Papers by Christopher Mayer
Brookings-Wharton Papers on Urban Affairs, 2004
United States during the next decades. Conventional wisdom, supported by recent research, suggest... more United States during the next decades. Conventional wisdom, supported by recent research, suggests that spending on local public schools may decline in real terms as a growing percentage of elderly voters becomes more influential.1 However, recent research has found that ...
We propose a new three-pronged plan to address the recent harmful flood offoreclosures. Our plan ... more We propose a new three-pronged plan to address the recent harmful flood offoreclosures. Our plan would address the major barriers that inhibit the ability of third-party servicers to modify mortgages the way portfolio lenders are now doing with greater success. The plan provides greater compensation for servicers to perform their duties, removes legal constraints that inhibit modification, and addresses critical second liens that often get in the way of effective mortgage modifications. Our plan has more modest costs than competing plans and is likely to be the most effective while still protecting the rights of investors in mortgage-backed securities.
ABSTRACT Within the concept of pulse wave analysis, arterial pressure and flow curves over a whol... more ABSTRACT Within the concept of pulse wave analysis, arterial pressure and flow curves over a whole cardiac cycle are analyzed. The ratio of pressure to flow in the frequency domain is called impedance. The characteristic impedance (Zc) is obtained when pressure and flow waves are not influenced by wave reflection. 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. The simplest model to approximate aortic blood flow is a curve of triangular shape. Another approach is to use an averaged flow curve from readings of different subjects, and recently a new blood flow model based on Windkessel theory was developed (ARCSolver flow model). In a study population of 148 patients for the evaluation of the different models the input impedance and subsequently the characteristic impedance is calculated in the frequency domain. The mean characteristic impedance using flow curves from ultrasound images is 0.22 (0.08 SD) AU. For the triangular flow a mean difference to the ultrasound flow for Zc of -0.148 (0.097 SD) is found. For the averaged flow a mean difference for Zc of 0.027 (0.036 SD) AU and for the ARCSolver flow a mean difference of 0.016 (0.039 SD) AU compared to the ultrasound flow is obtained. These 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.
Simulation Modelling Practice and Theory, Sep 1, 2008
The aim of the presented work has been the development of an algorithm for a non-invasive, portab... more The aim of the presented work has been the development of an algorithm for a non-invasive, portable, easy-to-use, and affordable device for measuring systemic cardiovascular parameters such as cardiac output and peripheral resistance. The data acquisition is based on a common oscillometric measurement using an occlusive blood pressure cuff, and no additional calibration is necessary. The novel algorithm introduced here combines several simulation techniques like neural networks or differential equations, which will be explained briefly. The determination of the hemodynamical parameters is based on the idea that the ejection work of the left ventricle is subject to an optimization principle. This kind of model needs no additional external calibration and opens therefore good perspectives for non-expert use in cardiovascular risk stratification and hypertension therapy optimization. To verify the approach we present some clinical results and a relevant discussion on it, followed by a view of future work.
Heart rate variability is the variation of the time interval between consecutive heartbeats. Entr... more 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. 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 σ, 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. 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 σ 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 = 0.2σ. 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.
PloS one, 2015
Arterial stiffness and wave reflection parameters assessed from both invasive and non-invasive pr... more Arterial stiffness and wave reflection parameters assessed from both invasive and non-invasive pressure and flow readings are used as surrogates for ventricular and vascular load. They have been reported to predict adverse cardiovascular events, but clinical assessment is laborious and may limit widespread use. This study aims to investigate measures of arterial stiffness and central hemodynamics provided by arterial tonometry alone and in combination with aortic root flows derived by echocardiography against surrogates derived by a mathematical pressure and flow model in a healthy middle-aged cohort. Measurements of carotid artery tonometry and echocardiography were performed on 2226 ASKLEPIOS study participants and parameters of systemic hemodynamics, arterial stiffness and wave reflection based on pressure and flow were measured. In a second step, the analysis was repeated but echocardiography derived flows were substituted by flows provided by a novel mathematical model. This wa...
Recent research has proposed a pro-cyclical link between sales volume and prices in the real esta... more Recent research has proposed a pro-cyclical link between sales volume and prices in the real estate market through changes in the equity of existing homeowners. This article uses data from the Boston condominium market to show that owners with high loan-to-value ratios take longer to sell their properties than owners with low loan-to- value ratios. Properties with high loan-to-value ratios
Data from downtown Boston in the 1990s show that loss aversion determines seller behaviour in the... more Data from downtown Boston in the 1990s show that loss aversion determines seller behaviour in the housing market. Condominium owners subject to nominal losses: (1) set higher asking prices of 25-35% of the difference between the property’s expected selling price and their original purchase price; (2) attain higher selling prices of 3-18% of that difference; and (3) exhibit a much
2015 IEEE Sensors Applications Symposium (SAS), 2015
Journal of Ambient Intelligence and Smart Environments, 2015
Blood Pressure Monitoring, 2015
A number of operator-independent oscillometric devices to measure hemodynamics and arterial stiff... more A number of operator-independent oscillometric devices to measure hemodynamics and arterial stiffness became available recently, but some and in particular VaSera VS-1500 do not provide estimates of aortic pressures and aortic pulse wave velocity (aPWV). The aim of this work was the retrospective application of the ARCSolver algorithm to pulse wave signals acquired with the VaSera VS-1500 device to estimate central systolic blood pressure (cSBP) and aPWV. ARCSolver estimates of cSBP and aPWV, on the basis of brachial cuff measurements, were compared pair-wise with results from the tonometric SphygmoCor device in 68 individuals (mean age 51±18 years). We used variation estimates, correlation coefficients, age group-related t-tests, and the Bland-Altman method to analyze the reproducibility and agreement of the two methods. cSBP reproducibility expressed as variability was 14.9% for ARCSolver and 11.6% for SphygmoCor. PWV reproducibility was better for ARCSolver, with a variation estimate of 6.5%, compared with 20.9% using SphygmoCor. The mean cSBP difference was 0.5 mmHg (SD 6.9 mmHg) and 0.32 m/s (SD 1.20 m/s) for PWV, respectively. The age-related differences between ARCSolver and SphygmoCor are in line with previous studies. Bland-Altman plots showed considerable agreement between the two methods without signs of systematic bias. These results show that the combined application of the ARCSolver method with the VaSera VS-1500 device is feasible and the results are comparable with tonometric determination of cSBP and aPWV. This successful application of the ARCSolver may potentially help to improve cardiovascular risk stratification and prevention at an early stage in a community setting.
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Papers by Christopher Mayer