Biomedical subjects

M P Mintchev

Publications and source records attributed to M P Mintchev.

At least 19 recordsLinked to original sources

PubMed2002

Microprocessor controlled movement of solid colonic content using sequential neural electrical stimulation.

BACKGROUND AND AIMS: Invoked peristaltic contractions and movement of solid content have not been attempted in normal canine colon. The purpose of this study was to determine if movement of solid content through the colon could be produced by microprocessor controlled sequential stimulation. METHODS: The study was performed on six anaesthetised dogs. At laparotomy, a 15 cm segment of descending colon was selected, the proximal end closed with a purse string suture, and the distal end opened into a collecting container. Four sets of subserosal stimulating electrodes were implanted at 3 cm intervals. The segment of bowel was filled with a mixture of dog food and 50 plastic pellets before each of 2-5 random sessions of non-stimulated or stimulated emptying. Propagated contractions were generated using microprocessor controlled bipolar trains of 50 Hz rectangular voltage having 20 V (peak to peak) amplitude, 18 second stimulus duration, and a nine second phase lag between stimulation trains in sequential electrode sets. RESULTS: Electrical stimulation using the above mentioned parameters resulted in powerful phasic contractions that closed the lumen. By phase locking the stimulation voltage between adjacent sets of electrodes, propagated contractions could be produced in an aboral or orad direction. The number of evacuated pellets during the stimulation sessions was significantly higher than during the non-stimulated sessions (p<0.01). CONCLUSIONS: Microprocessor controlled electrical stimulation accelerated movement of colonic content suggesting the possibility of future implantable colonic stimulators.

Animals↗

PubMed2001

Dynamics of the level of deterministic chaos associated with gastric electrical uncoupling in dogs.

This study investigated the impact of gastric electrical uncoupling on the dynamics of the level of deterministic chaos in cutaneous gastric electrical signals. Eight-channel electrogastrograms (EGG) were recorded from 16 unconscious dogs. Controlled gastric electrical uncoupling was introduced by circumferentially cutting the whole gastric muscle at two different locations. Three separate 30-min EGG recordings were obtained from each dog in the three different states (basal, after the first cut, and after the second cut). The Lyapunov exponents were calculated from sixteen 6.31-min intervals with 75% overlap obtained from each channel in each state. Inadequate EGG signals from which the Lyapunov exponent could not be reliably calculated were quantitatively discarded. The variance and the standard deviation of the three Lyapunov exponent distributions obtained from each channel were studied, and the mean values were subjected to a Student t-test. In 65.6% of all studied channels, the level of chaos was significantly different (p< 0.01) after the first cut compared to the basal state, but no predominant direction of variation was observed (47. 7% increment vs. 52.5% decrement). After the second cut, 63.6% of the channels studied showed significantly greater Lyapunov exponent compared to the basal state, and 63.1% exhibited significantly greater (p< 0.01) level of chaos compared to the intercut state. The dynamics of the level of deterministic chaos in canine electrogastrograms is highly sensitive to severe gastric electrical uncoupling. Moreover, some channel configurations seem to be more sensitive than others in detecting uncoupling.

Animals↗

PubMed2001

Volterra series modelling and compensation of non-linear distortions caused by susceptibility difference artefacts related to the presence of ferromagnetic implants in magnetic resonance imaging.

Magnetic resonance imaging is popular in medical settings due to its unique technical characteristics. However, its full potential has been limited by imaging artefacts caused by various phenomena. Previously, a methodology was proposed to characterize and reduce artefacts caused specifically by magnetic susceptibility differences. In the present work, the Volterra series approach is suggested as an alternative method for describing non-linear distortions induced by susceptibility artefacts. A second-order Volterra series is utilized for characterizing the image non-linearities using a block-by-block processing approach. Subsequently, a corresponding second-order inverse Volterra series is applied to compensate for the quantified distortions. In addition, a technique for automatic demarcation of recoverable and non-recoverable regions in magnetic resonance images is proposed to ameliorate the developed methodology. Experimental results indicate that this approach offers improved accuracy and flexibility in reducing non-linear distortions caused by magnetic susceptibility artefacts.

Algorithms↗

PubMed2000

Microprocessor-controlled movement of solid gastric content using sequential neural electrical stimulation.

BACKGROUND & AIMS: Gastric electrical stimulation has been attempted for years without much success. The aim of this study was to determine if movement of solid gastric content could be achieved using microprocessor-controlled sequential electrical stimulation. METHODS: The study was performed on 9 anesthetized dogs. The dogs underwent laparotomy, pyloroplasty, and implantation of 4-6 sets of bipolar stainless-steel wire electrodes. Each set consisted of 2-6 electrodes (10 x 0.25 mm, 3 cm apart) implanted circumferentially. The stomach was filled with solid food mixed with plastic pellets, and the process of gastric emptying was monitored. Artificial contractions were produced using microprocessor-controlled phase-locked bipolar trains of 50-Hz rectangular voltage with flexible amplitudes. RESULTS: Using the above stimulating parameters, we were able to produce circumferential gastric contractions that were artificially propagated distally by embedding and phase-locking the stimulating voltage. The number of expelled pellets after the stimulation sessions was significantly higher than the number of pellets emptied during the nonstimulation sessions (P < 0.01). CONCLUSIONS: Microprocessor-controlled electrical stimulation produced artificial peristalsis and markedly accelerated the movement of solid gastric content.

Animals↗

PubMed2000

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

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.

Artifacts↗

PubMed2000

Nonlinear adaptive noise compensation in electrogastrograms recorded from healthy dogs.

Adaptive noise compensation is a popular method for improving signal-to-noise ratio in a variety of biomedical applications with its major disadvantage being the requirement for a reference channel containing noise strongly correlated to the noise in the primary channel. In many biomedical applications the utilization of a channel containing such noise without any representation of the information signal is difficult if not impossible. In this study we investigated the possibility of applying adaptive compensation in nonideal noise environments containing substantial presence of information signal in the reference channel. The signal in the reference channel was subjected to nonlinear manipulations for reducing the signal-to-noise ratio, thus diminishing the representation of information signal. The methodology was tested on canine electrogastrographic (EGG) signals of four unconscious dogs which underwent laparotomy and implantation of six pairs internal stainless steel electrodes in addition to the eight-channel abdominal EGG. Fourteen-channel (six internal and eight cutaneous) were obtained from each dog for 1/2 h. The signals were digitized and processed by computer. All internal signals showed regular and coupled gastric electrical activity with frequency of repetition in the normogastric range [3-9 cycles-per-minute (cpm)]. A single pair of primary and reference channels was selected from each cutaneous recording and exponential manipulators in the reference channels were introduced. The manipulators were tuned to maximize the percent distribution of spectral components in the canine normogastric range of each frequency spectrum calculated from the signal at the output of the adaptive compensator. Significant increment in the percent distributions in the normogastric range (p < 0.01) was noted after tuning the exponential manipulator, and in many frequency spectra the recovery of the genuine dominant frequency peak of gastric electrical activity as determined by the internal recordings was noted. This study indicated that low percent distributions registered by some EGG channels are related to external nonlinear factors, the impact of which can be partially compensated.

Animals↗

PubMed2000

Application of an object-oriented programming paradigm in three-dimensional computer modeling of mechanically active gastrointestinal tissues.

The aim of this study was to develop a novel three-dimensional (3-D) object-oriented modeling approach incorporating knowledge of the anatomy, electrophysiology, and mechanics of externally stimulated excitable gastrointestinal (GI) tissues and emphasizing the "stimulus-response" principle of extracting the modeling parameters. The modeling method used clusters of class hierarchies representing GI tissues from three perspectives: 1) anatomical; 2) electrophysiological; and 3) mechanical. We elaborated on the first four phases of the object-oriented system development life-cycle: 1) analysis; 2) design; 3) implementation; and 4) testing. Generalized cylinders were used for the implementation of 3-D tissue objects modeling the cecum, the descending colon, and the colonic circular smooth muscle tissue. The model was tested using external neural electrical tissue excitation of the descending colon with virtual implanted electrodes and the stimulating current density distributions over the modeled surfaces were calculated. Finally, the tissue deformations invoked by electrical stimulation were estimated and represented by a mesh-surface visualization technique.

Biomechanical Phenomena↗

PubMed1999

Dynamics of level of randomness of electrogastrograms can be indicative of gastric electrical uncoupling in dogs.

Gastric electrical uncoupling is the lack of electrical synchronization in different parts of the stomach. The aim of this study was to investigate the impact of gastric electrical uncoupling on the level of randomness of canine electrogastrograms (EGG). Electrogastrograms were obtained from 11 unconscious acute dogs. Gastric electrical uncoupling was produced surgically by performing two consecutive circumferential cuts through the entire thickness of the gastric muscle layer. Three separate 1/2-hr eight-channel bipolar EGGs were obtained from each dog in the basal state and after each cut. The signals were amplified using amplifiers with a flexible frequency range, digitized with 10-Hz sampling frequency, and 4.27-min portions of the digital EGGs were subjected to a turning point test for randomness. The number of turning points (NTPs) was determined from successive time intervals calculated from all EGG channels. Distributions of NTPs were calculated for each dog. An average NTPs (ANTP) for each dog in a given state (basal, after the first cut, and after the second cut) was calculated from the ANTPs of all channels. In six of 11 dogs the ANTP were greater after the first cut. The number rose to nine of 11 dogs after the second cut. In only 45% of the dogs were the ANTP distributions significantly different (P < 0.01) after the first cut (sensitivity 45%). After the second cut the sensitivity rose to 64%. In two specific EGG channels NTP distribution was significantly different (P < 0.01) in nine of 11 dogs (sensitivity: 82%) after the second cut. The dynamics of the level of randomness in EGG can be indicative of severe gastric electrical uncoupling. Some EGG channel configurations are more sensitive than others in recognizing gastric electrical uncoupling.

Animals↗

PubMed1998

Computer simulation of the impact of different dimensions of the stomach on the validity of electrogastrograms.

The impact of the dimensions of the stomach on cutaneous recordings of gastric electrical activity (GEA) has not been adequately studied. The stomach was represented as a truncated conoid in a spherical coordinate system. The gastric electric field was modelled using a previously described methodology. Electrical potentials were calculated from sets of points simulating standard cutaneous recordings. The frequency of the signals was maintained at 3 cycles min-1 (period of repetition: 20 s), while the velocity of propagation of the depolarisation waves was reduced relative to the reduction in gastric dimensions. The signals were digitally contaminated with a random artificial artefact with a constant amplitude range of 0.2 mV, while the dimensions of the conoid (the circumferential radii and the length of the central axis) were decreased by factors of 1.5, two, four, six and eight. Simulated EGG signals were evaluated quantitatively. Simulated EGG records contaminated with random signals recorded from stomachs with decreasing dimensions exhibited non-linearly increasing standard deviations (p < 0.001). Randomly contaminated EGGs calculated from stomachs with dimensions reduced four, six and eight times were abnormal according to previously established quantitative criteria. Computer modelling indicated that gastric dimensions can significantly influence the validity of EGGs. These findings could be particularly important in a paediatric electrogastrography.

Computer Simulation↗

PubMed1998

Comparative quantification of gastric electrical activity and electrogastrograms.

The aim of this study was to compare quantitatively the variability of gastric electrical activity (GEA) recorded from asymptomatic patients with implanted serosal electrodes and patients with implanted and cutaneous electrodes. Three pairs of electrodes were inserted into the gastric wall in six patients undergoing laparotomy for other reasons. Normal GEA was assessed visually once patients were tolerating a normal diet. Mean frequency (MF) values of the GEA signal in successive 256 s intervals were obtained. Standard deviations of the MF values for each separate channel of each patient were calculated. Probability density functions (pdfs) of these values were also obtained and compared. 36 1 h simultaneous recordings were made for three patients with implanted and cutaneous electrodes. The recordings were assessed both visually and with computer. A fast Hartley transform was used to obtain the dominant MF values in 256 s time intervals. These values were statistically evaluated for each channel. Normal internal GEA had a mean frequency of 2.5-3.75 cycles min-1 (cpm) and a standard deviation range of 0-0.45 cpm. Bell-shaped pdfs with coinciding maxima were observed in all these recordings, indicating normal electrical coupling. In the comparative 36 h study, using the above definitions of normality, different cutaneous recordings were found to reflect GEA with a sensitivity of 94% and a specificity of 79%.

Adult↗

PubMed1998

Computer simulation of the effect of changing abdominal thickness on the electrogastrogram.

The effect of different abdominal thickness on cutaneous recordings of gastric electrical activity (GEA) known as electrogastrograms (EGG) have not been adequately studied. The stomach was represented as a truncated conoid in spherical system of coordinates. Gastric electrical field was modelled using previously described methodology. Electrical voltages were calculated in simulated standard cutaneous recordings. The effect of increased thickness of the abdominal layers was quantitatively examined. Changes of the thickness of the abdominal layers significantly affected signal-to-noise ratio of EGG. When the critical abdominal thickness of 7 cm was exceeded, EGGs were quantified as abnormal although the internal GEA was normal. Computer modelling indicated that changeable abdominal thickness caused by the abdominal layers separating the stomach from the recording electrodes significantly influence the EGG recordings even if the layers are homogeneous.

Abdomen↗

PubMed1998

Dynamics of the level of randomness in gastric electrical activity.

This study was undertaken to investigate the dynamics of the level of randomness in gastric electrical signals. Combined recordings of internal gastric electrical activity (GEA) and electrogastrograms (EGG) were obtained from 16 unconscious dogs and two postoperative patients. The signals were amplified using specially designed amplifiers with flexible frequency range and were digitized with 10-Hz sampling frequency. The 4.27-min portions of the digital signals were subjected to a previously described turning point test for randomness. The distributions of the number of turning points (NTP) in successive time intervals calculated from all GEA signals were compared to the estimated NTP distribution of a random signal. NTP dynamics of internal GEA signals was also correlated to the NTP dynamics of cutaneous EGG. In five of 16 recordings from the dogs and in two of the 14 recordings from the patients, NTP values calculated from some internal GEA channels exceeded the 1% probability level for entering the normal NTP distribution of a random signal (P > 0.01). In all measurements the distributions of the NTP values recorded from cutaneous EGG channels were significantly different (P < 0.01) from the NTP distribution of a random signal. There was significant correlation (P < 0.01) between the NTP dynamics of internal GEA and EGG. The level of randomness in internal GEA recorded with the short-distance bipolar technique is substantially higher than that in cutaneous EGG, probably due to the occurrence of spike activity. Although the level of randomness in EGG is affected by many external factors, its dynamics correlated significantly with the level of randomness in internal GEA.

Animals↗

PubMed1998

Microprocessor controlled movement of liquid gastric content using sequential neural electrical stimulation.

BACKGROUND: Gastric electrical stimulation has been attempted for several years with little success. AIMS: To determine whether movement of liquid gastric content could be achieved using microprocessor controlled sequential electrical stimulation. METHODS: Eight anaesthetised dogs underwent laparotomy and implantation of four sets of bipolar stainless steel wire electrodes. Each set consisted of two to six electrodes (10x0.25 mm, 3 cm apart) implanted circumferentially. The stomach was filled with water and the process of gastric emptying was monitored. Artificial contractions were produced using microprocessor controlled phase locked bipolar four second trains of 50 Hz, 14 V (peak to peak) rectangular voltage. In four of the dogs four force transducers were implanted close to each circumferential electrode set. In one gastroparetic patient the effect of direct electrical stimulation was determined at laparotomy. RESULTS: Using the above stimulating parameters circumferential gastric contractions were produced which were artificially propagated distally by phase locking the stimulating voltage. Averaged stimulated gastric emptying times were significantly shorter than spontaneus emptying times (t1/2 6.7 (3.0) versus 25.3 (12.9) minutes, p<0.01). Gastric electrical stimulation of the gastroparetic patient at operation produced circumferential contractions. CONCLUSIONS: Microprocessor controlled electrical stimulation produced artificial peristalsis and notably accelerated the movement of liquid gastric content.

Animals↗

PubMed1998

Electrogastrography: a noninvasive technique to evaluate gastric electrical activity.

Electrogastrography (EGG) is the recording of gastric electrical activity (GEA) from the body surface. The cutaneous signal is low in amplitude and consequently must be amplified considerably. The resultant signal is heavily contaminated with noise, and visual analysis alone of an EGG signal is inadequate. Consequently, EGG recordings require special methodology for acquisition, processing and analysis. Essential components of this methodology involve an adequate system of digital filtering, amplification and analysis, along with minimization of the sources of external noise (random motions of the patient, electrode-skin interface impedance, electrode bending, obesity, etc) and a quantitative interpretation of the recordings. There is a close relationship between GEA and gastric motility. Although it has been demonstrated that EGG satisfactorily reflects internal GEA frequency, there is not acceptable correlation with gastric contractions or gastric emptying. Many attempts have been made to relate EGG 'abnormalities' with clinical syndromes and diseases; however, the diagnostic and clinical value of EGG is still very much in question.

Artifacts↗

PubMed1997

Comparative assessment of power dynamics of gastric electrical activity.

This study was undertaken to investigate the correlation between power dynamics of gastric electrical activity (GEA) assessed with different recording techniques. A total of seven eight-channel 1-hr combined recordings were obtained from three subjects in five consecutive postoperative days. Four channels were recorded from bipolar electrodes implanted into the gastric antral wall, and four channels were electrogastrographic (EGG). Six pairs of bipolar electrodes were inserted into the antral wall (three anterior; three posterior) of 16 anaesthetized dogs. Fourteen-channel (six internal GEA and eight EGG) 1/2-hr recordings were obtained from each dog. Sets of power values calculated from channel pairs (internal, EGG or mixed) were cross-correlated and the significance of the obtained correlation coefficients was examined (P < 0.05). The majority of power correlations of internal GEA channel pairs, and those of mixed (internal GEA-EGG) channel pairs were insignificant. These findings question the claims that EGG power dynamics mirrors the power dynamics of internal GEA.

Animals↗

PubMed1997

Electrogastrography can recognize gastric electrical uncoupling in dogs.

BACKGROUND & AIMS: Electrical uncoupling is the lack of electrical synchronization in different parts of the stomach. The ability of electrogastrography (EGG) to recognize gastric electrical uncoupling has not been adequately studied. The aim of this study was to determine the impact on EGG of surgically introduced gastric uncoupling in anesthesized dogs. METHODS: Six pairs of bipolar electrodes were inserted into the antral gastric wall of 16 anesthetized dogs at laparotomy. Eight-channel bipolar cutaneous EGGs were simultaneously recorded. Three separate half-hour recordings were made from each dog in the basal state and after each of two circumferential cuts of all gastric muscle. The stomach was divided into three equally sized areas, each with an electrode pair in its anterior and posterior walls. Gastric electrical activity was assessed visually. EGG was digitized and processed by computer. RESULTS: Criteria for EGG normality were defined from 9 dogs with normal gastric electrical activity. After the first antral cut, internal recordings from the area below the division were at a lower frequency and often irregular. The second cut produced three different frequencies. Suggested criteria for normality allowed correct recognition of 93% of all severely abnormal records. Records with mild gastric electrical abnormalities were recognized with a sensitivity of 74%. CONCLUSIONS: EGG can recognize severe electrical uncoupling.

Animals↗

PubMed1997

Reliability of percent distribution of power of the electrogastrogram in recognizing gastric electrical uncoupling.

The aim of this study was to examine the reliability of percent distribution of electrogastrographic (EGG) power in recognizing gastric electrical uncoupling. Sixteen anaesthetized dogs underwent laparotomy and implantation of six pairs of stainless-steel wire electrodes. Distal stomach was measured and three sections with approximately equal lengths were defined. Two pairs of electrodes were implanted in each section. Eight-channel EGG was also recorded. Three separate half-hour recordings were made: in the basal state; after a full circumferential separation of the distal antral section from the rest; after a second circumferential cut completely separating the middle from the proximal sections. EGG digital power spectra were split into three frequency ranges and dynamics of percent distribution of power was statistically examined. After the first cut, changes in the percent distribution of EGG power in the normal range were not significant (p = 0.2). Significant changes in the low range were noted (p < 0.05) and changes in the high range were borderline nonsignificant (p = 0.056). After the second cut, changes in percent distribution in the normal and the high range became significant (p < 0.01) while changes in the low range were insignificant (p = 0.075). Severe uncoupling was reflected in EGG by significant changes in the high-frequency range without internal tachygastria necessarily being present.

Animals↗

PubMed1996

Extracting quantitative information from digital electrogastrograms.

Cutaneous recordings of gastric electrical activity (electrogastrography (EGG)) could become a valuable non-invasive tool for recognising gastric electrical abnormalities. Although signals obtained with internally implanted electrodes deliver quantitative information, this technique cannot be used for diagnostic purposes because of its invasive nature. On the other hand, the objectivity of electrogastrography is still in question. The aims of this work are to develop computer techniques for extracting quantitative information from digital electrogastrograms, and to evaluate quantitatively EGG recordings from healthy volunteers. The dynamics of all four EGG parameters are studied: amplitude, frequency, time shift between different channels, and waveform. Four separate two-dimensional computer plots are developed using specially designed digital signal-processing procedures. Each parameter is evaluated in a study of 20 healthy volunteers. Frequency is found to be the only EGG parameter that shows quantitative consistency and merit.

Electrodiagnosis↗