Misinterpretation of human electrogastrograms related to inappropriate data conditioning and acquisition using digital computers

Despite the fact that digital techniques for data acquisition and processin g were widely used in electrogastrographic (EGG) research during the last d ecade, inappropriate signal conditioning and digitization are still potenti al pitfalls threatening the reliability of the experiments. The aim of this paper was to review: (1) the importance of the antialiasing low-pass filte ring 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 part icular attention to the percent distribution ranges, and (4) the "leakage e ffect" related to the finite number of samples processed simultaneously in frequency domain representation of the recordings. A model of electrogastro graphic (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 fit. The cutoff frequency of the first-order low-pass filter was altered from 0.5 to 0.1 Hz. Amplitude f requency spectra of the digitized recordings were investigated. An example with a real human electrogastrogram in which an ECG artifact was present co nfirmed 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 du ration of the recordings and the use of the discrete Fourier transform shou ld be considered when frequency domain analysis is performed. Misinterpreta tion of the "bradygastric" and "tachygastric" ranges in the percent distrib ution of EGG frequency components is possible if inappropriate signal condi tioning and digitization are employed.