Biomagnetic and bioelectric detection of gastric slow wave activity in normal human subjects--a correlation study

Abstract

We measured gastric slow wave activity simultaneously with a Superconducting Quantum Interference Device (SQUID) magnetometer, mucosal electrodes and cutaneous electrodes in 18 normal human subjects (11 women and 7 men). We processed signals with Fourier spectral analysis and SOBI blind-source separation techniques. We observed a high waveform correlation between the mucosal electromyogram (EMG) and multichannel SQUID magnetogastrogram (MGG). There was a lower waveform correlation between the mucosal EMG and cutaneous electrogastrogram (EGG), but the correlation improved with the application of SOBI. There was also a high correlation between the frequency of the electrical activity recorded in the MGG and in mucosal electrodes (r = 0.97). We concluded that SQUID magnetometers noninvasively record gastric slow wave activity that is highly correlated with the activity recorded by invasive mucosal electrodes.

Figure 1

X-ray photograph showing the placement of NG tube in the patient’s stomach

Figure 2

(a–c) Electromyogram (EMG), electrogastrogram (EGG) and magnetogastrogram (MGG) filtered data (upper row) and their corresponding frequency spectra (lower row) during postprandial period. (d–e) EGG and MGG components isolated with SOBI (upper row) and their corresponding frequency spectra (lower row).

Figure 3

Waveform characteristics of the signal best correlated with the mucosal EMG signal for MGG, EGG, SOBI-MGG and SOBI-EGG components.

Figure 4

Correlation between gastric slow wave frequencies recorded by mucosal electrodes (EMG) to those recorded by (a) SQUID magnetometer (MGG), (b) cutaneous electrodes (EGG), (c) SOBI-MGG, and (d) SOBI-EGG. Data points represent peaks detected in FFT of 9 samples of magnetic and electric data. The peak frequencies determined by mucosal electrodes and SQUID are strongly correlated (correlation coefficient, r = 0.97 for EMG/MGG, r = 0.99 for EMG/SOBI- MGG) than between mucosal and cutaneous electrodes (r = 0.93 for EMG/EGG, r = 0.95 for EMG/SOBI- EGG). A linear fit to the data is also shown to emphasize the degree of correlation.

Figure 5

Waveform correlations, i.e., the mean value of the maximum cross-correlation coefficient between EMG/MGG, EMG/EGG, EMG/ SOBI-MGG and EMG/ SOBI-EGG waveforms. Over all nine experiments, the average correlation coefficient was 0.68 ± 0.04 (mean ± SEM) for MGG, 0.55 ± 0.02 for EGG, 0.69 ± 0.03 for SOBI-MGG and 0.60 ± 0.04 for SOBI-EGG components. A statistically significant difference between MGG and EGG correlation with mucosal EMG was observed (denoted by *).