Cerebral cortical representation of reflexive and volitional swallowing in humans

The purpose of this study was to compare cerebral cortical representation of experimentally induced reflexive swallow with that of volitional swallow. Eight asymptomatic adults (24-27 yr) were studied by a single-trial functional magnetic resonance imaging technique. Reflexive swallowing showed bilateral activity concentrated to the primary sensory/motor regions. Volitional swallowing was represented bilaterally in the insula, prefrontal, cingulate, and parietooccipital regions in addition to the primary sensory/motor cortex. Intrasubject comparison showed that the total volume of activity during volitional swallowing was significantly larger than that activated during reflexive swallows in either hemisphere (P < 0.001). For volitional swallowing, the primary sensory/motor region contained the largest and the insular region the smallest volumes of activation in both hemispheres, and the total activated volume in the right hemisphere was significantly larger compared with the left (P < 0.05). Intersubject comparison showed significant variability in the volume of activity in each of the four volitional swallowing cortical regions. We conclude that reflexive swallow is represented in the primary sensory/motor cortex and that volitional swallow is represented in multiple regions, including the primary sensory/motor cortex, insular, prefrontal/cingulate gyrus, and cuneus and precuneus region. Non-sensory/motor regions activated during volitional swallow may represent swallow-related intent and planning and possibly urge.

Loss of secondary esophageal peristalsis is not a contributory pathogenetic factor in posterior laryngitis

Secondary esophageal peristalsis helps prevent the entry of gastric acid into the pharynx by clearing the refluxed gastric contents back into the stomach. Because the loss of this mechanism may contribute to the pathogenesis of reflux-induced laryngeal disorders, our aim was to study the frequency of stimulation and parameters of secondary esophageal peristalsis in patients with posterior laryngitis (PL). We studied 14 patients (45 +/- 5 years) with PL documented by videolaryngoscopy and 11 healthy controls (46 +/- 6 years). The upper esophageal sphincter (UES) pressure was monitored by a sleeve assembly incorporating an injection port 5 cm distal to the sleeve. The esophageal body and lower esophageal sphincter (LES) pressures were measured by an LES sleeve assembly. Primary esophageal peristalsis was induced by 5-mL water swallows. Secondary esophageal peristalsis was induced by abrupt injection of volumes of air, incrementally increased by 5 mL, into the esophagus. Secondary esophageal peristalsis could not be elicited by injection of any volume (up to 60 mL) in 3 PL patients and 2 controls. These 5 subjects had normal primary peristalsis. The threshold volume of air required to stimulate secondary esophageal peristalsis in PL patients (median, 15 mL) was similar to that of controls (median, 10 mL). The parameters of the secondary esophageal peristaltic pressure wave were similar in both groups, and in both groups, they were similar to those of primary peristalsis. The UES response to the injection of the threshold volume that induced secondary esophageal peristalsis in PL patients was contraction in 58% of the trials, partial relaxation in 3%, and no response in 39%. The findings were similar to those in the controls. The LES response to injection of the threshold volume was complete relaxation in both the PL patients and the controls. We conclude that the integrity of secondary esophageal peristalsis is preserved in PL patients.

Outcomes of acid suppressive therapy in patients with posterior laryngitis

OBJECTIVE

To evaluate the results of acid suppressive therapy (AST) in posterior laryngitis (PL) patients with and without documented pharyngeal acid reflux (PAR).

METHODS

The charts of all patients with PL who received AST and who had undergone pharyngeal pH monitoring were reviewed. Results of AST in patients with PL with and without documented PAR were evaluated by laryngeal examination, symptom scores, and self-reported overall benefit.

RESULTS

Thirty-nine patients with PL had received AST and undergone pharyngeal pH monitoring. Follow-up ranged from 2 to 27 months. Laryngeal findings were improved in patients with and without PAR. Pretreatment total symptom scores were significantly greater than that of posttreatment in patients with and without documented PAR. Overall benefit from AST was reported by the majority of PL patients with and without documented PAR.

CONCLUSION

These findings support the use of AST to reduce or eliminate signs and symptoms in PL regardless of documentation of PAR.

Effect of ageing on the upper and lower oesophageal sphincters

OBJECTIVE

To determine the effect of ageing on length and resting pressure of the upper and lower oesophageal sphincters (UOSs, LOSs).

BACKGROUND

The effectiveness of upper and lower oesophageal sphincters (UOSs and LOSs, respectively) in the control of retrograde trans-sphincteric flow is influenced by sphincteric pressure and length.

METHODS

Nine young and nine elderly healthy volunteers were studied. Resting UOS and LOS pressures were measured by sleeve devices and lengths were measured by the station pull-through technique.

RESULTS

The length of the UOS high pressure zone in the elderly (2.1 +/- 0.7 cm posterior; 1.9 +/- 0.1 cm anterior) was significantly shorter than that of the young (2.9 +/- 0.1 cm posterior; 3.1 +/- 0.2 cm anterior) (P< 0.01). Resting UOS pressure in the elderly (42 +/- 5 mmHg) was significantly lower than that of the young (62 +/- 7 mmHg) (P< 0.05). The intersphincteric length of the oesophagus in the elderly (21 +/- 0.2 cm) was similar to that of the young (21 +/- 0.4 cm). Total length of the LOS high pressure zone in the young (4.0 +/- 0.1 cm) was similar to that of the elderly (4.1 +/- 0.1 cm). LOS resting pressure was similar between young and elderly subjects (17 +/- 5 mmHg and 15 +/- 3 mmHg, respectively).

CONCLUSIONS

Ageing affects the UOS and LOS differently. With regard to resting pressure and length, ageing weakens the UOS, but has no significant effect on the LOS.

Deterioration of the pharyngo-UES contractile reflex in the elderly

OBJECTIVES/HYPOTHESIS

Deterioration of aerodigestive tract reflexes such as the esophagoglottal and pharyngoglottal closure reflexes and pharyngeal swallow has been documented in the elderly. However, the effect of aging on the contractile response of the upper esophageal sphincter (UES) to pharyngeal water stimulation has not been studied. The aim of this study was to characterize the pharyngo-UES reflex in the healthy elderly.

METHODS

We studied nine healthy elderly (77 +/- 1 y [SD]; four men, five women) and nine healthy young volunteers (26 +/- 2 y [SD]; four men, five women). AUES sleeve sensor was used to measure the pressure. We tested pharyngeal stimulation induced by rapid pulse and slow continuous injection of water.

RESULTS

The volume of water required to stimulate the pharyngo-UES contractile reflex by rapid pulse injection in the elderly (0.5 +/- 34 0.1 mL) was significantly higher than that in the young (0.1 +/- 0.02 mL) (P < .05). In contrast to young subjects, there was no pressure increase in resting UES pressure observed in the elderly for continuous pharyngeal water infusion. In both young and elderly, the threshold volume for the pharyngo-UES contractile reflex was significantly lower than that for pharyngeal swallows.

CONCLUSIONS

The pharyngo-UES contractile reflex deteriorates with aging. This deterioration is primarily due to abnormalities of the afferent limb of the reflex.

Event-related fMRI of tasks involving brief motion

The assessment of brain function by blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) for tasks involving motion near the field of view is compromised by artifacts arising from the motion. The aim of this study is to demonstrate that these artifacts can be reduced by acquiring the average response from a brief stimulus (a "single-trial," or "event-related," paradigm) as opposed to alternating blocks of repeated task with rest (a "block-trial" paradigm). The basis of this technique is that the NMR signal changes from neuronal activation are delayed relative to the motion due to a slow hemodynamic response. By acquiring the average response from a brief stimulus, motion-induced signal changes occur prior to neuronal activation-induced signal changes, and the two can thus be distinguished. This technique is applied to the tasks of speaking out loud, swallowing, jaw clenching, and tongue movement. Functional activation maps derived from the single-trial paradigm contain significantly less artifact than functional activation maps derived from a more traditional block-trial paradigm.

Does open access endoscopy close the door to an adequately informed patient?

BACKGROUND

The use of open access endoscopy is increasing. Its effect on the adequacy of patient informed consent, procedure acceptance and the impact on subsequent communication/transfer of procedure results to the patient have not been evaluated. The aim of our study was to compare the extent of preknowledge of procedures and test explanation, patient medical complexity, information transfer and overall patient satisfaction between a patient group referred for outpatient open access endoscopy versus a patient group from a gastrointestinal (GI) subspecialty clinic.

METHODS

Information was obtained from all patients presenting for outpatient upper and lower endoscopy by using a 1-page questionnaire. Patients from the two groups who had an outpatient upper/lower endoscopic procedure were contacted by phone after the procedure to obtain information with a standardized questionnaire.

RESULTS

The open access patients reported receiving significantly less information to help them identify the procedure (p < 0.01) and less explanation concerning the nature of the procedure than the group of patients referred from the subspecialty clinic (p < 0.005). There was no difference between the two groups in satisfaction scores for examinations performed under conscious sedation. For flexible sigmoidoscopy without sedation, however, the GI clinic patient group were more satisfied with their procedure. The majority of patients, regardless of access, were more likely to receive endoscopic results from a gastroenterologist than the referring physician. Furthermore, the patients in the GI clinic group who underwent colonoscopy felt significantly better at follow-up.

CONCLUSIONS

Patients undergoing open access procedures are less likely to be properly informed about their endoscopic procedure. Our results indicate that with open access endoscopy, a defined mechanism needs to be in place for communication of endoscopic results to the patient.

Disruption of primary and secondary esophageal peristalsis by afferent stimulation

Recent studies have shown that afferent signals originating from the pharynx inhibit progression of primary esophageal peristalsis. Our aim was to further elucidate the effect of esophageal and pharyngeal afferent stimulation on primary and secondary esophageal peristalsis. We studied the effect of esophageal air distension and pharyngeal water stimulation on progression of primary and secondary peristalsis in nine healthy volunteers aged 27 +/- 2 yr (4 men, 5 women). At a threshold volume, rapid injection of water into the pharynx, directed posteriorly, resulted in complete halt of the progressing secondary and primary esophageal peristalses in both the proximal and distal esophagus. The threshold volume of injected water for inducing inhibition was similar for secondary (0.6 +/- 0.2 ml) and primary (0.5 +/- 0.1 ml) esophageal peristalsis. Progression of primary peristalsis induced by a dry swallow and secondary peristalsis induced by intraesophageal air distension were completely inhibited by intraesophageal injection of 15 +/- 2 ml of air in 70% and 75% of the trials, respectively. We conclude that afferent signals induced by esophageal air distension and pharyngeal water stimulation inhibit propagation of both primary and secondary esophageal peristalsis, suggesting a shared neural control mechanism for these types of peristalsis.

Upper esophageal sphincter function during gastroesophageal reflux events revisited

Upper esophageal sphincter (UES) function during gastroesophageal reflux events is not completely elucidated because previous studies addressing this issue yielded conflicting results. We reexamined the UES pressure response to intraluminal esophageal pressure and pH changes induced by reflux events. We studied 14 healthy, asymptomatic volunteers (age 49 +/- 6 yr) and 7 gastroesophageal reflux disease patients (age 48 +/- 5 yr). UES pressure, intraesophageal pressure, and pH were monitored at the distal, middle, and proximal esophagus concurrently in the supine position 1 h before and 2 h after a 1,000-calorie meal. A total of 321 reflux events were identified by the development of abrupt reflux-induced intraesophageal pressure increase (IPI); 285 events occurred in patients and 36 in control subjects. In control subjects 33 of 36 and in patients 252 of 285 IPI events were associated with a pH drop. Among patients and control subjects, 99% and 100%, respectively, of all IPI events irrespective of pH drop were associated with abrupt increase in UES pressure (34 +/- 2 and 27 +/- 6 mmHg, respectively). The average percentage of maximum UES pressure increase over prereflux values ranged between 66% and 96% (control subjects) and 34% and 122% (patients). IPIs induced by both acidic and nonacidic reflux events evoke strong UES contractile responses.

An overview of the upper esophageal sphincter

The anatomy and physiology of the upper esophageal sphincter (UES) are complex. Much progress has been made over the past few years in our understanding this important sphincter. The closing muscles of the UES include the inferior pharyngeal sphincter, the cricopharyngeus (CP), and the cervical esophagus. The CP is composed of two parts, which may have different functions. The CP is innervated by the pharyngeal plexus and the recurrent laryngeal nerve. Tone of the UES is probably generated by numerous reflexes rather than by specific tone-generating circuitry. The major tone-generating muscle is the CP, which is highly elastic and produces more active tension the more it is stretched. The UES opens by relaxation of the closing muscles, traction by muscles attached to the hyoid bone and thyroid cartilage, and pulsion of the bolus. The various muscles of the UES behave differently during its many dynamic states, so that similar functions are accomplished by different muscles.

Spectral analysis of surface electromyography (EMG) of upper esophageal sphincter-opening muscles during head lift exercise

Although recent studies have shown enhancement of deglutitive upper esophageal sphincter opening in healthy elderly patients performing an isometric/isotonic head lift exercise (HLE), the muscle groups affected by this process are not known. A shift in the spectral analysis of surface EMG activity seen with muscle fatigue can be used to identify muscles affected by an exercise. The objective of this study was to use spectral analysis to evaluate surface EMG activities in the suprahyoid (SHM), infrahyoid (IHM), and sternocleidomastoid (SCM) muscle groups during the HLE. Surface EMG signals were recorded continuously on a TECA Premiere II during two phases of the HLE protocol in eleven control subjects. In the first phase of the protocol, surface EMG signals were recorded simultaneously from the three muscle groups for a period of 20 s. In the second phase, a 60 s recording was obtained for each of three successive trials with individual muscle groups. The mean frequency (MNF), median frequency (MDF), root mean square (RMS), and average rectified value (ARV) were used as spectral variables to assess the fatigue of the three muscle groups during the exercise. Least squares regression lines were fitted to each variable data set. Our findings suggest that during the HLE the SHM, IHM, and SCM muscle groups all show signs of fatigue; however, the SCM muscle group fatigued faster than the SHM and IHM muscle groups. Because of its higher fatigue rate, the SCM muscle group may play a limiting role in the HLE.

Pharyngeal dysphagia in postesophagectomy patients: correlation with deglutitive biomechanics

BACKGROUND

Because of the transient nature of pharyngeal phase dysphagia, posttranshiatal esophagectomy patients provide a model for studying the correlation of dysphagic symptoms and aspiration with deglutitive biomechanics.

METHODS

We studied 8 transhiatal esophagectomy patients (age range, 51 to 78 years) and 8 normal age-matched controls in upright position using lateral and anteroposterior (AP) projection videofluoroscopy during three 5 mL barium swallows.

RESULTS

The maximum upper esophageal sphincter (UES) AP diameter and maximum anterior excursion of the hyoid bone in patients with transhiatal esophagectomy who experienced aspiration (6.2+/-0.6 and 9.0+/-2.0 mm, respectively) were significantly smaller than those of age-matched normal controls (9.4+/-0.7 and 17.0+/-1.0 mm, respectively). Resolution of aspiration was associated with a significant increase in AP diameter of the UES as well as anterior and superior excursion of the hyoid bone (p<0.05).

CONCLUSIONS

Dysphagic symptoms and aspiration in posttranshiatal esophagectomy patients are associated with significant abnormalities of deglutitive biomechanics. Improvement in deglutitive biomechanics is associated with resolution of dysphagic symptoms as well as postdeglutitive aspiration in these patients.

Life after antireflux surgery

Laparoscopic fundoplication technique has become the operative modality of choice for antireflux surgery. An increasing number of patients and physicians have enthusiastically embraced this "minimally-invasive" technologic development for treatment of gastroesophageal reflux disease (GERD). However, laparoscopic fundoplication has been frequently advertised as the therapeutic solution for all GERD patients. Subsequently, the number and severity of complications resulting from laparoscopic surgery--often performed indiscriminately--has increased dramatically. This article reviews the efficacy of the laparoscopic fundoplication operation for GERD based on current, relatively short-term reports from centers specializing in this treatment modality. The majority of these reports are very positive. Unfortunately, the results of fundoplication operations performed by community surgeons are unknown. There are a number of disturbing factors relating to laparoscopic treatment for GERD that should raise a red flag of caution to the medical community, particularly primary-care physicians and their patients. The central portion of this report devotes itself to discussing the problems associated with this new minimally-invasive technique for fundoplication operations. These problems include the selectivity of current reports on outcomes of the laparascopic fundoplication operation and the lack of uniform data acquisition associated with these postoperative studies. The technical difficulties of the laparascopic fundoplication surgery are discussed, and the need for operator expertise and appreciation of esophageal physiology and anatomy are stressed. Finally, the long-term durability of the fundoplication wrap is questioned and the morbidity associated with the operation--particularly dysphagia--is addressed. In the final segment, the complications encountered after laparoscopic fundoplication operations are detailed and the techniques for evaluating the symptomatic postfundoplication patient are discussed. Laparoscopic fundoplication operation is good therapy in an appropriate clinical setting when performed by a well-trained and experienced surgeon. However, the operation should not be first-line therapy for the majority of GERD patients. An esophagus disabled by an inappropriate or dysfunctional fundoplication wrap is a terrible price to pay for control of acid reflux.

Reflex-mediated enhancement of airway protective mechanisms

The upper esophageal sphincter (UES) and lower esophageal sphincter (LES) comprise the basal mechanisms against entry of gastric content into the aerodigestive tract and the airway. There are, however, other mechanisms referred to here as "response mechanisms" that become activated after certain stimulation, such as distention of the esophagus or tactile/pressure stimulation of the pharyngeal wall, and result either in fortification of the UES barriers--i.e., esophago-UES, pharyngo-UES, and laryngo-UES contractile reflexes--or closure of the glottis--i.e., esophagoglottal and pharyngoglottal closure reflexes. In addition, there are other reflexes included among the response mechanisms--such as pharyngeal swallow and secondary peristalsis induced by pharyngeal stimulation by liquid and esophageal distention by refluxate--that result in pharyngeal and esophageal volume clearance, thus reducing the chance for contact of refluxate with the tracheal, bronchial, and glottal structures.

Electromyographic recording of the cricopharyngeus muscle in humans

Electromyography of the cricopharyngeus muscle is helpful in the study of normal swallowing and in the evaluation of various conditions leading to dysphagia. This article describes the technical aspects of the studies and the findings in normal controls and in various disease states.

Supraesophageal complications of gastroesophageal reflux

Supraesophageal complications of GERD have become more commonly recognized or suspected by physicians. However, the direct association between these complications and GERD has often been difficult, if not impossible, to establish. Furthermore, the majority of patients with suspected supraesophageal complications of GERD do not have either the characteristic symptoms of heartburn and regurgitation or the definitive findings of esophageal inflammation, which would help reinforce the suspicion of a connection between the supraesophageal complications and GERD. Frequent acid reflux has been shown in patients with various bron-chopulmonary, laryngopharyngeal, or oral cavity disorders. GERD is one of the most common gastrointestinal complaints in the population. It is possible that the supraesophageal problems and acid reflux are mutually independent disorders that occur in the same person. The suspected mechanisms of GERD-related supraesophageal complications appear to be directed through two pathways: by a vagal reflex between the esophagus and tracheobronchial tree triggered by acid reflux or by microaspiration that causes contact damage to mucosal surfaces. The most useful diagnostic modality available to the clinician to aid in the diagnosis of supraesophageal GERD complications is the ambulatory pH recording technique. However, the sensitivity and specificity of this test for recording esophageal or pharyngeal acid reflux events has been critically challenged. Despite the many clinical studies that support the theory that GER has a role in suspected supraesophageal complications, only 1 long-term prospective controlled study of a large group of patients with asthma has shown the positive effects of the elimination of acid reflux. With the focus now on "outcomes medicine," there is a serious need for appropriately designed, controlled studies to answer the many questions surrounding a cause-and-effect association between acid reflux and supraesophageal disorders. Because of the lack of convincing proof between acid reflux and suspected supraesophageal complications, the physician must resort to an intent-to-treat strategy as both a primary therapy and a diagnostic trial. High-dose PPI therapy for prolonged periods is the recognized conservative therapy. Operative therapy (i.e., fundoplication operation) is the procedure of choice when overt regurgitation occurs or when medical therapy, although successful, is not practical for long periods. Controlled, well-designed clinical trials and more sophisticated techniques to measure and quantify acid reflux are crucial in the future to help determine which patients with suspected supraesophageal complications actually have acid reflux as a primary cause. The medical community needs to be alerted to the possibility of an association between GERD and supra-esophageal complications so that patients with a GERD-related complication will be recognized and effectively treated.

Pharyngeal acid reflux in patients with single and multiple otolaryngologic disorders

OBJECTIVE

This study was designed to determine the prevalence and characteristics of pharyngeal acid reflux (PAR) events in single and multiple otolaryngologic disorders.

METHODS

Sixty-seven patients with otolaryngologic symptoms and objective findings and 34 healthy control subjects were studied with an ambulatory 24-hour, 3-site pharyngoesophageal pH monitoring technique. Otolaryngologic diagnosis included isolated posterior laryngitis (PL) in 28 patients, isolated chronic rhinosinusitis (SIN) in 12, combined PL and SIN (PL+SIN) in 6, PL plus laryngotracheal stenosis (PL+LTS) in 12, and PL plus vocal cord nodules (PL+VCN) in 9.

RESULTS

PAR events were documented in 68% of patients with PL, 34% of patients with SIN, 67% of patients with PL+SIN, 67% of patients with PL+LTS, 78% of patients with PL+VCN, and 21% of controls. The prevalence of PAR events in patients with isolated PL as well as those with PL combined with other disorders was significantly higher than that in patients without PL and that in controls. As a group, patients with PL had a greater number of PAR events and acid exposure time than other patients and controls. Distal and proximal esophageal reflux parameters were not significantly different among groups.

CONCLUSIONS

The prevalence of PAR is significantly higher in patients with isolated PL compared to patients with other isolated otolaryngologic disorders and in controls. The prevalence of PAR in isolated otolaryngologic disorders other than PL is similar to that in healthy controls. The prevalence of PAR is significantly higher in patients with both PL and other otolaryngologic disorders than in controls and in patients with isolated otolaryngologic disorders.

Comparison of upper esophageal sphincter opening in healthy asymptomatic young and elderly volunteers

Deglutitive upper esophageal sphincter opening (UES) in the elderly has been incompletely studied. Our aim was to determine in the elderly the temporal and dimensional characteristics of deglutitive UES opening; anterior and superior hyoid and laryngeal excursions as measures of distracting forces imparted on the UES; and hypopharyngeal intrabolus pressure (IBP). Fourteen healthy elderly and 14 healthy young volunteers were studied by concurrent videofluoroscopy and hypopharyngeal manometry during swallowing of 5- and 10-mL barium boluses. The anteroposterior UES diameter, as well as the anterior hyoid bone and laryngeal excursion, was significantly smaller in the elderly compared to the young (p < .05) for 5-mL barium boluses, but not for 10-mL boluses. The lateral diameter of UES opening was similar between groups for all boluses. The IBP for 5- and 10-mL swallows in the elderly was significantly higher than that in the young (p < .05). We conclude that anteroposterior deglutitive UES opening and hyoid bone and thyroid cartilage anterior excursion are reduced in the elderly. These changes are associated with increased IBP, suggesting a higher pharyngeal outflow resistance in the elderly compared to the young.

Gastrointestinal motor and myoelectric correlates of motion sickness

The objectives of this study were to characterize the digestive tract motor and myoelectric responses associated with motion sickness. Twenty-two cats (1.5-3.0 kg) were chronically implanted with force transducers and electrodes on the stomach and small intestine. Motion sickness was activated by vertical oscillation (VO) at +/-0.5 g and identified as salivation, licking, or vomiting. Vomiting was initiated chemically by UK-14304 (2.5-15 microg/kg iv) or CuSO4 (10-50 mg ig). We found that VO caused vomiting (45% of trials), a decrease in gastrointestinal (GI) motility (69% of trials), salivation or licking (59% of trials), bradygastria (39% of trials), retrograde giant contraction (RGC, 43% of trials), giant migrating contraction (GMC, 5% of trials), and defecation (18% of trials). The decrease in GI motility occurred with (62% of trials) or without (69% of trials) vomiting. Motion sickness was accompanied by bradygastria (52% of trials) and decreased GI motility (70% of trials). Similar events occurred after CuSO4 and UK-14304, but the incidences of responses after CuSO4 were less frequent, except for vomiting, RGC, and GMC. UK-14304 never caused GMCs or defecation. The magnitude and velocity of the RGC were the same during all emetic stimuli, and RGCs never occurred without subsequent vomiting. Supradiaphragmatic vagotomy (n = 1) or atropine (n = 2, 10 or 50 microg/kg iv) blocked the RGC, but not vomiting, due to VO. We concluded that 1) oculovestibular stimulation causes digestive tract responses similar to other types of emetic stimuli, 2) decreased GI motility and bradygastria may be physiological correlates of the motion sickness, and 3) motion sickness may not be dependent on any specific GI motor or myoelectric response.