Small intestinal blood flow

Mechanical Stimuli Affect Escherichia coli Heat-Stable Enterotoxin-Cyclic GMP Signaling in a Human Enteroid Intestine-Chip Model

Modeling host-pathogen interactions with human intestinal epithelia using enteroid monolayers on permeable supports (such as Transwells) represents an alternative to animal studies or use of colon cancer-derived cell lines. However, the static monolayer model does not expose epithelial cells to mechanical forces normally present in the intestine, including luminal flow and serosal blood flow (shear force) or peristaltic forces. To determine the contribution of mechanical forces in the functional response of human small intestine to a virulence factor of a pathogenic intestinal bacterium, human jejunal enteroids were cultured as monolayers in microengineered fluidic-based Organ-Chips (Intestine-Chips) exposed to enterotoxigenic Escherichia coli heat-stable enterotoxin A (ST) and evaluated under conditions of static fluid, apical and basolateral flow, and flow plus repetitive stretch. Application of flow increased epithelial cell height and apical and basolateral secretion of cyclic GMP (cGMP) under baseline, unstimulated conditions. Addition of ST under flow conditions increased apical and basolateral secretion of cGMP relative to the level under static conditions but did not enhance intracellular cGMP accumulation. Cyclic stretch did not have any significant effect beyond that contributed by flow. This study demonstrates that fluid flow application initiates changes in intestinal epithelial cell characteristics relative to those of static culture conditions under both baseline conditions and with exposure to ST enterotoxin and suggests that further investigations of the application of these mechanical forces will provide insights into physiology and pathophysiology that more closely resemble intact intestine than study under static conditions.

On non-invasive measurement of gastric motility from finger photoplethysmographic signal

This article investigates the possibility of extracting gastric motility (GM) information from finger photoplethysmographic (PPG) signals non-invasively. Now-a-days measuring GM is a challenging task because of invasive and complicated clinical procedures involved. It is well-known that the PPG signal acquired from finger consists of information related to heart rate and respiratory rate. This thread is taken further and effort has been put here to find whether it is possible to extract GM information from finger PPG in an easier way and without discomfort to the patients. Finger PPG and GM (measured using Electrogastrogram, EGG) signals were acquired simultaneously at the rate of 100 Hz from eight healthy subjects for 30 min duration in fasting and postprandial states. In this study, we process the finger PPG signal and extract a slow wave that is analogous to actual EGG signal. To this end, we chose two advanced signal processing approaches: first, we perform discrete wavelet transform (DWT) to separate the different components, since PPG and EGG signals are non-stationary in nature. Second, in the frequency domain, we perform cross-spectral and coherence analysis using autoregressive (AR) spectral estimation method in order to compare the spectral details of recorded PPG and EGG signals. In DWT, a lower frequency oscillation (≈0.05 Hz) called slow wave was extracted from PPG signal which looks similar to the slow wave of GM in both shape and frequency in the range (0-0.1953) Hz. Comparison of these two slow wave signals was done by normalized cross-correlation technique. Cross-correlation values are found to be high (range 0.68-0.82, SD 0.12, R = 1.0 indicates exact agreement, p < 0.05) for all subjects and there is no significant difference in cross-correlation between fasting and postprandial states. The coherence analysis results demonstrate that a moderate coherence (range 0.5-0.7, SD 0.13, p < 0.05) exists between EGG and PPG signal in the "slow wave" frequency band, without any significant change in the level of coherence in postprandial state. These results indicate that finger PPG signal contains GM-related information. The findings are sufficiently encouraging to motivate further exploration of finger PPG as a non-invasive source of GM-related information.

Superior mesenteric artery blood flow in celiac disease

Measurements of the hemodynamic parameters of the superior mesenteric artery were performed in 18 patients with celiac disease. Ten were studied at the time of diagnosis, when a small bowel biopsy showed a flat mucosa. The remaining eight patients were studied after complete clinical and histological recovery induced by a gluten-free diet. Doppler ultrasound flowmetry was used to measure blood flow in physiological and fasting conditions and after a mixed liquid test meal (Ensure-Plus). The results were compared with those of healthy subjects (N = 7). Mean basal flow was 50% higher in untreated celiac disease patients than in healthy controls and patients with chronic pancreatitis (P = NS). Postprandial mesenteric blood flow was significantly increased (P < 0.002) and delayed in time (P < 0.005) in celiac disease as compared to controls. Successful treatment reduced the mesenteric blood flow in celiac disease to normal values. Our study demonstrates that pathophysiological changes in the small bowel mucosa during the active clinical phase of celiac disease induce an abnormal splanchnic circulation.

Peritoneal clearance of creatinine and inulin during dialysis in dogs: effect of splanchnic vasodilators

The peritoneal clearance of creatinine and inulin during isotonic peritoneal dialysis was studied in dogs before and after the administration of two vasodilators: isoproterenol and glucagon. One-liter exchanges with 15-min dwell times were used. Blood flow in the superior mesenteric artery was recorded with an electromagnetic flow probe and used as an index for total splanchnic flow. Intravenous isoproterenol (2.4 microgram/min) increased blood flow by 88%, but did not alter peritoneal clearance. When isoproterenol was given i.p. (0.5 microgram/ml dialysis fluid), blood flow increased by 81%, and inulin clearance rose by 26.8% (2.06 +/- 0.18 to 2.61 +/- 0.23 ml/min; P less than 0.05). Creatinine clearance increased by 17.5%, from 10.94 +/- 0.32 to 12.85 +/- 0.34 ml/min (P less than 0.05). When blood flow was returned to control levels with a clamp, clearances also returned to control levels. Glucagon given i.p. (1.0 microgram/ml) had no effect on any measured variable. Glucagon given i.v. at 10 microgram/min caused blood flow to rise by 81% and inulin clearance to rise by 25% from 1.88 +/- 0.16 to 2.35 +/- 0.19 ml/min (P less than 0.05). Cp, inulin clearance remained at control levels. Vasodilators seem to exercise two effects in augmenting clearance of small and middle-sized molecules: a direct permeability effect and a blood-flow related effect, possibly in increasing the surface area available for exchange and/or increasing permeability of the capillary endothelium.

Two-to-three day intestinal preservation utilizing hypothermic pulsatile perfusion

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Influence of antidiuretic hormone on peritoneal membrane area and permeability

The present study was carried out to determine if antidiuretic hormone (ADH) altered the solute handling characteristics of the peritoneal membrane. Lightly anesthetized dogs primed with urea-(14)C (60 mol wt) and inulin (5200 mol wt) were volume expanded with hypotonic saline solution to suppress endogenous ADH as assessed by urine/plasma osmolality. With ADH suppressed, two to three control peritoneal dialysis exchanges were carried out. A constant infusion of ADH in a physiologic dose of 150 mU/hr in saline was begun and the urine/plasma osmolality followed until it was significantly greater than one. Two to three experimental dialysis exchanges were then carried out. Dialysance across the peritoneal membrane was calculated for inulin (D(I)) and urea (D(U)). In 16 such studies D(U) fell in all but three (the mean value for the fall was 2.8 +/-2.6 ml/min; P < 0.001). D(I) varied randomly and showed no significant change. In all 16 studies D(I)/D(U) rose (D(I)/D(U) = 0.054 +/- 0.054; P < 0.005). Seven dogs were studied with an identical protocol but saline was infused without ADH. D(U) and the dialysance ratio varied randomly. D(U) fell in one and did not change or rose in four and D(I)/D(U) rose in two and fell in three. The data are interpreted to show a fall in area but an increase in mean pore radius of the "peritoneal membrane" in response to physiologic amounts of intravenous ADH. The fall in area is consistent with a decreasing splanchnic blood flow.

Effect of antidiuretic hormone on human small intestinal water and solute transport

The effect of i.v. Pitressin (ADH) in a dose of 1 U/hr on permeability characteristics and on absorptive capacity of the normal human small intestine was investigated. The method of continuous intestinal perfusion was employed with polyethylene glycol 4000 as a nonabsorbable marker. Unidirectional flux rates of Na and H(2)O were calculated from the disappearance of (22)Na and of (3)HOH from isotonic saline solution within the intestinal lumen. Each study consisted of two successive perfusion periods: one while the subject was hydrated, the other during ADH infusion or while the subject was dehydrated. Water and sodium absorption from isotonic NaCl occurred in the hydrated state and was abolished by ADH as well as by dehydration in the jejunum. In some instances, net gain of water and sodium in the lumen occurred. In the ileum, ADH and dehydration caused a decrease in water and sodium absorption rate. By contrast, unidirectional flux into the intestinal lumen of water and sodium, as well as dextrose and D-xylose diffusion, remained unchanged by ADH. During perfusions with hypertonic urea solutions the rates of sodium and water entry into the intestine were greatly increased during i.v. ADH infusion, whereas urea loss from the study segment remained constant. ADH in the dosage used did not affect human intestinal motility. The results suggest that circulating ADH in physiologic concentrations affects the small intestine in one of two ways: increased secretion of water and salt into the lumen or direct interference with the active sodium transport mechanism.

Experimental mesenteric venous occlusion: 3. Diagnosis and treatment of induced mesenteric venous thrombosis

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