Normalization of atropine-induced postprandial dysrhythmias with gastric pacing

Validation of noninvasive body-surface gastric mapping for detecting gastric slow-wave spatiotemporal features by simultaneous serosal mapping in porcine

Gastric disorders are increasingly prevalent, but reliable noninvasive tools to objectively assess gastric function are lacking. Body-surface gastric mapping (BSGM) is a noninvasive method for the detection of gastric electrophysiological features, which are correlated with symptoms in patients with gastroparesis and functional dyspepsia. Previous studies have validated the relationship between serosal and cutaneous recordings from limited number of channels. This study aimed to comprehensively evaluate the basis of BSGM from 64 cutaneous channels and reliably identify spatial biomarkers associated with slow-wave dysrhythmias. High-resolution electrode arrays were placed to simultaneously capture slow waves from the gastric serosa (32 × 6 electrodes at 4 mm spacing) and epigastrium (8 × 8 electrodes at 20 mm spacing) in 14 porcine subjects. BSGM signals were processed based on a combination of wavelet and phase information analyses. A total of 1,185 individual cycles of slow waves were assessed, out of which 897 (76%) were classified as normal antegrade waves, occurring in 10 (71%) subjects studied. BSGM accurately detected the underlying slow wave in terms of frequency (r = 0.99, P = 0.43) as well as the direction of propagation (P = 0.41, F-measure: 0.92). In addition, the cycle-by-cycle match between BSGM and transitions of gastric slow wave dysrhythmias was demonstrated. These results validate BSGM as a suitable method for noninvasively and accurately detecting gastric slow-wave spatiotemporal profiles from the body surface.NEW & NOTEWORTHY Gastric dysfunctions are associated with abnormalities in the gastric bioelectrical slow waves. Noninvasive detection of gastric slow waves from the body surface can be achieved through multichannel, high-resolution, body-surface gastric mapping (BSGM). BSGM matched the spatiotemporal characteristics of gastric slow waves recorded directly and simultaneously from the serosal surface of the stomach. Abnormal gastric slow waves, such as retrograde propagation, ectopic pacemaker, and colliding wavefronts can be detected by changes in the phase of BSGM.

The gastric conduction system in health and disease: a translational review

Gastric peristalsis is critically dependent on an underlying electrical conduction system. Recent years have witnessed substantial progress in clarifying the operations of this system, including its pacemaking units, its cellular architecture, and slow-wave propagation patterns. Advanced techniques have been developed for assessing its functions at high spatiotemporal resolutions. This review synthesizes and evaluates this progress, with a focus on human and translational physiology. A current conception of the initiation and conduction of slow-wave activity in the human stomach is provided first, followed by a detailed discussion of its organization at the cellular and tissue level. Particular emphasis is then given to how gastric electrical disorders may contribute to disease states. Gastric dysfunction continues to grow in their prevalence and impact, and while gastric dysrhythmia is established as a clear and pervasive feature in several major gastric disorders, its role in explaining pathophysiology and informing therapy is still emerging. New insights from high-resolution gastric mapping are evaluated, together with historical data from electrogastrography, and the physiological relevance of emerging biomarkers from body surface mapping such as retrograde propagating slow waves. Knowledge gaps requiring further physiological research are highlighted.

Electrical neuromodulation at acupoint ST36 normalizes impaired colonic motility induced by rectal distension in dogs

Electroacupuncture (EA) has been shown to improve impaired gastric motility and slow waves in both humans and animals. However, its effects on colonic motility have rarely been investigated. The aim of this study was to investigate the effects and underlying mechanisms of EA on impaired colonic motility induced by rectal distension (RD)in dogs. Colon contractions and transit were measured in various sessions with and without EA in hound dogs chronically placed with a colonic cannula. Colonic contractile activity was assessed by motility index (MI). Autonomic functions were determined by the spectral analysis of the heart rate variability derived from the electrocardiogram. It was found 1) RD suppressed colonic motility by 40.5% (10.8 ± 0.9 with RD vs. 6.4 ± 0.8 at baseline, P < 0.002). EA at ST36 normalized colonic contractions suppressed by RD (12.9 ± 2.8, P < 0.002 vs. RD and P = 0.1 vs. control). 2) Administration of atropine blocked the ameliorating effect of EA on colon motility. 3) RD also delayed colonic transit (65.0 ± 2.0% with RD vs. 86.0 ± 1.9% without RD, P < 0.001) that was restored with EA (84.0 ± 1.9%, P = 0.178 vs. control). 4) EA increased vagal activity suppressed by RD (0.37 ± 0.07 with RD + EA vs. 0.09 ± 0.03 with RD without EA, P < 0.001). In conclusion, RD inhibits colonic contractions and delays colonic transit in dogs; EA at ST36 restores the RD-induced impairment in both colonic contraction and transit by enhancing vagal activity and mediated via the cholinergic pathway.

Pacing the gut in motility disorders

Similar to cardiac pacing, gastrointestinal (GI) pacing is an attractive idea and may become a promising therapy, as the GI organs, like the heart, have their own natural pacemakers. Over the past 10 years, electrical stimulation of the gut has received increasing attention among researchers and clinicians. Several clinical studies have shown that gastric electrical stimulation (GES) with short pulses is able to reduce nausea and vomiting in patients with gastroparesis and that GES with long pulses is able to pace the intrinsic gastric slow waves and thus normalize gastric dysrhythmia. However, possible placebo effects cannot be ruled out, although recent animal studies have revealed various peripheral and central mechanisms involved with GES. Electrical stimulation of the small intestine, colon, or anal sphincter also has been reported for the treatment of dumping syndrome, constipation, and fecal incontinency. Similarly, there is a lack of placebo-controlled studies. In our opinion, pacing of the gut has great potential for the treatment of various GI motor disorders. However, none of the commercially available devices is designed for pacing the gut. The lack of well-suited devices and the invasive nature of gut pacing slow down the progress and clinical applications of gut pacing.

Gastric electrical stimulation for gastroparesis: a goal greatly pursued, but not yet attained

The lack of an effective medical treatment for gastroparesis has pushed the research of new techniques of gastric electrical stimulation (GES) for nearly half a century of experimentation with a large variety of electrical stimuli delivered to the gastric wall of animals and patients with gastroparesis. Three principal methods are currently available: gastric low-frequency/high-energy GES with long pulse stimulation, high-frequency/low-energy GES with short pulse stimulation and neural sequential GES. The first method aims to reset a regular slow wave rhythm, but has variable effects on contractions and requires devices with large and heavy batteries unsuitable for implantation. High-frequency/low-energy GES, although inadequate to restore a normal gastric electro-mechanical activity, improves dyspeptic symptoms, such as nausea and vomiting, giving patients a better quality of life together with a more satisfactory nutritional status and is suitable for implantation. Unfortunately, the numerous clinical studies using this type of GES, with the exception of two, were not controlled and there is a need for definitive verification of the effectiveness of this technique to justify the cost and the risks of this procedure. The last method, which is neural sequential GES, consists of a microprocessor-controlled sequential activation of a series of annular electrodes along the distal two thirds of the stomach and is able to induce propagated contractions causing forceful emptying of the gastric content. The latter method is the most promising, but has been used only in animals and needs to be tested in patients with gastroparesis before it is regarded as a solution for this disease.

Cellular effects of gastric electrical stimulation on antral smooth muscle cells in rats

The cellular effects of gastric electrical stimulation (GES), which has recently been introduced as a potential therapy for the treatment of gastroparesis and obesity, were investigated in rat antrum smooth muscle cells (SMCs). Effects on cell membrane potentials of single electrical current pulses (pulse width from 0.1 ms to 200 ms) and 2-s pulse train stimuli with different pulse widths (0.1–4 ms), different frequencies (20–200 Hz), and different intensities were studied: 1) the stimulus amplitude had an exponential relationship to the pulse width from 2 ms to 200 ms, along with a rapidly rising strength-duration curve at pulse widths less than 5 ms, and a relatively flat curve at pulse widths greater than 50 ms; 2) when the pulse frequency was at 80 Hz or above, pulse train electrical stimulation, with a pulse width of 2 ms or above but not ≤1 ms, was able to depolarize cell membrane potentials to above −30 mV and/or generate action potentials. Electrical stimulation with a single long pulse and a width of 50 ms or greater is effective in depolarizing cell membrane potentials of SMCs with low amplitude. Pulse train electrical stimulation with a pulse width of ≤1 ms fails to generate action potentials in SMCs, whereas pulse train electrical stimulation with a pulse width of 2–4 ms and a sufficiently high pulse frequency is able to generate action potentials. These cellular findings may be useful in optimizing stimulation parameters of GES.

Effect of two-channel gastric electrical stimulation with trains of pulses on gastric motility

AIM: To investigate the effect of two-channel gastric electrical stimulation (GES) with trains of pulses on gastric emptying and slow waves.

METHODS: Seven dogs implanted with four pairs of electrodes and equipped with a duodenal cannula were involved in this study. Two experiments were performed. The first experiment included a series of sessions in the fasting state with trains of short or long pulses, each lasted 10 min. A 5-min recording without pacing was made between two sessions. The second experiment was performed in three sessions (control, single-channel GES, and two-channel GES). The stimulus was applied via the 1st pair of electrodes for single-channel GES (GES via one pair of electrodes located at 14 cm above the pylorus), and simultaneously via the 1st and 3rd channels for two-channel GES (GES via two pairs of electrodes located at 6 and 14 cm above the pylorus). Gastric liquid emptying was collected every 15 min via the cannula for 90 min.

RESULTS: GES with trains of pulses at a pulse width of 4 ms or higher was able to entrain gastric slow waves. Two-channel GES was about 50% more efficient than single-channel GES in entraining gastric slow waves. Two-channel but not single-channel GES with trains of pulses was capable of accelerating gastric emptying in healthy dogs. Compared with the control session, two-channel GES significantly increased gastric emptying of liquids at 15 min (79.0% ± 6.4% vs 61.3% ± 6.1%, P < 0.01), 30 min (83.2% ± 6.3 % vs 68.2% ± 6.9%, P < 0.01), 60 min (86.9% ± 5.5 % vs 74.1% ± 5.9%, P < 0.01), and 90 min (91.0% ± 3.4% vs 76.5% ± 5.9%, P < 0.01).

CONCLUSION: Two-channel GES with trains of pulses accelerates gastric emptying in healthy dogs and may have a therapeutic potential for the treatment of gastric motility disorders.

Effect of intestinal pacing on small bowel transit and nutrient absorption in healthy volunteers

BACKGROUND

Intestinal pacing (IP) has been previously shown to delay gastric emptying and reduce food intake in animals. The aims of this study were to investigate the effect and mechanism of IP on nutrient absorption in healthy volunteers.

METHODS

Twelve healthy volunteers (six men, six women) were involved in a two-session (one session without IP and one with IP) study. At the beginning of each session, a nasal-duodenal feeding tube, with two ring electrodes (used for IP) on the tip of the tube, was incubated into the duodenum under endoscopy. After a complete recovery from the incubation, the duodenum was infused via the feeding tube with 150 ml 30% intralipid + 25 g D-xylose within 30 min, and the stool was collected for 24 h for the analysis of fecal lipid during which a controlled meal was taken. Then 100 ml 1mCi(99)Tc-labeled non-absorbable solution was infused within 3 min. The subject was asked to lie under a gamma camera for at least 1 h for the measurement of small bowel transit. The movement of isotopes was monitored by gamma camera at an interval of 10 s. The first appearance of isotopes in the cecum was considered as small intestinal transit time. The order of the two sessions was randomized and 1 week apart. In the IP session, intestinal pacing was performed via the pair of the ring electrodes for 2 h initiated at the beginning of infusion with a pacing frequency of 13 pulses/min, pulse width of 300 ms and amplitude of 5 mA.

RESULTS

(1) IP significantly reduced lipid and D-xylose absorption. The fecal lipid was 6.6 +/- 4.6 g without IP and almost doubled with IP (11.1 +/- 6.5 g, P = 0.047). Similarly, the D-xylose in urine was 3.46 +/- 2.22 g with IP, which was significantly lower than that without IP (6.63 +/- 5.06 g, p = 0.049). (2) IP accelerated intestinal transit. The transit time was 39 +/- 17 min in the control session and reduced to 28 +/- 10 min in the IP session (p < 0.03). (3) Diarrhea was reported in one subject without IP but in six subjects with IP (p < 0.05).

CONCLUSIONS

The increased fecal lipid and induction of diarrhea with intestinal pacing suggest that intestinal pacing is capable of inducing malabsorption. This effect maybe contributed to the acceleration of intestinal transit.

The effect on gastric tone of gastric electrical stimulation with trains of short pulses varies with sites and stimulation conditions

BACKGROUND

Gastric electrical stimulation (GES) can improve symptoms in patients with gastroparesis and induce weight loss in obese subjects.

AIMS

To evaluate the effect on gastric tone of GES under different conditions at different sites of the stomach.

METHODS

Eleven dogs were implanted with a gastric cannula and two pairs of stimulation electrodes (in the middle of the lesser curvature and of the greater curvature, 10 cm from the pylorus). Gastric tone was assessed with a barostat. GES was applied using: (1) Enterra conditions (14 Hz, 5 mA, 0.3 ms, 0.1 s on, 5 s off); (2) modified Enterra conditions (40 Hz, 5 mA, 0.3 ms, 0.1 s on, 5 s off); and (3) implantable gastric stimulation (IGS) conditions (40 Hz, 5 mA, 0.3 ms, 2 s on, 3 s off). Six sessions were performed randomly with each animal on six separate days.

RESULTS

(1) At the lesser curvature, GES with modified Enterra conditions significantly elevated gastric volume from 96.9 +/- 8.3 ml at baseline to 133.9 +/- 11.7 ml (P = 0.015) and a similar effect was observed with IGS (91.3 +/- 7.1 ml vs. 186.3 +/- 27.1 ml, P = 0.013). GES with Enterra conditions had no such an effect. (2) At the greater curvature, GES with Enterra conditions significantly increased gastric volume from basal 94.1 +/- 4.4 ml to 122.1 +/- 11.3 ml (P = 0.032); modified Enterra conditions had the opposite effect (96.5 +/- 9.0 ml vs. 77.4 +/- 11.7 ml, P = 0.025) and no significant effect was observed with IGS conditions.

CONCLUSION

The effects of GES on gastric tone vary with the conditions and sites of stimulation. These findings may help to explain the distinct effects of GES therapy in patients with gastroparesis and obesity.

Two-channel gastric pacing with a novel implantable gastric pacemaker accelerates glucagon-induced delayed gastric emptying in dogs

BACKGROUND

The aim of the current study was to investigate the efficacy of 2-channel gastric electrical stimulation (GES) with a custom-made implantable pacemaker on delayed gastric emptying and gastric dysrhythmia induced by glucagon in dogs.

METHODS

Six dogs were studied in 4 randomized session (saline, glucagon, glucagon with single-channel or 2-channel GES). GES was applied via the first pair of electrodes for single-channel GES or the first and third pairs of electrodes for 2-channel GES. Gastric emptying was assessed for 90 minutes and gastric slow waves were recorded at the same time.

RESULTS

Both single-channel and 2-channel GES improved gastric dysrhythmia (P < .05 vs glucagon session). Two-channel GES but not single-channel GES improved glucagon-induced delayed gastric emptying at 30 minutes, 45 minutes, 60 minutes, 75 minutes, and 90 minutes.

CONCLUSION

Two-channel GES with a novel implantable pacemaker is more efficient and effective than single-channel GES in improving delayed gastric emptying induced by glucagon. This implantable multipoint pacemaker may provide a new option for treatment of gastric motility disorders.

Gastric electrical stimulation inhibits postprandial antral tone partially via nitrergic pathway in conscious dogs

Gastric electrical stimulation (GES) has recently been explored as a therapeutic option for gastrointestinal motility disorders or obesity. The mechanism behind it is not fully elucidated. The aims of this study were to assess the effects of GES with different parameters on antral tone and to explore the involvement of the nitrergic pathway. Eight dogs equipped with a gastric cannula and one pair of serosal electrodes in the greater curvature 4 cm above the pylorus were studied on separate days. The study was composed of seven randomized sessions in the fed state [control, GES with different parameters, and GES plus neuronal nitric oxide synthase (nNOS) inhibitor]. Each session included three consecutive 30-min periods (baseline, GES, and recovery). GES was performed with long pulses or pulse trains. The antral volume was measured using an intragastric balloon connected with a barostat device. Behaviors of the dogs during each stimulation period were also noted. We found that 1) postprandial antral tone was reduced with GES with all tested parameter settings, reflected as a significant and substantial increase in antral volume ranging from 179 to 309%; 2) the inhibitory effect of GES on antral tone was partially blocked (decreased by 39.5%) with an nNOS inhibitor; and 3) mild symptoms were induced with GES and found to be correlated with the GES-induced increase in antral volume. We conclude that retrograde GES with long pulses or pulse trains inhibits antral tone, and this inhibitory effect is partially mediated via the nitrergic pathway. These results suggest that retrograde GES may have a therapeutic potential for obesity.

Cross-talk along gastrointestinal tract during electrical stimulation: effects and mechanisms of gastric/colonic stimulation on rectal tone in dogs

Gastric electrical stimulation (GES) has been shown to alter motor and sensory functions of the stomach. However, its effects on other organs of the gut have rarely been investigated. The study was performed in 12 dogs implanted with two pairs of electrodes, one on the serosa of the stomach and the other on the colon. The study was composed of two experiments. Experiment 1 was designed to study the effects of GES on rectal tone and compliance in nine dogs compared with colonic electrical stimulation (CES). Rectal tone and compliance were assessed before and after GES or CES. Experiment 2 was performed to study the involvement of sympathetic pathway in 8 of the 12 dogs. The rectal tone was recorded for 30-40 min at baseline and 20 min after intravenous guanethidine. GES or CES was given for 20 min 20 min after the initiation of the infusion. It was found that both GES and CES reduced rectal tone with comparable potency. Rectal compliance was altered neither with GES, nor with CES. The inhibitory effect of GES but not CES on rectal tone was abolished by an adrenergic blockade, guanethidine. GES inhibited rectal tone with a comparable potency with CES but did not alter rectal compliance. The inhibitory effect of GES on rectal tone is mediated by the sympathetic pathway. It should be noted that electrical stimulation of one organ of the gut may have a beneficial or adverse effect on another organ of the gut.

Gastroduodenal motility

Several major themes emerged over the past year in the area of gastroduodenal motility. Mostly, these themes represented extensions of research areas discussed in prior reviews in this series rather than the emergence of completely new concepts. Thus, for example, considerable emphasis has again been placed on regional gastric motor function in dyspepsia and on the role of fundic relaxation and accommodation, in particular. Not surprisingly, basic physiologic research has also shown a keen interest in the regulation of fundic relaxation. One new and exciting development is the recognition of the stomach's role in satiety. The spectrum of gastric motor dysfunction in diabetes mellitus continues to be explored, and the important role of hyperglycemia in regulating gastric function has been further emphasized. More data have been provided on noninvasive alternatives to gastric motor function testing, and several studies have looked at factors that may influence variability in these various tests. There have been few innovations over the past year in the therapeutic arena; rather, the indications and limitations of current therapies have been further developed.