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  • 1
    ISSN: 1573-2568
    Keywords: gastric recordings ; data acquisition ; digital signal processing ; aliasing ; filtering ; Fourier transform ; Nyquist theorem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Despite the fact that digital techniques for data acquisition and processing were widely used in electrogastrographic (EGG) research during the last decade, inappropriate signal conditioning and digitization are still potential pitfalls threatening the reliability of the experiments. The aim of this paper was to review: (1) the importance of the antialiasing low-pass filtering for reducing recording artifacts and interferences, (2) the advantages brought by the proper choice of filter cutoff frequency and the slope for the decrement of the minimal required sampling frequency, (3) the impact of incorrectly selected sampling frequency on data interpretations, with particular attention to the percent distribution ranges, and (4) the “leakage effect” related to the finite number of samples processed simultaneously in frequency domain representation of the recordings. A model of electrogastrographic (EGG) recording was mixed with a model of electrocardiographic (ECG) artifact. The resulting finite-duration signal was low-pass filtered and then digitized with a sampling frequency of 1 Hz. The cutoff frequency of the first-order low-pass filter was altered from 0.5 to 0.1 Hz. Amplitude frequency spectra of the digitized recordings were investigated. An example with a real human electrogastrogram in which an ECG artifact was present confirmed the simulation results. When a first-order anti-aliasing filter is utilized at least a fivefold difference between the filter cutoff frequency and the sampling frequency is recommended for compliance with the Nyquist theorem of digitization. Leakage effects associated with the finite-time duration of the recordings and the use of the discrete Fourier transform should be considered when frequency domain analysis is performed. Misinterpretation of the “bradygastric” and “tachygastric” ranges in the percent distribution of EGG frequency components is possible if inappropriate signal conditioning and digitization are employed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Digestive diseases and sciences 42 (1997), S. 1154-1157 
    ISSN: 1573-2568
    Keywords: ELECTROGASTROGRAMS ; GASTRIC ELECTRICAL ACTIVITY ; POWER DYNAMICS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This study was undertaken to investigate thecorrelation between power dynamics of gastric electricalactivity (GEA) assessed with different recordingtechniques. A total of seven eight-channel 1-hr combined recordings were obtained from three subjects infive consecutive postoperative days. Four channels wererecorded from bipolar electrodes implanted into thegastric antral wall, and four channels wereelectrogastrographic (EGG). Six pairs of bipolar electrodes wereinserted into the antral wall (three anterior; threeposterior) of 16 anaesthetized dogs. Fourteen-channel(six internal GEA and eight EGG) 1/2-hr recordings were obtained from each dog. Sets of powervalues calculated from channel pairs (internal, EGG ormixed) were cross-correlated and the significance of theobtained correlation coefficients was examined (P 〈 0.05). The majority of powercorrelations of internal GEA channel pairs, and those ofmixed (internal GEA-EGG) channel pairs wereinsignificant. These findings question the claims thatEGG power dynamics mirrors the power dynamics of internalGEA.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Digestive diseases and sciences 43 (1998), S. 953-956 
    ISSN: 1573-2568
    Keywords: GASTRIC ELECTRICAL ACTIVITY ; ELECTROGASTROGRAPHY ; RANDOMNESS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This study was undertaken to investigate thedynamics of the level of randomness in gastricelectrical signals. Combined recordings of internalgastric electrical activity (GEA) and electrogastrograms(EGG) were obtained from 16 unconscious dogs and twopostoperative patients. The signals were amplified usingspecially designed amplifiers with flexible frequencyrange and were digitized with 10-Hz sampling frequency. The 4.27-min portions of the digitalsignals were subjected to a previously described turningpoint test for randomness. The distributions of thenumber of turning points (NTP) in successive time intervals calculated from all GEA signalswere compared to the estimated NTP distribution of arandom signal. NTP dynamics of internal GEA signals wasalso correlated to the NTP dynamics of cutaneous EGG. In five of 16 recordings from the dogs andin two of the 14 recordings from the patients, NTPvalues calculated from some internal GEA channelsexceeded the 1% probability level for entering thenormal NTP distribution of a random signal (P 〉0.01). In all measurements the distributions of the NTPvalues recorded from cutaneous EGG channels weresignificantly different (P 〈 0.01) from the NTPdistribution of a random signal. There was significantcorrelation (P 〈 0.01) between the NTP dynamics ofinternal GEA and EGG. The level of randomness ininternal GEA recorded with the short-distance bipolartechnique is substantially higher than that in cutaneousEGG, probably due to the occurrence of spike activity.Although the level of randomness in EGG is affected bymany external factors, its dynamics correlated significantly with the level of randomness ininternal GEA.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-2568
    Keywords: GASTRIC ELECTRICAL ACTIVITY ; ELECTROGASTROGRAPHY ; RANDOMNESS ; GASTRIC ELECTRICAL UNCOUPLING
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Gastric electrical uncoupling is the lack ofelectrical synchronization in different parts of thestomach. The aim of this study was to investigate theimpact of gastric electrical uncoupling on the level of randomness of canine electrogastrograms(EGG). Electrogastrograms were obtained from 11unconscious acute dogs. Gastric electrical uncouplingwas produced surgically by performing two consecutivecircumferential cuts through the entire thickness of thegastric muscle layer. Three separate 1/2-hreight-channel bipolar EGGs were obtained from each dogin the basal state and after each cut. The signals wereamplified using amplifiers with a flexible frequencyrange, digitized with 10-Hz sampling frequency, and4.27-min portions of the digital EGGs weResubjected toa turning point test for randomness. The number of turning points (NTPs) was determined fromsuccessive time intervals calculated from all EGGchannels. Distributions of NTPs were calculated for eachdog. An average NTPs (ANTP) for each dog in a givenstate (basal, after the first cut, and after thesecond cut) was calculated from the ANTPs of allchannels. In six of 11 dogs the ANTP were greater afterthe first cut. The number rose to nine of 11 dogs after the second cut. In only 45% of the dogs werethe ANTP distributions significantly different (P 〈0.01) after the first cut (sensitivity 45%). After thesecond cut the sensitivity rose to 64%. In two specific EGG channels NTP distribution wassignificantly different (P 〈 0.01) in nine of 11 dogs(sensitivity: 82% ) after the second cut. The dynamicsof the level of randomness in EGG can be indicative of severe gastric electrical uncoupling. SomeEGG channel configurations are moResensitive thanoThers in recognizing gastric electricaluncoupling.
    Type of Medium: Electronic Resource
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