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1.
Gastric accommodation: Physiology, diagnostic modalities, clinical relevance, and therapies.
Febo-Rodriguez, L, Chumpitazi, BP, Sher, AC, Shulman, RJ
Neurogastroenterology and motility. 2021;(12):e14213
Abstract
BACKGROUND Gastric accommodation is an essential gastric motor function which occurs following ingestion of a meal. Impaired gastric fundic accommodation (IFA) is associated with dyspeptic symptoms. Gastric accommodation is mediated by the vagal pathway with several important physiologic factors such as duodenal nutrient feedback playing a significant role. IFA has been described as a pathophysiologic factor in several gastrointestinal disorders including functional dyspepsia, diabetic gastropathy, post-Nissen fundoplication, postsurgical gastrectomy, and rumination syndrome. Modalities for gastric accommodation assessment include gastric barostat, intragastric meal distribution via scintigraphy, drinking tests (eg, water load), SPECT, MRI, 2D and 3D ultrasound, and intragastric high-resolution manometry. Several treatment options including sumatriptan, buspirone, tandospirone, ondansetron, and acotiamide may improve symptoms by increasing post-meal gastric volume. PURPOSE Our aim is to provide an overview of the physiology, diagnostic modalities, and therapies for IFA. A literature search was conducted on PubMed, Google Scholar, and other sources to identify relevant studies available until December 2020. Gastric accommodation is an important gastric motor function which if impaired, is associated with several upper gastrointestinal disorders. There are an increasing number of gastric accommodation testing modalities; however, each has facets which warrant consideration. Evidence regarding potentially effective therapies for IFA is growing.
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2.
Elicitation of the Swallowing Reflex by Esophageal Stimulation in Healthy Subjects: An Evaluation Using High-Resolution Manometry.
Taniguchi, H, Aoyagi, Y, Matsuo, K, Imaeda, S, Hirumuta, M, Saitoh, E
Dysphagia. 2020;(4):657-666
Abstract
The purposes of this human study using high-resolution manometry were to verify whether the swallowing reflex can be evoked by intra-esophageal fluid injection and whether the reflex latency and manometric variables differ depending on the injected location, amount, or speed. Ten healthy individuals participated in this study. The tip of the intranasal catheter for injection was placed at 5 cm (upper), 10 cm (upper-middle), 15 cm (lower-middle), or 20 cm (lower) from the distal end of the upper esophageal sphincter (UES). An intra-esophageal injection of 3 mL or 10 mL of thickened water was administered and controlled at 3 mL/s or 10 mL/s. Latencies from the start of the injection to the onset of UES relaxation were compared regarding injection locations, amounts, and rates. Manometric variables of intra-esophageal injection and voluntary swallowing were compared. The latency became shorter when the upper region was injected. Latency after the 10-mL injection was shorter than that after the 3-mL injection (p < 0.01) when faster injection (10 mL/s) was used. Faster injection induced shorter latency (p < 0.01) when a larger volume (10 mL) was injected. Pre-maximum and post-maximum UES pressures during voluntary swallowing or during spontaneous swallowing when injecting the upper esophageal region were significantly higher than spontaneous swallowing at other regions (p < 0.01). Intra-esophageal fluid injection induces the swallowing reflex in humans. The most effective condition for inducing the swallowing reflex involved a larger fluid amount with a faster injection rate in the upper esophagus.
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3.
Augmented reflex cutaneous vasodilatation following short-term dietary nitrate supplementation in humans.
Levitt, EL, Keen, JT, Wong, BJ
Experimental physiology. 2015;(6):708-18
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Abstract
What is the central question of this study? Nitrate supplementation via beetroot juice has been shown to have several benefits in healthy humans, including reduced blood pressure and increased blood flow to exercising muscle. Whether nitrate supplementation can improve blood flow to the skin in heat-stressed humans has not been investigated. What is the main finding and its importance? Similar to previous studies, we found that nitrate supplementation reduces blood pressure. Nitrate supplementation increased vasodilatation in the skin of heat-stressed humans but did not directly increase skin blood flow. Nitrate supplementation has been shown to increase NO-dependent vasodilatation through both NO synthase (NOS)-dependent and NOS-independent pathways. We hypothesized that nitrate supplementation would augment reflex cutaneous active vasodilatation. Subjects were equipped with two microdialysis fibres on the forearm randomly assigned as control (Ringer solution) or NOS inhibition (20 mm l-NAME). Whole-body heating was performed to raise core temperature by 0.8°C above baseline core temperature. Maximal cutaneous vasodilatation was achieved via 54 mm sodium nitroprusside and local heating to 43°C. Skin blood flow (measured by laser-Doppler flowmetry) and blood pressure were measured. Cutaneous vascular conductance (CVC) was calculated as skin blood flow divided by mean arterial pressure (MAP) and expressed as a percentage of maximal CVC (%CVCmax ). Subjects underwent heat stress before and after nitrate supplementation (3 days of beetroot juice; 5 mm, 0.45 g nitrates per day). During heat stress, MAP was reduced following nitrate supplementation compared with the control conditions (before 88 ± 3 mmHg versus after 78 ± 2 mmHg; P < 0.05); however, resting MAP was not different between conditions (before 88 ± 3 mmHg versus after 83 ± 2 mmHg; P = 0.117). Nitrate supplementation increased plateau CVC at control sites (before 67 ± 2%CVCmax versus after 80 ± 5%CVCmax ; P = 0.01) but not at l-NAME-treated sites (before 45 ± 4%CVCmax versus after 40 ± 5%CVCmax ; P = 0.617). There was no change in the calculated percentage of NOS-dependent vasodilatation before and after supplementation (before 59 ± 4% versus after 64 ± 6%; P = 0.577). These data suggest that nitrate supplementation augments CVC and reduces MAP during heat stress.
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Pharyngeal pressure differences between four types of swallowing in healthy participants.
Al-Toubi, AK, Doeltgen, SH, Daniels, SK, Corey, DM, Huckabee, ML
Physiology & behavior. 2015;:132-8
Abstract
PURPOSE The aim of this observational study was to identify biomechanical differences, as measured by pharyngeal manometric pressure patterns, between discrete and continuous water swallowing, as well as volitionally initiated and reflexive swallowing. METHODS Using pharyngeal manometry, swallowing-related pressures from 24 young healthy individuals were recorded at three locations: upper pharynx, mid-pharynx and upper oesophageal sphincter (UES) during four swallowing conditions: discrete saliva swallowing, discrete 10ml water swallowing, volitional continuous water swallowing, and reflexive continuous water swallowing. Measures of peak pressure and pressure duration at each level were compared across conditions using repeated-measures analysis of variance. RESULTS UES nadir pressure during saliva swallowing was lower than during water swallowing conditions (p<0.05). In addition, nadir pressure during discrete 10ml water swallowing was lower than during reflexive and volitional continuous water swallowing conditions (p<0.05). Saliva swallowing produced longer pressure duration than water swallowing conditions at the upper pharynx (p<0.05). Saliva swallowing produced pressure of greater duration than reflexive continuous water swallowing at mid-pharynx (p<0.05). Further, discrete 10ml water swallowing produced longer UES opening duration and longer pharyngeal pressure generation (p<0.05) than reflexive continuous water swallowing or saliva swallowing. CONCLUSION Pressure generation differs between swallowing types and bolus types at the level of the UES in particular. These physiological differences between swallowing and bolus types may support clinical decisions for individuals with impaired swallowing.
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Priming of the sweat glands explains reflex sweating in the heat.
Avila, S, Buono, MJ
International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group. 2012;(1):19-23
Abstract
The purpose of this study was to determine whether reflex sweating during isometric handgrip exercise (IHG) in the heat was due to a priming effect in the sweat glands or an increase in skin temperature. Ten male subjects completed four trials where they performed IHG for three minutes at 40% of their maximal voluntary contraction (MVC). The four trials included: (1) a control trial in thermoneutral conditions (23±1°C), (2) after sitting in hyperthermic conditions (35±1°C) for 30 min, (3) a local heating trial after having their non-exercising arm wrapped in a heat pad that maintained forearm skin temperature at ~35°C for 30 min, 4) and after pilocarpine iontophoresis to a 5 cm(2) area of the forearm. The sweating rate (SR), as measured by resistance hygrometry, was not significantly different (P>0.05) from baseline during IHG in either the control or local heating trial, but was significantly increased (P<0.05) from baseline during the hyperthermic and pilocarpine trials. Baseline SR values of the hyperthermic and pilocarpine trials (~0.25mg/cm(2)/min) were significantly greater than the control and local heating trials (~0.05 mg/cm(2)/min). These results suggest that reflex sweating in the heat during IHG is primarily due to a priming effect in the sweat glands and not because of an increase in skin temperature.
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The inhibitory effect of a chewing task on a human jaw reflex.
Maillou, P, Cadden, SW, Lobbezoo, F
Muscle & nerve. 2010;(6):845-9
Abstract
This study was undertaken to investigate whether an inhibitory jaw reflex could be modulated by experimentally controlled conditions that mimicked symptoms of temporomandibular disorders. Reflecting on previous work, we anticipated that these conditions might suppress the reflex. Electromyographic recordings were made from a masseter muscle in 18 subjects, while electrical stimuli were applied to the upper lip. An inhibitory reflex wave (mean latency 47 ms) was identified and quantified. Immediately following an accelerated chewing task, which in most cases produced muscle fatigue and/or pain, the size of the reflex wave decreased significantly by about 30%. The suppression of inhibitory jaw reflexes by fatigue and pain may result in positive feedback, which may contribute to the symptoms of temporomandibular disorders. Future studies of temporomandibular disorder sufferers will help to determine whether such reflex changes reflect the underlying etiology and/or are a result of the temporomandibular disorder itself.
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Reproducible effects of subjectively assessed muscle fatigue on an inhibitory jaw reflex in humans.
van der Kaaij, NC, Maillou, P, van der Weijden, JJ, Naeije, M, Lobbezoo, F
Archives of oral biology. 2009;(9):879-83
Abstract
OBJECTIVE To evaluate the effects of exercise-induced, subjectively assessed muscle fatigue on an inhibitory jaw reflex, evoked by electrical stimulation of the upper lip. In addition, the reproducibility of these effects was assessed. DESIGN Eight subjects participated in two experimental sessions that were two weeks apart. During each session, a baseline recording, a post-conditioning recording, and two recovery recordings were obtained. The post-conditioning recording was obtained immediately after provocation of jaw muscle fatigue by intense chewing. The endpoint of provocation was reached 30s after a subject had crossed the value '6' on a 10 cm long visual analogue scale. RESULTS Subjectively assessed jaw muscle fatigue caused a decrease of about 50% in the size of the late inhibition in the post-conditioning recording (ANOVA p=0.001; Bonferroni contrasts: p<0.05). Full recovery to baseline values was already achieved at the first recovery recording. No significant differences were found between both sessions (ANOVA, p=0.677). CONCLUSION Exercise-induced, subjectively assessed jaw muscle fatigue causes a reproducible, transient suppression in the size of the late inhibitory jaw reflex wave.
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Contribution of different triggers to the gastric accommodation reflex in humans.
Vanden Berghe, P, Janssen, P, Kindt, S, Vos, R, Tack, J
American journal of physiology. Gastrointestinal and liver physiology. 2009;(5):G902-6
Abstract
Accommodation of the stomach consists of a vagally mediated relaxation of the proximal stomach, providing the meal with a reservoir. Our aim was to study whether, similar to other vagally mediated processes, the accommodation reflex is also determined by cephalic, oropharyngeal, gastric, and intestinal phases. Eleven healthy subjects underwent in randomized order five gastric barostat studies and two satiety drinking tests. In all studies, isobaric tone measurements (at minimal distending pressure + 2 mmHg) were performed 20 min before and 20 min after a nutrient stimulus. The stimuli included only visual and olfactory exposure to a meal (cephalic stimulation), taking liquid nutrient in the mouth without swallowing (sham feeding), ingestion of a 200-ml 300-kcal nutrient meal with blocked outflow to the pylorus (gastric retention), and meal infusion through a nasointestinal tube (duodenal instillation), or normal ingestion (control). During satiety testing, subjects ingested liquid nutrient at a fixed rate of 15 ml/min until maximum satiety, with an inflated or deflated intrapyloric balloon assembly. Progressively bigger gastric relaxatory responses were seen with cephalic stimulation (18 +/- 19 ml), sham feeding (54 +/- 21 ml), gastric retention (95 +/- 47), duodenal instillation (144 +/- 33), and control (232 +/- 33 ml). The amount of nutrient ingested at maximum satiety was significantly lower with an inflated intrapyloric balloon (1,223 +/- 103 vs. 1,392 +/- 124 ml, P < 0.05). The accommodation reflex in humans lacks a cephalic phase, but it can be activated from the oropharynx, the stomach, and the duodenum. Blocking passage to the duodenum significantly decreases the amplitude of the accommodation reflex and induces early satiety.
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Chronic low-dose aspirin therapy attenuates reflex cutaneous vasodilation in middle-aged humans.
Holowatz, LA, Kenney, WL
Journal of applied physiology (Bethesda, Md. : 1985). 2009;(2):500-5
Abstract
Full expression of reflex cutaneous vasodilation is dependent on cyclooxygenase- (COX) and nitric oxide synthase- (NOS) dependent mechanisms. Low-dose aspirin therapy is widely prescribed to inhibit COX-1 in platelets for atherothrombotic prevention. We hypothesized that chronic COX inhibition with daily low-dose aspirin therapy (81 mg) would attenuate reflex vasodilation in healthy human skin. Two microdialysis fibers were placed in forearm skin of seven middle-aged (57 +/- 3 yr), normotensive, healthy humans with no preexisting cardiovascular disease, taking daily low-dose aspirin therapy (aspirin: 81 mg), and seven unmedicated, healthy, age-matched control (no aspirin, 55 +/- 3 yr) subjects, with one site serving as a control (Ringer) and the other NOS inhibited (NOS inhibited: 10 mM N(G)-nitro-l-arginine methyl ester). Red cell flux was measured over each site by laser-Doppler flowmetry, as reflex vasodilation was induced by increasing core temperature (oral temperature) 1.0 degrees C using a water-perfused suit. Cutaneous vascular conductance (CVC) was calculated (CVC = flux/mean arterial pressure) and normalized to maximal CVC (CVC(max); 28 mM sodium nitroprusside). CVC(max) was not affected by either aspirin or NOS inhibition. The plateau in cutaneous vasodilation during heating (change in oral temperature = 1.0 degrees C) was significantly attenuated in the aspirin group (aspirin: 25 +/- 3% CVC(max) vs. no aspirin: 50 +/- 7% CVC(max), P < 0.001 between groups). NOS inhibition significantly attenuated %CVC(max) in both groups (aspirin: 17 +/- 2% CVC(max), no aspirin: 23 +/- 3% CVC(max); P < 0.001 vs. control), but this attenuation was less in the no-aspirin treatment group (P < 0.001). This is the first observation that chronic low-dose aspirin therapy attenuates reflex cutaneous vasodilation through both COX- and NOS-dependent mechanisms.
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Modulation of human exteroceptive jaw reflexes during simulated mastication.
Lobbezoo, F, Sowman, PF, Türker, KS
Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology. 2009;(2):398-406
Abstract
OBJECTIVE To investigate changes in synaptic input from lower lip afferents to human jaw muscle motoneurons during simulated mastication. METHODS The lower lip of 14 subjects was stimulated electrically under static and dynamic conditions. In the static condition, subjects bit at mid-open position and received stimuli while keeping the masseteric excitation level at 20%, 40%, 60%, 80%, or 100% of the maximum EMG (generated during simulated chewing). In the dynamic condition, the subjects 'masticated' at their habitual chewing pace, and stimuli were delivered whenever the jaw crossed a predetermined gape. In both conditions, mildly (scores of 2-3 on a 0-10 rating scale) and moderately (scores of 5-6) painful stimulus intensities were used. RESULTS Under static conditions, there was no modulation of the inhibitory masseteric reflexes with the level of the background level of excitation used in these experiments. However, under dynamic conditions there were significant strength modulations with gape that differed between mildly and moderately painful stimuli. CONCLUSIONS Reflexes in response to mildly painful stimuli were 'gated' during simulated mastication: as the teeth moved closer toward occlusion, the inhibitory response was progressively reduced. Conversely, responses to moderately painful stimuli became stronger as the teeth moved closer toward occlusion. SIGNIFICANCE The modulation described allows smooth mastication to occur as it gates out mildly painful signals while responding strongly when the signal indicates potential or actual damage closer to occlusion.