PATIENTS AND ASYMPTOMATIC CONTROLS

Seventeen patients with non-ulcer dyspepsia (12H pylori negative, fiveH pylori positive) and 16 asymptomatic individuals (eight H pylori negative, eightH pylori positive) participated in the study after signing informed consent. The protocol for the study had been approved by the Institutional Review Board of the Mayo Clinic. Females of childbearing potential were required to have a negative plasma beta human chorionic gonadotrophin pregnancy test within 48 hours of study.

Patients with non-ulcer dyspepsia were recruited from the outpatient Gastroenterology Clinic of the Mayo Medical Center, Rochester, Minnesota. Inclusion criteria for patients with non-ulcer dyspepsia were: (a) at least two of the following symptoms related to meal ingestion: upper abdominal pain or discomfort, bloating, nausea, vomiting, and early satiety;(b) symptom duration of more than six months, occurring at least three times per week;(c) no evidence of ulceration (break in epithelial lining more than 5 mm diameter) or more than two erosions (each not more than 4 mm diameter) on upper gastrointestinal endoscopy;(d) normal abdominal ultrasonography;(e) no evidence of organic or systemic disease known to affect gastrointestinal motility or major psychiatric disturbances; (f) absence of nocturnal gastro-oesophageal reflux symptoms or reflux symptoms postprandially;(g) absence of previous abdominal surgery except for uncomplicated appendectomy, cholecystectomy, or hernia repair; (h) no intake of antibiotics, bismuth salts, steroids, or non-steroidal anti-inflammatory drugs in the preceding four weeks; (i) cessation of all medications that might influence gastrointestinal sensorimotor function at least 48 hours prior to the study.

The asymptomatic controls were recruited from the local community by public advertisement. Screening for H pyloriinfection was performed using a serological test forH pylori. Following further confirmation ofH pylori status as described below, the first eight consecutive H pylori negative subjects (four women, four men; age range 19–58 years) and the first eight H pylori positive subjects (five women, three men; age range 27–45 years) were enrolled for further study. None had undergone previous abdominal surgery except for uncomplicated appendectomy. None was taking medications with the exception of oral contraceptives. Clinical interview and a validated screening questionnaire (the Bowel Disease Questionnaire20) were used to exclude subjects with significant gastrointestinal symptoms. The physiological observations on asymptomatic volunteers have been published elsewhere33and are included here only where comparisons are made with the results in patients with functional dyspepsia. The observations in asymptomatic controls are not discussed in this paper.

ASSESSMENT OF H PYLORI STATUS

All patients and healthy volunteers underwent serological testing (PYLORI ELISA II, Bio-Whittaker, Walkersville, Maryland, USA) and upper gastrointestinal endoscopy to obtain eight antral biopsy specimens for assessing H pylori status.H pylori infection was diagnosed if two of the following three tests were positive: (1) H pylori IgG antibodies in serum as determined by ELISA; (2) histology using Giemsa stain and haematoxylin and eosin from four antral biopsy specimens; and (3) bacteriological culture of four antral biopsy specimens performed on Brucella based media (containing haem, vancomycin, trimethoprim, polymyxin B, defibrinated sheep blood, vitamin K, and actidione). Patients and asymptomatic controls were considered negative forH pylori if all three tests were negative. After the study, patients and controls were offered treatment for eradication of H pylori infection with explanation that it was unclear whether this was clinically indicated from the currently published guidelines and literature.

ASSESSMENT OF GASTROINTESTINAL AND PSYCHOLOGICAL SYMPTOM PROFILES

A comprehensive, modified bowel disease questionnaire assembled from previously validated instruments (the Bowel Disease Questionnaire20) was used to assess symptomatology in all participants (patients and asymptomatic controls). The Minnesota Multiphasic Personality Inventory (MMPI)21 was used to screen for psychological disorders in all participants. The data obtained from the MMPI were analysed using a validated computer program22 and assessed by a staff psychologist coinvestigator (DEW).

MEASUREMENT OF GASTRIC AND OROCAECAL TRANSIT

The transit studies were performed after an overnight fast on a day separate from all other studies. We quantitated gastric and small bowel transit by means of a validated scintigraphic method that utilises technetium-99m radiolabelled pellets (Amberlite 410, Sigma Chemical Co., St Louis, Missouri, USA) in an egg meal (0.92 MJ). The preparation, conduct, and analysis of transit studies have been previously published.23 Briefly, patients ingested the egg meal after an overnight fast; scans of the abdomen were obtained with the patient standing using an anterior and posterior large field of view gamma camera (GE Starcam, Milwaukee, Wisconsin, USA). Images were obtained immediately after the meal, and two, four, and six hours later.24 A second non-radiolabelled, standardised solid-liquid meal (2.24 MJ) was ingested after the four hour scan. A region of interest program was used to quantitate radioactivity within the stomach and colon. Corrections were made for isotope decay and for tissue attenuation by calculation of the geometric mean of counts obtained using anterior and posterior images. Gastric emptying was expressed as the percentage isotope remaining in the stomach at two and four hours.24 The more sensitive index for gastric emptying delay is the percentage emptied at four hours.24Orocaecal transit was estimated by the percentage colonic filling at six hours.24

ASSESSMENT OF VAGAL FUNCTION

Efferent vagal function25 ,26 was tested by the plasma pancreatic polypeptide27 response during 30 minutes of modified sham feeding—that is, chewing and spitting a bacon and cheese toasted sandwich. The sham feeding test is less sensitive but more specific for vagal dysfunction than the alternative insulin hypoglycaemia test.28 The sandwich was cooked on a hotplate with the patient or asymptomatic control present. Subjects were instructed to extend the neck slightly to avoid swallowing any food during modified sham feeding. Five ml blood samples for pancreatic polypeptide were collected into chilled EDTA vacutainers, once at baseline before sham feeding, and then at minutes 0, 5, 10, 15, 20, 25, and 30 during the sham feeding. Plasma concentrations of pancreatic polypeptide were determined by a validated and specific radioimmunoassay.27 A change from baseline of greater than 25 pg/ml is considered normal26; failure of plasma pancreatic polypeptide levels to increase by more than 25 pg/ml after modified sham feeding suggests abdominal vagal dysfunction.4 ,29

MEASUREMENT OF PROXIMAL GASTRIC TONE

The tone of the proximal stomach30 was assessed by a barostatic device (Distender Series II, G&J Electronics Inc., Willowdale, Ontario, Canada). A double lumen assembly was inserted through the mouth such that a finely folded one litre capacity spherical polyethylene bag (Hefty Baggies, Mobil Chemical Company, Pittsford, New York, USA) at the end of the polyvinyl tube was positioned within the proximal stomach under fluoroscopic control. The baseline operating pressure within the polyethylene bag for each individual was set 1 mm Hg above the pressure at which the bag volume was greater than 30 ml, as in other papers in the literature.31-33 Velocity of air inflation was 25 ml/sec. The method of measuring proximal gastric motility was similar to that successfully used in previous studies in our laboratory.32-34 The range of baseline operating pressure was 5–11 mm Hg.

Briefly, the polyethylene bag which is infinitely compliant at the inflation volumes observed in this study, is kept under constant pressure within the proximal stomach by means of the electronic barostat. Changes in volume within the bag reflect changes in gastric contractility. Two types of contractile responses can be detected: firstly, slow baseline volume variation that reflects relaxation (increased baseline volume) or increased contraction (decreased baseline volume); and secondly, phasic volume fluctuations (more than 5 ml over baseline; 5–40 seconds duration) from the baseline volume which reflect contractions superimposed on the background state of contractility. This background contractility is summarised as “tone” to reflect terminology used in the published literature.30-32

MEASUREMENT OF PROXIMAL GASTRIC COMPLIANCE

Gastric compliance was assessed as the volume response to 2 mm Hg stepwise increments of intrabag pressure at 30 second intervals up to 12 mm Hg above the baseline operating pressure, or until the subject perceived abdominal pain. The bag was then deflated (2 mm Hg steps at 30 second intervals) until the intrabag pressure returned to the previous baseline operating pressure.

ASSESSMENT OF PERCEPTION DURING GASTRIC MECHANICAL DISTENSIONS

Gastric sensory function was assessed in the fasting state and twice postprandially by three intermittent increases in intrabag pressure of 4, 8, and 12 mm Hg above baseline operating pressure. The order of pressure distensions was randomised; each phasic pressure increment was maintained for one minute with a two minute interval when the intrabag pressure was deflated to the baseline operating pressure. Subjects received a standardised information sheet prior to sensory testing and a seven point adjectival perception scale was reviewed with them. Thereafter, there was minimal interaction between the subjects and investigators to avoid introducing any bias. The perceptions of three symptoms were recorded: nausea, fullness, and abdominal discomfort (or pain for grades 5 and 6 of discomfort). Symptoms were graded as follows: 0 = none; 1 = vague; 2 = mild; 3 = moderate; 4 = severe; 5 = very severe; 6 = worst ever. The subjects were asked to record their perceptions 30 seconds after the onset of each one minute distension. This method of sensory assessment has been used extensively in this laboratory and has been shown to be responsive to physiological or pharmacological perturbations, and to be reproducible in previous studies in the human stomach34 and colon.35 ,36

The same randomised sequence of phasic distensions was repeated twice postprandially: firstly, in the early postprandial period when the bag volume had returned to 2.5 times the average fasting volume measured on line or at 20 minutes after the standardised meal, whichever occurred first. Distensions were not performed earlier after the meal in order to allow for adequate assessment of the accommodation response to the meal. A second assessment of sensory function in the late postprandial period was performed when the bag volume had returned to fasting levels, or at least 90 minutes after the meal, whichever occurred first.

WATER BOLUS TEST

We measured the volume of cold tap water that could be ingested over a five minute period before the perception of abdominal fullness. This approach was described in a recent preliminary report as a simple non-invasive test of gastric sensitivity.37 Subjects were fasting for at least three hours prior to this test.

MEASUREMENT OF SOMATIC SENSITIVITY BY THE COLD STRESS TEST

Subjects were asked to immerse the non-dominant hand up to the wrist in ice cold water (0°C) for a maximum of five minutes or as long as they could tolerate the cold pain. The responses assessed were the maximum duration of pain tolerance in seconds and the pain intensity using a 100 mm visual analogue scale.38

EXPERIMENTAL PROTOCOL

All subjects were admitted to the General Clinical Research Center at St Mary’s Hospital for tests that were performed over a period of three days. The intubated studies (gastric tone, gastric compliance, gastric sensation; see fig 1) were performed following an overnight fast. The double lumen tube assembly with the bag folded was introduced perorally and positioned in the proximal stomach under fluoroscopic control. The polyethylene bag was then slowly inflated with 500 ml of air via a syringe to unfold it and immediately deflated. The subjects were seated upright in an armchair and the double lumen assembly was connected to the electronic barostat. The studies were recorded on a computerised system and stored for later analysis. After a 30 minute equilibration period, during which the baseline operating pressure was set as described above and baseline recordings were obtained, gastric compliance was measured. Premeal gastric sensation was measured 15 minutes after the end of compliance measurements by standard phasic bag distensions (4, 8, 12 mm Hg) performed in random order. When the volume within the bag had returned to baseline values following the last distension, premeal (fasting) bag volume fluctuations were monitored for at least 20 minutes. Thereafter, subjects drank 200 ml (0.64 MJ; 55% carbohydrate, 31% fat, and 14% protein) of chocolate flavored Ensure (Abbott Laboratories, Columbus, Ohio, USA) with a straw during a five minute period. The chocolate drink was served at room temperature. Proximal gastric tone was monitored for at least 20 minutes after the meal. Gastric perception was then measured postprandially on two occasions as described above. After removal of the gastric tube, the somatic sensitivity was performed. The vagal function test was performed either on a separate day after a three hour fast or on the day of the intubated study at least three hours after the study meal. The gastric emptying study and the water bolus test were performed on separate days.

• Download figure
• Open in new tab
• Download powerpoint

Figure 1

Experimental design for measurement of gastric compliance, tone, and sensation using a barostatically controlled polyethylene bag in the proximal stomach.

DATA ANALYSIS

Gastric emptying was summarised by the percentage remaining in the stomach at two and four hours, and orocaecal transit by percentage colonic filling of isotope at six hours after ingestion of the meal. The initial gastric distribution of the meal was calculated from the image taken immediately after the end of the meal ingestion (zero hour scan): 

• Download figure
• Open in new tab
• Download powerpoint

Gastric tone was estimated from the baseline volume of the polyethylene bag, as in previous studies.32-34 Changes in both pressure and volume of the barostat bag were sampled as analogue signals at 4 Hz and converted to digital signals before entry into a computer. A customised computer method (VAXLAB, Digital Equipment Corp., Maynard, Mississippi, USA) was utilised to detect respiratory and motion artefacts and to separate baseline gastric tone and phasic volume peaks. For the accommodation response to meal ingestion, the averaged baseline barostat volume during the first 20 minutes postprandially was compared with the average value during the preprandial 20 minutes.We compared the percentage change in intrabag baseline volume between the patients and controls. The percentage change was used in order to normalise for interindividual differences in bag volume during fasting.

Gastric compliance was defined as the linear slope of a pressure-volume curve with values obtained during ramp inflations, where pressure (mm Hg) is represented on the x axis and bag volume (ml) on the y axis.

Gastric phasic volume peaks were calculated as an area under the curve for the 20 minute premeal and postmeal periods. Phasic volume peaks were expressed as the barostat index (BI) per hour: .

The ratios of post:premeal measurements of phasic volume peaks were summarised as a barostat index ratio.

To assess gastric sensitivity, the individual scores for nausea, fullness, and discomfort on the seven point adjectival scale (marked 0 to 6) during each of the three distensions were summed to provide an aggregate perception score for each subject (minimal score 0 and maximal score 18 for each distension).

STATISTICAL ANALYSIS

The sample size for the study was based on 80% power (at α=0.05) that assessed the variances of gastric emptying and postprandial accommodation in a previously studied group of healthy controls. All data are presented as mean values (SEM). Statistical comparisons between groups were performed by one way analysis of variance (ANOVA) with multigroup comparisons—that is,H pylori negative and H pylori positive patients with non-ulcer dyspepsia, and each dyspeptic group versus the respective asymptomatic controls unless otherwise stated (see below). These comparisons were performed for gastric tone, phasic events, and compliance. The Kruskal-Wallis test (one way ANOVA on ranks) was used for non-parametric data: gastric emptying, orocaecal transit, and initial distribution of the meal within the stomach.

As our previous study33 showed that the gastric accommodation response in asymptomatic volunteers was significantly different among H pylori negative andH pylori positive participants, all comparisons for gastric motor functions are made with the two respective subgroups of controls. However, as gastric and somatic sensation were not different for H pylorinegative and H pylori positive asymptomatic volunteers, we pooled sensation data for comparisons with the two dyspeptic groups. Fisher’s exact test was used to compare the proportion of the two patient groups with abnormal sensation.

Comparisons between H pylori positive andH pylori negative dyspeptics were assessed at α=0.05. Where multigroup comparisons were performed, a p value of less than 0.017 was considered to be statistically significant. Thus, Bonferroni’s correction was applied to correct for three pairwise comparisons of the main end points (transit, accommodation, sensation) between controls and two dyspeptic groups, and betweenH pylori positive and negative patients.

CLINICAL CHARACTERISTICS OF PATIENTS

Table 1 summarises the clinical features of patients with non-ulcer dyspepsia. Patients had a mean symptom duration of 4.5 years; there was no significant difference in the duration of dyspepsia between H pylori negative patients (3.7 (1) years) and H pylori positive patients (5 (1.1) years). There was also no difference in sex, age, or body mass index (BMI) between patients and asymptomatic controls (control data not shown).

Overlap symptoms indicative of irritable bowel syndrome were present in seven of 17 patients with non-ulcer dyspepsia. By MMPI, eight of the 17 dyspeptic patients had significant psychopathology, chiefly somatisation and depression.

Upper endoscopy revealed antral erythema in five of 12H pylori negative patients and four of fiveH pylori positive patients. One patient in each group had a single antral or pyloric erosion.

GASTRIC EMPTYING, INTRAGASTRIC MEAL DISTRIBUTION, AND OROCAECAL TRANSIT

Overall group comparison of patients and controls showed that gastric emptying at four hours (fig 2) was significantly different (p=0.036); at two hours it was not (p=0.1).H pylori negative patients had slower gastric emptying at four hours than H pyloripositive patients (p=0.015) and H pylorinegative asymptomatic controls (p=0.05). However, only four of 12H pylori negative patients had delayed gastric emptying relative to a large cohort of healthy subjects studied with the same test.24 The group of patients who wereH pylori positive had similar gastric emptying compared with their controls.

• Download figure
• Open in new tab
• Download powerpoint

Figure 2

Gastric residual data at four hours. The shaded area shows normal ranges in our laboratory.23 NUD, non-ulcer dyspepsia.

Initial intragastric meal distribution (p=0.5) and orocaecal transit (p=0.06) were not significantly different in the four groups. However, subgroup analysis showed that the percentage of colonic filling tended to be less in H pylorinegative dyspepsia compared with the H pylori positive dyspepsia group (p=0.04).

ABDOMINAL VAGAL FUNCTION

In each of the dyspepsia groups, there was one patient with an abnormal pancreatic polypeptide response to modified sham feeding (table 2).

PROXIMAL GASTRIC TONE, PHASIC ACTIVITY, AND COMPLIANCE

Fasting proximal gastric tone and gastric compliance were similar in all groups (table 2). The gastric accommodation response to meal ingestion in H pylori positive asymptomatic controls and dyspeptics, and in H pylorinegative dyspeptics was significantly lower compared withH pylori negative controls (p<0.01; fig 3). There was no statistically significant difference between the two groups of dyspeptics. Eight of 12 H pylorinegative patients had a lower accommodation than any of theH pylori negative controls. Figure 4 shows representative examples of the accommodation response in the early postprandial period.

• Download figure
• Open in new tab
• Download powerpoint

Figure 3

Individual accommodation data for all groups studied. NUD, non-ulcer dyspepsia.

• Download figure
• Open in new tab
• Download powerpoint

Figure 4

Representative tracings of gastric relaxation (accommodation) induced by meal ingestion. NUD, non-ulcer dyspepsia.

Phasic contractility of the proximal stomach (barostat index in table2) in the fasting period was generally similar in all groups; however, the H pylori negative asymptomatic controls had a lower postmeal phasic response resulting in a lower barostat index ratio than in the H pylori negative patients.

PERCEPTION DURING GASTRIC MECHANICAL DISTENSION

Aggregate perception scores during fasting were similar in asymptomatic controls and H pylori negative or H pylori positive patients (at 4 mm Hg: p=0.06; at 8 mm Hg: p=0.08; at 12 mm Hg: p=0.3; see fig 5). Early and late postprandially, H pylori positive patients had significantly greater sensitivity to distension with 8 mm Hg (early: p=0.003; late: p=0.01) and 12 mm Hg (early: p=0.005; late: p=0.003) compared with asymptomatic controls. H pylori negative dyspeptics had increased sensitivity (p<0.017) only in the early postprandial period with one of three distensions (8 mm Hg).

• Download figure
• Open in new tab
• Download powerpoint

Figure 5

Aggregate sensation scores during fasting, early, and late postprandial periods in response to 4, 8, and 12 mm Hg distensions above baseline operating pressure. NUD, non-ulcer dyspepsia. *p⩽0.01 versus asymptomatic controls; †p<0.017 versus asymptomatic controls.

The interquartile range (IQR) of the mean aggregate perception scores to each of the three distensions in asymptomatic controls was 3–6 early postprandially and 3–7 late postprandially. Compared with this IQR, mean aggregate perception was higher in 4/12 H pylori negative dyspeptics, and 4/5 H pylori positive dyspeptics in the early postprandial period, and in 2/12 and 4/5 dyspeptics in the late postprandial period. The proportion of H pylori positive andH pylori negative patients with increased sensitivity was not significantly different.

WATER BOLUS TEST

The ingested volume of cold water required to evoke abdominal fullness was similar in the asymptomatic control group (938 (75) ml) and H pylori negative (833 (67) ml) or positive dyspeptic patients (679 (174) ml).

SOMATIC SENSITIVITY

There were no significant differences in cold pain rating and the maximum time of cold pain tolerance between H pylori negative dyspeptics (77 (5) mm and 119 (31) seconds respectively) or H pylori positive dyspeptics (86 (4) mm and 56 (18) seconds), and asymptomatic controls (77 (5) mm and 145 (27) seconds).