF/nEF, P<0.01). However, these differences could be explained by the shortened ejection duration (ED) in rEF (ED: 269/308ms rEF/nEF, P<0.01; AIx: 22.2/22.8 rEF/nEF, P=0.7; RM: 59.3/60.6 rEF/nEF, P=0.47 after adjustment for ED). Ventricular function was positively associated with central pulse pressures in SHF in contrast to no or even a slightly negative association in controls. The results suggest that the decreased measures of pulsatile function may be caused by impaired systolic function and altered interplay of left ventricle and vascular system rather than by a real reduction of wave reflections or aortic stiffness in SHF. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.
    International journal of cardiology 07/2015; 190. DOI:10.1016/j.ijcard.2015.04.183 · 6.18 Impact Factor
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    ABSTRACT: Williams-Beuren syndrome (WBS) is a genetic disorder that involves elastin gene causing cardiovascular abnormalities and increased risk. However, data on arterial function in these patients are only few and conflicting. Aim of this study was to evaluate dynamic behaviour of central and peripheral blood pressure (BP) and arterial stiffness parameters early in the course of WBS. We enrolled 19 WBS paediatric patients (age 13 ± 4 years) and 23 age, height and BP-matched controls (10 ± 4 years). We evaluated 24-h ambulatory BP values via an ambulatory blood pressure monitoring (ABPM) system (Mobil-O-Graph) also capable to calculate 24-h central BP and 24-h arterial stiffness parameters. Carotid-femoral PWV (cf-PWV) was assessed in all WBS individuals (Complior). BP values were similar in WBS and control, during the daytime and the night-time. The same behaviour applies to 24-h central BP. However, during the night, WBS showed heart rate values (HR; 78 ± 10 vs. 71 ± 9 bpm; P < 0.03), augmentation index (Aix; 24.6 ± 13.5% vs. 16.5 ± 8.9%; P = 0.03) and reflection magnitude (68 5.8 vs. 63.5 8.1; P = 0.02) higher than controls. The HR, Aix and reflection magnitude reduction in the day-night shift was lower in WBS than in controls. Cf-PWV in WBS children did not differ when compared with their normalized expected value. In WBS children, the higher night-time HR, Aix and reflection magnitude and their impaired physiological reduction in the day-night shift suggests an abnormal sympathetic cardiovascular control, an augmented wave reflection and an increase in small arteries resistance. These alterations possibly due to a sympathetic overactivity can be regarded as earlier hallmarks of cardiovascular dysfunction in these patients.
    Journal of Hypertension 04/2015; 33(4):804-809. DOI:10.1097/HJH.0000000000000454 · 4.22 Impact Factor
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    ABSTRACT: To compare noninvasive methods to assess pulse wave velocity (PWV) with the invasive gold standard in terms of absolute values, age-related changes, and relationship with subclinical organ damage. Invasive aortic PWV (aoPWVinv) was measured in 915 patients undergoing cardiac catheterization (mean age 61 years, range 27-87 years). Carotid-femoral PWV (cfPWV) was measured with tonometry, using subtracted distance (cfPWVsub), body height-based estimated distance (cfPWVbh), direct distance × 0.8 (cfPWVdir0.8), and caliper-based distance (cfPWVcalip) for travel distance calculation. Aortic PWV was estimated (aoPWVestim) from single-point radial waveforms, age, and SBP. Invasive and noninvasive transit times were strikingly similar (median values 60.8 versus 61.7 ms). In the entire group, median value of aoPWVinv was 8.3 m/s, of cfPWVsub and cfPWVbh 8.1 m/s, and of aoPWVest 8.5 m/s. CfPWVsub overestimated aoPWVinv in younger patients by 0.7 m/s and underestimated aoPWVinv in older patients by 1.7 m/s, with good agreement from 50 to 70 years of age. AoPWVestim differed from aoPWVinv by no more than 0.4 m/s across all age groups. CfPWVdir0.8, measured in 632 patients, overestimated aoPWVinv by 1.7 m/s in younger patients, with good agreement in middle-aged and older patients. CfPWVcalip, measured in 336 patients, underestimated aoPWVinv in all ages. In 536 patients with preserved systolic function, aoPWVinv and aoPWVestim were superior to cfPWVs in predicting coronary atherosclerosis, renal function impairment, left atrial enlargement, and diastolic dysfunction. CfPWVsub, cfPWVdir0.8, and aoPWVestim are reasonable surrogates for aoPWVinv. AoPWVinv predicts subclinical organ damage better than cfPWVs, and as good as aoPWVestim.
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    ABSTRACT: The non-invasive quantification of arterial wave reflection is an increasingly important concept in cardiovascular research. It is commonly based on pulse wave analysis (PWA) of aortic pressure. Alternatively, wave separation analysis (WSA) considering both aortic pressure and flow waveforms can be applied. Necessary estimates of aortic flow can be measured by Doppler ultrasound or provided by mathematical models. However, this approach has not been investigated intensively up to now in subjects developing systolic heart failure characterized by highly reduced ejection fraction (EF). We used non-invasively generated aortic pressure waveforms and Doppler flow measurements to derive wave reflection parameters in 61 patients with highly reduced and 122 patients with normal EF. Additionally we compared these readings with estimates from three different flow models known from literature (triangular, averaged, Windkessel). After correction for confounding factors, all parameters of wave reflection (PWA and WSA) were comparable for patients with reduced and normal EF. Wave separations assessed with the Windkessel based model were similar to those derived from Doppler flow in both groups. The averaged waveform performed poorer in reduced than in normal EF, whereas triangular flow represented a better approximation for reduced EF. Overall, the non-invasive assessment of WSA parameters based on mathematical models compared to ultrasound seems feasible in patients with reduced EF.
    Physiological Measurement 01/2015; 36(2):179-190. DOI:10.1088/0967-3334/36/2/179 · 1.62 Impact Factor
  • Artery 2014, Masstricht; 10/2014
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    ABSTRACT: We investigated whether aortic characteristic impedance (Zc), that is, the ratio between the pulsatile change in pressure and flow in the proximal aorta, is related to left ventricular hypertrophy and geometry independently of blood pressure (BP). A total of 438 never-treated hypertensive individuals (men 62%, age 48 ± 11 years, BP 147/90 ± 16/10 mmHg) underwent echocardiography and 24 h BP monitoring. Aortic pressure waveform was obtained from radial tonometry with a generalized transfer function (SphygmoCor). Using a validated aortic blood flow model based on higher order Windkessel theory (ARCSolver), aortic Zc, forward (Pf) and backward (Pb) wave amplitudes and their ratio (Pb/Pf = reflection magnitude) were calculated from central waveform.
    Journal of Hypertension 09/2014; 33(1). DOI:10.1097/HJH.0000000000000354 · 4.22 Impact Factor
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    David Nunan, Susannah Fleming, Bernhard Hametner, Siegfried Wassertheurer
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    ABSTRACT: We have previously reported that estimation of central blood pressure (BP) and augmentation using an automated oscillometric device are robust and feasible in a community setting. The same method has recently been validated for estimating aortic pulse wave velocity (aPWV) in laboratory settings, and its prognostic value has been confirmed in a prospective clinical trial.
    Blood Pressure Monitoring 07/2014; DOI:10.1097/MBP.0000000000000066 · 1.18 Impact Factor
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    ABSTRACT: BACKGROUND:Heart rate variability is the variation of the time interval between consecutive heartbeats. Entropy is a commonly used tool to describe the regularity of data sets. Entropy functions are defined using multiple parameters, the selection of which is controversial and depends on the intended purpose. This study describes the results of tests conducted to support parameter selection, towards the goal of enabling further biomarker discovery.METHODS:This study deals with approximate, sample, fuzzy, and fuzzy measure entropies. All data were obtained from PhysioNet, a free-access, on-line archive of physiological signals, and represent various medical conditions. Five tests were defined and conducted to examine the influence of: varying the threshold value r (as multiples of the sample standard deviation sigma, or the entropy-maximizing rChon), the data length N, the weighting factors n for fuzzy and fuzzy measure entropies, and the thresholds rF and rL for fuzzy measure entropy. The results were tested for normality using Lilliefors' composite goodness-of-fit test. Consequently, the p-value was calculated with either a two sample t-test or a Wilcoxon rank sum test.RESULTS:The first test shows a cross-over of entropy values with regard to a change of r. Thus, a clear statement that a higher entropy corresponds to a high irregularity is not possible, but is rather an indicator of differences in regularity. N should be at least 200 data points for r = 0.2 sigma and should even exceed a length of 1000 for r = rChon. The results for the weighting parameters n for the fuzzy membership function show different behavior when coupled with different r values, therefore the weighting parameters have been chosen independently for the different threshold values. The tests concerning rF and rL showed that there is no optimal choice, but r = rF = rL is reasonable with r = rChon or r = 0.2sigma.CONCLUSIONS:Some of the tests showed a dependency of the test significance on the data at hand. Nevertheless, as the medical conditions are unknown beforehand, compromises had to be made. Optimal parameter combinations are suggested for the methods considered. Yet, due to the high number of potential parameter combinations, further investigations of entropy for heart rate variability data will be necessary.
    BMC Bioinformatics 05/2014; 15(Suppl 6-Suppl 6):S2. DOI:10.1186/1471-2105-15-S6-S2 · 2.67 Impact Factor
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    Siegfried Wassertheurer, Klaus Burkhardt, Uwe Heemann, Marcus Baumann
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    ABSTRACT: Pulse pressure amplification (PPA) reflects large artery function. Its contribution in chronic kidney disease (CKD) remains uncertain. The authors assessed PPA in CKD progression in patients with CKD stage 2 to 4 (n=128) and 89 controls (follow-up: 42 months). PPA was reduced in CKD patients as compared with control patients and associated with decline in renal function. Sixteen renal endpoints, defined by 50% loss of renal function or start of renal replacement therapy, were detected. In Cox regression analysis, PPA, estimated glomerular filtration rate, and proteinuria predicted renal endpoints. Patients with CKD stage 4 and low PPA had the highest risk for developing renal endpoints (unadjusted 8.1; 2.4–27.7 and adjusted for age and proteinuria 5.6; 1.5–21.9, log-rank P<.001). Taken together, PPA is reduced in CKD and is associated with declining renal function. In addition, low PPA predicts renal endpoints in severe CKD. Furthermore, this study emphasizes the role of systolic blood pressure as a major determinant of PPA.
    Journal of Clinical Hypertension 04/2014; 16(6). DOI:10.1111/jch.12316 · 2.96 Impact Factor
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    ABSTRACT: Chronic kidney disease (CKD) is characterized by aortic stiffness and increased cardiovascular mortality. In end-stage renal disease, aortic stiffness predicts mortality, whereas this role remains uncertain in mild-to-moderate CKD. We aimed to investigate whether aortic pulse wave velocity (aPWV) predicts mortality and renal disease progression in CKD patients. We enrolled 135 CKD patients stages 2-4 [estimated glomerular filtration rate (eGFR): 41.1 (28.5-61.6) ml/min per 1.73 m] in the study and assessed aPWV. The combined renal end-point was defined as at least 50% decline in renal function and/or start of renal replacement therapy. During the observational period of 42 (30-50) months six patients were lost of follow-up, 13 patients died and 16 patients reached the combined renal end-point. Stratification according to the mean of aPWV (10 m/s), Kaplan-Meier analysis revealed increased mortality with aPWV ≥10 m/s (log-rank P < 0.05). Stepwise logistic regression analysis confirmed aPWV as an independent predictor for mortality in CKD stage 2-4. The hazard ratio of mortality in the cohort with an aPWV at least 10 m/s was 5.1 (1.1-22.9). By contrast, Kaplan-Meier analysis revealed no effect of aPWV on the combined renal end-point (log-rank P = 0.90). These results provide the first direct evidence that in patients with CKD stage 2-4, increased aortic stiffness determined by aPWV is a strong independent predictor of all-cause mortality.
    Journal of Hypertension 04/2014; 32(4):899-903. · 4.22 Impact Factor
  • Journal of the American College of Cardiology 02/2014; 63(21). DOI:10.1016/j.jacc.2013.12.046 · 15.34 Impact Factor
  • Thomas Weber, Siegfried Wassertheurer
    Hypertension 01/2014; 63(4). DOI:10.1161/HYPERTENSIONAHA.113.02885 · 7.63 Impact Factor
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    ABSTRACT: Analysis of the arterial pressure curve plays an increasing role in cardiovascular risk stratification. Measures of wave reflection and aortic stiffness have been identified as independent predictors of risk. Their determination is usually based on wave propagation models of the circulation. Another modeling approach relies on modified Windkessel models, where pressure curves can be divided into reservoir and excess pressure. Little is known of their prognostic value. The aim of this study is to evaluate the predictive value of parameters gained from reservoir theory applied to aortic pressure curves in a cohort of high-risk patients. Furthermore the relation of these parameters to those from wave separation analysis is investigated. Central pressure curves from 674 patients with preserved ejection fraction, measured by radial tonometry and a validated transfer function, were analyzed. A high correlation between the amplitudes of backward traveling pressure waves and reservoir pressures was found (R=0.97). Various parameters calculated from the reservoir and excess pressure waveforms predicted cardiovascular events in univariate Cox proportional hazards modeling. In a multivariate model including several other risk factors such as brachial blood pressure, the amplitude of reservoir pressure remained a significant predictor (HR=1.37 per SD, p=0.016). Based on very different models, parameters from reservoir theory and wave separation analysis are closely related and can predict cardiovascular events to a similar extent. Although Windkessel models cannot describe all of the physiological properties of the arterial system, they can be useful to analyze its behavior and to predict cardiovascular events.
    International journal of cardiology 11/2013; 171(1). DOI:10.1016/j.ijcard.2013.11.039 · 6.18 Impact Factor
  • M. Bachler, C. Mayer, B. Hametner, S. Wassertheurer
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    ABSTRACT: Pulse wave velocity (PWV) in arteries is an estimator for arterial stiffness. As velocity is calculated as distance per time, the accuracy and reliability of PWV measurements depends heavily on the estimation of the pulse transit time (PTT). Several methods for the estimation of the PTT exist, often resulting in different PWV values. They rely on the exact determination of specific points in the pulse wave, which are easily affected by small changes of the signal. As there is still no agreement on the accuracy of these methods, only the reliability and stability of these commonly used "foot-to-foot" algorithms are compared in this paper. These algorithms are based on the detection of the diastole-minimum, the maximum of the first or second derivative or combinations thereof. We also adapted a new approach called "diastole-patching" based on the matching of a specific region of the pulse waves. The methods were tested using 2348 pulse waves from the MIMIC Database, collected from 46 subjects. Intra-subject deviation and relative outliers per subject were lowest in the adapted diastole-patching algorithm (4.9 ± 3ms and 0.6 ± 2.7%, respectively). Therefore, this study has shown that the diastole-patching method is the most stable and reliable of the algorithms under investigation.
    Proceedings of the 2013 8th EUROSIM Congress on Modelling and Simulation; 09/2013
  • T. Weber, B. Hametner, B. Eber, S. Wassertheurer
    Artery Research 09/2013; 7(3-4):150-151. DOI:10.1016/j.artres.2013.10.174
  • B. Hametner, T. Weber, C. Mayer, J. Kropf, S. Wassertheurer
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    ABSTRACT: Within the concept of pulse wave analysis, arterial pressure and flow curves over a whole cardiac cycle are analysed. Characteristic impedance is obtained as ratio of pressure to flow when waves are not influenced by reflections. The aim of this work is to evaluate the effects of different blood flow models on the determination of the characteristic impedance compared to flow curves gained from ultrasound measurements. Beside a simple triangular and an averaged flow, a new blood flow model based on Windkessel theory is used. In a study population of 148 patients for the evaluation of the different models, the characteristic impedance is calculated in the frequency domain. The results indicate that the characteristic impedance strongly depends on the accuracy of the used flow model. While the averaged and the ARCSolver flow provide good estimates for impedance, the triangular flow curve seems to be too simplistic for getting accurate values.
    Mathematical and Computer Modelling of Dynamical Systems 08/2013; 19(4-ahead-of-print):1-12. DOI:10.1080/13873954.2013.763831 · 0.98 Impact Factor
  • S Wassertheurer, B Hametner
    Journal of human hypertension 07/2013; 28(2). DOI:10.1038/jhh.2013.65 · 2.69 Impact Factor
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    ABSTRACT: We present a lattice Boltzmann (LB) model for the simulation of hemodynamic flows in the presence of compliant walls. The new scheme is based on the use of a continuous bounce-back boundary condition, as combined with a dynamic constitutive relation between the flow pressure at the wall and the resulting wall deformation. The method is demonstrated for the case of two-dimensional (axisymmetric) pulsatile flows, showing clear evidence of elastic wave propagation of the wall perturbation in response to the fluid pressure. The extension of the present two-dimensional axisymmetric formulation to more general three-dimensional geometries is currently under investigation.
    International Journal of Modern Physics C 05/2013; 24(5):50030-. DOI:10.1142/S0129183113500307 · 1.13 Impact Factor
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    ABSTRACT: OBJECTIVES: Recently, a novel method to estimate aortic pulse wave velocity (aPWV) noninvasively from an oscillometric single brachial cuff waveform reading has been introduced. We investigated whether this new approach provides acceptable estimates of aPWV compared with intra-aortic catheter measurements. METHODS: Estimated values of aPWV obtained from brachial cuff readings were compared with those obtained using an intra-aortic catheter in 120 patients (mean age 61.8±10.8 years) suspected for coronary artery disease undergoing cardiac catheterization. Differences between aPWV values obtained from the test device and those obtained from catheter measurements were estimated using Bland-Altman analysis. RESULTS: The mean difference±SD between brachial cuff-derived values and intra-aortic values was 0.43±1.24 m/s. Comparison of aPWV measured by the two methods showed a significant linear correlation (Pearson's R=0.81, P<0.0001). The mean difference for repeated oscillometric measurements of aPWV was 0.05 m/s, with 95% confidence interval limits from -0.47 to 0.57 m/s. CONCLUSION: aPWV can be obtained using an oscillometric device with brachial cuffs with acceptable accuracy compared with intra-aortic readings.
    Blood pressure monitoring 04/2013; 18(3). DOI:10.1097/MBP.0b013e3283614168 · 1.18 Impact Factor
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    ABSTRACT: OBJECTIVES: To test whether measures of pulsatile arterial function are useful for diagnosing heart failure with preserved ejection fraction (HFPEF), in comparison with and in addition to Tissue Doppler Echocardiography (TDE). BACKGROUND: Increased arterial stiffness and wave reflections are present in most patients with HFPEF. METHODS: Patients with dyspnea as major symptom were categorized as having HFPEF or no HFPEF, based on invasively derived filling pressures and natriuretic peptide levels. Pulse wave velocity was measured invasively (aoPWV). Aortic pulse pressure (aoPP) and its components (incident pressure wave height - P1, forward wave amplitude - Pf; augmented pressure - AP; backward wave amplitude - Pb) were quantified non-invasively. RESULTS: 71 patients were classified as HFPEF, and 65 as no HFPEF (223 patients had intermediate results). Patients with HFPEF were older, more often had hypertension and diabetes, had larger left atria and higher left ventricular mass. Brachial (bPP) and aortic pulse pressures and all measures of arterial stiffness and wave reflections were higher in HFPEF patients. Receiver operating curve analysis derived area under the curve (AUC) values for separating HFPEF from no HFPEF were 0.823 for E/E'med, the best TDE parameter, 0.816 for bPP, and 0.867, 0.851, and 0.825 for aoPWV, aoPP, and Pb, respectively. Adding measures of pulsatile function to TDE resulted in an increase in AUC to 0.875 (bPP; p=0.03) and 0.901 (aoPP; p=0.005). In comparison with a TDE-based algorithm, net reclassification improvement was 32.9 % (p<0.0001). CONCLUSION: Measures of pulsatile arterial hemodynamics may complement TDE for the diagnosis of HFPEF.
    Journal of the American College of Cardiology 03/2013; 61(18). DOI:10.1016/j.jacc.2013.02.013 · 15.34 Impact Factor

Publication Stats

381 Citations
147.36 Total Impact Points

Institutions

  • 2010–2015
    • AIT Austrian Institute of Technology
      • Department of Health & Environment
      Wien, Vienna, Austria
  • 2014
    • Université Paris-Sorbonne - Paris IV
      Lutetia Parisorum, Île-de-France, France
  • 2003–2013
    • Vienna University of Technology
      • Institute of Analysis and Scientific Computing
      Wien, Vienna, Austria