Estimating ankle torque and dynamics of the stabilizing mechanism: No need for horizontal ground reaction forces.

Changes in human balance control can objectively be assessed using system identification techniques in combination with support surface translations. However, large, expensive and complex motion platforms are required, which are not suitable for the clinic. A treadmill could be a simple alternative to apply support surface translations. In this paper we first validated the estimation of the joint stiffness of an inverted pendulum using system identification methods in combination with support surface translations, by comparison with the joint stiffness calculated using a linear regression method. Second, we used the system identification method to investigate the effect of horizontal ground reaction forces on the estimation of the ankle torque and the dynamics of the stabilizing mechanism of 12 healthy participants. Ankle torque and resulting frequency response functions, which describes the dynamics of the stabilizing mechanism, were calculated by both including and excluding horizontal ground reaction forces. Results showed that the joint stiffness of an inverted pendulum estimated using system identification is comparable to the joint stiffness estimated by a regression method. Secondly, within the induced body sway angles, the ankle torque and frequency response function of the joint dynamics calculated by both including and excluding horizontal ground reaction forces are similar. Therefore, the horizontal ground reaction forces play a minor role in calculating the ankle torque and frequency response function of the dynamics of the stabilizing mechanism and can thus be omitted.

Effect of gastric distension on cardiovascular parameters: gastrovascular reflex is attenuated in the elderly.

Stretching the stomach wall in young healthy subjects causes an increase in muscle sympathetic nerve activity and in blood pressure, the gastrovascular reflex. We compared healthy elderly subjects with healthy young subjects to find out whether the gastrovascular reflex attenuates in normal ageing and we studied whether there was a difference in autonomic function or gastric compliance that could explain this possible attenuation. Muscle sympathetic nerve activity, finger blood pressure and heart rate were continuously recorded during stepwise isobaric gastric distension using a barostat in eight healthy young (6 men and 2 women, 27 +/- 3.2 years, mean +/-s.e.m.) and eight healthy elderly subjects (7 men and 1 woman, 76 +/- 1.5 years). Changes in cardiac output and total peripheral arterial resistance were calculated from the blood pressure signal. The baseline mean arterial pressure and muscle sympathetic nerve activity were higher in the elderly group (both P < 0.05) and muscle sympathetic nerve activity increase during the cold pressor test was lower in the elderly group (P = 0.005). During stepwise gastric distension, the elderly subjects showed an attenuated increase in muscle sympathetic nerve activity compared to the young subjects (P < 0.01). The older group tended to show a higher increase in mean arterial pressure (P = 0.08), heart rate (P = 0.06) and total peripheral arterial resistance (P = 0.09) The cardiac output rose slightly in both groups without significant difference between groups. The fundic compliance did not differ between groups. We conclude that stepwise gastric distension caused an increase in muscle sympathetic nerve activity in both groups, but the increase in the elderly was attenuated.

The gastro-oesophageal pressure inversion point revisited.

BACKGROUND: The pressure inversion point (PIP) is defined as the point at which, during stationary pull-through manometry of the oesophago-gastric junction, the polarity of the respiratory-associated pressure variations changes. Traditionally, the PIP is ascribed to transition of the pressure sensor from the abdominal to the thoracic cavity. We used high-resolution manometry to investigate the validity of this concept in six healthy volunteers and six patients with a sliding hiatus hernia. METHODS: In the analysis, the position of the PIP was identified. When there was a second, more distal, PIP, its position was also noted. The amplitude of the respiratory-associated pressure variations, defined as the difference between end-expiratory and end-inspiratory pressure, was measured. RESULTS: Double PIPs were found both in healthy controls (23 +/- 8% of time) and in patients (38 +/- 9% of time). Amplitudes of the respiratory-associated pressure variations were significantly higher at the proximal and distal border of the PIP (3.36 +/- 0.2 kPa and 2.29 +/- 0.2 kPa) than in the oesophageal body (0.54 +/- 0.03 kPa, P < 0.001) and in the stomach (0.54 +/- 0.03 kPa, P < 0.001). We also observed a relationship between the localization of the highest end-expiratory pressure and the position of the PIP. During TLOSRs respiratory variation amplitudes at the proximal and distal border of the PIP decreased to 0.61 +/- 0.02 kPa and 0.29 +/- 0.01 kPa, approximating respiratory pressure variation in oesophagus and stomach. CONCLUSION: Our findings suggest that the PIP is caused by sliding of the high-pressure zone along pressure sensors rather than by the transition from the thoracic to the abdominal compartment.

Association between pain episodes and high amplitude propagated pressure waves in patients with irritable bowel syndrome.

OBJECTIVES: In the pathogenesis of irritable bowel syndrome (IBS), both increased visceral sensitivity and altered colonic motility seem to play a role. The aim of this study was to quantify the temporal relationship between pain episodes and the occurrence of high amplitude propagated pressure waves (HAPPWs). METHODS: A total of 11 IBS patients with the nonconstipation predominant pattern of IBS and 10 sex- and age-matched healthy volunteers were studied. On day 1, a solid state manometric catheter was positioned in the left colon and connected to a data logger. The subjects then went home. Thereafter they pressed a button on the data logger at the beginning and end of each pain episode. The 24-h manometric signal recorded on day 2 was divided into consecutive 5-min periods. These periods were evaluated for the occurrence of pain and HAPPWs. Fisher's exact test was applied to calculate the probability that HAPPWs and pain episodes were unrelated. The symptom association probability (SAP) was calculated as (1.0 - P) x 100%. A SAP of >95% was considered to indicate that the observed association did not occur by chance. RESULTS: In four of seven patients with pain on day 2, the SAP was >95%. HAPPWs that were related to pain originated at a more proximal level (p = 0.026) and occurred earlier (p = 0.007) than HAPPWs that were not related to pain. The duration of a pain period was correlated with the number of pain-related HAPPWs in that period (r = 0.906, p = 0.013). Two of the 10 healthy subjects experienced pain, and these pain episodes were not associated with HAPPWs. CONCLUSIONS: Using objective analysis techniques, an association between pain episodes and HAPPWs was found in nonconstipated IBS patients with pain. HAPPWs that are associated with pain are only slightly different from HAPPWs not associated with pain.

Elicitation of transient lower oesophageal sphincter relaxations in response to gastric distension and meal ingestion.

The aim of this study was to compare the effect of graded gastric barostat distension and meal-induced fundic relaxation on the elicitation of transient lower oesophageal sphincter relaxation (TLOSR). In 15 healthy subjects, stepwise fundic distension and oesophageal manometry were performed simultaneously. Next, the effect of meal ingestion on proximal stomach volume and lower oesophageal sphincter function was studied. During stepwise barostat distension of the proximal stomach, a significant linear correlation between intragastric pressure (r = 0.91; P < 0.01) and the TLOSR rate during inflation and subsequent deflation (r = 0.96; P < 0.01) was found. A similar relationship was found for volume. In addition, after meal ingestion, the TLOSR rate increased significantly from 1.40 +/- 3 to 5.4 +/- 1.5 h-1 (P < 0.01) and 5.2 +/- 1.7 h-1 (P < 0.01), respectively, during the first and second 30-min postprandially. However, at similar calculated intragastric volumes, barostat distension led to a significantly higher TLOSR rate than the meal. Similarly, distension-induced increase in gastric wall tension, estimated from the measured bag pressure and volume using Laplace's law, was associated with significantly higher TLOSR rates (P < 0.01). In conclusion, the rate of TLOSRs in healthy volunteers is directly related to the degree of proximal gastric distension and pressure-controlled barostat distension is a more potent trigger of TLOSRs than a meal. The latter finding suggests that tension receptor activation is an important stimulus for TLOSRs.

Effect of coffee on motor and sensory function of proximal stomach.

Some people attribute dyspeptic symptoms to drinking coffee, suggesting that coffee affects one or more functions of the proximal gastrointestinal tract. In a randomized controlled, cross-over, single-blinded study, the effects of coffee on gastric relaxation, gastric wall compliance and sensations, elicited by distension, were investigated in 10 healthy volunteers. Using the barostat technique, volume changes of an intragastric bag were recorded for 20 min after intragastric administration of 280 ml of coffee or water. Then, after deflation, the volume of the bag was increased stepwise every 3 min to assess gastric wall compliance and wall tension. At the end of every volume step, sensations (nausea, pain, and bloating) were scored. During the first 20 min after coffee administration, the volume change of the intragastric bag was larger than after water (P < 0.05). There were no differences in gastric wall compliance, wall tension, or symptom scores. In conclusions, coffee, in comparison with water, enhances the adaptive relaxation of the proximal stomach, but has no effect on its wall compliance, wall tension, or sensory function.

Effects of intraduodenal bile on interdigestive gastrointestinal and gallbladder motility in healthy subjects.

BACKGROUND/AIMS: The enterohepatic circulation of bile acids is related to normal inter-digestive gastrointestinal motility, with the gut peptide motilin also being involved. This study aimed to investigate the effect of intraduodenal artificial bile infusion on antroduodenal and gallbladder motility so as to further elucidate the controlling factors. METHODS: Twelve fasting, healthy male volunteers received artificial bile (80 mol% bile acids; 15 mol% phospholipids; 5 mol% cholesterol) or placebo (saline) intraduodenally for 10 min starting 30 min after the end of phase III, according to a double-blind, randomised, cross-over design. Antroduodenal motility, gallbladder volumes, and plasma motilin levels were measured. All values are means +/- SEM. RESULTS: The interval between infusion and the subsequent phase III, as well as the origin of this phase III were not significantly different between bile and saline. Antral pressure waves were significantly more frequent during and immediately after bile infusion compared with saline infusion (p < 0.05). The duration of phase I following infusion was significantly longer after bile (24.8 +/- 3.7 min) than after saline infusion (13.1 +/- 1.7 min; p < 0.05). The mean gallbladder volume tended to increase in the hours following bile infusion, but to decrease after saline infusion (p = 0.06). Plasma motilin increased after bile and saline infusion in an almost identical way. CONCLUSION: This study provides no clear evidence for a role of intraduodenal artificial bile (i.e. its main constituents) in the regulation of migrating motor complex cycling or feedback inhibition of inter-digestive gallbladder emptying.

Tonic motor activity of the narrow gastric tube used as an oesophageal substitute.

OBJECTIVE: To assess the compliance, the existence of basal tone, the sensory response to distension, and the integrity of the neurohumoral enterogastric inhibitory reflex of the narrow gastric tube as an oesophageal substitute. DESIGN: Explanatory experimental study. SETTING: University hospital, The Netherlands. PATIENTS: Eight patients after oesophagectomy, formation of a narrow gastric tube, and cervical gastro-oesophagostomy. INTERVENTIONS: Measurements of intragastric tonic motor activity with a Barostat. MAIN OUTCOME MEASUREMENTS: Compliance, sensations during stepwise pressure increments, and changes in tone induced by glucagon and intraduodenal feeding. RESULTS: The compliance of the narrow gastric tube was found to be low (median 13.5 ml/mmHg (range 5-21)). Most of the patients perceived minimal sensation on distension. All patients had phasic tonic contractions during distension of the gastric tube. The median (range) relaxation after glucagon had been given intravenously was 14 ml (range 3-57) (p < 0.05). The tonic reaction to nutrients in the duodenum was not significant. CONCLUSIONS: The compliance of the narrow gastric tube is low. Postprandial symptoms are not caused by distension of the proximal part of the narrow gastric tube. Basal gastric tone and phasic activity were at least partially restored over time after operation. The enterogastric inhibitory reflex is eliminated by oesophageal resection and reconstruction of a gastric tube.

Functional characterization of two promoters in the human bone morphogenetic protein-4 gene.

Bone morphogenetic protein-4 (BMP-4) is a member of the BMP family, which consists of important regulators of bone formation and embryonic development. We have previously isolated the human BMP-4 encoding gene, which is associated with the heritable disorder Fibrodysplasia Ossificans Progressiva. In this study, we describe the molecular cloning and functional characterization of two promoters involved in the transcriptional regulation of the human BMP-4 gene, one upstream of exon 1, the second located in intron 1, upstream of exon 2. These two promoters give rise to different transcripts in a cell type- and differentiation-dependent manner. Mutational analysis showed cell type-specific regulation of both promoter activities. Gel mobility shift assays indicated the presence of cell type-specific transcription factor binding sites in promoter 1. In addition, evidence was found for a novel BMP-4 transcript. Since various human diseases can be linked directly to aberrant expression of BMP genes, the present findings are of great importance in attempts to develop strategies for therapeutic interference with such diseases.

The effect of cisapride on duodenal acid exposure in the proximal duodenum in healthy subjects.

AIM: To investigate the effect of the prokinetic drug, cisapride, on fasting and postprandial acid exposure in the proximal duodenum. METHODS: Using a double-blind, placebo-controlled crossover study design, 12 healthy male volunteers were studied. After 1 week of dosing (cisapride 20 mg b.d. orally or placebo), fasting and postprandial antroduodenal pH-and pressure-recordings were made. Using a small-caliber (4 mm) catheter, containing one antral and two duodenal pH electrodes, and two antral and three duodenal pressure recording sites. Transmucosal potential difference was measured to ensure proper catheter position. Infusions of 0.1 N HCl were given in the duodenal bulb. RESULTS: Endogenous acidification of the duodenal bulb occurred more frequently during phase II and postprandially, compared to phase I (P<0.001). During phase I, alkalinization of the antrum was observed. Cisapride significantly increased the postprandial number of duodenal acidic periods (P<0.02), but shortened their duration (P<0.04). The duodenal motor response elicited by exogenous acid was lower during phase I (P<0.05). CONCLUSIONS: Antral and proximal duodenal acidity vary with the phases of the interdigestive motor complex. Cisapride shortens the individual periods of duodenal acidification.

Gastrointestinal motility and gastric tube feeding in mechanically ventilated patients.

OBJECTIVE: To determine the fasted and fed gastrointestinal motility characteristics that are possibly responsible for gastric retention in mechanically ventilated patients. DESIGN: Prospective, case series. SETTING: Surgical intensive care unit of a university hospital. PATIENTS: Seven patients who required mechanical ventilation for thoracic or combined thoracic-neurologic injuries and nine healthy volunteers. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Antroduodenal manometry was performed during fasting and gastric feeding with a polymeric diet in patients during mechanical ventilation, weaning, and after detubation. Gastric retention volumes were determined during gastric tube feeding. Motility data were compared with recordings from nine healthy volunteers. During the fasting state, under sedation and morphine, the migrating motor complex in patients was significantly (p < .001) shortened: median 32.0 vs. 101.0 mins in healthy volunteers. During gastric tube feeding, the motility pattern did not convert to a normal postprandial pattern until morphine was discontinued. An interdigestive or mixed interdigestive-postprandial pattern was seen during gastric tube feeding in most patients during morphine administration. Most (94%) of the activity fronts during gastric feeding started in the duodenum. Gastric retention percentages during gastric tube feeding were negatively correlated (r2=.44; p < .01) with antral motor activity. CONCLUSIONS: These data suggest that morphine administration affects antroduodenal motility in mechanically ventilated patients. The gastrointestinal motor pattern involved in impaired gastric emptying in morphine-treated patients is characterized by antral hypomotility and persisting duodenal activity fronts during continuous intragastric feeding. The observed motility patterns suggest that early administration of enteral feeding might be more effective into the duodenum or jejunum than into the stomach of mechanically ventilated patients.

Responses to gastric distension in functional dyspepsia.

BACKGROUND: Studies have shown that an altered visceral perception threshold plays a role in the pathogenesis of upper gastrointestinal tract symptoms in dyspeptic patients. However, it is not clear whether the compliance and adaptive relaxation of the proximal stomach contribute to the symptoms. AIMS: To investigate whether abnormal relaxation or adaptation of the proximal stomach during the interdigestive state and the postprandial phase could explain the symptoms of functional dyspepsia. SUBJECTS: Twelve volunteers and 12 patients with dysmotility-like functional dyspepsia were included in the study. METHODS: An electronic barostat was used to investigate adaptation to distension of the proximal stomach and accommodation in response to a liquid meal. Dyspeptic symptoms during distension and accommodation were assessed. RESULTS: When the subjects were in the fasting state, the pressure-volume curve showed slightly higher compliance in the dyspeptic patients (p < 0.05). Patients not only had a higher score for nausea, bloating, and pain but also the increase in nausea and pain scores with intragastric pressure was higher than in volunteers (p < 0.05). The increase in intragastric bag volume in response to a meal was significantly lower in patients (p < 0.05). Both bloating and pain significantly increased in the patients (p < 0.05), but not in the healthy volunteers. CONCLUSIONS: Patients with functional dyspepsia show slightly higher compliance to mechanical distension. Their visceral perception of mechanical stress is enhanced. In contrast with the balloon distension, relaxation after a meal was less. Therefore the postprandial symptoms cannot be explained fully by greater global tension in the stomach wall, as assessed by the barostat technique. Visceral hypersensitivity plays a major role in the pathogenesis of the symptoms.

Proximal gastric motor activity in response to a liquid meal in type I diabetes mellitus with autonomic neuropathy.

Disordered gastric emptying occurs in 30-50% of patients with diabetes mellitus. Although the rate of gastric emptying is dependent on the integration of motor activity in different regions of the stomach, there is limited information about the function of the proximal stomach in diabetes mellitus. In the present study the response of the proximal stomach to a liquid meal was examined in eight diabetic patients with autonomic neuropathy and gastrointestinal symptoms and in 10 healthy volunteers, using an intragastric bag connected to an electronic barostat. Postprandial relaxation of the proximal stomach was measured as an increase of intragastric bag volume at a constant pressure level of 1 mm Hg above the intraabdominal pressure. During the experiment the blood glucose levels were maintained within the euglycemic range. Before ingestion of the meal the intragastric bag volume was larger in the diabetic patients than in the healthy volunteers, 234.4 +/- 29.1 ml vs 155.3 +/- 15.3 ml (P = 0.06). The maximum volume was not different in diabetics compared to the healthy controls (386.3 +/- 45.2 ml versus 399.0 +/- 35.2 ml). However, the maximum volume increase was significantly less in diabetics (143.7 +/- 38.6 ml) compared to the controls (231.4 +/- 30.5 ml, P < 0.04). Bloating was inversely correlated with the volume changes, which suggests that impaired relaxation of the proximal stomach may play a role in the genesis of this sensation. In conclusion, this study shows a lower fasting fundal tone and a decrease in volume change of the gastric fundus after a nutrient drink in patients with autonomic neuropathy due to type I diabetes mellitus. These abnormalities may play a role in the abnormal distribution of food, disordered liquid gastric emptying, and in the genesis of the sensation of bloating observed in these patients.

Function of the proximal stomach after Nissen fundoplication.

BACKGROUND: After Nissen fundoplication patients frequently report upper abdominal (dyspeptic) symptoms. Theoretically, these symptoms may be the result of changes in function of the proximal stomach as induced by fundoplication. METHODS: In this case-control study the response of the proximal stomach to both distension by an air-filled bag and a liquid meal were evaluated with the use of a barostat. In 12 patients after fundoplication and 12 healthy volunteers (age- and sex-matched) perception of symptoms was evaluated during both bag distension and liquid meal stimulus. RESULTS: The minimal distending pressure required to overcome the intra-abdominal pressure was significantly different between patients and controls (mean(s.e.m.) 9.34(0.26) versus 6.73(0.43) mmHg; P < 0.001). There was no difference between groups in either the fasted state, volume-pressure curve (compliance) or total symptom score. After ingestion of the liquid meal the adaptive relaxation in the fundoplication group was significantly less than that in controls (mean(s.e.m.) 150(29.2) versus 244(34.8) ml; P = 0.04). CONCLUSION: This study showed that after Nissen fundoplication compliance of the proximal stomach is no different from that in healthy volunteers. Postprandial relaxation of the proximal stomach is decreased and this abnormality may be involved in the pathogenesis of reported dyspeptic symptoms.

Stomach distension increases efferent muscle sympathetic nerve activity and blood pressure in healthy humans.

Although the enteric nervous system is usually described as a separate and independent entity, animal studies show that gastric distension causes a reflex increase in arterial pressure and a sympathetically mediated increase in heart rate and peripheral vascular resistance. To assess the influence of gastric distension on sympathetic outflow and blood pressure, we recorded muscle sympathetic nerve activity (MSNA) from the peroneal nerve by microneurography in eight healthy volunteers. The stomach was distended by means of a barostat, using a single staircase protocol by which pressure was increased by 2 mmHg every 3 min. Gastric sensory function was assessed at each distension step by using a visual analog scale (VAS) for sensations of fullness, nausea and pain. For comparison, we also performed a cold pressor test. The MSNA increased on barostat-induced gastric distension with an almost concomitant elevation of blood pressure. The increase in both was proportional to the intragastric pressure and both decreased towards initial values after the end of distension. Heart rate increased inconsistently and only at higher distension pressures that were associated with high VAS scores. The opposite was found for the cold pressor test. The results of this study confirm the existence of a functional relationship between gastrointestinal distension and cardiovascular function. Decrease in this gastrovascular response may play a role in postprandial hypotension in the elderly, since the MSNA responses to simulated microgravity decrease with age.

Objective determination of pH thresholds in the analysis of 24 h ambulatory oesophageal pH monitoring.

In 24 h oesophageal pH monitoring, pH 4 is widely but arbitrarily used as the threshold between reflux and non-reflux pH values. The aim of the study was to define pH thresholds objectively, based on Gaussian curve fitting of pH frequency distributions. Single-channel 24 h oesophageal pH monitoring was performed in 26 healthy volunteers and 26 patients with pathological gastro-oesophageal reflux, and five-channel pH-metry was performed in 14 healthy volunteers and 14 patients. The calculated pH thresholds varied between healthy volunteers from 5 center dot 0 to 6 center dot 4 in the upright position and from 4 center dot 5 to 5 center dot 7 in the supine position, but were constant between different oesophageal recording sites. In 15 and nine patients (single-channel and five-channel pH-metry respectively), pH thresholds could not be determined at the distal oesophageal sites. However, the calculated pH thresholds in the proximal oesophagus were in the same range as in the control subjects. The authors conclude that the use of the conventional threshold of pH 4 leads to underestimation of the extent of gastrooesophageal reflux, but are reluctant to advocate the use of higher thresholds in clinical practice.

Compliance of the proximal stomach and dyspeptic symptoms in patients with type I diabetes mellitus.

UNLABELLED: In the present study the function of the proximal stomach and its role in eliciting dyspeptic symptoms were evaluated in patients with diabetes mellitus. Eight type I diabetics with cardiovascular autonomic neuropathy and dyspeptic symptoms, and 10 healthy volunteers were studied using an electronic barostat device connected to a intragastric bag. The intragastric bag was inflated and deflated by stepwise pressure increments, creating pressure-volume curves. During the experiment the blood glucose concentrations were maintained within the euglycemic range in the diabetics. The volume-pressure curves showed a larger volume during the pressure increase in the diabetics than in the controls (P < 0.01). This resulted in a significant difference in compliance (dV/dP), 57.2 +/- 4.2 ml/mm Hg in diabetics and 43.7 +/- 3.5 ml/MM Hg in controls (P < 0.014). The volume-pressure curves during deflation of the intragastric balloon were different from the curves during inflation, creating a hysteresis loop. The area between the inflation and deflation curves was 827 ml/mm Hg in diabetics and 627 ml/mm Hg in the controls (P = 0.21). Gastric distension induced more upper gastrointestinal sensations in the patients than in the volunteers: nausea (P < 0.002), bloating (P < 0.003), upper abdominal pain (P < 0.001). IN CONCLUSION: this study showed that the compliance of the proximal stomach is increased in diabetic patients with autonomic neuropathy and gastrointestinal symptoms. This abnormality, probably due to autonomic neuropathy, is associated with increased symptom generation during gastric distension.

The symptom-association probability: an improved method for symptom analysis of 24-hour esophageal pH data.

BACKGROUND/AIMS: All methods currently used to quantify the temporal relationships between symptoms and episodes of gastroesophageal reflux, as assessed by 24-hour pH monitoring, have major shortcomings. The aim of this study was to develop and validate a simple, all-comprising statistical method to calculate the probability that gastroesophageal reflux episodes and symptoms are associated. METHODS: The 24-hour pH signal was divided into consecutive 2-minute periods. These periods and the 2-minute periods preceding the onset of symptoms were evaluated for the occurrence of reflux. Fisher's Exact Test was then applied to calculate the probability (P value) that reflux and symptom episodes were unrelated. Finally, the symptom-association probability (SAP) was calculated as (1.0 - P) x 100%. The SAP values found in 184 24-hour esophageal pH tests were compared with the symptom index and the symptom sensitivity index. RESULTS: Discordance between the SAP and the symptom index was found in 21 patients (11%) and discordance between the SAP and the symptom-sensitivity index in 28 (15%). False-positive and false-negative symptom index values occurred preferentially in patients with small and large numbers of symptom episodes during the test, respectively (P < 0.05). CONCLUSIONS: The SAP is a single, simple, quantitative measure of the strength of the association between symptoms and reflux episodes that is devoid of the disadvantages inherent to previously used methods.

What is the optimal time window in symptom analysis of 24-hour esophageal pressure and pH data?

Since noncardiac chest pain is the only well-established indication for 24-hr esophageal pH and pressure recording, the analysis of the association between chest pain episodes and esophageal motility abnormalities or reflux is the most important part of data analysis in 24-hr monitoring. Until now, different time windows have arbitrarily been used by various research groups. The aim of this study was to determine the optimal time window for symptom analysis in 24-hr esophageal pH and pressure monitoring. For this purpose repetitive symptom association analysis was carried out, using time windows of various onsets and durations. For each time window, the symptom indices for reflux and dysmotility were calculated. The symptom index for both reflux and dysmotility showed a gradual increase for windows with increasingly early onset, following a pattern that would be predicted on the basis of Poisson's theory. However, both indices had a relatively sharp cutoff point at 2 min before the onset of pain. Both indices only showed a predictable gradual increase when the time window starting at -2 min was extended beyond the moment of pain onset. It is concluded that the optimal time window for symptom analysis in 24-hr esophageal pH and pressure recording begins at 2 min before the onset of pain and ends at the onset of pain.