Correlation and comparison of magnetic and electric detection of small intestinal electrical activity

Abstract

superconducting quantum interference device magnetometer; basic electrical rhythm; spectral analysis; volume conductor; small intestine; electrical control activity; electrical recordings SMOOTH MUSCLE in the gastrointestinal tract displays two types of electrical activities. A high-frequency spiking activity known as the electrical response activity is associated with muscle contraction, whereas an oscillating slow wave, known as the electrical control activity or basic electrical rhythm (BER), is present continuously (8, 9, 24). The BER has typically been detected with invasive serosal electrodes that measure the local potential difference of a section of bowel. Recently, Chen et al. (6) reported detecting the human small bowel BER using cutaneous electrodes. To record small bowel BER, a band-pass filter was used to filter out all other biologically active tissues (stomach, heart, and colon). The results indicate that the small bowel potentials result in low-amplitude cutaneous potentials that give a low signal-to-noise ratio. Moreover, the studies by Chen et al. (6) involved subjects in whom the jejunum had been attached to the abdominal wall, providing for increased electrical contact between the bowel and the cutaneous electrode. Presumably, even lower signal-to-noise ratios than Chen et al. (6) reported would be obtained if the direct electrical contact between the bowel and the cutaneous electrode, provided by attaching the bowel segment to the abdominal wall, were broken.Because magnetic fields are not attenuated by lowconductivity layers such as those found in the abdominal wall, another option is to measure the magnetic field produced by small bowel electrical activity (27). Biomagnetic fields are typically several orders of magnitude smaller than the magnetic field of the Earth, so a sensitive detection device is necessary. Superconducting quantum interference device (SQUID) magnetometers are able to detect the weak magnetic fields of biological origin. Previous studies have shown that SQUIDS can detect small intestine BER in vitro (25) and in vivo (11). Magnetoencephalography researchers routinely measure the magnetic field of the brain (27), which is at least an order of magnitude smaller than the magnetic field of the small intestine (21).We present an experiment to examine the effect of a nonconducting layer placed between the small bowel and the abdominal wall on the transabdominal magnetic field, the serosal potential, and the cutaneous potential. We hypothesized that the magnetic fields of small bowel electrical activity recorded with the SQUID would correlate with the potentials measured with invasive electrodes and would not be attenuated by the placement of a nonconducting layer between the bowel and the abdominal wall. Transabdominal magnetic measurements are not expected to suffer from the same problems (attenuation and smoothing by electrically insulating layers) as cutaneous electrical recordings. A previous study utilizing a mathematical model for the magnetic fields and electric poten...

Biomagnetic detection of gastric electrical activity in normal and vagotomized rabbits

“…In a previous paper, we showed that the magnetic field from intestinal smooth muscle recorded outside the abdomen correlated highly with serosal electrode recordings. 15 We have also shown that the changes in small bowel electrical activity caused by intestinal ischaemia are reflected in SQUID recordings. 16 We showed that SQUID recordings were able to non-invasively detect the different frequencies of gastric magnetic fields (GMFs) at about 3 cpm and intestinal magnetic fields from 8 to 12 cpm, and that the locations of these frequencies was consistent with the known slow wave frequency profile of the gastrointestinal tract.…”

Magnetogastrographic detection of gastric electrical response activity in humans

“…In 1997, Bradshaw et al showed that a high degree of correlation exists between the ECA frequency values determined using EGG and MGG (Bradshaw et al 1997). Whereas bioelectric fields depend on tissue permittivity and are therefore much attenuated by the multiple layers of electrical insulators of the abdominal walls and omentum, magnetic fields depend on the permeability of biological tissues, which is nearly equal to that of free space.…”

Prony’s method implementation for slow wave identification of electroenterogram signals

“…However, this method entails several technical and intestinal signal coincides with the repetition rate of the internal intestinal SW both in physiological conditions [4] and in pathological conditions [8]. Nevertheless, the clinical application of surface EEnG recording still poses a series of difficulties: Surface-recorded myoelectrical signals are very weak [5,8], due to spatial filtering and the insulating effects of the abdominal layers [8]. In addition, external EEnG recording is contaminated by strong physiological interferences: cardiac activity, respiration, very lowfrequency components, and movement artifacts.…”

“…None of these methods can yet be used in clinical diagnosis, either because they require high-cost equipment, or because they are still in the experimental stage. The identifi cation of bowel slow wave (SW) activity at the abdominal surface has been accomplished by other authors [4,6,8]. In dogs, it has been proven that the dominant frequency of the external myoelectrical…”