Biomedical subjects

Mateo Aboy

Publications and source records attributed to Mateo Aboy.

15 recordsLinked to original sources

PubMed2006

Unsupervised classification of ventricular extrasystoles using bounded clustering algorithms and morphology matching.

Ventricular extrasystoles (VE) are ectopic heartbeats involving irregularities in the heart rhythm. VEs arise in response to impulses generated in some part of the heart different from the sinoatrial node. These are caused by the premature discharge of a ventricular ectopic focus. VEs after myocardial infarction are associated with increased mortality. Screening of VEs is typically a manual and time consuming task that involves analysis of the heartbeat morphology, QRS duration, and variations of the RR intervals using long-term electrocardiograms. We describe a novel algorithm to perform automatic classification of VEs and report the results of our validation study. The proposed algorithm makes use of bounded clustering algorithms, morphology matching, and RR interval length to perform automatic VE classification without prior knowledge of the number of classes and heartbeat features. Additionally, the proposed algorithm does not need a training set.

Algorithms↗

PubMed2006

Reliability and accuracy of heart rate variability metrics versus ECG segment duration.

Despite the exponential growth in heart rate variability (HRV) research, the reproducibility and reliability of HRV metrics continues to be debated. We estimated the reliability of 11 metrics calculated from 5 min records. We also compared the accuracy of the HRV metrics calculated from ECG records spanning 10 s to 10 min as compared with the metrics calculated from 5 min records. The mean heart rate was more reproducible and could be more accurately estimated from very short segments (<1 min) than any of the other HRV metrics. HRV metrics that effectively highpass filter the R-R interval series were more reliable than the other metrics and could be more accurately estimated from very short segments. This indicates that most of the HRV is caused by drift and nonstationary effects. Metrics that are sensitive to low frequency components of HRV have poor repeatability and cannot be estimated accurately from short segments (<10 min).

Adult↗

PubMed2006

An automatic algorithm for stationary segmentation of extracellular microelectrode recordings.

Extracellular microelectrode recordings (MER) often contain artifact from a variety of sources that confound traditional signal-processing techniques that require stationary signal segments. We designed an algorithm to locate the longest stationary segment of MER signals. In this paper we provide a description of the segmentation algorithm and its performance assessment. Simulation results demonstrate that the automatic segmentation algorithm we proposed is capable of accurately identifying the boundaries of the longest stationary segments in MER signals. In our simulation study the segmentation algorithm correctly identified the boundaries of the longest MER stationary segments in 99.5% of the cases.

Algorithms↗

PubMed2006

Complex analysis of intracranial hypertension using approximate entropy.

OBJECTIVE: To determine whether decomplexification of intracranial pressure dynamics occurs during periods of severe intracranial hypertension (intracranial pressure >25 mm Hg for >5 mins in the absence of external noxious stimuli) in pediatric patients with intracranial hypertension. DESIGN: Retrospective analysis of clinical case series over a 30-month period from April 2000 through January 2003. SETTING: Multidisciplinary 16-bed pediatric intensive care unit. PATIENTS: Eleven episodes of intracranial hypertension from seven patients requiring ventriculostomy catheter for intracranial pressure monitoring and/or cerebral spinal fluid drainage. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: We measured changes in the intracranial pressure complexity, estimated by the approximate entropy (ApEn), as patients progressed from a state of normal intracranial pressure (<25 mm Hg) to intracranial hypertension. We found the ApEn mean to be lower during the intracranial hypertension period than during the stable and recovering periods in all the 11 episodes (0.5158 +/- 0.0089, 0.3887 +/- 0.077, and 0.5096 +/- 0.0158, respectively, p < .01). Both the mean reduction in ApEn from the state of normal intracranial pressure (stable region) to intracranial hypertension (-0.1271) and the increase in ApEn from the ICH region to the recovering region (0.1209) were determined to be statistically significant (p < .01). CONCLUSIONS: Our results indicate that decreased complexity of intracranial pressure coincides with periods of intracranial hypertension in brain injury. This suggests that the complex regulatory mechanisms that govern intracranial pressure may be disrupted during acute periods of intracranial hypertension. This phenomenon of decomplexification of physiologic dynamics may have important clinical implications for intracranial pressure management.

Acute Disease↗

PubMed2006

The individual RDH index: a novel vector index for statistical assessment of antihypertensive treatment reduction, duration, and homogeneity.

We propose a new vector index for the statistical assessment of antihypertensive treatment duration and homogeneity from ambulatory blood pressure monitoring. We termed this approach for evaluating and comparing blood pressure coverage offered by antihypertensive drugs over 24 h as the reduction-duration-homogeneity index. The reduction-duration-homogeneity index is a three-component vector index that incorporates information about the reduction, duration, and homogeneity of antihypertensive treatment, as well as their statistical significance. The advantages of the reduction-duration-homogeneity index are demonstrated by several comparative examples.

Adult↗

PubMed2006

The population RDH index: a novel vector index and graphical method for statistical assessment of antihypertensive treatment reduction, duration, and homogeneity.

Current indices used in the evaluation of antihypertensive treatment duration and homogeneity such as the trough-peak, smoothness index, and normalized smoothness index were designed to be applied to ambulatory blood pressure monitoring recordings from individual participants. Evaluation of antihypertensive treatment in populations is often carried out by calculating these individual indices for each of the participants and providing summarizing statistics about the population, such as the mean and median. We describe a new population vector index and graphical method for the statistical assessment of antihypertensive treatment reduction, duration, and homogeneity (RDH) from ambulatory blood pressure monitoring. The population (RDH) was specifically designed as a tool to evaluate and compare blood pressure coverage offered by antihypertensive drugs over 24 h in populations. The population RDH is a three-component vector index that incorporates information about the reduction, duration, and homogeneity of antihypertensive treatment, as well as their statistical significance over the 24 h period. In addition to defining the RDH index, in this paper we also demonstrate its usefulness and advantages as an index and graphical method for antihypertensive treatment duration and homogeneity assessment by using it to analyze two data sets.

Adult↗

PubMed2006

Variability, regularity, and complexity of time series generated by schizophrenic patients and control subjects.

We analyzed time series generated by 20 schizophrenic patients and 20 sex- and age-matched control subjects using three nonlinear methods of time series analysis as test statistics: central tendency measure (CTM) from the scatter plots of first differences of data, approximate entropy (ApEn), and Lempel-Ziv (LZ) complexity. We divided our data into a training set (10 patients and 10 control subjects) and a test set (10 patients and 10 control subjects). The training set was used for algorithm development and optimum threshold selection. Each method was assessed prospectively using the test dataset. We obtained 80% sensitivity and 90% specificity with LZ complexity, 90% sensitivity, and 60% specificity with ApEn, and 70% sensitivity and 70% specificity with CTM. Our results indicate that there exist differences in the ability to generate random time series between schizophrenic subjects and controls, as estimated by the CTM, ApEn, and LZ. This finding agrees with most previous results showing that schizophrenic patients are characterized by less complex neurobehavioral and neuropsychologic measurements.

Adolescent↗

PubMed2006

Interpretation of the Lempel-Ziv complexity measure in the context of biomedical signal analysis.

Lempel-Ziv complexity (LZ) and derived LZ algorithms have been extensively used to solve information theoretic problems such as coding and lossless data compression. In recent years, LZ has been widely used in biomedical applications to estimate the complexity of discrete-time signals. Despite its popularity as a complexity measure for biosignal analysis, the question of LZ interpretability and its relationship to other signal parameters and to other metrics has not been previously addressed. We have carried out an investigation aimed at gaining a better understanding of the LZ complexity itself, especially regarding its interpretability as a biomedical signal analysis technique. Our results indicate that LZ is particularly useful as a scalar metric to estimate the bandwidth of random processes and the harmonic variability in quasi-periodic signals.

Algorithms↗

PubMed2005

Methodological considerations in the evaluation of the duration of action of antihypertensive therapy using ambulatory blood pressure monitoring.

We review the potential limitations of the two current methodologies for evaluating the duration of action of antihypertensive therapy: the smoothness index (SI) and the trough : peak ratio (TP). We propose a simple correction factor for the SI. The correction factor prevents the SI from reaching erroneous high values in situations in which the reduction in blood pressure (BP) is inadequate but very homogeneous. We refer to the corrected index as the SIn (normalized SI).

Antihypertensive Agents↗

PubMed2005

Adaptive modeling and spectral estimation of nonstationary biomedical signals based on Kalman filtering.

We describe an algorithm to estimate the instantaneous power spectral density (PSD) of nonstationary signals. The algorithm is based on a dual Kalman filter that adaptively generates an estimate of the autoregressive model parameters at each time instant. The algorithm exhibits superior PSD tracking performance in nonstationary signals than classical nonparametric methodologies, and does not assume local stationarity of the data. Furthermore, it provides better time-frequency resolution, and is robust to model mismatches. We demonstrate its usefulness by a sample application involving PSD estimation of intracranial pressure signals (ICP) from patients with traumatic brain injury (TBI).

Computer Simulation↗

PubMed2005

Interpretation of approximate entropy: analysis of intracranial pressure approximate entropy during acute intracranial hypertension.

We studied changes in intracranial pressure (ICP) complexity, estimated by the approximate entropy (ApEn) of the ICP signal, as subjects progressed from a state of normal ICP (< 20-25 mmHg) to acutely elevated ICP (an ICP "spike" defined as ICP > 25 mmHg for < or = 5 min). We hypothesized that the measures of intracranial pressure (ICP) complexity and irregularity would decrease during acute elevations in ICP. To test this hypothesis we studied ICP spikes in pediatric subjects with severe traumatic brain injury (TBI). We conclude that decreased complexity of ICP coincides with episodes of intracranial hypertension (ICH) in TBI. This suggests that the complex regulatory mechanisms that govern intracranial pressure are disrupted during acute rises in ICP. Furthermore, we carried out a series of experiments where ApEn was used to analyze synthetic signals of different characteristics with the objective of gaining a better understanding of ApEn itself, especially its interpretation in biomedical signal analysis.

Adolescent↗

PubMed2005

An automatic beat detection algorithm for pressure signals.

Beat detection algorithms have many clinical applications including pulse oximetry, cardiac arrhythmia detection, and cardiac output monitoring. Most of these algorithms have been developed by medical device companies and are proprietary. Thus, researchers who wish to investigate pulse contour analysis must rely on manual annotations or develop their own algorithms. We designed an automatic detection algorithm for pressure signals that locates the first peak following each heart beat. This is called the percussion peak in intracranial pressure (ICP) signals and the systolic peak in arterial blood pressure (ABP) and pulse oximetry (SpO2) signals. The algorithm incorporates a filter bank with variable cutoff frequencies, spectral estimates of the heart rate, rank-order nonlinear filters, and decision logic. We prospectively measured the performance of the algorithm compared to expert annotations of ICP, ABP, and SpO2 signals acquired from pediatric intensive care unit patients. The algorithm achieved a sensitivity of 99.36% and positive predictivity of 98.43% on a dataset consisting of 42,539 beats.

Algorithms↗

PubMed2004

Prediction of paroxysmal atrial fibrillation by analysis of atrial premature complexes.

Currently, no reliable method exists to predict the onset of paroxysmal atrial fibrillation (PAF). We propose a predictor that includes an analysis of the R-R time series. The predictor uses three criteria: the number of premature atrial complexes (PAC) not followed by a regular R-R interval, runs of atrial bigeminy and trigeminy, and the length of any short run of paroxysmal atrial tachycardia. An increase in activity detected by any of these three criteria is an indication of an imminent episode of PAF. Using the Physionet database of the Computers in Cardiology 2001 Challenge, the predictor achieved a sensitivity of 89% and a specificity of 91%.

Algorithms↗

PubMed2004

A microcontroller-based portable electrocardiograph recorder.

We describe a low cost portable Holter design that can be implemented with off-the-shelf components. The recorder is battery powered and includes a graphical display and keyboard. The recorder is capable of acquiring up to 48 hours of continuous electrocardiogram data at a sample rate of up to 250 Hz.

Amplifiers, Electronic↗

PubMed2004

A novel algorithm to estimate the pulse pressure variation index deltaPP.

We designed a new methodology to estimate the pulse pressure variation index (deltaPP) in arterial blood pressure (ABP). The method uses automatic detection algorithms, kernel smoothing, and rank-order filters to continuously estimate deltaPP. The technique can be used to estimate deltaPP from ABP alone, eliminating the need for simultaneously acquiring airway pressure.

Algorithms↗