Research on Biomedical Engineering
http://www.rbejournal.periodikos.com.br/article/5889fbcc5d01231a018b47d7
Research on Biomedical Engineering
Original Article

PROPRIEDADES ESTATÍSTICAS DE PARÂMETROS OBTIDOS DE SINAIS DE ULTRA-SOM DOPPLER

STATISTICAL PROPERTIES OF PARAMETERS EXTRACTED FROM DOPPLER ULTRASOUND WAVEFORMS

Fuentes, Gonzalo G.T.; Filho, Willian S.; Brum, O.F.; Panerai, R.B.

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Resumo

A variabilidade, distribuição e variação longitudinal de 13 parâmetros obtidos a partir da forma de onda de velocidade de fluxo sanguineo, medida com ultra-som Doppler na artéria femoral, foram estudados em 9 registros de longa duração obtidos em 7 pacientes. Os sinais foram gravados em fita magnética, juntamente com o eletrocardiograma, e analisados em um computador digital. O processamento desses dados forneceu o coeficiente de variação para cada um dos indices estudados e os graus de liberdade por ponto, extraidos a partir da função de autocorrelação. A influência da frequência cardiaca na variabilidade de cada um dos parâmetros foi também verificada através de técnicas de correlação cruzada. Como resultado final são fornecidos os dados necessários para o dimensionamento correto de amostras para estimação de cada um dos 13 parâmetros em estudos clinicos.

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Abstract

The statistical properties of parameters extracted from non-invasive blood velocity waveforms, measured in the common femoral artery of humans, using Doppler continuous wave ultrasound has been studied in nine records obtained from seven patients. Three of these had obstructive arterial disease confirmed by arteriography. A total of thirtheen parameters have been analysed: systolic peak velocity, reverse diastolic peak velocity, area of reverse velocity, mean velocity, pulsatility index; time intervals between the R wave of the ECG and a) the peak systolic velocity, b) the 50% level of the rising phase of systolic flow, c) the 50% leveI of the falling phase of systolic flow; time difference between b) and c), proximal damping coefficient, variance of forward velocity, maximun derivate, and minimum derivate. The Doppler signal and the electro-cardiogram (ECG) were sampled at 200 Hz using a PDP 11/34 computer with 16 kwords of core and permanently stored on diskettes. The R wave of the ECG was used as a time reference, and the parameters were automatically extracted for each heart cycle and structured in records containing data from 112 ininterrupted beats. These records were then analysed considering its time varying pattern, coefficient of variation, autocorrelation function, cross correlatiori with the heart rate signal, and re-ordered sequence for each parameter. In general the results show that parameters depending on the amplitude of systolic and reverse velocities present a slow varying component whose origin cannot be identified at present. On the other hand, the time interval derived parameters only show random fluctuations. The coefficient of variation and the distribution (re-ordered sequences) curves allow a better understanding of the variability of the parameters under investigation and adequate criteria for the experimental planniog of future research.
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