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Wavelet analysis of scaling properties of gastric electrical activity

Bruce J. West,¹ Artur Maciejewski,² Miroslaw Latka,² Tadeusz Sebzda,³ Zbigniew Swierczynski,⁴ Sylwia Cybulska-Okoow,⁵ and Eugeniusz Baran⁵

¹Mathematical and Information Science Directorate, Army Research Office, Research Triangle Park, North Carolina; ²Institute of Physics, Wroclaw University of Technology; ³Department of Pathophysiology, Wroclaw Medical University; ⁴Department of Electronic and Photonic Metrology, Wroclaw University of Technology; and ⁵Department of Dermatology, Venerology and Allergology, Wroclaw University of Medicine, Wroclaw, Poland

Submitted 8 December 2004 ; accepted in final form 10 May 2006

We present a novel approach to the analysis of fluctuations in human myoelectrical gastric activity measured noninvasively from the surface of the abdomen. The time intervals between successive maxima of the wavelet transformed quasi-periodic electrogastrographic waveform define the gastric rate variability (GRV) time series. By using the method of average wavelet coefficients, the statistical fluctuations in the GRV signal in healthy individuals are determined to scale in time. Such scaling was previously found in a variety of physiological phenomena, all of which support the hypothesis that physiological dynamics utilize fractal time series. We determine the scaling index in a cohort of 17 healthy individuals to be 0.80 ± 0.14, which compared with a set of surrogate data is found to be significant at the level P < 0.01. We also determined that the dynamical pattern, so evident in the spectrum of average wavelet coefficients of the GRV time series of healthy individuals, is significantly reduced in a cohort of systemic sclerosis patients having a scaling index 0.64 ± 0.17. These results imply that the long-term memory in GRV time series is significantly reduced from healthy individuals to those with systemic sclerosis. Consequently, this disease degrades the complexity of the underlying gastrointestinal control system and this degradation is manifest in the loss of scaling in the GRV time series.

electrogastrography; gastric rate variability; systemic sclerosis; fractal physiology; average wavelet coefficients; fractal time series