Constricted Segment Research Articles

The First Robotic Day Care Procedure in the Management of Testicular Vein Syndrome: A Rare Cause of Hydroureteronephrosis

Clinical History: A 46-year-old gentleman with no comorbidities presented with dull aching pain in the left loin for 6 months. Physical Examination: Examination was unremarkable. Diagnosis: He was evaluated with contrast-enhanced CT scan of the urinary tract that revealed left gross hydroureteronephrosis secondary to midureteral stricture caused by compression of the left testicular vein. Renogram (diethylenetriamine pentaacetate scan) was performed that showed 44% split renal function of the left kidney with a glomerular filtration rate of 86 mL/min. Intervention: He underwent a day-case robotic ureteroureterostomy and intraoperatively the upper ureter was dilated with testicular vein transposing above the midureter that had a stricture, causing dilatation of proximal ureter with hydronephrosis. Upper ureter was transected above the stricture and brought anterior to the testicular vein and the constricted segment was excised. Ureteroureterostomy was performed over 5F/26 cm Double-J stenting using 2-0 Stratafix suture. Outcomes: Follow-up included stent removal at 6 weeks and serial creatinine thereafter has been normal. Follow-up imaging was done in the form of ultrasonography that showed resolution of hydronephrosis at 3 months and 6 months. Patient Consent Statement: Written informed consent was obtained from the patient to publish this research. No competing financial interests exist.This research received no specific grant from any funding agency, commercial or nonprofit sectors. All authors confirm that they have been involved in the conception and design of the study, drafting of the study for intellectual content, and are accountable to the accuracy of all aspects of the content.Author(s) have received and archived patient consent for video recording/publication in advance of video recording of procedure Runtime of video: 4 mins 17 secs

The Effect of Large Wood Accumulations With Rootwads on Local Geomorphic Changes

AbstractLarge wood (LW) can be transported along a river during floods, increasing flood‐associated hazards, particularly when it accumulates at river‐spanning infrastructures such as bridges and weirs. While most flume studies have explored LW movement with simple wooden elements (dowels), only a few studies have used elements with more complex LW geometries, such as rootwads, under unsteady flow conditions. Quantitative assessment of interactions amongst more complex wood elements and river flow has rarely been attempted the effect of this additional complication has even been ignored, in both field and laboratory studies. In this study, flume experiments were conducted to assess the effect of rootwads on local scour and deposition in a flume with a mobile gravel‐bed. The experiment was conducted under unsteady flow conditions, with a constricted segment of the reach, recreating conditions to wood accumulations and blockage. Results revealed that LW with rootwads tends to generate more stable accumulations than LW without rootwads, leading to the formation of more porous loosely packed accumulations. In this initial set of flume experiments, the patterns of scour were quite variable, but on average, the porous and stable LW accumulations with rootwads showed more spatially extensive disturbance of the bed. LW accumulations without rootwads led to the development of scour pits that reached the bottom of the flume more quickly than in the LW accumulations without rootwads. The mean accumulated bedload volumes were of similar magnitude overall, however, highlighting the many contingencies in the chain of processes between dam formation and resultant bed scour.

Asymptomatic thoracoabdominal aortic coarctation

Aortic coarctation is a congenital cardiac anomaly consisting of a constricted aortic segment, usually involving the aortic isthmus.1 Coarctation of the distal thoracic aorta and/or the abdominal aorta and its major branches is rare and accounts for 0.5% to 2.0% of coarctations.2,3 These coarctation are most often secondary to Takayasu's disease or aortitis, atherosclerosis, neurocutaneous syndrome, and Williams syndrome. However, no single genesis seems to explain every case and beside vasculitis as a cause; some are thought to be congenital in origin and others are associated with von Recklinghausen's disease.

Thermal Effect on Deformation of Nanofluid-Encapsulated Double Emulsion Droplets Flowing in a Constricted Microchannel

Double emulsions have been intensively used as a template to form core/shell structured microcapsules encapsulating and releasing a substance of interest in a controllable way for wide spectrum of chemical and biological applications. Herein a numerical model was established to investigate the thermal effect on breakup dynamics of a double emulsion flowing through a microchannel with a constricted segment which mimics the structure of microcapillaries using two groups of cases. In the first group, double emulsion was formed with water dispersed in oil which is surrounded by water (W/O/W); and in the second group, double emulsion was formed with water dispersed in oil which is surrounded by nanofluids where single-wall carbon nanotubes (SWCN) was dispersed in an ethylene glycol (EG) solution with volume fraction of 0.05% (W/O/SWCN-EG). In both groups, the thermal effect study was extended to other temperature dependent physical properties such as viscosity, density, and thermal conductivity. Thermal effects on the shear stress distribution in the constricted microchannel will lead to significant difference in deformation between the two groups. The investigation provides new insights to understanding the thermal effect in multiphase flow through complex microstructures where nanofluids have found significant increase in biomedical applications.

Harmonic tremor model during the 2011 Shinmoe-dake eruption, Japan

Summary The Shinmoe-dake volcano started with three sub-Plinian eruptions from 26 to 27 January 2011, followed by a magma effusive stage from 28 to 31 January 2011, and Vulcanian eruptions occurred frequently during 1 to 10 February 2011. During the magma effusive and Vulcanian stages, multiple episodes of harmonic tremors were observed at stations near the summit crater. Although harmonic tremors have been observed at various volcanoes worldwide, the source mechanism remains poorly understood. This paper proposes a source model for harmonic tremors, which is composed of a nonlinear viscous fluid flow in a flexible channel. A simple lumped parameter model is used to consider the process. The dynamics are described by a third-order system of ordinary differential equations using model variables for a cross-sectional area of the constricted segment and the fluid velocities in the upstream and downstream tubes. This model produces various kinds of trajectories for self-sustained oscillations that change the reservoir pressure connected on the upstream channel of the model. Linearization analysis around the stationary point and global analysis employing nullcline planes reveal the mechanism of self-sustained oscillations of the system qualitatively. To consider both the frequency peaks of the harmonic tremor and the characteristics of observed phase spectra, the qualitative characteristics of an observed phase portrait are compared to those of a simulated one. This tremor model simulates the frequency peaks and the phase portraits of typical harmonic tremors observed during the 2011 Shinmoe-dake eruption. Because this model involves several geometrical configuration parameters, it has the potential to reveal the source mechanism of various kinds of harmonic tremors.

The Scar-y Side of Endometriosis Resection: Small Bowel Obstruction by Postoperative Scar Tissue

A 38-year-old nulligravid female with a long-standing history of severe endometriosis requiring 4 previous excisional procedures, including ileocecal resection and reanastomosis, developed severe epigastric and right upper quadrant pain without an inciting incident. The abdominal upright film revealed multiple dilated small bowel loops with air/fluid levels. Conservative management with bowel decompression was initiated. A computed tomography scan 2 days later demonstrated dilated loops of small bowel consistent with a small bowel obstruction with a transition point at the ileocecal junction near the anastomotic line from her previous resection. The patient was taken to the operating room for diagnostic laparoscopy. A hand-assisted enterolysis was performed, and a stricture of the small bowel was discovered to be a dense band of scar tissue (Fig. 1, Fig. 2). The surrounding bowel was noted to be ischemic. A wedge resection of the distal ileum with a primary suture closure was required to alleviate this stricture. Her prior anastomosis was found to be widely patent. The surgical pathology revealed the band to be scar tissue with ischemic changes and intramural hemorrhage but no evidence of endometriosis. Fig. 2Mesenteric view of constricted segment of ileum with fibrotic band of scar tissue visible between black arrows. View Large Image Figure Viewer Download Hi-res image

Spontaneous peripheral nerve palsy with hourglass-like fascicular constriction in the upper extremity.

Spontaneous paralysis from hourglass-like fascicular constriction of peripheral nerves is rare, its clinical manifestations are not well documented, and its pathogenesis remains unknown. The unclear origin of this disorder and difficulty in diagnosis result in its uncertain management. The authors sought to gain a more thorough understanding of this condition through describing the anatomy, clinical features, etiology, and treatment of hourglass-like constriction. The authors retrospectively reviewed 20 patients (22 nerves) with hourglass-like constriction. The patients' clinical information was reviewed. Preoperative sonographic assessment and electrophysiological examination of involved nerves were performed. Surgical treatments included interfascicular neurolysis and neurorrhaphy. Samples of tissue subjected to resected constriction were sent for pathological analysis. The patients had regular face-to-face follow-up visits. Acute pain was always the first symptom and was followed by paralysis. Paralysis progression was rapid and serious. Surgical exploration indicated an hourglass-like constricted segment completely unrelated to the compressive structures. Electrophysiological analysis showed severe denervation, and histopathological examination showed inflammatory cell infiltration, demyelination, and reduction of nerve fibers. Hourglass-like fascicular constrictive neuropathy has an integrative effect from multiple different mechanisms. Surgical intervention is beneficial for selected patients who do not recover in a timely fashion and have hourglass-like lesions confirmed by preoperative ultrasound imaging. The authors recommend that early surgical intervention of the nerve be offered to patients who do not show any signs of recovery 3 months after onset. Both interfascicular neurolysis and neurorrhaphy are effective treatment methods. Mild to moderate constriction can usually be treated successfully by interfascicular neurolysis alone, whereas more advanced lesions with loss of fascicle continuity (severe constriction) may be best treated with resection and direct neurorrhaphy.

Fremanezumab inhibits vasodilatory effects of CGRP and capsaicin in rat cerebral artery - Potential role in conditions of severe vasoconstriction

CGRP plays a major role in the pathophysiology of migraine. Concomitant, CGRP plays a role in endogenous neurovascular protection from severe vasoconstriction associated with e.g. cerebral or cardiac ischemia.The CGRP antagonistic antibodies Fremanezumab (TEVA Pharmaceuticals) and Erenumab (Novartis/Amgen) have successfully been developed for the prevention of frequent migraine attacks. Whereas these antibodies might challenge endogenous neurovasular protection during severe cerebral or coronary vasoconstriction, potential future therapeutic CGRP agonists might induce migraine-like headaches in migraineurs.In the current study segments of cerebral artery have been used to obtain mechanistic insight of the CGRP-neutralizing anti-body Fremanezumab in neurovascular regulation in vitro. The basilar artery was selected due to its relevance in subarachnoid hemorrhage (SAH).Erenumab is known to block the human CGRP receptor and Fremanezumab to neutralize both human and rat CGRP. Results confirmed that Erenumab does not block the rat CGRP receptor and that Fremanezumab inhibits the vasodilatory effect induced by both human CGRP, rat CGRP and the metabolically stable CGRP analog, SAX in rat basilar artery.Fremanezumab also inhibits the vasodilatory effect of capsaicin in constricted segments of basilar artery. Capsaicin is used as a pharmacological tool to induce secretion of endogenous perivascular CGRP and our studies confirm that the antibody reach the perivascular sensory synaptic cleft and blocks the vasodilatory response of released CGRP in the present in vitro model.Thus, CGRP neutralization might have the mechanistic potential to block vasoprotective responses to severe vasoconstriction provided they reach the site of action and Fremanezumab is an important tool for future investigations of the impact of CGRP physiology.

Small-Angle Neutron Scattering Study of Temperature-Induced Structural Changes in Liposomes.

Liposomes of specific artificial phospholipids, such as Pad-PC-Pad and Rad-PC-Rad, are mechanically responsive. They can release encapsulated therapeutics via physical stimuli, as naturally present in blood flow of constricted vessel segments. The question is how these synthetic liposomes change their structure in the medically relevant temperature range from 22 to 42 °C. In the present study, small-angle neutron scattering (SANS) was employed to evaluate the temperature-induced structural changes of selected artificial liposomes. For Rad-PC-Rad, Pad-Pad-PC, Sur-PC-Sur, and Sad-PC-Sad liposomes, the SANS data have remained constant because the phase transition temperatures are above 42 °C. For Pad-PC-Pad and Pes-PC-Pes liposomes, whose phase transitions are below 42 °C, the q-plots have revealed temperature-dependent structural changes. The average diameter of Pad-PC-Pad liposomes remained almost constant, whereas the eccentricity decreased by an order of magnitude. Related measurements using transmission electron microscopy at cryogenic temperatures, as well as dynamic light scattering before and after the heating cycles, underpin the fact that the non-spherical liposomes flatten out. The SANS data further indicated that, as a consequence of the thermal loop, the mean bilayer thickness increased by 20%, associated with the loss of lipid membrane interdigitation. Therefore, Pad-PC-Pad liposomes are unsuitable for local drug delivery in the atherosclerotic human blood vessel system. In contrast, Rad-PC-Rad liposomes are thermally stable for applications within the human body.

X-ray micro computed tomography for the visualization of an atherosclerotic human coronary artery

Atherosclerosis refers to narrowing or blocking of blood vessels that can lead to a heart attack, chest pain or stroke. Constricted segments of diseased arteries exhibit considerably increased wall shear stress, compared to the healthy ones. One of the possibilities to improve patient’s treatment is the application of nano-therapeutic approaches, based on shear stress sensitive nano-containers. In order to tailor the chemical composition and subsequent physical properties of such liposomes, one has to know precisely the morphology of critically stenosed arteries at micrometre resolution. It is often obtained by means of histology, which has the drawback of offering only two-dimensional information. Additionally, it requires the artery to be decalcified before sectioning, which might lead to deformations within the tissue. Micro computed tomography (μCT) enables the three-dimensional (3D) visualization of soft and hard tissues at micrometre level. μCT allows lumen segmentation that is crucial for subsequent flow simulation analysis. In this communication, tomographic images of a human coronary artery before and after decalcification are qualitatively and quantitatively compared. We analyse the cross section of the diseased human coronary artery before and after decalcification, and calculate the lumen area of both samples.

Brachio-Cubital Fasciotomy for Resistant Stenosis of Arterio-Venous Fistula

Purpose: Radio-cephalic arterio-venous fistula can become dysfunctional due to venous outflow stenosis along its course. When the median cubital and the upper arm cephalic vein are small or obliterated, all the forearm cephalic vein blood flow can go through the perforating deep median vein into the brachial vena comitans. These deeply located veins, when dilated, become compressed by the overlying antecubital fascia and bicipital aponeurosis. These ensuing stenoses are usually resistant to endovascular balloon dilatation angioplasty or recur rapidly afterwards. Brachio-cubital fasciotomy was utilized to help relieve the compression and salvage the access. Methods: For the confirmed resistant stenoses of the AVF, open fasciotomy was performed along the medial aspect of the antecubital fossa. Endovascular angioplasty of the stenotic lesions was accomplished in conjunction with vascular skeletonization while the balloon was inflated inside the AVF. Results: Nineteen patients recognized to have resistant stenoses of their AVF underwent brachio-cubital fasciotomy. Through the fasciotomy, stenoses were resolved and intra-access pressure reduced to satisfactory levels in all patients. Three patients required resection of the constricted segment and reanastomosis of the mobilized fistula in addition to the fasciotomy. At the follow-up observation of minimum 9 months, all but one of the rescued stenotic lesions stayed patent and required no further intervention. Conclusions: Radio-cephalic arterio-venous fistula can become dysfunctional due to the development of outflow stenosis from compression by overlying fascia and this stenosis is usually resistant to the dilatation angioplasty. Brachio-cubital fasciotomy resolves these stenoses successfully and allows complete angioplasty with vascular skeletonization and open revision if required.

Conversion of Basal Plane Dislocations to Threading Edge Dislocations by Annealing 4H-SiC Epilayers at High Temperatures

Basal plane dislocations (BPDs) converting to threading edge dislocations (TEDs) has been observed in 4H-SiC epilayers after thermal annealing at high temperatures. Grazing incidence reflection synchrotron X-ray topography was used to investigate the dislocation behaviors. It is argued that the conversion is achieved by constricted BPD segments cross-slipping to the prismatic plane and TED glide on its slip plane. Higher conversion ratio and better surface morphology were achieved by performing ion implantation and annealing before epitaxial growth.

Conversion of basal plane dislocations to threading edge dislocations in 4H-SiC epilayers by high temperature annealing

Conversion of basal plane dislocations (BPDs) to threading edge dislocations (TEDs) is found in 4H-SiC epilayers after being annealed simply at high temperatures. Grazing incidence reflection synchrotron x-ray topography for the dislocations in the epilayers before and after annealing confirmed that some of the BPDs in the epilayers had converted to TEDs from the epilayer surface by the annealing. Observations on the dislocation behavior during annealing are explained in detail, and the mechanism of BPD conversion is discussed. It is argued that the conversion proceeds through the cross slip of constricted BPD segments towards the surface on the prismatic plane driven by the image force as well as TED glide driven by the line tension. Certain kinetic processes during annealing may facilitate the formation of constriction.

Conversion of Basal Plane Dislocations to Threading Edge Dislocations by High Temperature Annealing of 4H-SiC Epilayers

ABSTRACTConversion of basal plane dislocations (BPDs) to threading edge dislocations (TEDs) has been observed in 4H-SiC epilayers by simple high temperature annealing. Grazing incidence reflection synchrotron X-ray topography was used to image the dislocations in the epilayers. By comparing the X-ray topographs before and after annealing, some of the BPDs were confirmed to convert to TEDs from the epilayer surface. The dislocation behaviors during annealing are explained and the mechanism of BPD conversion is discussed. It is argued that the conversion process is realized by constricted BPD segments cross-slipping to the prismatic plane driven by the image force and TED glide on its slip plane driven by the line tension. Certain kinetic processes may assist the formation of constrictions on the BPDs.

Coarctation of Aorta-Management Options and Decision Making

Coarctation of the Aorta (CoA) is a congenital cardiac anomaly consisting of a constricted aortic segment with a prevalence of 5 to 8% of all Congenital Heart Defects (CHD). The classic CoA is located in the thoracic aorta distal to the origin of the left subclavian artery, at about the level of the ductal structure. Significant hypertension and/or congestive heart failure are indications of intervention. If hypertension (rather that heart failure) is the clinical problem, it is better to relieve the aortic obstruction promptly rather that attempting to “treat” hypertension with antihypertensive medications. Surgical relief of the aortic obstruction and catheter interventional techniques (balloon angioplasty and stents) are available alternatives. Since the introduction of surgical correction by Crafoord and Nylin and Gross and Hufnagel in early 1940s, surgical therapy has been the treatment of choice for aortic coarctation. Gruntzig’s technique of balloon angioplasty was adopted by Singer and Sperling and their associates to enlarge coarcted aortic segments in post-surgical recoarctation and native coarctation, respectively in early 1980s. This is followed by the application of the technique by other cardiologists to treat native CoA. The procedure consists of inserting a balloon angioplasty catheter across the site of coarctation and inflating the balloon with diluted contrast material. Both immediate and followup results are reasonably good. Residual and recurrent obstructions following surgery and prior balloon angioplasty are also amenable for balloon angioplasty. Despite reasonably good short-term and long-term results of balloon angioplasty, some problems remain and include restenosis, probability of aortic rupture, formation of aneurysms and inability to effectively treat long-segment tubular narrowing. Because of these and other reasons, endovascular stenting of aortic coarctation has gained acceptance over the last decade. The balloon catheter, with the stent mounted on it, is advanced over a stiff guide wire and positioned across the coarctation segment and the balloon inflated, thus implanting the stent. Most cardiologists use stents in adolescents and adults and restrict their use in younger children because of issues related to growth. Stent therapy appears to be an attractive method for treatment of native or recurrent coarctation, aneurysm formation following prior surgical or balloon intervention and for long segment hypoplasia. Role of covered stents to manage aortic coarctation is limited and are used when the assessed risk for development of aneurysm or dissection is high. A comparison of all available treatment modalities was made and while it is difficult to make a definitive statement, the overall data seem to indicate that transcatheter methods may be better than surgery. Selection of the method of therapy is largely based on the age at presentation and anatomy of the coarcted segment and surrounding structures; surgery for infants and long segment coarctations, balloon angioplasty for discrete native and post-surgical coarctations in children and stents for long segment coarctations as well as any type of coarctations in adolescents and adults seem to be the current trend.

Abstract 8966: C1q/TNF-Related Proteins (CTRPs), a Family of Novel Adipokines, Induce Vascular Relaxation through the Adiponectin Receptor-1/AMPK/eNOS/Nitric Oxide Signaling Pathway

Reduced plasma adiponectin (APN) in diabetic patients is associated with endothelial dysfunction and vascular injury. However, APN knockout animals manifest only modest systemic dysfunction unless metabolically challenged. The CTRP (C1q/TNF-related proteins) family has recently been identified as APN paralogs. Some CTRP members share APN’s metabolic regulatory function. However, the vascular biology of CTRPs remains completely unknown. This study assessed the vasoactivity of currently identified murine CTRP members utilizing in vitro and in vivo experimental models, and elucidated underlying molecular mechanisms in HUVECs. Of eight CTRPs investigated, three CTRPs (3, 5, and 9) caused significant vasorelaxation in concentration-dependent fashion, while the remaining CTRPs neither constricted nor dilated aortic segments. The vasodilatory potency of CTRP9 exceeded that of APN (3-fold), is endothelium-dependent, and mediated by nitric oxide (NO). Plasma CTRP9 levels were markedly increased in APN knockout mice, and significantly reduced in high-fat-diet induced obesity/diabetic mice (P<0.05). One week of in vivo CTRP9 administration initiated after 3 weeks high-fat-diet, at a dose restoring physiological CTRP9 levels, significantly improved vascular endothelial function (P<0.01). Mechanistically, CTRP9 increased AMPK/Akt/eNOS phosphorylation and increased endothelial NO production. AMPK knockdown completely blocked CTRP9-induced Akt/eNOS phosphorylation and NO production. Akt knockdown had no significant effect upon CTRP9-induced AMPK phosphorylation, but blocked eNOS phosphorylation and NO production. Adiponectin receptor 1 (AdipoR1), but not receptor 2 (AdipoR2), knockdown blocked CTRP9-induced AMPK/Akt/eNOS phosphorylation and NO production. Finally, pre-incubating vascular rings with an AMPK-inhibitor abolished CTRP9-induced vasodilatory effects. Collectively, we have provided the first evidence that CTRP9 is a novel vasodilatory/vasculoprotective adipokine, potentially compensatory for APN’s vascular effects in APN knockout animals. Moreover, we have demonstrated that CTRP9 exerts its vascular biological effects via the AdipoR1/AMPK/eNOS dependent/NO mediated signaling pathway.

Modelling of arterial stenosis and its effect on flow of blood

We have proposed and analyzed a mathematical model for studying the non-Newtonian flow of blood through a constricted arterial segment. The problem is investigated by using two different fluids. The result for resistance to flow across the length of the artery is obtained. It has been observed that increase or decrease in resistance to flow in both the fluids depends on the height of the stenosis. Because of non-Newtonian behaviour of blood these variations are lesser than that of Newtonian fluid. The graphical analysis of the variants of resistance to flow at maximum height of the stenosis is compared with a known investigation.

Circumferential mural bands in the small intestine causing simple obstructive colic: a case series

Circumferential mural band (CMB) in the small intestine is an emerging condition in Ireland. The clinical presentation is a simple obstruction of the small intestine of unknown aetiology. Horses affected with CMB in the small intestine have a good prognosis following surgical decompression into the caecum. A retrospective study was carried out and 28 cases identified from 559 colic surgeries performed over a 5.5 year period. An exploratory celiotomy was performed in every case. A simple obstruction at the mid or distal jejunum was identified caused by a CMB, which was multiple in some cases. All of the horses except 2 had undergone a regular anthelmintic programme. Manual decompression of the small intestine into the caecum resulted in resolution of the simple jejunal obstruction. A constricted segment of small intestine was resected in one case, as the degree of constriction was severe. A full thickness biopsy was taken from another case. Histopathology was performed on both samples. All horses recovered from surgery and were discharged from the hospital 7-32 days post operatively. Short-term complications were observed. Survival rate was 100% at long-term follow-up. Histopathology showed inflammatory infiltration in the submucosa, muscularis and serosa with eosinophils predominating. Parasites were not detected. Small intestine circumferential mural bands have a good prognosis after surgical decompression of the small intestine into the caecum.

Spatial and temporal variability of sediment and dissolved loads from two alpine watersheds of the Lesser Himalayas

Abstract Estimation of sediment load from Himalayan basins is of considerable importance for the planning, designing, installation and operation of hydro-power projects, including management of reservoirs. In the present study, an assessment of physical and chemical load, sediment yield and erosion rate has been undertaken at eight different locations in the Sainj and Tirthan watersheds. The analysis revealed that the maximum load was transferred during the monsoon season. Moreover, the estimated average chemical erosion rate of the Sainj (83 t km − 2 yr − 1 ) and Tirthan (80 t km − 2 yr − 1 ) watersheds were higher than that of the Indian average (69 t km − 2 yr − 1 ) representing all the rivers. Both watersheds were eroding physically and chemically at a faster rate than that of the world global average erosion rate (185 t km − 2 yr − 1 ). The flattish nature of the channels in some segments of these watersheds showed a lower transport of sediments, where as the constricted segments having steep bed slopes increased the velocity of flow and the sediment transport rate. These findings have important implications for water resource management in the context of sediments mobilization, erosion, channel management, ecological functions and operation of the hydro-power projects in the Lesser Himalayan region.

Analysis of the interplay between neurochemical control of respiration and upper airway mechanics producing upper airway obstruction during sleep in humans

Increased loop gain (a function of both controller gain and plant gain), which results in instability in feedback control, is of major importance in producing recurrent central apnoeas during sleep but its role in causing obstructive apnoeas is not clear. The purpose of this study was to investigate the role of loop gain in producing obstructive sleep apnoeas. Owing to the complexity of factors that may operate to produce obstruction during sleep, we used a mathematical model to sort them out. The model used was based on our previous model of neurochemical control of breathing, which included the effects of chemical stimuli and changes in alertness on respiratory pattern generator activity. To this we added a model of the upper airways that contained a narrowed section which behaved as a compressible elastic tube and was tethered during inspiration by the contraction of the upper airway dilator muscles. These muscles in the model, as in life, responded to changes in hypoxia, hypercapnia and alertness in a manner similar to the action of the chest wall muscles, opposing the compressive action caused by the negative intraluminal pressure generated during inspiration which was magnified by the Bernoulli Effect. As the velocity of inspiratory airflow increased, with sufficiently large increase in airflow velocity, obstruction occurred. Changes in breathing after sleep onset were simulated. The simulations showed that increases in controller gain caused the more rapid onset of obstructive apnoeas. Apnoea episodes were terminated by arousal. With a constant controller gain, as stiffness decreased, obstructed breaths appeared and periods of obstruction recurred longer after sleep onset before disappearing. Decreased controller gain produced, for example, by breathing oxygen eliminated the obstructive apnoeas resulting from moderate reductions in constricted segment stiffness. This became less effective as stiffness was reduced more. Contraction of the upper airway muscles with hypercapnia and hypoxia could prevent obstructed apnoeas with moderate but not with severe reductions in stiffness. Increases in controller gain, as might occur with hypoxia, converted obstructive to central apnoeas. Breathing CO2 eliminated apnoeas when the activity of the upper airway muscles was considered to change as a function of CO2 to some exponent. Low arousal thresholds and increased upper airway resistance are two factors that promoted the occurrence and persistence of obstructive sleep apnoeas.