Identification of the slow wave component of the electroenterogram from Laplacian abdominal surface recordings in humans

Abstract

The electroenterogram (EEnG) is a surface recording of the myoelectrical activity of the smooth muscle layer of the small intestine. It is made up of two signals: a low-frequency component, known as the slow wave (SW), and high-frequency signals, known as spike bursts (SB). Most methods of studying bowel motility are invasive due to the difficult anatomic access of the intestinal tract. Abdominal surface EEnG recordings could be a noninvasive solution for monitoring human intestinal motility. However, surface EEnG recordings in humans present certain problems, such as the low amplitude of the signals and the influence of physiological interference such as the electrocardiogram (ECG) and respiration. In this study, a discrete estimation of the abdominal surface Laplacian potential was obtained using Hjorth's method. The objective was to analyze the enhancement given by Laplacian EEnG estimation compared to bipolar recordings. Eight recording sessions were carried out on eight healthy human volunteers in a state of fasting. First, the ECG interference content present in the bipolar signals and in the Laplacian estimation were quantified and compared. Secondly, to identify the SW component of the EEnG, respiration interference was removed by using an adaptive filter, and spectral estimation techniques were applied. The following parameters were obtained: the dominant frequency (DF) of the signals, stability of the rhythm (RS) of the DF detected and the percentage of DFs within the typical frequency range for the SW (TFSW). Results show the better ability of the Laplacian estimation to attenuate ECG interference, as compared to bipolar recordings. As regards the identification of the SW component of the EEnG, after removing respiration interference, the mean value of the DF in all abdominal surface recording channels and in their Laplacian estimation ranged from 0.12 to 0.14 Hz (7.3 to 8.4 cycles min(-1) (cpm)). Furthermore in 80% of the cases, the detected DFs were inside the typical human SW frequency range, and the ratio of frequency change in the surface bipolar and Laplacian estimation signals, in 90% of the cases, was within the frequency change accepted for human SW. Significant statistical differences were also found between the DF of all surface signals (bipolar and Laplacian estimation) and the DF of respiration. In conclusion, it was demonstrated that the discrete Laplacian potential estimation attenuated the physiological interference present in bipolar surface recordings, especially ECG. Furthermore, a slow frequency component, whose frequency, rhythm stability and amplitude fitted with the SW patterns in humans, was identified in bipolar and Laplacian estimation signals. This could be a useful non-invasive tool for monitoring intestinal activity by abdominal surface recordings.

Enhancement of the non-invasive electroenterogram to identify intestinal pacemaker activity

“…However, the applicability of adaptive filtering for this purpose has been questioned by some authors (Liang, Lin, & Mccallum 2000d;Wang, Cheung, & Chen 1999c), given that it requires a reference signal that is the comprehensive signal of the various interferences to be removed. Therefore, its ability to reduce interferences strongly depends on the reference signal which is used Lin and Chen 1994;Prats-Boluda et al 2007). Like the adaptive filter, in this work it has been proved that the EMD method could also be employed to reduce the respiratory interference in external myoelectrical recording, In this context, the advantage of the EMD-based method lies in the fact that there is no need to find an optimal reference signal, since it is only necessary to know the respiration frequency.…”

“…Besides the above mentioned method, other techniques, such as adaptive filtering Lin and Chen 1994;Prats-Boluda et al 2007) and independent component analysis (ICA) (Irimia and Bradshaw 2005;Wang et al 1999), also have been proposed to remove the interferences from external myoelectrical…”

“…This could explain why the variability of the processed surface signals remains slightly higher than that of internal signals (see table 3). The latest research in this field indicates that the spatial resolution of conventional bipolar surface recordings could be improved by using electrodes based on the estimation of the laplacian of the potential (Prats-Boluda et al 2007). Theoretically, the laplacian of the potential contains the information which is inherent to the potential recording, but it provides better spatial resolution than bipolar recordings of the potential (Prats-Boluda et al 2007).…”

“…The latest research in this field indicates that the spatial resolution of conventional bipolar surface recordings could be improved by using electrodes based on the estimation of the laplacian of the potential (Prats-Boluda et al 2007). Theoretically, the laplacian of the potential contains the information which is inherent to the potential recording, but it provides better spatial resolution than bipolar recordings of the potential (Prats-Boluda et al 2007). This is because the laplacian of the potential is more sensitive to electrical sources which are perpendicular to the abdominal surface, with the result that there is greater rejection of distant signal sources.…”

Estudio espectral del ritmo eléctrico básico del intestino delgado para la monitorización no invasiva del marcapasos intestinal

“…ET. AL, 1993], causando cambios de la línea base de los registros de señales, lo que puede causar una confusión entre la señal respiratoria y la señal intestinal al tener valores de frecuencia cercanos LIN Z. Y., CHEN J. D. 1994;PRATS-BOLUDA G. ET. AL, 2007].…”