Marcelino Martinez_Sober⁽¹⁾, Juan Guerrero⁽²⁾, Gustavo Camps i Valls⁽³⁾, Antonio J. Serrano López⁽⁴⁾, José David Martín Guerrero^(5)
(1)Universidad de Valencia - Burjassot. Spain
⁽²⁾Departamento de Electrónica. Universidad de Valencia - Burjassot. Spain
⁽³⁾Universitat de València - Burjassot, Valencia. Spain
⁽⁴⁾Dpto. Electrónica. Universidad de Valencia - Burjasot. Spain
⁽⁵⁾G.P.D.S. Departament d´Enginyeria Electrònica. Universitat de València - Burjassot. Spain

	[Cardiolovascular Diseases]	[Health Informatics]

TIME SERIES PROCESSING

The study of time series in Cardiology is applied defining the occurrence of the wave R of the electrocardiogram (ECG) as an event, and the statistics associated to the interval among pulses (interval RR) are studied. We talk then of variability of the heart rhythm (HRV). The study of the HRV is usually carried out with short registrations (from 2 to 5 minutes) and long ones (24 hours: Holter), and it provides information on the operation of the physiologic mechanisms of regulation of the HRV. In the spectrum of the HRV they can be distinguished 4 bands:

1.-ULF: associated with the modulation of the rhythm to hormonal influence, etc. Cycles from 2.8 hours to 5.6 minutes).

2.-VLF: associated to the temperature, etc. Cycles from 5.6 minutes to 25 seg.

3.-LF: associated to the vegetative system. Cycles from 25 to 6.7 seg.

4.-HF: associated to the breathing cycles from 6.7 seg to 2.5 seg.

In this work a program developed for the standard study ⁽³⁾ of series RR Holter is presented.

The program for processing the signal has been developed with Matlab v4.2. The one processed is carried out in the following phases:

1.-Detection of non valid tracts and anomalous pulses (echtopics): The echtopic detection is made checking a value of more joining that 20% of the previous RR, or a value outside of the range RR_min - RR_max. If the number of data to eliminate is superior to a maximum value (usually, 20%), the series is rejected.

2.-Elimination of non valid periods and echtopics: It is eliminated the echtopic pulse and the following one (compensatory pause), and it is substituted by values RR obtained by some of the methods: to) Eliminate and Paste; b) Lineal Interpolation; c) Splines Interpolation; d) AR predicction. The relative number and the relative duration of the intervals omitted or interpolated RR are saved ⁽⁴⁾. Figure 4 fig. 4 shows an original RR series with echtopics and non-valid tracts, and after eliminating both types.

3.-Division in short series: the series is divided in tracts of 5 ´. The study in the frequency domain is carried out averaging the values of the bands LF and HF calculated for each subseries of 5 ´, and the obtained sampled series is undersampled to calculate VLF.

4.-Sampling of the five minutes series. Due to the RR series is not uniformly sampled a continuous signal in the time that is later on regularly sampled before carrying out the spectrum study is obtained by means of interpolation. The program admits polynomials interpolation methods of order 0, 1 or splines.

5.-Elimination of tendencies and calculation of the spectrum with Welch method.

6.-Calculation of parameters in the domain of the frequency for series of 5 ´: to) MLF (Frequency of the maximum in LF); b) MHF (Frequency of the maximum in HF); c) PLF (Power in the band LF); d) PHF (Power in the band HF); and) PLFN (normalised Power PLF/(PLF+PHF)); f) PHFN (normalised Power PHF/(PLF+PHF)); g) LF_HF (PLF/PHF rate).

7.- Undersampling of the series of 5 ´ to study the band VLF of the total series.

8.-Obtaining of the total spectrum and parameters in VLF: h) MVLF (Frequency of the maximum in VLF); i) PVLF (Power in the band VLF).

9.-Calculation of the parameters in the time domain: ANN (mean RR), SDNN (std of all the RR), RMSSD (value RMS of the differences among adjacent RR), CV (variance coefficient: SDNN/ANN), SDANN (std of the ANN of the subseries of 5 ´), Triangular index (integral of the histogram / maximum value).

Discussion Board

Any Comment to this presentation?

[ABSTRACT] [INTRODUCTION] [DIGITALISATION AND TIME SERIES OBTENTION] [TIME SERIES PROCESSING] [IMAGES] [CONCLUSIONS] [ACKNOWLEDGEMENTS] [BIBLIOGRAPHY] [Discussion Board]

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	[Cardiolovascular Diseases]	[Health Informatics]

Marcelino Martinez_Sober, Juan Guerrero, Gustavo Camps i Valls, Antonio J. Serrano López, José David Martín Guerrero
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Last update: 14/01/00