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We present a similarity-based searching and pattern matching algorithm that identifies time series data with similar temporal dynamics in large-scale, multi-parameter databases. We represent time series segments by feature vectors that reflect the dynamical patterns of single and multi-dimensional physiological time series. Features include regression slopes at varying time scales, maximum transient...
We describe a novel search engine that is capable of rapid execution of queries concerning changes in the gradients and absolute (and relative) values of multiple irregularly sampled and asynchronous physiological parameters over many time scales. The search engine enables search criteria for multiple physiological parameters using gradient bounds, rates of change, and threshold breeches over various...
To make effective use of web archives such as PhysioNetpsilas multi-terabyte collections of ICU recordings, investigators need robust and flexible tools for finding data relevant to their studies. We have designed and implemented web-based visualization and search tools for this purpose. In addition to selecting recordings with desired demographic, clinical, and technical features, the search tool...
Modern intensive care units (ICUs) employ an impressive array of technologically sophisticated instrumentation to provide detailed measurements of the pathophysiological state of each patient. Providing life support in the ICU is becoming an increasingly complex task, however, because of the growing volume of relevant data from clinical observations, bedside monitors, mechanical ventilators, and a...
Fidelity of the arterial blood pressure (ABP) waveform is often critical to computations that involve processing of the waveform. The ABP waveform may be used for cardiac output (CO) estimation, suppression of ECG-based false alarms, and tracking long term trends such as mean pressure. An abnormal ABP waveform may cause these applications to give undesirable results. In this paper, we present a signal...
Intensive Care Unit (ICU) false alarm rates can be as high as 86%, leading to a desensitization of the clinical attending staff, slowing of response times and even ignoring true alarms. False alarms are commonly caused by single channel artifacts and could be avoided if information from other independent signals were fused to form a more robust hypothesis of the etiology of the alarm. We used a standard...
Time-varying elastance models have been used extensively in the past to simulate the pulsatile nature of cardiovascular waveforms. Frequently, however, one is interested in dynamics that occur over longer time scales, in which case a detailed simulation of each cardiac contraction becomes computationally burdensome. In this paper, we apply circuit-averaging techniques to a periodically driven, closed-loop,...
We have developed a computational model of the cardiovascular system with the aim of analyzing the hemodynamic response to orthostatic stress. Using the model, we investigate the hemodynamic effects of changes in model parameters that are thought to contribute to the syndrome of post-space flight orthostatic intolerance. Our simulations indicate that changes in total blood volume have the largest...
In this paper, we present a simulation study that aims at estimating parameters of a hemodynamic model using observable data typically available in an intensive care unit (ICU). Tracking model parameters in time reveals disease progression, and hence can be very useful for patient monitoring purposes. However, the observable data is generally not rich enough to allow for reliable estimation of all...
A method to segment cardiovascular time series is proposed using ECG-derived metrics. Segmentation of cardiovascular time series into quasi-stationary and low noise segments is important for the construction of models (based around fixed operational points) and the evaluation of a variety of indices, including cardiovascular (such as HRV) and signal quality-based metrics. Noise and activity-related...
Patients that are over-sedated or dangerously agitated in the Intensive Care Unit (ICU) have longer lengths of stays, and poorer outcomes in the ICU. The authors have evaluated heart rate (HR), blood pressure (BP) and respiratory rate (RR) in 2938 patients with 124,591 separate Riker (agitation/sedation) class scores over a three year period. The mean and standard deviation for HR, BP and RR in each...
All personally identifiable information must be removed from patient medical records before the data can be shared with other researchers. We present an automated method of removing protected health information (PHI) from free-text nursing notes taken from a U.S. hospital. We have previously shown that one clinician can locate PHI in nursing notes with an average sensitivity of 0.81, and for teams...
The double-knockout (dKO) mouse model, with homozygous null encoding for the apoE lipoprotein molecule and SRB-I receptor, shows extremely elevated LDL and severely depressed HDL levels in blood serum. The subjects show 100% mortality by the age of 8 weeks, with accompanying cardiac hypertrophy, reduced ejection fraction and high incidence of atherosclerosis and multiple regions of myocardial infarct...
Cardiac output (CO) estimation using arterial blood pressure (ABP) waveforms has been an active area of physiology research over the past century. However, the effectiveness of the estimators has not been extensively studied in a clinical setting. In this paper, we evaluate 11 well-known CO estimators using clinical radial ABP waveforms from the multi-parameter intelligent monitoring for intensive...
In this paper we present a novel Web-based service, available through Physionet (www.physionet.org) that utilizes a Java applet front-end for visualization and integrates seamlessly with WFDB-based back-end CGI scripts to facilitate simple point-and-click user interaction and data annotation. The service allows users to peruse visually all ECG databases available on Physionet through a Web browser...
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