IVC Pressure Research Articles

In Silico Evaluation of a Self-powered Venous Ejector Pump for Fontan Patients.

The Fontan circulation carries a dismal prognosis in the long term due to its peculiar physiology and lack of a subpulmonic ventricle. Although it is multifactorial, elevated IVC pressure is accepted to be the primary cause of Fontan's high mortality and morbidity. This study presents a self-powered venous ejector pump (VEP) that can be used to lower the high IVC venous pressure in single-ventricle patients. A self-powered venous assist device that exploits the high-energy aortic flow to lower IVC pressure is designed. The proposed design is clinically feasible, simple in structure, and is powered intracorporeally. The device's performance in reducing IVC pressure is assessed by conducting comprehensive computational fluid dynamics simulations in idealized total cavopulmonary connections with different offsets. The device was finally applied to complex 3D reconstructed patient-specific TCPC models to validate its performance. The assist device provided a significant IVC pressure drop of more than 3.2mm Hg in both idealized and patient-specific geometries, while maintaining a high systemic oxygen saturation of more than 90%. The simulations revealed no significant caval pressure rise (< 0.1mm Hg) and sufficient systemic oxygen saturation (> 84%) in the event of device failure, demonstrating its fail-safe feature. A self-powered venous assist with promising in silico performance in improving Fontan hemodynamics is proposed. Due to its passive nature, the device has the potential to provide palliation for the growing population of patients with failing Fontan.

S2943 Budd-Chiari Syndrome Diagnosis Achieved With High Clinical Suspicion Raised by EUS-Guided Portal Pressures and Liver Biopsy

Introduction: Budd Chiari syndrome (BCS) is a rare syndrome due to hepatic venous obstruction in the absence of cardiac cause, mostly secondary to thrombosis. As high as 80%of patients present with ascites. The diagnosis should be suspected in patient with acute or chronic liver disease without identified cause. Venous obstruction can be seen on Doppler ultrasound, CT, or MRI of the hepatic veins and inferior vena cava. In some cases, hepatic venogram is needed for its diagnostic and therapeutic advantages. We report a 50-year-old woman with BCS who underwent successful wire recanalization, angioplasty and thrombolysis of the right hepatic vein. Case Description/Methods: 50-year-old woman with no significant past medical history presented with abdominal distension and bilateral lower extremity swelling of two weeks duration. On exam, abdomen was distended with positive signs of fluid collection with +3 bilateral lower extremity edema. Labs revealed total bilirubin 3.3 direct bilirubin 1.4, ALP 477, ALT 38, AST 96, PT 14.4, INR 1.35. Ultrasound showed Heterogeneous appearance of liver and large volume ascites. Doppler study showed normal hepatic and portal venous flow. Abdominal MRI showed hepatic steatosis and caudate lobe hypertrophy. Large volume paracentesis was done with analysis showing SAAG of 3.1, WBC 364, Neutrophils 8. EGD revealed large esophageal varices. Viral hepatitis panel, ceruloplasmin, alpha-1antitripsin, ASMA, AMA antibodies were negative. EUS guided liver biopsy and portal pressure measurement was done showing venous pressure gradient of 13 consistent with portal hypertension. Liver biopsy showed grade 2 fibrosis and zone 3 congestion. Hepatic venogram showed chronically occluded right hepatic vein on which successful wire recanalization was done. Pt was worked up for hypercoagulable state and was found to have JAK 2 mutation and Protein C deficiency. Apixaban, Beta blocker and diuretics were started. Patient showed significant improvement with ascites and MELD score. Discussion: First line investigation for diagnosis of BCS is doppler ultrasound. Doppler US and MRI venography didn’t reveal the hepatic venous thrombosis in our patient. However, high index of suspicion, finding of elevated IVC pressure on EUS, and caudate lobe hypertrophy found on imaging as well as congestion liver biopsy findings led us to further investigate with hepatic venogram which confirmed the diagnosis and provided therapeutic advantages. Table 1. - Prothrombotic risk factors for BCS ACG Clinical Guideline A. Acquired thrombophilia B. Inherited thrombophilia C. Systemic factors D. Hormonal factors Myeloproliferative disorderPolycythemia veraEssential thrombocytosisIdiopathic myelofibrosisJAK 2 mutationPNH Hyperhomocysteinemia Factor V LeidenProthrombin gene G20210A mutationMTHFR C677T mutationThalassemiaPC deficiencyProtein C deficiencyAntithrombin deficiency SarcoidosisVasculitisBehcet’s diseaseConnective tissue diseaseInflammatory bowel diseases OCP usePregnancy Disorders of the Hepatic and Mesenteric Circulation Simonetto, Douglas A.; Singal, Ashwani K.; Garcia-Tsao, Guadalupe; Caldwell, Stephen H.; Ahn, Joseph; Kamath, Patrick S. Official journal of the American College of Gastroenterology | ACG115(1):18-40, January 2020. doi: 10.14309/ajg.0000000000000486

Characterization of the mesenteric circulatory physiology during hemorrhagic shock in a swine model

This study aimed to characterize blood flow through the mesenteric circulation during hemorrhage and resuscitation in a large animal model. Five male swine (50-70 kg) underwent anesthesia and placement of flow probes and pressure catheters around and within the superior mesenteric artery, portal vein, and inferior vena cava. A laser doppler flow probe was placed on the intestine to measure end-organ perfusion. Animals were then exsanguinated to a systolic blood pressure of <50mmHg with 60-minutes of shock followed by resuscitation for 120-minutes. Animals were placed into hemorrhagic shock (lactate peak 5.9 ± 2.1 mmol/L vs baseline: 3.4 ± 0.7 mmol/L) with lower pressures and flows during shock and restoration to baseline following resuscitation: SMA (70 vs 36 vs 75 mmHg, p<0.001; 856 vs 371 vs 762 mL/min, p<0.001), portal vein (9 vs 8 vs 10mmHg, p<0.001; 200 vs 52 vs 141 mL/min, p<0.001), IVC (12 vs 7 vs 10 mmHg, p<0.001; 209 vs 27 vs 163 mL/min, p<0.001), and mean arterial pressure (MAP) (67 vs 36 vs 69 mmHg, p<0.001). LDF fell during hemorrhage (1.38 vs 0.38 blood perfusion units (BPU), p<0.001) and did not return to baseline during resuscitation (0.70 BPU, p<0.001). The intestine achieved only 51% of baseline LDF perfusion after resuscitation despite return of mesenteric hemodynamics. Despite macrovascular physiologic restoration after hemorrhagic shock, end organ perfusion did not adequately recover following resuscitation to baseline MAP. Continuous physiologic insult to the mesentery is likely ongoing after systemic hemodynamic restoration.

Comparison of Intra Abdominal Pressure Monitoring Techniques and the Effects of the Abdominal Compartment Syndrome

Background: Abdominal compartment syndrome (ACS) is a life-threatening condition that develops in the setting of increasing and uncontrolled intra-abdominal hypertension (IAH), leading to cardiovascular, respiratory, neurologic and/or renal dysfunction. Aims: To establish a porcine model for the evaluation of the effects of IAH on renal blood flow (RBF) and to determine if IVC pressure and/or Camino fiberoptic direct intraabdominal pressure measurements can accurately predict IAPs that have been derived using bladder pressure measurements. Methods: Abdominal laparotomy, placement of IAP and RBF measuring devices, and fascial closure were performed on six adult feeder pigs with a mean body weight of 25 +/- 5 kg. A Transonic Doppler flow probe, a suprapubic bladder catheter, a Camino fiberoptic probe, and a triple lumen central venous catheter were placed and then baseline measurements were taken of renal blood flow, bladder pressure, direct intra-peritoneal Camino pressure and IVC pressure, respectively. Normal saline was then infused into the abdomen to simulate increasing IAP. Following a 5–10-minute stabilization period, all measurements were again taken. Results: The correlation between IVC pressure and bladder pressure was 0.98, with a mean bias of -0.5 (SD 2.0; 95% CI: -0.9, -0.2). The correlation between direct IAP readings by Camino probe and bladder pressure was 0.91, with a mean bias of -3.9 (SD 4.3; 95% CI: -4.6, -3.2). There was a strong negative correlation (-0.95) between RBF and bladder pressure. At an IAP of 20 mmHg, RBF reduced by an average of 45.4% (95% CI: 40%, 50.8%). Upon abdominal decompression, RBF returned to 66.6% (95% CI: 54.3%, 78.9%) of its baseline value. Conclusions: A porcine model is effective in accurately measuring changes in real time RBF. RBF progressively declines as IAP increases, however upon decompression, it fails to achieve complete recovery. IVC pressure measurements correlate well with, and therefore may substitute, the gold standard bladder pressure measurements as representatives of IAP. Keywords: Abdominal Compartment syndrome, renal blood flow, intrabdominal hypertension, bladder pressure

Collapsibility of caval vessels and right ventricular afterload: decoupling of stroke volume variation from preload during mechanical ventilation.

Collapsibility of caval vessels and stroke volume and pulse pressure variations (SVV, PPV) are used as indicators of volume responsiveness. Their behavior under increasing airway pressures and changing right ventricular afterload is incompletely understood. If the phenomena of SVV and PPV augmentation are manifestations of decreasing preload, they should be accompanied by decreasing transmural right atrial pressures. Eight healthy pigs equipped with ultrasonic flow probes on the pulmonary artery were exposed to positive end-expiratory pressure of 5 and 10 cmH2O and three volume states (Euvolemia, defined as SVV < 10%, Bleeding, and Retransfusion). SVV and PPV were calculated for the right and PPV for the left side of the circulation at increasing inspiratory airway pressures (15, 20, and 25 cmH2O). Right ventricular afterload was assessed by surrogate flow profile parameters. Transmural pressures in the right atrium and the inferior and superior caval vessels (IVC and SVC) were determined. Increasing airway pressure led to increases in ultrasonic surrogate parameters of right ventricular afterload, increasing transmural pressures in the right atrium and SVC, and a drop in transmural IVC pressure. SVV and PPV increased with increasing airway pressure, despite the increase in right atrial transmural pressure. Right ventricular stroke volume variation correlated with indicators of right ventricular afterload. This behavior was observed in both PEEP levels and all volume states. Stroke volume variation may reflect changes in right ventricular afterload rather than changes in preload.NEW & NOTEWORTHY Stroke volume variation and pulse pressure variation are used as indicators of preload or volume responsiveness of the heart. Our study shows that these variations are influenced by changes in right ventricular afterload and may therefore reflect right ventricular failure rather than pure volume responsiveness. A zone of collapse detaches the superior vena cava and its diameter variation from the right atrium.

Abstract 16662: Central Lymphatic Dysfunction is a Contributing Cause of Tissue Congestion in Heart Failure

Introduction: Symptomatic Heart failure (HF) is a leading cause of morbidity and mortality in the world. HF with right sided symptoms may result in fluid overload including edema and ascites. The pathophysiology of fluid overload is poorly understood with no clear association between symptoms and hemodynamic parameters. Hypothesis: In animals with RHF and elevated CVP, the presence of ascites correlates with changes in lymphatic function and is independent of myocardial function and hemodynamic parameters. Methods: RHF was induced in fifteen swine animals by creating severe tricuspid regurgitation. Hemodynamics and anatomic changes were characterized using fluoroscopy, echocardiogram, and MRI. Measurements of the thoracic duct (TD) were made in the abdomen and thorax and the cross-sectional area was calculated. TD regurgitant flow was identified with ethiodized oil injection into the TD and was noted to be present or absent. Data is reported as median (IQR). Results: All 15 animals developed RHF with a dilated right atrium (RA) and right ventricle (RV). Nine animals developed ascites. Comparing animals with and without ascites, there were no differences in IVC pressure(mmHg) 11.5 (7.7-13.4) vs. 11.9 (10.2-17.4) (p= 0.364), SVC pressure 12.8 (11.3-16.8) vs. 12 (8.3-14.9) (p=0.343). Other hemodynamics parameters including pulmonary artery (PA), RV, and RA pressure were also not significantly different. In addition, left ventricular (LV) ejection fraction was normal in both groups (68.7% (57.9-74.8) vs. 55% (53.1-69.4) (p=0.135)). However, animals in the ascites group had larger relative liver volume (mL/Kg) 59.1 (65.1-51.9) vs. 34.85 (42.3-24.1) (p = 0.003), larger dimension of the minimal TD size (mm) 3.2 (5.8-2.7) vs. 2.2 (2.6-2.0) (p=0.04), and more animals had TD regurgitant flow 89% vs. 16% (p=0.01). Conclusion: In animal model with RV failure, there is no association between hemodynamic parameters and occurrence of ascites, consistent with observations in humans. In contrast, parameters of lymphatic congestion differ significantly between the two groups supporting the notion that lymphatic dysfunction is a contributing cause of tissue congestion in patients with HF and elevated CVP.

S2543 Polycystic Liver Disease, Portal Hypertension, and Refractory Ascites: Is PLD the Cause?

INTRODUCTION: Polycystic liver disease (PLD) is a rare genetic disorder typically characterized by the presence of more than twenty hepatic cysts. The prevalence of autosomal dominant polycystic kidney disease (ADPKD) associated PLD is 0.2%. We present an unusual case of PLD associated with refractory ascites in the absence of liver fibrosis or hepatic venous outflow obstruction. CASE DESCRIPTION/METHODS: This is a 54-year-old female with a history of ADPKD status post kidney transplant without evidence of cirrhosis or any decompensating events pre-transplant. Her post-transplant course was complicated by cecal and mesenteric volvulus status post right hemicolectomy. Roughly five weeks later, she developed severe ascites. Initial lab evaluation revealed no hepatocellular dysfunction. Diagnostic paracentesis indicated a SAAG of 1.4, ascitic total protein 2.1 and no evidence of SBP. Portal package showed abnormally tortuous venous vasculature. Right hepatic vein was difficult to wedge but measured 70-80 mm Hg; free right hepatic vein pressure was 5 mm Hg, IVC pressure was 4 mm Hg and a right atrial pressure was 5 mm Hg; overall, findings were consistent with portal hypertension. Liver biopsy showed no significant fibrosis or evidence of congenital hepatic fibrosis, but did show mild sinusoidal dilatation, potentially indicative of a vascular outflow abnormality. An abdominal CT was without evidence of extrinsic compression of the large hepatic veins. Due to anatomic difficulties, TIPS was not technically feasible, so she had a Denver shunt placed for refractory ascites with good control thereafter. DISCUSSION: Portal hypertension and ascites in the presence of PLD typically arises from three etiologies: liver cirrhosis, congenital hepatic fibrosis and hepatic venous outflow obstruction. This patient had no imaging to support large hepatic venous outflow obstruction, but given her histologic findings it is possible that her presentation is due to cystic compression of small venules, which cannot be visualized on cross sectional imaging. However, there is not any literature to support hepatic venule compression leading to portal hypertension. Due to chronic injury from elevated outflow pressures, these patients can develop fibrotic replacement of the hepatic parenchyma and may ultimately develop cirrhosis. Recognition and surveillance of these patients is necessary, as liver transplant may need to be considered if progressive cirrhosis complications become apparent.

Associated Factors of Liver Disease After Fontan Operation in Relation to Ultrasound Liver Elastography.

Although the Fontan operation can improve outcomes, surviving patients still face Fontan-associated liver disease (FALD). The aim of this study was to determine the associated factors of FALD in relation to ultrasound liver elastography. A cross-sectional study was conducted for all patients on whom an ultrasound upper-abdomen and ultrasound liver elastography was performed at more than 1year after the Fontan operation. The data consisted of the age at operation, type of Fontan operation, and laboratory data such as gamma-glutamyl transferase (GGT), aspartate aminotransferase-to-platelet ratio index (APRI), and fibrosis-4 (FIB-4) score. Cardiovascular evaluations included echocardiography and cardiac catheterization. Eighty patients with a median age of 12years (range 5-36years) were eligible for the study. The prevalence of FALD was 41%. For the purpose of univariate logistic regression analysis, the age at the Fontan operation, time elapsed since the Fontan operation, previous Glenn shunt, presence of fenestration, mean pulmonary artery pressure and IVC pressure post-Fontan operation, platelet count, GGT, and FIB-4 score were considered to be factors significantly associated with FALD. Following an adjustment by multivariate logistic regression analysis, age greater than 7 years at the time of Fontan procedure, time elapsed of more than 9 years since the procedure, and GGT level > 130 U/L were found to be significantly associated with FALD. Patients with these factors should be investigated for FALD.

ASSESSMENT OF INFERIOR VENA CAVA DIAMETER MEASURED BY ULTRA-SONOGRAPHY IN CORRELATION WITH CENTRAL VENOUS PRESSURE VALUE IN PATIENTS WITH SEPSIS

Background: Bedside ultrasound is potentially a useful noninvasive adjunct to estimate the intravascular volume status in sepsis. Aim of the work: Evaluating the correlation between inferior vena cava diameter measured non-invasively with ultrasonography versus central venous pressure in assessment of intravascular volume status in patients with sepsis.Patients and methods: The study was conducted on sixty patients with sepsis (30 ventilated and 30 non-ventilated) in the Respiratory Intensive Care Unit at Abbassia Chest Hospital from January 2018 to September 2018. For all included patients demographic data were collected Recording vital sings, mean arterial pressure and Pao2/ Fio2were done. Laboratory investigation including complete blood count, serum lactic acid, arterial blood gas, quantitative C-reactiveprotein were also done. Sequential Organ Failure Assessment score (SOFA), Qsofa and Acute Physiology And Chronic Health Evaluation II score (APACHE II) were recorded. Finally measurement of IVC, CVP and intra-abdominal pressure were done Results: Males represent 75%while female were 25%withmean age of (47.40±14.49) years. The mean CVP was 12.48±3.78 cmH2O with an IVC maximum diameter of 17.95±3.28 mm and collapsibility index of 50.55±11.83 %. There was statistically significant positive correlation between CVP and IVC dmax and statistically significant negativecorrelation between CVP and IVC CI (%)in both ventilated and non ventilated groups. Also, CVP and IVC dmax were significantly correlated with outcome in both ventilated and non ventilated patients. The higher values of CVP and IVC dmax and the lower the value of IVC CI, the higher rates of mortality. Conclusion: US assessment of IVC diameter and caval index are simple and non invasive methods to assess intravascular volume status.

Physiological Fontan Procedure.

Objective: The conventional Fontan circulation deviates the superior vena cava (SVC = 1/3 of the systemic venous return) toward the right lung (3/5 of total lung volume) and the inferior vena cava (IVC = 2/3 of the systemic venous return) toward the left lung (2/5 of total lung volume). A “physiological” Fontan deviating the SVC toward the left lung and the IVC toward the right lung was compared with the conventional setting by computational fluid dynamics, studying whether this setting achieves a more favorable hemodynamics than the conventional Fontan circulation.Materials and Methods: An in-silico 3D parametric model of the Fontan procedure was developed using idealized vascular geometries with invariant sizes of SVC, IVC, right pulmonary artery (RPA), and left pulmonary artery (LPA), steady inflow velocities at IVC and SVC, and constant equal outflow pressures at RPA and LPA. These parameters were set to perform finite-volume incompressible steady flow simulations, assuming a single-phase, Newtonian, isothermal, laminar blood flow. Numerically converged finite-volume mass and momentum flow balances determined the inlet pressures and the outflow rates. Numerical closed-path integration of energy fluxes across domain boundaries determined the flow energy loss rate through the Fontan circulation. The comparison evaluated: (1) mean IVC pressure; (2) energy loss rate; (3) kinetic energy maximum value throughout the domain volume.Results: The comparison of the physiological vs. conventional Fontan provided these results: (1) mean IVC pressure 13.9 vs. 14.1 mmHg (= 0.2 mmHg reduction); (2) energy loss rate 5.55 vs. 6.61 mW (= 16% reduction); (3) maximum kinetic energy 283 vs. 396 J/m3 (= 29% reduction).Conclusions: A more physiological flow distribution is accompanied by a reduction of mean IVC pressure and by substantial reductions of energy loss rate and of peak kinetic energy. The potential clinical impact of these hemodynamic changes in reducing the incidence and severity of the adverse long-term effects of the Fontan circulation, in particular liver failure and protein-losing enteropathy, still remains to be assessed and will be the subject of future work.

In Vitro Examination of the VentriFlo True Pulse Pump for Failing Fontan Support.

The current methodology of Fontan palliation results in a one "pump" circulatory system with passive flow to the lungs. Inherent hemodynamic differences exist between a biventricular circulatory system and this modified physiology, leading to a host of long-term complications. Mechanical circulatory support (MCS) is a potential option to combat these pathophysiological conditions. In this study, we examine the VentriFlo True Pulse Pump as a MCS option to support a failing Fontan patient. An in vitro circulatory loop was used to model a failing Fontan patient, reproducing pathophysiological pressures and flow rates. The VentriFlo True Pulse Pump was positioned as a right sided support, testing multiple cannulation and baffle restriction strategies, as well as various pumping parameters including flow rate, frequency, stroke volume and the ejection to filling time ratio. A 10 mmHg decrease in IVC pressure and 0.75L/min increase in cardiac output were achieved using a complete baffle restriction strategy. Additional cannulation and banding strategies were not as successful. Pump flow rate and frequency significantly impacted hemodynamics, while the ejection to filling time ratio did not. Though not ideal, complete baffle restriction was necessary to achieve successful support. The ability to tune individual pumping parameters for a given MCS device will have a substantial impact on the pressures and flow augmentation seen in a Fontan circulation. Both future pump design and off-label VADs for Fontan use should consider the pump configuration and parameter combinations presented here, which offered successful support.

Effect of Fontan operation on liver stiffness in children with single ventricle physiology.

Assess liver stiffness using ultrasound point shear wave elastography (US P-SWE) in children before and after the Fontan operation. Eighteen children undergoing the Fontan operation were prospectively enrolled. Eight US P-SWE measurements were obtained from the right hepatic lobe before surgery, and at multiple postoperative time points. Temporally related inferior vena cava pressure (IVC) data was collected from medical records, when available. Changes in mean liver shear wave speed (SWS) were assessed using a mixed-effect model with post hoc Tukey correction. Changes in IVC pressure were evaluated using the Wilcoxon signed-rank test. A p value less than 0.05 was considered significant. Mean age at enrolment was 33.5 ± 10.5months. Baseline mean liver SWS was normal at 1.18 ± 0.29m/s, increased to 2.28 ± 0.31m/s at 2.5 ± 1.2days (p < 0.0001) and to 2.22 ± 0.38m/s at 7.5 ± 1.4days (p < 0.0001). Five subjects returned at a mean of 185 ± 28days, and mean liver SWS remained elevated at 2.08 ± 0.24m/s (p < 0.0001). Mean IVC pressure increased from 7.2 ± 2.6mmHg at baseline to 16.44 ± 3.3mmHg at 2.2 ± 0.8days post-surgery (p = 0.004). The Fontan operation immediately and chronically increases liver stiffness and IVC pressure. Our study provides further evidence that congestion is a key driver of Fontan-associated liver disease. • The Fontan operation triggers immediate hepatic congestion and marked liver stiffening. • Congestion, not fibrosis, drives early increased liver stiffness in Fontan patients. • Hepatic congestion persists chronically for months after the Fontan operation. • Congestion confounds shear wave elastography as a post-Fontan liver fibrosis biomarker.

A computational study of DME-methanol fractions with controlling several factors on HCCI combustion

Two-stage fuel and single stage fuel have different effects on ignition delay and other combustion characteristics. If we mix two fuels with variable fractions, combustion characteristics will be represented with dependence on the fraction. We first investigated the change of combustion characteristics and combustion ranges by dimethyl ether (DME)/methanol fraction, IVC temperature and IVC pressure. By increasing methanol fraction, Heat release rate (HRR) showed higher rate than the case containing less methanol after 1250 K. However, it didn’t mean that Accumulated heat release (AHR) was also higher than the cases which contained less methanol. AHR of D90/M10 was the first case which surpassed AHR of D100 at about 1808K, and D80/M20 surpassed D100 at about 2318K. The result was caused by change of reaction mechanism and the change was remarkably shown in the Thermal ignition preparation (TIP) range and the Thermal ignition (TI) range. Above all, strengthened H2O2 Loop reactions affected heat production to increase in TIP range, and also one of the loop reactions, CH2O + OH = HCO + H2O, quickly produced formyl radical with increase of net reaction rate by methanol. Those results naturally led to higher reaction rates of HCO-CO-CO2 oxidation with higher heat production. As a result, D50/M50 case showed the highest maximum Pressure rise rate (PRR). Furthermore, dispersion rate of PRR was increased by increasing methanol fraction in the range which was from back end of TIP to forepart of TI range. Finally, we focused the reaction paths of two fuels and the production and consumption rate of main radicals on the basis of combustion ranges such as LTO, Negative temperature coefficient (NTC), Thermal ignition preparation (TIP) and Thermal ignition (TI) to understand the results of this study.

Respiratory-Induced Haemodynamic Changes: A Contributing Factor to IVC Filter Penetration.

The purpose of the study is to evaluate the influence of respiratory-induced vena caval hemodynamic changes on filter migration/penetration. After placement of either a Gunther Tulip or Celect IVC filter, 101 consecutive patients scheduled for filter retrieval were prospectively enrolled in this study. Pre-retrieval CT scans were used to assess filter complications and to calculate cross-sectional area in three locations: at level of filter strut fixation, 3 cm above and 3 cm below. A 3D finite element simulation was constructed on these data and direct IVC pressure was recorded during filter retrieval. Cross-sectional areas and pressures of the vena cava were measured during neutral breathing and in Valsalva maneuver and identified filter complications were recorded. A statistical analysis of these variables was then performed. During Valsalva maneuvers, a 60 % decrease of the IVC cross-sectional area and a fivefold increase in the IVC pressure were identified (p < 0.001). There was a statistically significant difference in the reduction of the cross-sectional area at the filter strut level (p < 0.001) in patient with filter penetration. Difficulty in filter retrieval was higher in penetrated or tilted filters (p < 0.001; p = 0.005). 3D computational models showed significant IVC deformation around the filter during Valsalva maneuver. Caval morphology and hemodynamics are clearly affected by Valsalva maneuvers. A physiological reduction of IVC cross-sectional area is associated with higher risk of filter penetration, despite short dwell times. Physiologic data should be used to improve future filter designs to remain safely implanted over longer dwell times.

Steady Flow Analysis of Mechanical Cavopulmonary Assistance in MRI‐Derived Patient‐Specific Fontan Configurations

This numerical study examined the performance of an intravascular axial flow blood pump for mechanical hemodynamic support of patients in the setting of Fontan failure, which presently has few treatment options. Three anatomically accurate geometries of the total cavopulmonary connection (TCPC) were generated using patients' magnetic resonance imaging data. These patient-specific geometries, as well as an idealized version with cylindrical vessels, were computationally analyzed with and without a pump in the inferior vena cava. Pressure flow characteristics, energy gain calculations, and blood damage analyses were performed for each model. The pump produced pressures of 1-14 mm Hg for 1500-4000 revolutions per minute, flow rates of 1-4 L/min, and pulmonary artery pressures of 8-24 mm Hg. Comparison of pump performance among the four models showed minimal intermodel differences (<5% deviation) in the pressure rise generated by the pump, the IVC pressure, and the energy imparted to the system by the pump. Blood damage analysis showed maximum fluid scalar stress values of 372 Pa or less, and the blood damage index was less than 2% in all of the models. These results suggest that this axial flow blood pump performs consistently in a variety of TCPC vessel geometries with low risk of blood trauma.

Abstract No. 342: The clot filled vena cava filter: Acute IVC pressure gradients in blunt abdominal trauma

Abstract No. 342: The clot filled vena cava filter: Acute IVC pressure gradients in blunt abdominal trauma

Diagnosis and Surgical Treatment of Nutcracker Syndrome: A Single-Center Experience

Conclusion: Left renal vein transposition is an efficient surgical treatment for nutcracker syndrome. In some cases however pelvic pain remains following left renal vein transposition. Summary: The nutcracker syndrome is an unusual problem where the left renal vein is narrowed as it passes between an angle formed between the abdominal aorta and the superior mesenteric artery. This narrowing of the left renal vein can lead to increase venous pressure within the renal circulation and promote development of varices of the renal pelvis and ureter with resulting hematuria. Other symptoms associated with nutcracker syndrome include orthostatic proteinuria, flank pain, left-sided varicocele, pelvic congestion, and chronic fatigue. The authors retrospectively reviewed 23 patients with the diagnosis of nutcracker syndrome treated at their institution from July 1998 to July 2007. Nutcracker syndrome was suspected based on the combination of clinical examination, ultrasound, CT imaging, and MRI imaging. Hematuria was the most common presenting symptom (21 of 23 patients). One patient presented with orthostatic proteinuria and 1 with pelvic congestion syndrome. No patient had renal function deterioration and 13 of 23 undergoing cystoscopy had bleeding noted from the left ureteral orifice. Only 7 underwent transposition of the left renal vein with the indication of transposition being recurrent gross hematuria in 6 patients and persistent orthostatic proteinuria in 1 patient. Sixteen patients who had more mild symptoms were followed without operation. Patients with microscopic hematuria or intermittent short periods of painless gross hematuria were followed closely without treatment. Patients with flank or abdominal pain were treated with low-dose aspirin treatment. Four women with pelvic congestion syndrome were treated with medroxyprogesterone acetate. Patients undergoing left renal vein transposition did so through a mid-line abdominal incision with mobilization of the left colon and small bowel to give access to the retroperitoneum. The inferior adrenal vein, ovarian/testicular vein, and the lumbar vein draining into the left renal vein were ligated and transected. The left renal vein was excised with the small rim of vena cava and injected with heparin. Reanastomosis was then performed to a more caudad portion of the inferior vena cava. All 7 patients treated with renal vein transposition had normal pre-operative creatinine levels with no increase following renal vein transposition. Hematuria and proteinuria ceased spontaneously 5 to 14 days following surgery with no clinical relapses. Of the 16 patients treated conservatively, clinical improvement occurred in 11 with total relief of symptoms in 2 patients and partial relief in 9 patients. There was no relief of symptoms in 5 patients following a mean follow-up of 41.2 months. Comment: The pressure gradient between the left renal vein near the renal hilum is normally between 0 and 1 mmHg (J Urology 1982; 127: 1070-1071). An elevated gradient of more than 3 mmHg between the left renal vein and the vena cava is used as a criteria to diagnose nutcracker syndrome. All patients in this series had such a gradient. The study indicates that left renal vein transposition works well to alleviate symptoms in patients with nutcracker syndrome and elevated renal vein IVC pressure gradients. Equally important is that patients with mild symptoms do well treated conservatively. It would appear reasonable to reserve surgical treatment of nutcracker syndrome to those patients with recurrent gross hematuria or persistent orthostatic proteinuria who are not responsive to conservative management. The authors also point out that children and adolescents can have nutcracker syndrome that will frequently resolve as the child matures into adulthood. Surgical treatment of nutcracker syndrome in children and adolescents therefore, in most cases, should be avoided.

A Computational Investigation of Two-Stage Combustion in a Light-Duty Engine

The objective of this investigation is to optimize light-duty diesel engine operating parameters using Adaptive Injection Strategies (AIS) for optimal fuel preparation. A multi-dimensional Computational Fluid Dynamics (CFD) code with detailed chemistry, the KIVA-CHEMKIN code, is employed and a Multi-Objective Genetic Algorithm (MOGA) is used to study a Two-Stage Combustion (TSC) concept. The combustion process is considered at a light load operating condition (nominal IMEP of 5.5 bar and high speed (2000 rev/min)), and two combustion modes are combined in this concept. The first stage is ideally Homogeneous Charge Compression Ignition (HCCI) combustion and the second stage is diffusion combustion under high temperature and low oxygen concentration conditions. Available experimental data on a 1.9L single-cylinder research engine is used for model validation. The results show that the computations are able to adequately predict the emissions trends and quantities over an injection timing sweep for the Partially Premixed Compression Ignition (PCCI) cases investigated. A preliminary investigation was performed to gain an understanding of two-stage combustion in the light duty engine. At this condition it was found that pure HCCI combustion could yield very low engine out emissions, but extreme pressure rise rates would lead to excessive combustion noise. A multi-dimensional optimization code, NSGAII, was used for optimization of six objectives (NOx, soot, CO, HC, ISFC, and peak PRR) by adjusting four parameters (boost pressure, EGR rate, fraction of premixed fuel, and start of late injection timing). The optimization has shown that two-stage combustion is a feasible concept for noise reduction while maintaining reasonable emissions and fuel consumption. A Pareto solution yielding a peak pressure rise rate of 4.3 bar/deg was found using a high EGR rate (54%), relatively low IVC pressure (1.74 bar), premixing 36% of the total fuel, and injecting the remainder of the fuel at 2.9 degrees after TDC. Introduction Since its introduction in the late 1800’s, the diesel engine has been utilized in almost every aspect of modern life, from transportation to energy generation to food production. Several emissions are of prime concern for air pollution: nitrogen oxides (NOx), carbon monoxide (CO), unburned hydrocarbons (HC), and particulates (soot). These pollutants are damaging to the environment and human health. Reduction of these harmful pollutants while maintaining fuel economy has been a primary driving factor for internal combustion engine research in recent years. Homogeneous Charge Compression Ignition (HCCI) and Premixed Charge Compression Ignition (PCCI) concepts have been shown as promising techniques for simultaneous NOx and soot reduction [1-3]. However, a major concern for light duty engines is noise generated during the combustion process. HCCI combustion tends to produce high rates of pressure rise and therefore can result in higher combustion noise than conventional diesel operation. Sun [4, 5] has shown the possibility of emissions reduction using a Two-Stage combustion concept in a heavy-duty diesel engine. The first stage is HCCI combustion and the second stage is diffusion combustion under high temperature and low oxygen concentration conditions. Because only a fraction of the total fuel is burnt in pure HCCI combustion it may be possible to use the TSC concept for noise reduction. This study aims to apply the TSC concept to a light-duty diesel engine in order to minimize pollutant emissions and to improve fuel economy while maintaining low engine noise. A multi-dimensional CFD code with detailed chemistry, the KIVA-CHEMKIN code, was employed in this investigation. Model validation was performed using experimental data of Opat et al. [3]. After model validation, a preliminary investigation was performed to gain a basic understanding of the two-stage combustion concept in a light-duty diesel engine. With a basic understanding of two-stage combustion, a multi-objective genetic algorithm (MOGA) was used to optimize engine parameters to minimize pollutants, engine noise, and fuel consumption.

Preservation of renal perfusion and postoperative renal function by side-to-side cavo-caval anastomosis in liver transplant recipients.

Postoperative renal failure is common after liver transplantation (LT). The aim of this study was to investigate peroperative renal perfusion and postoperative renal function in 12 patients who underwent LT with side-to-side cavo-caval anastomosis (SSCCA). Three phases were considered during the procedure: hepatectomy, the anhepatic phase, and the postreperfusion phase (phases 1, 2, and 3, respectively). Mean arterial pressure, IVC pressure, and renal perfusion pressure were significantly higher during phase 2 than during phases 1 and 3. Cardiac index and pulmonary capillary wedge pressure did not differ significantly during the three phases. Creatinine clearance did not significantly decrease postoperatively. We conclude that SSCCA is associated with both the preservation of renal perfusion pressure during the entire procedure and the preservation of postoperative creatinine clearance. It is, moreover, a technique that results in a low rate of postoperative renal failure after LT.

Regulation of splanchnic organ size during muscarinic receptor stimulation in the anaesthetized pig

To determine the mechanisms responsible for changes in splanchnic organ size during muscarinic receptor stimulation, acetylcholine was infused at 5 micrograms kg-1 min-1 in 11 anaesthetized pigs which had previously undergone carotid denervation and cervical vagotomy. Blood pressure decreased by 42 +/- 4 mmHg (P less than 0.005), portal vein pressure decreased by 1.0 +/- 0.3 mmHg (P less than 0.01), IVC pressure increased by 0.2 +/- 0.1 mmHg (P less than 0.01), hepatic arterial flow increased by 10 +/- 6 ml min-1 (NS), portal vein flow decreased by 89 +/- 20 ml min-1 (P less than 0.005), splenic segment length (SSL) decreased by 0.52 +/- 0.11 mm (P less than 0.005) (control 12.49 +/- 1.27) (measured with ultrasonic crystals) and hepatic segment length (HSL) increased by 0.29 +/- 0.06 mm (P less than 0.005) (control 13.94 +/- 1.16). Aortic constriction to decrease the splanchnic distending pressure by an amount comparable to that achieved with the acetylcholine-associated decrease in portal flow caused a similar decrease in SSL and increase in HSL. Graded constriction of the portal vein or IVC, to increase SSL or HSL respectively, in the presence and absence of acetylcholine demonstrated no change in splenic or hepatic compliance with acetylcholine. Ligation of the splenic vasculature reduced the acetylcholine-associated HSL increase from 0.41 +/- 0.09 to 0.20 +/- 0.07 mm (P less than 0.05). Acetylcholine infused directly into the portal vein did not alter HSL. Atropine abolished all acetylcholine-associated haemodynamic changes. Thus, muscarinic receptor stimulation does not appear to act directly on splanchnic capacity vessels. Splenic dimension decreases due to a decrease in splanchnic flow and pressure, and hepatic dimension increases due to an increase in IVC pressure and redistribution of volume from the spleen.