Effects of Gastric Electrical Stimulation with Short Pulses and Long Pulses on Gastric Dysrhythmia and Signs Induced by Vasopressin in Dogs

Aims: This study was to investigate the effect of gastric electrical stimulation (GES) with short pulses, long pulses, short-pulse trains or long-pulse trains on gastric dysrhythmia and motion-sickness signs induced by vasopressin. Methods: Seven male beagle dogs implanted with four pairs of electrodes on gastric serosa were studied. The study was performed in six sessions in a randomized order. In session 1 or 2, either saline or vasopressin was infused without GES. In session 3, 4, 5 and 6, GES with short pulses, long pulses, trains of short pulses or trains of long pulses was performed before and during vasopressin infusion. Gastric slow waves and motion-sickness signs were recorded in each session. Results: (1) Vasopressin induced gastric dysrhythmia and motion sickness-like signs (ANOVA, P < 0.001). (2) GES with short pulses or trains of short pulses was capable of preventing vasopressin-induced emetic response (P < 0.001), but did not normalize gastric dysrhythmia. (3) GES with long pulses or trains of long pulses was able to normalize gastric dysrhythmia induced by vasopressin (P < 0.001), but showed no effects on vasopressin-induced motion-sickness signs. Conclusion: GES with short pulses or trains of short pulses prevents vasopressin-induced emetic response with no improvement in gastric dysrhythmia. GES with long pulses or trains of long pulses normalizes gastric dysrhythmia induced by vasopressin with no effects on signs. Xiaohua Hou and Geng-Qing Song contributed equally to this work.     

Gastric Electrical Stimulation With Parameters for Gastroparesis Enhances Gastric Accommodation and Alleviates Distention-Induced Symptoms in Dogs

Gastric electrical stimulation (GES) improves symptoms in patients with gastroparesis. We sought to determine if stimulation at fundus with parameters used for gastroparesis could affect gastric accommodation and distention-induced symptoms in dogs. Nine dogs were implanted with a gastric cannula at the anterior stomach and 1 pair of stimulation electrodes in the fundus. Assessment of gastric accommodation and a series of gastric distention were performed using a barostat. Stimulation parameters were of short pulse trains of 14 Hz, 5 mA, 0.3 ms, and 0.1 s on, 5 s off. GES at fundus significantly decreased fasting gastric tone. Fasting gastric volume was significantly increased from 56.3+/-10.4 mL at baseline to 102.4+/-23.1 mL with stimulation (P=.011). Postprandial gastric accommodation was significantly enhanced with stimulation. The extent of accommodation increased from 249.3+/-39.9 mL in the control session to 325.8+/-25.1 mL with stimulation (P=.011). Symptom scores induced by balloon distention of the stomach were significantly lower during stimulation in comparison with those of baseline (P=.016). In conclusion, GES with parameters for gastroparesis enhances postprandial gastric accommodation and reduces visceral perception in normal dogs. This effect, if seen also in humans, may explain in part the symptomatic improvement associated with GES therapy in patients with gastroparesis.     

Inhibitory Effects of Gastrointestinal Electrical Stimulation on Rectal Tone are both Organ-Specific and Distance-Related in Dogs

Purpose A phenomenon of cross-talk has been noted that electrical stimulation of one part of the gut affects another part of the gut. This study was designed to investigate whether the effect of electrical stimulation of one part of the gut on another part of the gut was related to the organ or the distance between the stimulation site and the affected organ, and the mechanism of ileum electrical stimulation on rectal tone. Methods This study was performed in 13 healthy dogs (16–28 kg) in the fasting state. Experiments were performed to study 1) effects of gastric electrical stimulation, duodenal electrical stimulation, ileum electrical stimulation, and colonic electrical stimulation on rectal tone, and 2) the sympathetic and nitrergic pathways involved in the effects of ileum electrical stimulation on rectal tone. A computerized barostat was used to assess rectal tone. Results All methods of stimulations significantly inhibited rectal tone. Duodenal electrical stimulation was least effective in reducing rectal tone. The percentage of increase in rectal volume was distance-related with duodenal electrical stimulation, ileum electrical stimulation, and colonic electrical stimulation but organ-specific with gastric electrical stimulation. The inhibitory effect of ileum electrical stimulation on rectal tone was abolished by N _ω -nitro-L-arginine but not guanethidine. Conclusions Electrical stimulation of the stomach, intestine, or colon with long pulses has an inhibitory effect on rectal tone. This inhibitory effect is organ-specific as well as associated with the distance between stimulation site and affected organs. The inhibitory effect of ileum electrical stimulation on rectal tone is mediated by the nitrergic but not sympathetic pathway. Presented at Neurogastroenterology and Motility Joint International Meeting, Boston, Massachusetts, September 14 to 17, 2006.     

Inhibitory Effects and Mechanisms of Colonic Electric Stimulation on Gastric and Rectal Tone in Conscious Dogs

Purpose Colonic electric stimulation has been shown to alter motor functions of the colon; however, its effects on other organs of the gut have been investigated rarely. Methods This study was performed in 12 dogs implanted with one pair of colonic serosal electrodes and a gastric cannula. Experiments were performed to study: 1) the effect of colonic electric stimulation on proximal gastric tone and compliance; 2) the effect of colonic electric stimulation on rectal tone and compliance; 3) the sympathetic mechanism involved in the effects of colonic electric stimulation on gastric/rectal tone. A computerized barostat was used to assess gastric/rectal tone and compliance. Results Colonic electric stimulation inhibited both gastric and rectal tone with a higher potency in gastric tone. Colonic electric stimulation reduced gastric but not rectal compliance. The inhibitory effect of colonic electric stimulation on gastric tone but not rectal tone was abolished by an adrenergic blockade, guanethidine. Conclusions Colonic electric stimulation inhibits both gastric and rectal tone with a higher potency in inhibiting gastric tone. Colonic electric stimulation reduces gastric but not rectal compliance. The inhibitory effect of colonic electric stimulation on gastric tone seems to be mediated by the sympathetic pathway.     

Cisplatin-Induced Gastric Dysrhythmia and Emesis in Dogs and Possible Role of Gastric Electrical Stimulation

The aim of this study was to investigate the effect of cisplatin on gastric myoelectrical activity and the role of gastric electrical stimulation in the treatment of cisplatin-induced emesis in dogs. Seven dogs implanted with electrodes on the gastric serosa were used in a two-session study. Cisplatin was infused in both the control session and the gastric electrical stimulation session, and gastric electrical stimulation was applied in the gastric electrical stimulation session. Gastric slow waves and emesis, as well as behaviors suggestive of nausea, were recorded during each session. The results were as follows: (1) cisplatin induced vomiting and other symptoms and induced gastric dysrhythmia. The percentage of normal slow waves decreased significantly during the 2.5 h before vomiting (P = 0.01) and the period of vomiting (P < 0.001). (2) Gastric electrical stimulation reduced emesis and the symptoms score. The total score in the control session was higher than that in the gastric electrical stimulation session (P = 0.02). However, gastric electrical stimulation had no effects on gastric dysrhythmia. It is concluded that cisplatin induces emesis and gastric dysrhythmia. Gastric electrical stimulation may play a role in relieving chemotherapy-induced emetic responses and deserves further investigation.     

Effect of Acute Gastric Electrical Stimulation on the Systemic Release of Hormones and Plasma Glucose in Dogs

This study evaluated the effect of gastric electrical stimulation (GES) with various parameters on plasma concentrations of satiety-related peptides and glucose. GES was performed in nine healthy dogs via electrodes implanted in the middle of the lesser curvature. Four sessions were performed in each animal: control, stimulation with IGS (implantable gastric stimulation for obesity, 0.3 m sec), modified IGS (2 msec), and long pulses (300 msec). Blood samples were collected at 15 and 0 min before the meal and at 15, 30, and 60 min after the meal. GES was initiated 30 min before the first blood sample and maintained throughout collection. Plasma ghrelin, leptin, insulin and glucose were measured. The total AUCs of plasma ghrelin and leptin were not significantly affected by GES. The total AUC of plasma insulin was significantly lower with IGS and long pulse parameters (P < 0.05). The total AUC for plasma glucose was significantly lower in sessions with long pulses and modified IGS parameters (P < 0.05). We conclude that acute GES is able to change the release of some satiety-related peptides. Whether this is associated with the changed eating behavior and weight loss in obese patients needs further investigation.     

Gastric electrical stimulation: An emerging therapy for children with intractable gastroparesis

Management of gastroparesis remains challenging, particularly in pediatric patients. Supportive care and pharmacological therapies for symptoms remain the mainstay treatment. Although they are effective for mild and some moderately severe cases, often time they do not work for severe gastroparesis. There are a few prokinetics available, yet the use of these drugs is limited by a lack of persistent efficacy and/or safety concerns. Currently, the only modality for adult patients with severe intractable gastroparesis is surgery, e.g., pyloroplasty and partial gastrectomy, however, this option is generally considered too radical for a growing child. Novel therapeutic approaches, particularly those which are less invasive, are needed. This article explores gastric electrical stimulation (GES), a new therapy for gastroparesis. Unlike others, it neither needs medications nor gastrectomy; rather, it treats through the use of microelectrodes to deliver high-frequency low energy electric stimulation to the pacemaker area of the stomach. Thus, it is tolerated and safe in children. Like in adult patients, GES appears to work in releasing symptoms, improving nutrition, and enhancing the quality of life; it also helps wean off medications and eliminate many needs for hospitalization. Considering the transient nature of gastroparesis in children in many occasions, GES is considered a “bridging” therapy after failed medical interventions and before surgery.     

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 rain （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 rain （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.     

胃电刺激对胃电节律紊乱的作用

背景:胃电刺激已成为一种潜在的治疗胃动力障碍性疾病的方法。目的:观察、比较单导联和两导联长脉冲胃电刺激对胃电节律紊乱和呕吐相关样症状的作用。方法:以静脉滴注垂体后叶素(一种血管加压素)建立犬胃动力紊乱模型,将多导电刺激器与胃浆膜电极相连,输入最佳刺激参数以控制胃慢波,评估盐水组、垂体后叶素组和单导联、两导联胃电刺激组在静脉滴注生理盐水或垂体后叶素的30min里的症状评分并全程记录四导联胃肌电活动。结果:垂体后叶素能诱导胃电节律紊乱和呕吐相关样症状(P<0.05)。单导联和两导联长脉冲胃电刺激均能纠正胃电节律紊乱(P<0.01),但对呕吐相关样症状无明显缓解作用(P>0.05)。两导联胃电刺激纠正胃电节律紊乱的最佳刺激能量(320ms×mA±43ms×mA)显著低于单导联胃电刺激(2 750ms×mA±186ms×mA)(P<0.01)。结论:单导联和两导联长脉冲胃电刺激能纠正垂体后叶素诱导的胃电节律紊乱,但不能缓解呕吐相关样症状。两导联胃电刺激控制胃慢波所需的刺激能量较单导联胃电刺激低。     

外源性胃电刺激对犬胃慢波的作用

目的探讨外源性胃电刺激完全控制胃慢波的最佳刺激方法和最佳刺激参数。方法在8条比格犬的胃大弯浆膜层埋植4对电极,分4组:单导联刺激组、两导联刺激组、三导联刺激组和三导联延迟刺激组。多导联电刺激器与距胃窦上6、10和14cm的浆膜电极相连并输入不同宽度和振幅的脉冲以控制胃慢波。运用多导联胃电记录仪记录胃肌电活动。观察实验中胃慢波、脉冲宽度和振幅。结果长脉冲胃电刺激能控制胃慢波。单导联刺激组所需的最佳刺激能量最小(51.25±12.46,P<0.01)。三导联刺激组较其延迟刺激组所需的最佳刺激能量值低(P<0.01)。刺激前后胃肌电活动的主功和胃慢波的传播速度差异无统计学意义(P>0.05)。结论长脉冲胃电刺激能控制胃慢波,但对胃肌电活动的主功和传播速度无作用。单导联胃电刺激控制胃慢波所需的刺激能量最小。导联之间的延迟时间能增加控制胃慢波所需的最佳刺激能量。     

Entrainment of Segmental Small Intestinal Slow Waves with Electrical Stimulation in Dogs

The aim of this study was to derive effective pacing parameters for the entrainment of segmental intestinal myoelectrical activity. The study was performed in 12 dogs. Four pairs of electrodes were implanted on the serosa of the jejunum. Electrical stimulation of the small intestine was performed via the most proximal pair. For the slow waves within a distance of 5 cm, a complete entrainment was achieved with a pacing frequency of 1.1 times the intrinsic frequency (IF), a pulse width of 140 msec, and an amplitude of 4 mA. The time required for the entrainment was 25.6 ± 2.7 sec. The maximum driven frequency was 1.38 ± 0.03 IF. The percentage of the entrainment at this frequency was 44.0 ± 3.9%. The data indicate that pacing is able to completely entrain segmental intestinal myoelectrical activity, suggesting that normalization of intestinal myoelectrical dysrhythmia is feasible with pacing.     

Gastric Electrical Stimulation Does Not Significantly Affect Canine Gastric Acid Secretion and 24-Hour Gastric pH

Gastric electrical stimulation (GES) was shown to improve symptoms in patients with gastroparesis. However, the underlying mechanisms remain unclear. This study assessed the influence of various patterns of GES on fasting and postprandial gastric acid secretion and 24-hr gastric pH. Eight healthy dogs were studied and we found that in the fasting state, low-frequency, long-pulse (6/12-cpm, 375-msec, 4-mA) GES at the proximal stomach significantly inhibited the secretion of gastric juice (P < 0.05). No such effect was observed during GES (6/12 cpm) at the distal stomach. In the postprandial period, low-frequency, long-pulse GES at both proximal and distal sites and at both frequencies did not significantly affect gastric acid secretion. High-frequency, short-pulse GES, investigated for obesity (21 Hz, 8 mA, and 250 microsec, with 2 secs on, 3 sec off), at the proximal and distal stomach did not significantly affect the 24-hr gastric pH profile. In conclusion, GES with various stimulation parameters, and at various sites, has little effect on gastric acid secretion. The clinical effects induced by GES at these parameters may not be related to their effect on gastric acid homeostasis.     

Potassium and Magnesium Changes Associated with Programmed Electrical Stimulation

Serum potassium and magnesium concentrations decrease secondary to an increase in catecholamine concentrations. We hypothesized that during programmed electrical stimulation (PES), where stress of the procedure may elevate catecholamine levels, potassium and magnesium concentrations would decrease. To test this hypothesis, potassium and magnesium concentrations were measured at baseline, during, and after PES in 16 patients. Potassium concentrations (mean ± standard deviation) decreased from 4.5 ± 0.3 (mEq/L) at baseline to 3.9 ± 0.2 during PES (P < 0.05). At 2 hours post-PES, serum potassium concentrations returned to baseline values (mean 4.2 ± 0.5 mEq/L, P > 0.05 compared to baseline). Mean magnesium concentrations (mmol/L) decreased from 0.84 ± 0.07 at baseline to 0.81 ± 0.07 at the end of PES (P < 0.05) but did not decrease significantly during PES.
In conclusion, potassium concentrations decreased significantly during PES, whereas magnesium concentrations decreased slightly but significantly at the end of PES. These changes in electrolyte concentrations may be due to catecholamine influence secondary to the PES procedure. In light of these observations, serum concentrations of potassium and magnesium should be normalized prior to PES procedure in order to prevent hypokalemia and hypomagnesemia.     

Effects and Mechanisms of Vaginal Electrical Stimulation on Rectal Tone and Anal Sphincter Pressure

Purpose This study was designed to evaluate the effect of vaginal electrical stimulation on rectal tone and compliance and anal sphincter pressure and to explore possible mechanisms involved in the effects of vaginal electrical stimulation on rectal tone in conscious dogs. Methods Seven dogs inserted with a probe with two ring electrodes were studied. The study included two experiments. The first experiment was composed of two series of sessions rectal tone and compliance; and anal sphincter pressure. Each series included three sessions: vaginal electrical stimulation with long pulses, vaginal electrical stimulation with trains of long pulses, and vaginal electrical stimulation with trains of short pulses. The second experiment was performed in two sessions: vaginal electrical stimulation with long pulses plus guanethidine, and vaginal electrical stimulation with trains of long pulses plus guanethidine. In each session, rectal tone was recorded. Results 1) Vaginal electrical stimulation with long pulses or trains of long pulses but not trains of short pulses significantly decreased rectal tone and increased anal sphincter pressure. 2) None of the vaginal electrical stimulation methods altered rectal compliance. 3) The inhibitory effect of vaginal electrical stimulation on rectal tone was abolished by guanethidine. Conclusions Vaginal electrical stimulation with long pulses or trains of long pulses but not trains of short pulses reduces rectal tone and increases anal sphincter pressure. The inhibitory effect of vaginal electrical stimulation on rectal tone is mediated by the sympathetic pathway. These findings suggest that vaginal electrical stimulation may be a potential therapy for fecal incontinence. Presented at Digestive Disease Week, Los Angeles, California, May 21 to 26, 2006.     

Effects and Mechanisms of Anal Electrical Stimulation on Anorectal Compliance and Tone in Dogs

Purpose This study was designed to investigate the changes in rectal compliance and tone during anal electric stimulation and the involvement of the α-adrenergic pathway in conscious dogs. Methods Eight healthy dogs were studied in five randomized sessions. Anal sphincter pressure was quantified by using the area under the contractile curve. Rectal compliance and tone were measured in a pressure-controlled phasic and isobaric distention by using an electronic barostat. Anal electric stimulation was performed via a pair of ring electrodes attached to the catheter. Results The electric stimulation-induced increase in sphincter pressure was lowered by the presence of an α₁-adrenergic receptor antagonist, prazosin (18.6 ± 7.4 vs. 45.4 ± 9.7, P < 0.05), or α₂-adrenergic receptor antagonist, yohimbine (10.2 ± 8.2 vs. 38.3 ± 7.6, P < 0.05), compared with the control. The threshold volume in rectoanal inhibitory reflex during electric stimulation was significantly higher than during baseline (27.5 ± 0.9 vs. 22.5 ± 1.9 ml, P < 0.05). There were no significant differences between the percentage drops in sphincter pressure with and without stimulation at a rectal distention level of 45 ml of air. Anal electric stimulation significantly increased rectal compliance reflected as reduced P_1/2 (11.1 ± 1.5 vs. 16.7 ± 1.1, P = 0.027) and reduced κ (11.6 ± 2.5 vs. 20.5 ± 2.6, P = 0.0095), compared with the control session, but did not significantly alter rectal tone. Conclusions Anal electric stimulation increases anal sphincter pressure, mediated at least partially by the α-adrenergic pathway. It also increases rectal compliance but does not alter rectal anal inhibitory reflexes.     

Ultrarapid Train Stimulation Versus Conventional Programmed Electrical Stimulation for Induction of Ventricular Arrhythmias in Patients with Coronary Artery Disease

Conventional programmed electrical stimulation (PES) of the ventricle isuseful for establishing inducibility or noninducibility of clinicalventricular arrhythmias (VA) but is complex and time consuming. The presentstudy was designed to compare a standard PES protocol with an alternativemethod using ultrarapid train stimulation in patients with VA and coronaryartery disease (CAD). A prospective, randomized, crossover design was used.During each session in the electrophysiology laboratory, patients werestudied using both the trains and PES protocols in randomized order. In 82matched pairs of comparisons in 50 patients, results were concordant in85% (p < 0.0001). There were no differences related to type ofclinical arrhythmia or to the presence of antiarrhythmic drugs. There wereno significant differences in the induction of nonclinical arrhythmias withthe two methods (p < 0.0001 for concordance). There were no significantdifferences related to the cycle length of the trains (10, 20, or 30 ms,equivalent to 100, 50, or 33 Hz). The number of drive-extrastimuli sequencesand the time required to complete the trains protocol was significantlyshorter (p < 0.0001) using trains versus PES. Ultrarapid train stimulationprovides results in CAD patients that are comparable with those ofconventional PES protocols. There is a significant savings in time, addingpractical value to intrinsic electrophysiologic interest. Trains may beuseful when multiple inductions are desirable, for example, in the settingof antitachycardia pacing parameters in an implantable defibrillator (ICD),during ICD implantation, or in other circumstances where the main questionis inducibility of ventricular arrhythmias.     

胃起搏对大鼠胃窦肌间神经丛单胺氧化酶mRNA表达的影响

目的研究胃窦肌间神经丛中单胺氧化酶mRNA表达,探讨5羟色胺(5-HT)在胃起搏机制中的作用。方法通过手术建立Wistar大鼠胃起搏模型(近远端胃各缝制一对电极),分为起搏组(n=10)和对照组(n=6)。采用逆转录聚合酶链反应(RT-PCR)检测起搏组和对照组胃窦肌间神经丛中MAO-A mRNA、MAO-B mRNA的表达量,以恒定表达的β-actin作为内参照。计算MAO-AmRNA、MAO-B mRNA与β-actin mRNA表达积分光密度值的比例(MA/B,MB/B),以反映组织中MAO-AmRNA、MAO-B mRNA的相对表达量。结果RT-PCR研究显示起搏组MAO-A mRNA表达显著弱于对照组,起搏组MA/B比值明显较对照组较少(0.37±0.11vs0.95±0.57,P<0.001);而起搏组MAO-B mRNA表达与对照组无差别,两组间MB/B比值比较也无显著性意义(0.97±0.24vs1.01±0.58,P>0.05)。结论胃起博后胃肌间神经丛内单胺氧化酶mRNA表达量明显减少,表明胃窦肌间神经丛内5-HT可能在胃起搏中发生了重要作用。     

Endocardial Stimulation of Efferent Parasympathetic Nerves to the Atrioventricular Node in Humans: Optimal Stimulation Sites and the Effects of Digoxin

The purposes of this study were to identify optimal sites of stimulation of efferent parasympathetic nerve fibers to the human atrioventricular node via an endocardial catheter and to investigate the interaction between digoxin and vagal activation at the end organ. Methods: The ventricular rate was measured during atrial fibrillation, prior to and during parasympathetic nerve stimulation, in 8 patients taking digoxin and in 10 controls. High frequency electrical stimuli were delivered via an hexapolar or quadripolar electrode catheter, placed at the posteroseptal right atrium near the atrioventricular node (n=18 patients) or in the coronary sinus (n=12 of 18 patients). In 4 patients, stimulation was repeated after intravenous administration of 1 to 2[emsp4 ]mg of atropine. Results: Nerve stimulation prolonged the R-R interval in all patients. Stimulation close to the posteroseptal right atrium led to maximal atrioventricular nodal slowing. The mean R-R intervals at baseline and during parasympathetic nerve stimulation (60[emsp4 ]mA) from the posteroseptal right atrium and the proximal coronary sinus were 581±79[emsp4 ]ms, 2440±466, and 900±228[emsp4 ]ms respectively (p=0.0001). The response to nerve stimulation was greater in patients taking digoxin than in patients not taking the drug (p=0.02). Junctional rhythm occurred during nerve stimulation in 8/8 patients taking digoxin and 0/10 not taking the drug (p=0.0001). The response to stimulation was eliminated after atropine (p=0.01). Conclusions: Parasympathetic nerves to the atrioventricular node were stimulated from the proximal coronary sinus as well as the posteroseptal right atrium. Stimulation at the posteroseptal right atrium resulted in the greatest response, and digoxin enhanced this response. The augmented response suggests that an interaction may exist between parasympathetic stimulation and digoxin at the end organ.     

Effects of Intestinal Electrical Stimulation on Intestinal Dysrhythmia and Symptoms in Dogs

The aim of this study was to investigate the effect of intestinal electrical stimulation on small intestinal dysrhythmia and motion sickness-like symptoms induced by vasopressin. Female dogs chronically implanted with two pairs of electrodes on jejunum serosa were used in a four-session study. Saline and vasopressin were infused in sessions 1 and 2, respectively. Sessions 3 and 4 were the same as session 2, except a long- or short-pulse intestinal electrical stimulation was applied on the proximal pair of electrodes. Intestinal slow waves and motion sickness-like symptoms were recorded in each session. Results were as follows. (1) Vasopressin induced intestinal dysrhythmia, uncoupling of slow waves, and vomiting and motion sickness-like symptoms (P < 0.05, ANOVA). (2) Intestinal electrical stimulation with long pulses, but not short pulses, was capable of preventing vasopressin-induced intestinal dysrhythmia. (3) Intestinal electrical stimulation with short pulses, but not long pulses, prevented vomiting and the motion sickness-like symptoms. It is concluded that vasopressin induces intestinal dysrhythmia. Long-pulse intestinal stimulation normalizes vasopressin-induced intestinal slow-wave abnormalities with no improvement in symptoms. Short-pulse stimulation prevents emetic symptoms induced by vasopressin but has no effect on slow waves. These data suggest different mechanisms involved with different methods of intestinal stimulation.