1228 IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 44, NO. 12, DECEMBER 1997 Real-Time Multichannel Computerized Electrogastrograph Mingying Zhou,* Hui Zhang, Robert Shaw, and Frank S. Barnes, Life Fellow, IEEE Abstract— The purpose of this study was to develop a real- time multichannel computerized electrogastrograph (EGG) to measure and analyze electrical signals from the human abdom- inal surface. A soft-contact matrix composed of 25 cutaneous electrodes is embedded evenly in a latex mat. The mat can be firmly attached to the abdominal surface by drawing a vac- uum between the matrix and the stomach. Twenty-five high- amplification filter/amplifiers provide a high signal-to-noise ratio and flat amplitude response for a signal between 0.02 and 0.12 Hz (1.2–7.2 cpm). The computer program provides waveform and frequency analysis for any chosen channel and mapping analyses for all 25 channels. A two-dimensional propagation exploration program was also developed. Using four different mapping analysis program subroutines, the optimal points for analyzing the EGG signals can be reliably found and variability of these locations can be observed easily. Results show differences in the EGG mappings of normal and abnormal subjects. Index Terms—Amplifier, electrode, electrogastrogram, electro- gastrograph, filter, mapping, signal analysis, stomach. I. INTRODUCTION T HE first electrogastrogram (EGG) was made by Alvarez in 1921 [1]. The recorded signal resembled a sine wave with a frequency of three cycles per min (cpm) [1]. Since then, and especially since 1985, the EGG has been extensively investigated. The EGG provides information on the frequency and the degree of contraction as well as distension of the stomach [2]–[10]. The clinical usefulness of the EGG is now one of the main research areas. For instance, there have been reports of observations of gastric motility disorders [11]–[16], gastric ulcer and gastroparesis with the EGG [17], [18]. In order to explore the clinical validation of the EGG, the following needed improvements have been suggested [19]: • improved signal quality; • multiple electrodes; • validated, computer-assisted mapping analysis; • more study relating EGG results to gastric conditions. Manuscript received February 10, 1995; revised March 31, 1997. Asterisk indicates corresponding author. *M. Zhou is with the Medical Testing Technology Institute, 3601 Larkwood Court, Boulder, CO 80304 USA. H. Zhang is with Columbia University, New York, NY 10027 USA. He is also with the Medical Testing Technology Institute, Boulder, CO 80304 USA. R. Shaw is with Breece Hill Technologies, Inc., and the Medical Testing Technology Institute, Boulder, CO 80304 USA. F. S. Barnes is with the Department of Electrical and Computer Engineering, University of Colorado, Boulder, CO 80309 USA. Publisher Item Identifier S 0018-9294(97)07598-8. II. COMPOSITION OF THE REAL-TIME MULTICHANNEL COMPUTERIZED ELECTROGASTROGRAPH A. Configuration of the Electrogastrograph The electrodes are the sensors for acquiring the signals from the subject and sending them to the recording and analyzing apparatus. In principle any nonpolarizable electrode is appro- priate. However, the mechanical properties, size, and shape of electrodes must also to be considered. Ideally, electrodes for multichannel recordings should be of minimal size with short, highly flexible leads. Disposable electrodes from various electrocardiogram (EKG) suppliers were tried in this study. However, none of these electrodes was found suitable for mapping analysis because their large size resulted in placement difficulties. It was also extremely difficult to place many single electrodes and obtain both consistent contact impedance and consistent relative spacing. Additionally, the polystyrene foam of the electrodes did not have the flexibility required for the soft, moving abdominal area. In order to obtain the desired quality of the EGG signal, a soft-contact, multichannel, cutaneous, vacuum electrode ma- trix, embedded evenly in a latex mat, was developed. The matrix is a 5 5 array of 25 Ni on stainless-steel electrodes that are spaced 3.1 cm apart, center-to-center. The direct skin contact area of each electrode is 50 mm . The dc impedance of the electrodes ranged from 60–100 k . The mat can be firmly attached to the abdominal surface by extracting the air from a cavity formed by the electrodes, latex membrane, and the abdomen, through vacuum air flow tubes. With the subject lying in a supine position, the mat was placed on the abdominal area and connected to the filter/amplifier through disconnect plugs. The leads from the electrodes to the plugs are extra flexible, 26-gauge, seven-strand, shielded wire. Fig. 1 shows top and underside views of the multichannel electrode matrix. From the stomach, two distinct types of electrical activities have been observed and reported by researchers using internal electrodes. One is called electrical control activity (ECA) which occurs at a rate of about 3 cpm in man. The other is called electrical response activity (ERA), which can occur only once following each control activity. The periodic com- ponents of the EGG’s lie in the frequency band from 1 cpm (bradygastria) to 9 cpm (tachygastria). The gastric potentials on the abdomen are in the range of 50–500 V. The electrogastrograph, therefore, must be equipped with suitable filters and amplifiers to selectively amplify the signal in a useful frequency band, and eliminate interfering signals 0018–9294/97$10.00  1997 IEEE