Estimation procedures affect the center of pressure frequency analysis

Even though frequency analysis of body sway is widely applied in clinical studies, the lack of standardized procedures concerning power spectrum estimation may provide unreliable descriptors. Stabilometric tests were applied to 35 subjects (20-51 years, 54-95 kg, 1.6-1.9 m) and the power spectral density function was estimated for the anterior-posterior center of pressure time series. The median frequency was compared between power spectra estimated according to signal partitioning, sampling rate, test duration, and detrending methods. The median frequency reliability for different test durations was assessed using the intraclass correlation coefficient. When increasing number of segments, shortening test duration or applying linear detrending, the median frequency values increased significantly up to 137%. Even the shortest test duration provided reliable estimates as observed with the intraclass coefficient (0.74-0.89 confidence interval for a single 20-s test). Clinical assessment of balance may benefit from a standardized protocol for center of pressure spectral analysis that provides an adequate relationship between resolution and variance. An algorithm to estimate center of pressure power density spectrum is also proposed.

The effect of an aerobic training program on the electrical remodeling of the heart: high-frequency components of the signal-averaged electrocardiogram are predictors of the maximal aerobic power

Increased heart rate variability (HRV) and high-frequency content of the terminal region of the ventricular activation of signal-averaged ECG (SAECG) have been reported in athletes. The present study investigates HRV and SAECG parameters as predictors of maximal aerobic power (VO2max) in athletes. HRV, SAECG and VO2max were determined in 18 high-performance long-distance (25 ± 6 years; 17 males) runners 24 h after a training session. Clinical visits, ECG and VO2max determination were scheduled for all athletes during thew training period. A group of 18 untrained healthy volunteers matched for age, gender, and body surface area was included as controls. SAECG was acquired in the resting supine position for 15 min and processed to extract average RR interval (Mean-RR) and root mean squared standard deviation (RMSSD) of the difference of two consecutive normal RR intervals. SAECG variables analyzed in the vector magnitude with 40-250 Hz band-pass bi-directional filtering were: total and 40-æV terminal (LAS40) duration of ventricular activation, RMS voltage of total (RMST) and of the 40-ms terminal region of ventricular activation. Linear and multivariate stepwise logistic regressions oriented by inter-group comparisons were adjusted in significant variables in order to predict VO2max, with a P < 0.05 considered to be significant. VO2max correlated significantly (P < 0.05) with RMST (r = 0.77), Mean-RR (r = 0.62), RMSSD (r = 0.47), and LAS40 (r = -0.39). RMST was the independent predictor of VO2max. In athletes, HRV and high-frequency components of the SAECG correlate with VO2max and the high-frequency content of SAECG is an independent predictor of VO2max.

An automatic selections method for cerebral blood flow autoregulation signals from neonates

Interpretation and quantification of cerebral blood flow autoregulation can be carreid out from step responses to arterial blood pressure changes estimated with various identification methods. However estimates usually need to be visually inspected to rejected some that are not physiologically acceptable...

Clinical assessment of the effect of digital filtering on the detection of ventricular late potentials

Ventricular late potentials are low-amplitude signals originating from damaged myocardium and detected on the body surface by ECG filtering and averaging. Digital filters present in commercial equipment may interfere with the ability of arrhythmia stratification. We compared 40-Hz BiSpec (BI) and classical 40- to 250-Hz band-pass Butterworth bidirectional (BD) filters in terms of impact on time domain variables and diagnostic properties. In a transverse retrospective age-adjusted case-control study, 221 subjects with sinus rhythm without bundle branch block were divided into three groups after signal-averaged ECG acquisition: GI (N = 40), clinically normal controls, GII (N = 158), subjects with coronary heart disease without sustained monomorphic ventricular tachycardia (SMVT), and GIII (N = 23), subjects with heart disease and documented SMVT. Conventional variables analyzed from vector magnitude data after averaging to 0.3 æV final noise were obtained by application of each filter to the averaged signal, and evaluated in pairs by numerical comparison and by diagnostic agreement assessment, using conventional and optimized thresholds of normality. Significant differences were found between BI and BD variables in all groups, with diagnostic results showing significant disagreement between both filters [kappa value of 0.61 (P<0.05) for GII and 0.31 for GIII (P = NS)]. Sensitivity for SMVT was lower with BI than with BD (65.2 vs 91.3 percent, respectively, P<0.05). Filters provided significantly different numerical and diagnostic results and the BI filter showed only limited clinical application to risk stratification of ventricular arrhythmia

Capecitabine (CCB) en cáncer de mama metastásico: experiencia institucional / Capecitabine (CCB) in metastatic breast cancer: institutional experience

Introducción: CCB es una nueva fluoropirimidina que suma a las ventajas de la vía oral, su aceptable toxicidad y actividad, con bajo perfil costo-beneficio para el tratamiento paliativo del cáncer de mama. Objetivos: analizar nuestra experiencia en forma retrospectiva en relación a la utilización de CCB, en pacientes con cáncer de mama metastásico. Determinar su eficacia y perfil de toxicidad administrado por vía oral en régimen intermitente. Materiales y métodos: se evaluaron las historias clínicas de 67 pacientes (pts.), con diagnóstico de cáncer de mama metastásico que recibieron tratamiento con CCB, entre julio de 1999 y marzo de 2002, en el Instituto Alexander Fleming. Características de la población: edad mediana: 58 años (rango 32-79); receptores hormonales (RH) positivos 64,17 por ciento; el intervalo libre de enfermedad desde el diagnóstico a la primera manifestación metastásica, (ILE) fue de 115,5 meses (rango 0-231); presentaron patrón metastásico visceral (hepático y pulmonar) 41/67 pts., (61,19 por ciento). La mediana de líneas de tratamiento hormonal previo fue de 2 (rango 0-4) y de quimioterapia 4 (rango 0-7). El 17,91 por ciento de las pts. fueron resistentes a antraciclinas y el 79,10 por ciento, fueron expuestas a taxanos. En 6 pts. se efectuó tratamiento con altas dosis de quimioterapia. Las pacientes fueron tratadas con dosis de 1,5 a 2,5 gramos...

Sistema computadorizado para monitorizaçäo cardio-respiratória / Computerized system for cardiorespiratory monitoring

Um sistema baseado em computador pessoal é usado para a monitorização cardio-respiratória de pacientes, em tempo-real, integrando sinais obtidos de diferentes equipamentos: monitor fisiológico (ECG), espectrômetro de massa respiratória (EMR: frações gasosas) e pneumotacógrafo (fluxo ventilatório). O sistema detecta complexos QRS e ciclos respiratórios, e calcula freqüência cardíaca e vários parâmetros respiratórios. O desempenho dos algoritmos é avaliado com sinais simulados, o MIT-BIH Arrhytmia Database e experimentos in-vivo. O sistema é empregado em pesquisa da fisiologia do exercício

Abstract- A modular system based on a personal computer is used to perform real-time cardio-respiratory monitoring of patients. integrating data from different equipments: a bed side monitor (ECG ), a respiratory mass spectrometer (RMS: gas fractions) and a pneumothacograph (respiratory tlow). The system includes an automatic detection of the QRS complexes and the respiratory cycles and it calculates heart rate and severa! respiratory parameters. The performance of the algorithms is estimated with simulated data. the MIT-BIH Arrhythrnia Database and in rivo experirnents. This system is being used for research in exercise physiology

Recursos úteis ao desenvolvimento de microcomputadores para processamento de sinais em tempo-real / Useful tools for the development of microcomputers applied to real-time signal processing

A equipe vem há vários anos trabalhando no desenvolvimento de um monitor automático de arritmias cardíacas. Como subprodutos dessa linha de investigaçäo foram desenvolvidos microcomputadores de uso geral adequados ao processamento de sinais em tempo-real, bem como foi criada uma infra-estrutura que possibilita o desenvolvimento de microcomputadores dedicados a funçöes específicas de forma rápida e a baixo-custo. Vários recursos de "hardware" e "spftware" foram implementados com vistas a conferir maior capacidade de processamento a esses sistemas. Este trabalho apresenta alguns dos recursos mais úteis empregados, bem como procura analisar os efeitos da utilizaçäo dos mesmos sobre o desempenho geral dos sistema. Säo abordados os seguintes tópicos: conversores A/D com entrada multiplexada e um dispositivo de amostra e retençäo para cada entrada, técnica de exibiçäo de sinais em tempo-real baseada em memórias de duplo acesso, avaliaçäo de tempo de execuçäo de algoritmos para processamento em tempo-real, armazenadores circulares de amostras e programas monitores para desenvolvimento de sistemas