Gastric distension alters frequency and regularity but not amplitude of the gastric slow wave

Abstract The aim of this study was to assess effects of gastric distension on gastric slow waves using internal and cutaneous electrodes and the correlation between these two measurements. The study was performed in five dogs implanted with one pair of serosal electrodes and a gastric cannula. Gastric slow waves were recorded using both cutaneous and internal electrodes in several sessions with different volumes (150-600 mL) of gastric distension with a barostat balloon. Bethanechol was injected in one of sessions. The results revealed that (i) Gastric distension reduced slow wave frequency in a volume-dependent manner and induced bradyarrhythmia at a volume of 600 mL, but had no effects on the amplitude of gastric slow waves. (ii) The cutaneous electrogastrogram (EGG) was significantly correlated with the internal recording in slow wave frequency (r = 0.88, P < 0.001) and regularity (r = 0.44, P = 0.035). (iii) The EGG amplitude was not increased when the stomach was distended but increased after bethanechol. Gastric distension volume dependently reduces slow wave frequency and induces gastric dysrhythmia at a large volume. The frequency and rhythmicity of the slow wave measured from the EGG are significantly correlated with those recorded from the internal electrodes. Relative increase in EGG amplitude reflects contractility rather than the distension of the stomach.     

Gastric electrical activity and gastric emptying in term and preterm newborns

The aims of this study were to evaluate the gastric electrical activity and gastric emptying in preterm and term newborns and to assess the development of gastric motility by comparing newborns of different gestational ages. The cutaneous electrogastrography and the ultrasonographic study of the gastric emptying were performed before and after milk formula in three groups of infants: 12 preterm newborns with a gestational age of 28-32 weeks, 11 preterm newborns with a gestational age of 32-36 weeks, and 10 full-term newborns with a gestational age of 36-40 weeks. All recording sessions were performed 1 week after infants had reached full enteral feeding. The percentage of normal slow waves was similar in the three groups but it was not predominant compared to tachygastria in the earliest premature infants (59.3% (12.7-92.3) vs. 29.6% (3.7-78.8); P < 0.05). In addition, a progressive increase in the normal slow wave percentage (59.3% (17.4-87.4), 60.9% (38.1-89.7), 77.8% (66.4-84.8); P < 0.05) was observed as gestation advanced. As regards gastric emptying parameters, the antral area was greater and T(1/2) was longer in the preterm newborns of 28-32 weeks than preterm newborns of 32-36 weeks and full-term newborns (fasting antral area: 0.96 cm2 (0.6-1.5), 0.63 cm2 (0.4-1.2), 0.55 cm2 (0.1-0.9) respectively, P < 0.05; T(1/2): 83.4 min (76.0-108.5), 70 min (57.5-89.5) and 71.8 min (54.9-81.2), respectively P < 0.05). The comparisons of gastric emptying curves made among the three groups showed a reduced antral dilatation in preterm newborns of 28-32 weeks compared to full-term newborns at 30 and 60 min after a meal. In conclusion, although enteral feeding is important for the development process of gastrointestinal motility, gastric electrical activity and gastric emptying show an intrinsic maturation depending on the gestational age.     

Development of gastric slow waves and effects of feeding in pre-term and full-term infants

The aims of this study were to investigate the difference in developmental process of gastric slow waves and the effects of feeding in pre-term and full-term infants. Twenty-six pre-term and 31 full-term infants were enrolled in the study. Gastric myoelectrical activity was recorded using electrogastrography (EGG) from birth to month 6. An increase in the % of 2-4 cpm slow waves was noted in both pre-term (P < 0.01) and full-term infants (P < 0.04) from birth to month 4. The pre-term infants showed a reduced dominant EGG power at certain points of the study. (3) Breast or formula feeding resulted in no difference in the EGG in the full-term infants and showed a difference in the postprandial dominant power of the EGG in the pre-term infants only at month 2 after birth (P < 0.05) but not at other times. The gastric slow wave in pre-term infants is of a significantly reduced amplitude but similar rhythmicity. The method of feeding has no effects on the EGG in full-term infants and minimal effects (may be of non-clinical significance) on the EGG in pre-term infants as the difference was noted only at one time point during the 6-month follow-up study.     

Rapid high‐amplitude circumferential slow wave propagation during normal gastric pacemaking and dysrhythmias

Background Gastric slow waves propagate aborally as rings of excitation. Circumferential propagation does not normally occur, except at the pacemaker region. We hypothesized that (i) the unexplained high‐velocity, high‐amplitude activity associated with the pacemaker region is a consequence of circumferential propagation; (ii) rapid, high‐amplitude circumferential propagation emerges during gastric dysrhythmias; (iii) the driving network conductance might switch between interstitial cells of Cajal myenteric plexus (ICC‐MP) and circular interstitial cells of Cajal intramuscular (ICC‐IM) during circumferential propagation; and (iv) extracellular amplitudes and velocities are correlated. Methods An experimental–theoretical study was performed. High‐resolution gastric mapping was performed in pigs during normal activation, pacing, and dysrhythmia. Activation profiles, velocities, and amplitudes were quantified. ICC pathways were theoretically evaluated in a bidomain model. Extracellular potentials were modeled as a function of membrane potentials. Key Results High‐velocity, high‐amplitude activation was only recorded in the pacemaker region when circumferential conduction occurred. Circumferential propagation accompanied dysrhythmia in 8/8 experiments was faster than longitudinal propagation (8.9 vs 6.9 mm s^?1; P = 0.004) and of higher amplitude (739 vs 528 μV; P = 0.007). Simulations predicted that ICC‐MP could be the driving network during longitudinal propagation, whereas during ectopic pacemaking, ICC‐IM could outpace and activate ICC‐MP in the circumferential axis. Experimental and modeling data demonstrated a linear relationship between velocities and amplitudes (P < 0.001). Conclusions & Inferences The high‐velocity and high‐amplitude profile of the normal pacemaker region is due to localized circumferential propagation. Rapid circumferential propagation also emerges during a range of gastric dysrhythmias, elevating extracellular amplitudes and organizing transverse wavefronts. One possible explanation for these findings is bidirectional coupling between ICC‐MP and circular ICC‐IM networks.     

Detection of gastric slow wave uncoupling from multi-channel electrogastrogram: validations and applications

Current methodology of single channel electrogastrography is unable to detect coupling or uncoupling of gastric slow waves, which is crucial for gastric emptying. In this study, a new methodology, called cross-spectral analysis method, was established to compute the coupling percentage of multi-channel gastric slow waves recorded using serosal electrodes and electrogastrogram (EGG). Two experiments were performed to validate the method and demonstrate its applications in clinical research. In experiment 1, simultaneous recordings of gastric slow waves were made in five dogs from serosal electrodes and cutaneous electrodes. In experiment 2, four-channel fasting EGGs were made in 10 volunteers for 30 min during waking and 30 min during non-rapid eye movement (REM) sleep. The validation study (experiment 1) showed that the slow wave coupling calculated from the EGGs was correlated with that computed from the serosal recordings. The gastric slow wave coupling percentages detected from both serosal and cutaneous recordings were significantly impaired during vasopressin infusion (6.3 +/- 2.6 vs 62.4 +/- 6.3, P < 0.001 for serosal recordings; 6.7 +/- 3.0 vs 57.2 +/- 2.7, P < 0.001 for cutaneous recordings), and the coupling percentages respectively calculated from serosal and cutaneous recordings were significantly correlated during the baseline recording period (R = 0.922, P < 0.05) and vasopressin infusion period (R = 0.916, P < 0.05). In experiment 2, the gastric slow wave became less coupled when healthy volunteers fell asleep. The percentage of slow wave coupling calculated from the EGGs was 68.2 +/- 17.9% during waking but 41.9 +/- 20.8 during non-REM sleep (P < 0.05). The method developed in this study is reliable for the detection of slow wave uncoupling from multi-channel EGGs. Gastric slow wave coupling is impaired during vasopressin infusion and sleep. These data suggest that this method has potential applications in physiological and clinical studies.     

Inhibitory effects of stress on postprandial gastric myoelectrical activity and vagal tone in healthy subjects

The aim was to investigate gastric myoelectrical activity (GMA) and vagal activity in response to stress. The study was performed in 10 healthy subjects in three sessions (control, relaxation and stress). The control session was composed of 30-min recordings before and 30-min recordings after a test meal. The protocol of two other sessions was similar except that the fasting recording was extended to 60 min and the subjects were continuously watching a horror movie (stress) or guided meditation tape (relaxation) after the 30-min baseline. GMA was recorded using electrogastrography and heart rate variability (HRV) was derived from the electrocardiogram. Meal resulted in a postprandial increase in the dominant frequency (2.91 cpm vs 3.17 cpm, P < 0.007), dominant power (30.0 dB vs 32.5 dB, P < 0.05), and percentage of normal slow waves (79.8%vs 87.4%, P = 0.09). Similar responses were found in the relaxation session. Stress inhibited all these normal postprandial response and reduced the regularity of gastric slow waves (82.0%vs 66.0%, P < 0.01). In addition, spectral analysis of the HRV demonstrated an inhibition of postprandial vagal activity and an increase of postprandial sympathetic activity with stress. Stress has an inhibitory effect on postprandial GMA and this may involve both vagal and sympathetic pathway.     

Efficacy and efficiency of gastric electrical stimulation with short pulses in the treatment of vasopressin-induced emetic responses in dogs

The aim of this study was to determine the most effective and efficient anti-emetic parameters of short-pulse gastric electrical stimulation (GES) in dogs. Seven female beagle dogs implanted with four pairs of gastric electrodes were studied in eight randomized sessions (saline, vasopressin, and six GES sessions with different parameters). Each session consisted of four 20-min recordings of gastric slow waves and symptoms. In sessions 1 and 2, saline and vasopressin, respectively, were infused during the second 20-min period. The protocol of the other six sessions was the same as session 2 except that GES was continuously applied. It was found that: (1) vasopressin induced gastric dysrhythmia and emetic response (P < 0.01, anova); (2) short-pulse GES with a frequency of 14 or 40 Hz and pulse width of 0.1 or 0.3 ms, but not 0.6 ms was able to reduce symptoms induced by vasopressin; (3) short-pulse GES with a pulse width of 0.3 ms was the most effective in preventing vasopressin-induced symptoms; (4) none of the tested GES methods improved vasopressin-induced gastric dysrhythmia. We conclude that vasopressin induces gastric dysrhythmia and symptoms. Short-pulse GES with a pulse width of 0.3 ms and frequency of 14 Hz is most effective and efficient in preventing vasopressin-induced emetic responses in dogs.     

Biomagnetic characterization of spatiotemporal parameters of the gastric slow wave

Certain gastric disorders affect spatiotemporal parameters of the gastric slow wave. Whereas the electrogastrogram (EGG) evaluates electric potentials to determine primarily temporal parameters, fundamental physical limitations imposed by the volume conduction properties of the abdomen suggest the evaluation of gastric magnetic fields. We used a multichannel superconducting quantum interference device magnetometer to study the magnetogastrogram (MGG) in 20 normal human subjects before and after a test meal. We computed the frequency and amplitude parameters of the gastric slow wave from MGG. We identified normal gastric slow wave activity with a frequency of 2.6 +/- 0.5 cycles per minute (cpm) preprandial and 2.8 +/- 0.3 cpm postprandial. In addition to frequency and amplitude, the use of surface current density mapping applied to the multichannel MGG allowed us to visualize the propagating slow wave and compute its propagation velocity (6.6 +/- 1.0 mm s(-1) preprandial and 7.4 +/- 0.4 mm s(-1) postprandial). Whereas MGG and EGG signals exhibited strong correlation, there was very little correlation between the MGG and manometry. The MGG not only records frequency dynamics of the gastric slow wave, but also characterizes gastric propagation. The MGG primarily reflects the underlying gastric electrical activity, but not its mechanical activity.     

Impaired circadian rhythm of gastric myoelectrical activity in patients with multiple system atrophy

Abstract In order to evaluate gastric motility and its circadian rhythm in patients with multiple system atrophy (MSA) and healthy control subjects, we measured gastric myoelectrical activity (GMA) for 24 hours using a cutaneous electrogastrogram (EGG) recorder in 14 MSA patients and 9 age-matched controls.We analyzed six 10-minute segments of EGG before and after each meal and two 20-minute EGG segments during sleep; three parameters were used for the analysis: dominant frequency (DF), instability coefficient of dominant frequency (ICDF), and dominant power (DP). DF increased during daytime and decreased during sleep in the control, while this circadian variation was blunted in the patients with MSA. The average DF of the eight segments in the MSA patients did not differ from that of the control. Both MSA patients and control subjects did not show the circadian variation of ICDF and DP. The average ICDF of the eight segments in the patients with MSA was significantly decreased when compared with that of the control (p<0.01). No differences were observed in DP between the two groups. This study indicates that the healthy subjects appear to have a circadian rhythm of DF, and the patients with MSA appear to have impaired circadian rhythm of DF and decreased ICDF possibly due to the degeneration of the central autonomic neurons.     

NeuroQuest: a comprehensive analysis tool for extracellular neural ensemble recordings

Analyzing the massive amounts of neural data collected using microelectrodes to extract biologically relevant information is a major challenge. Many scientific findings rest on the ability to overcome these challenges and to standardize experimental analysis across labs. This can be facilitated in part through comprehensive, efficient and practical software tools disseminated to the community at large. We have developed a comprehensive, MATLAB-based software package - entitled NeuroQuest - that bundles together a number of advanced neural signal processing algorithms in a user-friendly environment. Results demonstrate the efficiency and reliability of the software compared to other software packages, and versatility over a wide range of experimental conditions.     

Effects of gastric electrical field stimulation with long pulses on gastric emptying in dogs

The aim was to investigate the effects of electrical field stimulation (EFS) with long and short pulses on gastric emptying, gastric contractility and vagal activity in dogs. Sixteen dogs were equipped with a duodenal cannula, electrodes and strain gauges (10 dogs) in the stomach. Each dog was fed with Ensure and gastric effluent was collected from the cannula. Electrical stimulation was applied via two electrodes (about 12 cm apart, one in the corpus and the other in the antrum) with long pulses (a frequency of 6 cycles min-1, pulse amplitude of 6 mA and width of 100 ms) in 10 dogs and with short pulses (frequency of 30 Hz and pulse width of 300 micros) in six dogs. The electrocardiogram was also recorded and heart rate variability was derived to assess the vagal activity. It was found that: (i). EFS with long pulses did not alter gastric emptying during stimulation but increased gastric emptying during the 45 min immediately after stimulation; (ii). EFS with long pulses increased gastric contractility in both proximal and distal antrum during and after the stimulation; (iii). EFS with long pulses resulted in an increase in vagal tone during the 45 min immediately after stimulation. However, there is no difference during the 45 min period of stimulation; (iv). EFS with short pulses had no effect on gastric emptying. We concluded that long pulse gastric electrical field stimulation with one electrode in the corpus and the other electrode in the antrum has postponed effects on gastric emptying of liquid, gastric contractility and vagal activity.     

Stimulation of gastric slow waves with manual acupuncture at acupuncture points ST36 and PC6--a randomized single blind controlled trial

Background To investigate the effects of stimulated and non‐stimulated manual acupuncture at ST36 and PC6 on gastric myoelectrical activity and autonomic function. Methods A total of 65 healthy volunteers were randomly assigned to a 1: 1: 2 ratio to receive either 15 min of verum acupuncture (VA) with stimulation followed by 15 min of VA without stimulation (nsVA), or 15 min of nsVA followed by 15 min of VA with stimulation (sVA), or 30 min of sham acupuncture (SA). Measures of autonomic function included electrogastrogram, electrocardiogram, impedance cardiography and assessment of blood pressure, breathing frequency, and electrodermal activity. Outcome parameters were compared between VA and SA, and between sVA and nsVA. The percentage of regular gastric slow waves (normogastria) was defined as the primary outcome. Key Results The percentage of normogastria was not significantly different between VA and SA. Differences in secondary outcomes such as power spectrum of gastric slow waves and heart rate variability parameters were pronounced in the comparison of sVA and nsVA. During sVA, the percentage of normogastria was lower (P = 0.005), the percentage of bradygastria was higher (P = 0.003) and power ratio was higher (P < 0.001), systolic blood pressure was lower (P = 0.039) and RMSSD was higher (P < 0.001) as compared with nsVA. Conclusions & Inferences Our study suggests that manual stimulation of acupuncture needles at ST36 and PC6 affects gastric myoelectrical as well as cardiac activities in healthy volunteers. The effect of stimulation in acupuncture deserves further investigation.     

Effect of high-frequency gastric electrical stimulation on gastric myoelectric activity in gastroparetic patients

The aim of this study was to investigate the effect of gastric electrical stimulation (GES) on gastric myoelectric activity (GMA) and to identify possible mechanisms that could help explain how high-frequency GES is effective in treating nausea and vomiting associated with gastroparesis. Fifteen gastroparetic patients who received high-frequency GES were enrolled. Two pairs of temporary pacing wires were implanted on the serosa of the stomach along the greater curvature during surgery for placement of the permanent stimulation device. Two-channel serosal recordings of GMA before and during GES were measured. A gastric emptying test and severity of nausea and vomiting were assessed at baseline and at 3 months of GES. Power spectral and cross correlation analyses revealed that impaired propagation of slow waves (50%), tachygastria (30%) and abnormal myoelectric responses to a meal (50%) were the main abnormalities observed at baseline. GES with a high frequency significantly enhanced the slow wave amplitude and propagation velocity, and resulted in a significant improvement in nausea and vomiting but did not entrain the gastric slow wave or improve gastric emptying after 3 months of GES.     

Biomagnetic signatures of uncoupled gastric musculature

Abstract  Gastric slow waves propagate in the electrical syncytium of the healthy stomach, being generated at a rate of approximately three times per minute in a pacemaker region along the greater curvature of the antrum and propagating distally towards the pylorus. Disease states are known to alter the normal gastric slow wave. Recent studies have suggested the use of biomagnetic techniques for assessing parameters of the gastric slow wave that have potential diagnostic significance. We present a study in which the gastric syncytium was uncoupled by mechanical division as we recorded serosal electric potentials along with multichannel biomagnetic signals and cutaneous potentials. By computing the surface current density (SCD) from multichannel biomagnetic recordings, we were able to quantify gastric slow wave propagation as well as the frequency and amplitude of the slow wave and to show that these correlate well with similar parameters from serosal electrodes. We found the dominant slow wave frequency to be an unreliable indicator of gastric uncoupling as uncoupling results in the appearance of multiple slow wave sources at various frequencies in external recordings. The percentage of power distributed in specific frequency ranges exhibited significant postdivision changes. Propagation velocity determined from SCD maps was a weak indicator of uncoupling in this work; we believe that the relatively low spatial resolution of our 19-channel biomagnetometer confounds the characterization of spatial variations in slow wave propagation velocities. Nonetheless, the biomagnetic technique represents a non-invasive method for accurate determination of clinically significant parameters of the gastric slow wave.     

Effects of vasopressin and long pulse–low frequency gastric electrical stimulation on gastric emptying, gastric and intestinal myoelectrical activity and symptoms in dogs

The aim of this study was to investigate the effect of vasopressin and long pulse-low frequency gastric electrical stimulation (GES) on gastric emptying, gastric and intestinal myoelectrical activity and symptoms in dogs. The study was performed in eight healthy female dogs implanted with four pairs of gastric serosal electrodes and two pairs of small bowel serosal electrodes, and a duodenal fistula for the assessment of gastric emptying. Each dog was studied in three sessions on three separate days in a randomized order with recordings of gastric and small bowel slow waves. Each study session consisted of 30-min baseline, 30-min stimulation and 30-min recovery period. In sessions 1 and 2, infusion of either saline or vasopressin (0.75 U kg(-1) in 30 mL saline instilled in 30 min) was given during the second 30-min period. The protocol of session 3 was the same as session 2 except long pulse-low frequency GES was performed during the second 30-min period. It was found that: (i) Vasopressin significantly delayed gastric emptying 30 and 45 min after meal and GES did not improve the vasopressin induced delayed gastric emptying; (ii) Vasopressin induced gastric dysrhythmias and GES significantly improved vasopressin induced gastric dysrhythmia; (iii) Vasopressin also induced intestinal slow wave abnormalities but GES had no effect on vasopressin induced small bowel dysrhythmia; (iv) Vasopressin induced symptoms and behaviours suggestive of nausea that were not improved by GES. We conclude that: (i) Vasopressin delays gastric emptying and induces gastric and small bowel dysrhythmias and symptoms in the fed state, and (ii) long pulse-low frequency GES normalizes vasopressin induced gastric dysrhythmia with no improvement in gastric emptying or symptoms.     

Effect of fat preload on gastric myoelectrical activity in normal humans

The aim of this study was to investigate the effect of fat preload on gastric myoelectrical activity in normal humans. The study was performed in 10 normal subjects (five males, five females) fasted for 6h or more. Gastric myoelectrical activity was recorded using surface abdominal electrodes. In the study session the subjects ingested a 40-g liquid fat meal (2 oz of lipomul) after a 30-min baseline recording. A test meal (225 kcal beef stew) was then consumed 15 min after drinking the lipomul, and the recording was continued for 2 h after the test meal. The control session performed on a separate day followed the same procedure except that the lipomul was replaced by 2 oz of water. The order of the study and control sessions was randomized. The cutaneous recording of gastric myoelectrical activity (electrogastrogram or EGG) was digitized and subjected to computerized quantitative data analysis. The peak power and the corresponding frequency of the EGG during every 15-min time interval were computed using spectral analysis. Student's t-test was applied to determine the effect of fat preload on the surface recording of gastric myoelectrical activity. It was found that: (1) the power of the 15-min EGG at the dominant frequency immediately after fat preload was significantly lower than that of the baseline EGG (P = 0.01); (2) the postprandial power increase of the EGG at the dominant frequency was significantly lower with fat preload than with placebo preload (P = 0.002); (3) the dominant frequency of the EGG was not affected by fat preload. It was concluded that fat preload significantly decreases the power of the EGG but does not affect the frequency of the gastric slow wave.