Effects of posture on the physiology of gastric emptying: A magnetic resonance imaging study

Objective. Gastric contents empty from the stomach despite frequent changes in body position. The mechanism that maintains gastric emptying independent of position is poorly understood. The aim of this study was to determine the effects of body position on gastric emptying and motor function. Material and methods. Twelve volunteers were investigated in seated position (SP) and upside-down position (UDP) after ingestion of 300 ml water. Magnetic resonance imaging provided a non-invasive assessment of gastric emptying and volumes, intragastric distribution and peristaltic function. Results. A marked difference in distal/proximal intragastric distribution between UDP and SP was present (7% versus 40%; p?0.01). Gastric-emptying time was similar but emptying pattern was linear in UDP and exponential in SP. Peristalsis was slower in UDP than SP (2.75 versus 2.96 min^?1; p?0.01), but no correlation was found between peristaltic frequency and the rate of gastric emptying in either position. Postprandial volume response (gastric relaxation) was greater in UDP than SP (280 versus 250 ml; p?0.05). A correlation was found between gastric relaxation and gastric-emptying time in SP (r²=0.46) but not in UDP. Conclusions. The stomach maintains the rate of gastric emptying despite radical changes in body position and intragastric distribution of gastric contents. In SP, hydrostatic pressure (modulated by gastric tone) dictates the gastric emptying. In UDP, gastric emptying also appears to be mediated by continuous adaptation of gastric tone. These findings provide support for the hypothesis that the mechanism of gastric emptying resembles a “pressure pump” rather than a “peristaltic pump”.     

Measurement of gastric emptying by magnetic resonance imaging in humans.

A new noninvasive radiation-free method to measure gastric emptying in humans was developed. The upper abdomen was recorded with a magnetic resonance imager after administration of a liquid meal containing Gadolinium tetraazacyclododecane tetraacetic acid as a magnetic resonance image (MRI) marker. Meal volumes, total gastric volumes, and secretory rates were measured. The MRI technique was validated simultaneously by the double indicator method in 5 healthy volunteers and in 5 patients with symptoms of disordered gastric emptying applying gamma camera scintigraphy and MRI in randomized order. Similar gastric meal emptying curves were obtained in volunteers and in patients by MRI and the reference methods as assessed by linear (r greater than 0.90; P less than 0.001) and intraclass correlation analysis (r greater than 0.905) for T1/2, areas under the curve, and percent of gastric meal retained. Furthermore, similar total gastric volumes and gastric secretory rates were measured by MRI and the double indicator technique. The new MRI method correctly reflected gastric emptying disorders in patients. Thus for the first time it is possible to combine these measurements of gastric functions in a single method and to relate them to gastric morphology visualized by the generation of three-dimensional images.     

Scintigraphic validation of a magnetic resonance imaging method to study gastric emptying of a solid meal in humans

Background—We have previously useda magnetic resonance imaging (MRI) method to study gastric emptying ofliquids. So far, however, it has not possible to assess solid gastricemptying with this technique.
Aims—To validate scintigraphicallyMRI as a method for measuring emptying of a mixed solid/liquid meal.
Methods—In eight healthy subjects,gastric emptying of a solid/liquid (SM) and a liquid meal (LM) ofidentical energy content and macronutrient composition was studied byscintigraphy and MRI for 120minutes.
Results—MRI and scintigraphy agreedwith respect to emptying profiles (intraclass correlationcoefficient (R_I) _SM: 0.988, R_{I, LM}:0.917), t_1/2 (SM_MRI: 129 (9),SM_Scinti: 123 (11) minutes, NS; LM_MRI: 100 (7),LM_Scinti: 110 (8) minutes, NS) and AUC (SM_MRI:8999 (232), SM_Scinti: 8788 (277) min%, NS;LM_MRI: 8819 (368), LM_Scinti: 8891 (321) min%, NS).
Conclusions—MRI can be used tomeasure reliably gastric emptying not only of liquid but also of mixedsolid/liquid meals in humans.

     

Evaluation of gastric emptying and motility in diabetic gastroparesis with magnetic resonance imaging: effects of cisapride

OBJECTIVE: The motor mechanisms that underlie both slow gastric emptying in diabetic gastroparesis and its acceleration by cisapride are poorly understood. We have recently shown that magnetic resonance imaging (MRI) allows concurrent evaluation of both gastric emptying and regional gastric motility. METHODS: Emptying and motility were measured in eight diabetic patients with previously demonstrated delayed gastric emptying using a rapid MRI technique during oral administration of cisapride and placebo. Studies were performed in a double blind fashion and each patient acted as his own control. Subjects were studied supine for 120 min in a 1.5 Tesla MRI scanner after ingestion of 500 ml of 10% Intralipid. Gastric emptying corrected for the volume of secretions was determined every 15 min using transaxial scans. Each transaxial scan was followed by 120 coronal scans at 1 s intervals. Coronal scans were angled to provide simultaneous imaging of the proximal and distal stomach. MRI studies were also performed in seven diabetic patients with normal emptying who served as disease controls. RESULTS: Emptying was slower in the gastroparetic patients (t(1/2): 124 +/- 10 min) compared to patients with normal emptying (81 +/- 9 min, p < 0.05). Cisapride accelerated gastric emptying (74 +/- 5 vs 124 +/- 10 min) in patients with gastroparesis. The contraction amplitudes in the proximal stomach of gastroparetic patients were increased during cisapride treatment (17.2% +/- 1.8% vs 13.2% +/- 0.6%; p < 0.02), whereas antral contraction frequency, amplitude, and velocity were unchanged. CONCLUSIONS: We conclude that cisapride-induced acceleration of liquid gastric emptying in diabetic gastroparesis does not appear to result from changes in antral contractility, but may be related to changes in proximal gastric tone or gastric outlet resistance.     

Effect of body posture on radionuclide measurements of gastric emptying

The purpose of this investigation was to compare the effect of body posture on gastric emptying measurements of radiolabeled meals. Eight healthy male subjects were studied on four separate days. During each study subjects were fed a standardized meal of beef stew labeled with technetium-99m sulfur colloid, and orange juice. Measurements of solid-phase gastric emptying rates were obtained by a gamma camera. Subjects were studied in the lying, sitting, standing, or combined sitting-standing postures. The results demonstrated that the lying position significantly slowed gastric emptying compared to all other positions. Conversely, a decrease in emptying times of 51% and 35% occurred in the combined sitting-standing position compared to the lying and sitting position. These results support a marked effect of body posture on the radionuclide measurement of gastric emptying.The authors wish to acknowledge the Salt Lake City Veterans Administration Medical Center, Department of Research for support of this work.     

Muscular atrophy in diabetic neuropathy: a stereological magnetic resonance imaging study

Summary Diabetic patients with polyneuropathy develop motor dysfunction. To establish whether motor dysfunction is associated with muscular atrophy the ankle dorsal and plantar flexors of the non-dominant leg were evaluated with magnetic resonance imaging in 8 patients with symptomatic neuropathy, in 8 non-neuropathic patients and in 16 individually matched control subjects. In the neuropathic patients the muscle strength of the ankle dorsal and plantar flexors was reduced by 41 % as compared to the non-neuropathic patients (p < 0.005). Volume of the ankle dorsal and plantar flexors was estimated with stereological techniques from consecutive cross-sectional images of the lower leg. The neuropathic patients had a 32 % reduction in volume as compared with the non-neuropathic patients (p < 0.005). To determine the regional distribution of atrophy cross-sectional magnetic resonance images were performed at predetermined levels of the lower leg in relation to bone landmarks. In the neuropathic patients there was an insignificant increase of 3 % of muscle area at the proximal lower leg level, whereas the atrophy was 43 % (p < 0.002) at the mid lower leg level and 65 % (p < 0.002) distally. Analysis of individual muscles confirmed that the atrophy predominated distally. We conclude that muscular atrophy underlies motor weakness at the ankle in diabetic patients with polyneuropathy and that the atrophy is most pronounced in distal muscles of the lower leg indicating that a length dependent neuropathic process explains the motor dysfunction. [Diabetologia (1997) 40: 1062–1069] Received: 17 January 1997 and in revised form: 24 April 1997     

Assessment of gastric motor function by cine magnetic resonance imaging

Background and Aim:  The aim of the present study was to evaluate gastric motor function by magnetic resonance imaging (MRI) and investigate whether this examination is a useful tool for therapeutic efficacy or postoperative gastric motor function.
Methods:  Twenty-five healthy volunteers and 10 gastric cancer patients with pylorus-preserving gastrectomy (PPG) underwent cine-MRI. Gastric volume was determined by 3D-volumetry. Gastric motility was quantified by calculating the gastric motility index (GMI).
Results:  The image acquisition and analysis were successfully carried out for all subjects. In healthy volunteers, mean frequency, amplitude, velocity of gastric peristaltic waves and GMI 30 min after the intake of jelly were 3/min, 8.8 mm, 2.2 mm/s and 19.6 mm²/s, respectively. Mean amplitude (8.8 vs 10.4 mm, P  = 0.027), velocity (2.2 vs 2.6 mm/s, P  < 0.001) of peristaltic waves, and GMI (19.6 vs 26.7 mm²/s, P  < 0.001) significantly increased at 30 min after giving mosapride citrate (MS). Mean gastric volume after MS administration was significantly decreased; 0 min (317.3 vs 272.9 mL, P  = 0.021), 45 min (263.4 vs 206.4 mL, P  = 0.004) and 60 min (228.7 vs 165 mL, P  = 0.001). PPG patients with postprandial symptoms were observed having antiperistalsis-like contraction waves and reflux of gastric contents from the pyloric region into the upper part of the stomach. Mean gastric volume in PPG patients with postprandial symptoms at 30 min after intake of jelly tended to be greater than in those without such symptoms.
Conclusions:  The present study demonstrates that cine-MRI is a sensitive and non-invasive imaging technique for simultaneously measuring gastric motility and emptying.     

Brain response to visceral aversive conditioning: a functional magnetic resonance imaging study

BACKGROUND & AIMS: Brain-imaging studies to date have confounded visceral pain perception with anticipation. We used functional magnetic resonance imaging of the human brain to study the neuroanatomic network involved in aversive conditioning of visceral pain and, thus, anticipation. METHODS: Eight healthy volunteers (5 male) participated in the study. We used a classic conditioning paradigm in which 3 neutral stimuli (differently colored circles) that acted as conditioned stimuli were paired with painful esophageal distention, air puff to the wrist, or nothing, which acted as unconditioned stimuli. Neural activity was measured during learning, anticipation (pairing only 50% of conditioned stimuli with their unconditioned stimuli), and extinction (unpaired conditioned stimuli) phases. For magnetic resonance imaging, axial slices depicting blood oxygen level-dependent contrast were acquired with a 1.5-T system. RESULTS: Neural responses during the learning phase included areas commonly associated with visceral pain (anterior cingulate cortex, insula, and primary and secondary somatosensory cortices) and innocuous somatosensory perception (primary and secondary somatosensory cortices and insula). During the anticipation and extinction phases of aversive stimulation, brain activity resembled that seen during actual painful esophageal stimulation. In contrast, anticipation and extinction of the innocuous somatic stimulus failed to show that effect. CONCLUSIONS: We have shown that actual and anticipated visceral pain elicit similar cortical responses. These results have implications for the design and interpretation of brain-imaging studies of visceral pain. They not only contribute to our understanding of the processing of visceral pain, but also have clinical implications for the management of chronic pain states.     

Perineal descent and levator ani hernia: a dynamic magnetic resonance imaging study

PURPOSE: Patients with symptomatic pelvic organ prolapse often have multifocal pelvic floor defects that are not always evident of physical examination. In this study, dynamic magnetic resonance imaging of symptomatic patients with pelvic floor prolapse demonstrated unsuspected levator ani hernia. This study was designed to identify any specific symptoms and/or physical findings associated with these hernias.METHODS: Eighty consecutive patients with pelvic organ prolapse, fecal and/or urinary incontinence, or chronic constipation received standardized questionnaires, physical examination, and dynamic magnetic resonance imaging. Fishers exact test was used to compare symptoms and examination findings between patients with or without levator ani hernia.RESULTS: Twelve patients (15 percent) were found to have unilateral (n = 8) or bilateral (n = 4) levator ani hernias on dynamic magnetic resonance imaging. No one specific symptom was directly associated with the presence of a levator ani hernia. Furthermore, levator ani hernias were not found more frequently in patients with previous pelvic floor surgery. Perineal descent on physical examination was associated with the finding of a levator ani hernia in nine patients (P = 0.02). Although not statistically significant, there was a trend toward a lower incidence of levator ani hernia in females using estrogen replacement therapy (P = 0.06).CONCLUSIONS: Patients with symptomatic pelvic organ prolapse and perineal descent on physical examination may have a levator ani hernia. Although the significance of levator ani hernia needs to be determined, the recurrence rate after the surgical management of pelvic organ prolapse remains unacceptably high, and ongoing investigation of all associated abnormalities is warranted.Data were obtained from the Johns Hopkins Pelvic Floor Database. Poster presentation at The American Society of Colon and Rectal Surgery Meeting, Boston, Massachusetts, June 24 to 29, 2000.     

黑血动态增强磁共振成像技术对早期动脉粥样硬化炎性反应的可行性研究

目的:探索新型黑血动态增强磁共振成像(MRI)技术对早期动脉粥样斑块炎性反应成像的可行性研究。方法:制备五指山小型猪(n=20)动脉粥样硬化模型。动物模型制备前、后分别行MRI黑血动态增强序列扫描(TR=750 ms; TE=12 ms; TI1=325 ms; TI2=125 ms,ETL=8)。对比剂采用Gd-DTPA(0. 05 mmol/kg),高压注射器的流速为0. 1 m L/s。对模型制备前、后MR图像数据进行定量分析,测量血管壁容积传输常数(Ktrans),血浆容积(Vp),血管外细胞外容积(Ve),曲线下面积(AUC)。通过与病理结果对照,分析MR图像数据参数与微血管及巨噬细胞的相关性。并比较模型制备前、后的差异。结果:成功建立五指山小型猪动脉粥样硬化模型15只。与病理结果相对照,Ktrans与微血管数目具有较好的相关性(r=0. 913,P=0. 000)。与巨噬细胞数目比较发现,Ktrans亦有具有较好的相关性(r=0. 781,P﹤0. 000)。与模型制备前比较,MR图像数据参数Ktrans、Vp、Ve及AUC数值均显著性升高(P≤0. 000)。结论:黑血动态增强MRI成像方法可以反映早期动脉粥样硬化斑块炎症特征。并可以作为定量测量炎性反应的影像指标,为早期动脉粥样硬化提供了一种新型无创的影像学监测手段。     

Occurrence of the Chiari network in a centenarian: echocardiographic study and magnetic resonance imaging

An occasional finding of Chiari network in the right atrium of a centenarian patient confirms that it may be considered as a "normal anatomic variation" compatible with a long life span. The finding is documented by using echocardiographic and cardiac nuclear magnetic resonance imaging in a 102-year-old man.     

Effect of sumatriptan on gastric emptying: a crossover study using the BreathID system

AIM:To determine the effect of oral sumatriptan on gastric emptying using a continuous 13 C breath test(BreathID system).METHODS:Ten healthy male volunteers participated in this randomized,2-way crossover study.The subjects fasted overnight and were randomly assigned to receive a test meal(200 kcal/200 mL) 30 min after pre-medication with sumatriptan 50 mg(sumatriptan condition),or the test meal alone(control condition).Gastric emptying was monitored for 4 h after administration of the test meal by the 13 C-acetic acid breath test performed continually using the BreathID system.Then,using Oridion Research Software(β version),the time taken for emptying of 50% of the labeled meal(T 1/2) similar to the scintigraphy lag time for 10% emptying of the labeled meal(T lag),the gastric emptying coefficient(GEC),and the regression-estimated constants(β and κ) were calculated.The statistical significance of any differences in the parameters were analyzed using Wilcoxon’s signed-rank test.RESULTS:In the sumatriptan condition,significant differences compared with the control condition were found in T 1/2 [median 131.84 min(range,103.13-168.70) vs 120.27 min(89.61-138.25);P = 0.0016],T lag [median 80.085 min(59.23-125.89) vs 61.11 min(39.86-87.05);P = 0.0125],and β [median 2.3374(1.6407-3.8209) vs 2.0847(1.4755-2.9269);P = 0.0284].There were no significant differences in the GEC or κ between the 2 conditions.CONCLUSION:This study showed that oral sumatriptan significantly delayed gastric emptying of a liquid meal.     

Effects of gastric pacing on gastric emptying and plasma motilin

AIM:To investigate the effects of gastric pacing on gastric emptying and plasma motilin level in a canine model of gastric motility disorders and the correlation between gastric emptying and plasma motilin level.METHODS: Ten healthy Mongrel dogs were divided into:experimental group of six dogs and control group of four dogs. A model of gastric motility disorders was established in the experimental group undergone truncal vagotomy combined with injection of glucagon. Gastric half-emptying time (GEt1/2) was monitored with single photon emission computerized tornography (SPECT), and the half-solid test meal was labeled with an isotope-^99mTc sulfur colloid. Plasma motilin concentration was measured with radioimmunoassay (RIA) kit. Surface gastric pacing at 1.1-1.2 times the intrinsic slow-wave frequency and a superimposed series of high frequency pulses (10-30Hz) was performed for 45min daily for a month in conscious dogs.RESULTS:After surgery, GEt1/2 in dogs undergone truncal vagotorny was increased significantly from 56.35&#177;2.99min to 79.42&#177;1.91min (P&lt;0.001), but surface gastric pacing markedly accelerated gastric emptying and significantly decreased GEt1/2 to 64.94&#177;1.75min (P&lt;0.001) in animals undergone vagotomy. There was a significant increase of plasma level of motilin at the phase of IMCⅢ (interdigestive myoelectrical complex, IMCⅢ) in the dogs undergone bilateral truncal vagotomy (baseline vsvagotomy, 184.29&#177;9.81pg/ml vs 242.09&#177;17.22pg/ml;P&lt;0.01).But plasma motilin concentration (212.55&#177;11.20pg/ml; P&lt;0.02) was decreased significantly after a long-term treatment with gastric pacing.Before gastric padng, GEt1/2 and plasma motilin concentration of the dogs undergone vagotomy showed a positive correlation (r=0.867, P&lt;0.01), but after a long-term gastric pacing, GEt1/2 and motilin level showed a negative correlation (r=-0.733, P&lt;0.04).CONCLUSION: Surface gastric pacing with optimal pacing parameters can improve gastric emptying parameters and significantly accelerate gastric emptying and can resume or alter motor function in a canine model of motility disorders. Gastric emptying is correlated well with plasma motilin level before and after padng, which suggests that motilin can modulate the mechanism of gastric pacing byaltering gastric motility.motilin can modulate the mechanism of gastric pacing by altering gastric motility.     

Declarative memory consolidation in humans: a prospective functional magnetic resonance imaging study

Retrieval of recently acquired declarative memories depends on the hippocampus, but with time, retrieval is increasingly sustainable by neocortical representations alone. This process has been conceptualized as system-level consolidation. Using functional magnetic resonance imaging, we assessed over the course of three months how consolidation affects the neural correlates of memory retrieval. The duration of slow-wave sleep during a nap/rest period after the initial study session and before the first scan session on day 1 correlated positively with recognition memory performance for items studied before the nap and negatively with hippocampal activity associated with correct confident recognition. Over the course of the entire study, hippocampal activity for correct confident recognition continued to decrease, whereas activity in a ventral medial prefrontal region increased. These findings, together with data obtained in rodents, may prompt a revision of classical consolidation theory, incorporating a transfer of putative linking nodes from hippocampal to prelimbic prefrontal areas.     

Hepatic triglyceride content and its relation to body adiposity: a magnetic resonance imaging and proton magnetic resonance spectroscopy study

BACKGROUND: Hepatic steatosis is associated with obesity and type II diabetes. Proton magnetic resonance spectroscopy (1H MRS) is a non-invasive method for measurement of tissue fat content, including intrahepatocellular lipids (IHCL) and intramyocellular lipids (IMCL). PATIENTS AND METHODS: We used 1H MRS and whole body magnetic resonance imaging (MRI) to assess the relationship between IHCL accumulation, total body adipose tissue (AT) content/distribution, and IMCL content in 11 subjects with biopsy proven hepatic steatosis and 23 normal volunteers. RESULTS: IHCL signals were detectable in all subjects but were significantly greater in hepatic steatosis (geometric mean (GM) 11.5 (interquartile range (IQR) 7.0-39.0)) than in normal volunteers (GM 2.7 (IQR 0.7-9.3); p=0.02). In the study group as a whole, IHCL levels were significantly greater in overweight compared with lean subjects (body mass index (BMI) >25 kg/m2 (n=23): GM 7.7 (IQR 4.0-28.6) v BMI <25 kg/m2 (n=11): GM 1.3 (IQR 0.3-3.6; p=0.004)). There was a significant association between IHCL content and indices of overall obesity (expressed as a percentage of body weight) for total body fat (p=0.001), total subcutaneous AT (p=0.007), and central obesity (subcutaneous abdominal AT (p=0.001) and intra-abdominal AT (p=0.001)), after allowing for sex and age. No correlation between IHCL content and IMCL was observed. A significant correlation was observed between serum alanine aminotransferase and liver fat content (r=0.57, p=0.006). CONCLUSIONS: Our results suggest that hepatic steatosis appears to be closely related to body adiposity, especially central obesity. MRS may be a useful method for monitoring IHCL in future interventional studies.