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This study assessed the effects of meal volume (MV) and calorie load (CL) on gastric function. MRI and a minimally invasive fiber-optic recording system (FORS) provided simultaneous measurement of gastric volume and pressure changes during gastric tilting and emptying of a liquid nutrient meal in physiological conditions. The gastric response to 12 iso-osmolar MV-CL combinations of a multinutrient drink (MV: 200, 400, 600, 800 ml; CL: 200, 300, 400 kcal) was tested in 16 healthy subjects according to a factorial design. Total gastric volume (TGV) and gastric content volume (GCV = MV + secretion) were measured by MRI during nasogastric meal infusion and gastric emptying over 60 min. Intragastric pressure was assessed at 1 Hz by FORS. The dynamic change in postprandial gastric volumes was described by a validated three-component linear exponential model. The stomach expanded with MV, but the ratio of GCV:MV at [t.sub.0] diminished with increasing MV (P < 0.01). Postprandial changes in TGV followed those of GCV. Intragastric pressure increased with MV, and this effect was augmented further by CL (P = 0.02); however, the absolute pressure rise was gastric accommodation; gastric emptying; intragastric pressure doi: 10.1152/ajpgi.00117.2009.

The effects of macronutrients on gastric volume changes, emptying, and gastrointestinal symptoms are incompletely understood. Three liquid meals of 500 ml (fat emulsion, 375 kcal; protein solution, 375 kcal; glucose solution, 400 kcal) were infused into the stomach of 12 healthy volunteers on three occasions. Studies were performed in seated body position using an open-configuration magnetic resonance imaging (MRI) system. MRI imaging sequences, assessing stomach and meal volumes, were performed prior to and at times t = 0, 3, 6, 9, 12, 15, 25, 35, 45, 60, 75, and 90 min after meal administration. Areas under the curve for the early emptying phase (0-15 and 0-45 rain) were calculated, and characteristics of the volume curves were analyzed by a gastric emptying model. Gastrointestinal symptoms were assessed by a self-report scale. Initial (t = 0 min) and early postprandial gastric volumes were highest for glucose because of lower initial emptying. However, in the early emptying phase the characteristics of the volume curves for stomach and meal were uniform for all macronutrients. Perceptions of fullness and satiety were linearly associated with postprandial gastric volumes, but not with macronutrient composition. Isovolumic macronutrient meals modulate gastric volume response by initial meal emptying patterns. Macronutrient specific accommodation responses, as shown in harostat studies, are not reflected as gastric volume responses under noninvasive conditions. accommodation; stomach response to meals; visceral sensitivity

Manometrically measured peristaltic pressure amplitude displays a well-defined trough in the upper esophagus. Whereas this manometric 'transition zone' (TZ) has been associated with striated-to-smooth muscle fiber transition, the underlying physiology of the TZ and its role in bolus transport are unclear. A computer model study of bolus retention in the TZ showed discoordinated distinct contraction waves above and below. Our aim was to test the hypothesis that distinct upper/lower contraction waves above/below the manometric TZ are normal physiology and to quantify space-time coordination between tone and bolus transport through the TZ. Eighteen normal barium swallows were analyzed in 6 subjects with concurrent 21-channel high-resolution manometry and digital fluoroscopy. From manometry, the TZ center (nadir pressure amplitude) and the upper/lower margins of the pressure trough were objectively quantified. Using fluoroscopy, we quantified space-time trajectories of the bolus tail and bolus tail pressures and maximum intraluminal pressures proximal to the tail with their space-time trajectories. In every swallow, the bolus tail followed distinct trajectories above/below the TZ, separated by a well-defined spatial 'jump' that terminated an upper contraction wave and initiated a lower contraction wave (3.32 [+ or -] 1.63 cm, P = 0.0004). An 'indentation wave' always formed within the TZ distal to the upper wave, increasing in amplitude until the lower wave was initiated. As the upper contraction wave tail entered the TZ, it slowed and the tail pressure reduced rapidly, while indentation wave pressure increased to normal tail pressure values at the initiation of the lower wave. The TZ was a special zone of segmental contraction. The TZ is, physiologically, the transition from an upper contraction wave originating in the proximal striated esophagus to a lower contraction wave that moves into the distal smooth muscle esophagus. Complete bolus transport requires coordination of upper/lower waves and sufficient segmental squeeze to fully clear the bolus from the TZ during the transition period. esophagus; pressure trough

Experiment was conducted to examine the role that cholecystokinin (CCK) and cholinergic mechanisms play in the postprandial regulation of gastric lipase (HGL) and pancreatic lipase (HPL) secretion in six humans. Gastric emptying of a mixed meal and outputs of pepsin, acid, HGL and HPL were analyzed using a double-indicator technique. Three experiments were performed which includes the intravenous infusion of placebo, low-dose atropine and the CCK-A receptor antagonist loxiglumide. Results show that CCK and cholinergic mechanisms have an important role in HGL and HPL secretion in humans.

Cholecystokinin (CCK) has been shown to play an important role in the regulation of pancreatic secretion and gallbladder contraction, but its role in gastric emptying has not been elucidated. Eight healthy subjects volunteered in an emptying study and the effects of the CCK-A receptor antagonist loxiglumide were investigated. Measures of gastric emptying of meals containing both solid and liquid components revealed an increase in the rate of gastric emptying. On the basis of this result, it is suggested that CCK regulates gastric emptying of both phases of the meal.

Indireshkumar, K., James G. Brasseur, Henryk Faas, Geoffrey S. Hebbard, Patrik Kunz, John Dent, Christine Feinle, Meijng Li, Peter Boesiger, Michael Fried, and Werner Schwizer. Relative contributions of 'pressure pump' and 'peristaltic pump' to gastric emptying. Am J Physiol Gastrointest Liver Physiol 278: G604-G616, 2000.--The relative contributions to gastric emptying from common cavity antroduodenal pressure difference ('pressure pump') vs. propagating high-pressure waves in the distal antrum ('peristaltic pump') were analyzed in humans by high-resolution manometry concurrently with time-resolved three-dimensional magnetic resonance imaging during intraduodenal nutrient infusion at 2 kcal/min. Gastric volume, space-time pressure, and contraction wave histories in the antropyloroduodenal region were measured in seven healthy subjects. The subjects fell into two distinct groups with an order of magnitude difference in levels of antral pressure activity. However, there was no significant difference in average rate of gastric emptying between the two groups. Antral pressure history was separated into 'propagating high-pressure events' (HPE), 'nonpropagating HPEs,' and 'quiescent periods.' Quiescent periods dominated, and average pressure during quiescent periods remained unchanged with decreasing gastric volume, suggesting that common cavity pressure levels were maintained by increasing wall muscle tone with decreasing volume. When propagating HPEs moved to within 2-3 cm of the pylorus, pyloric resistance was found statistically to increase with decreasing distance between peristaltic waves and the pylorus. We conclude that transpyloric flow tends to be blocked when antral contraction waves are within a 'zone of influence' proximal to the pylorus, suggesting physiological coordination between pyloric and antral contractile activity. We further conclude that gastric emptying of nutrient liquids is primarily through the 'pressure pump' mechanism controlled by pyloric opening during periods of relative quiescence in antral contractile wave activity. gastric motility; peristalsis; pressure wave; contraction wave; pump; mechanics