Tube Loop Research Articles

Optimal heparin surface concentration and antithrombin binding capacity as evaluated with human non-anticoagulated blood in vitro.

Contact between blood and a biomaterial surface takes place in many applications and is known to activate the coagulation and complement systems. Heparin surface coatings have been shown to reduce blood activation upon contact with artificial surfaces. To establish the optimal heparin surface concentration, blood was incubated in a tubing loop model at 37 degrees C. The tubing was coated with different surface concentrations of heparin and rotated at three different velocities. We demonstrate that the blood compatibility of a surface with regard to coagulation, complement, and platelet activation can be improved by increasing the heparin surface concentration in the 6-12 pmol antithrombin/cm2 concentration interval. The binding of factor H is not influenced by the increased heparin surface concentration, suggesting that this factor is not the primary regulator of complement on heparin surfaces. In addition, the heparin coating has no effect on the complement activation that occurs on gas surfaces in extracorporeal circuits.

The role of neural crest and epicardium-derived cells in conduction system formation.

During cardiac development the heart tube loops and is septated into a four-chambered structure. The initial peristaltic contraction of the primitive myocardium is replaced by a system of working myocardium and a myocardial-derived central and peripheral conduction system. The genes guiding this differentiation process are still under investigation and it has yet to be decided whether we are dealing with a recruitment or a specification model. We have shown that the complicated looping process of the heart tube brings together the essential parts of the sinoatrial and primary ring myocardium, that are the embryonic precursors of the definitive conduction system. From our studies it is evident that during development there are sinoatrial tracts that run between the sinoatrial and the atrioventricular node as well as tracts surrounding the pulmonary veins and the coronary sinus. Furthermore, we show that both in the chicken and mouse embryo neural crest cells reach the confinement of the central conduction system through the inflow and outflow tract. For the Purkinje system there is a close approximation with the epicardium-derived cells. We postulate that both extracardiac-derived cell types have an influence on the differentiation of the definitive conduction system.

Regulation of heart morphology: current molecular and cellular perspectives on the coordinated emergence of cardiac form and function.

During early heart development, in addition to cells being induced to differentiate into cardiomyocytes, pathways are activated that lead to cardiac morphogenesis or the development of form. Orchestration of organogenesis involves the incremental activation of regulatory pathways that lead to pivotal transition points, such as cardiac compartment delineation and looping. Each embryonic stage sets up the correct patterning of morphoregulatory molecules that will regulate the next process, until an organ is formed from the mesoderm layer after gastrulation. The current review provides an understanding of the morphoregulatory, cell adhesion and extracellular matrix-mediated, processes that coordinate development of heart form with that of function. The period reviewed encompasses the formation of a definitive cardiac compartment from the lateral plate mesoderm to the time-point in which the single, beating heart tube loops directionally to the right. Looping results in the correct spatial orientation for subsequent modeling of the four-chambered heart. Even subtle alterations in looping can form the basis upon which malformations of the inlet or the outlet regions of the heart, or both, are superimposed. In the future, DNA microarray data sets may allow modeling the specific sequence of gene regulatory dynamics leading to these transition points to discover the regulatory "modes" that the cells adopt during heart organogenesis. The regulatory genes, however, can only specify the proteins that will be present. To fully understand the timing and mechanisms underlying heart development, it is necessary to define the sequential synthesis, patterning, and interaction of the proteins, and of still other receptors, which eventually drive cells to organize into functioning organs.

The homeobox gene Lbx1 specifies a subpopulation of cardiac neural crest necessary for normal heart development.

Cardiac neural crest cells are known to play multiple roles during development of the inflow and outflow tract of the heart and the aortic arch. In addition, cardiac neural crest is required for normal heart tube looping and regulation of myocardial cell proliferation, as well as differentiation and function of the myocardium. We show that the homeobox gene Lbx1 is expressed in a subpopulation of the cardiac neural crest during tubular heart formation. Inactivation of the Lbx1 gene in mice resulted in defects in heart looping, changes in gene expression pattern, and increased cell proliferation ensuing in myocardial hyperplasia. We found that the activity of the Lbx1 promoter, as indicated by a LacZ reporter gene, is upregulated in the hearts of Lbx1(+/-):splotch(1H)/splotch(1H) and Lbx1(-/-) mice, indicating that Pax3 and Lbx1 participate in a negative regulatory feedback that might be necessary for normal differentiation and function of the myocardium during early heart development. Because migration of Lbx1-expressing neural crest cells was not altered in Lbx1(-/-) embryos, we postulate that Lbx1 gene function is critical for specification of a subpopulation of cardiac neural crest subsequent to migration.

Thrombogenicity of Various Endovascular Stent Types: An In Vitro Evaluation

The aim of this study was to evaluate the thrombogenicity of different peripheral stent types in a standardized in vitro model with fresh human whole blood. Different stents (N = 77; n = 7 of each of 11 types) were implanted in polyvinyl chloride tubing loops and filled with donor blood samples. After 120 minutes of blood circulation, the thrombin-antithrombin III complex (TAT) levels, beta-thromboglobulin (beta-TG) levels, and platelet counts were assessed. After 2 hours, significant differences were seen. TAT values (+/- SD) with the investigated stents were 31 micro g/mL +/- 20 (control, no stent), 328 micro g/mL +/- 206 (Saxx stent, peripheral medium CrNi31 L), 651 micro g/mL +/- 760 (Palmaz Corinthian Stent, 316 L stainless steel, electropolished), 1,609 micro g/mL +/- 1,264 (Palmaz Corinthian Stent, 316 L stainless steel, not electropolished), 810 micro g/mL +/- 578 (Palmaz Schatz long medium stent), 569 micro g/mL +/- 347 (Smart Nitinol stent), 1,037 micro g/mL +/- 577 (Megalink peripheral stent), 543 micro g/mL +/- 487 (peripheral stent, electropolished), 1,674 micro g/mL +/- 2,057 (peripheral stent, not electropolished), 3,128 micro g/mL +/- 1,812 (SelfX Nitinol stent, polished), 5,897 micro g/mL +/- 2,380 (SelfX Nitinol stent, unpolished), and 1,458 micro g/mL +/- 887 (bridge stent). The platelet count (x1,000/ micro L +/- SD) was 218 +/- 35 (control, no stent), 188 +/- 22 (Saxx stent), 187 +/- 20 (Palmaz Corinthian stent, electropolished), 135 +/- 37 (Palmaz Corinthian stent, not electropolished), 170 +/- 24 (Palmaz Schatz stent), 180 +/- 36 (Smart Nitinol stent), 159 +/- 26 (Megalink peripheral stent), 173 +/- 17 (peripheral stent, electropolished), 133 +/- 51 (peripheral stent, not electropolished), 123 +/- 37 (SelfX Nitinol stent, polished), 52 +/- 27 (SelfX Nitinol stent, unpolished), and 130 +/- 31 (bridge stent). This standardized study showed a wide range of platelet activation after stent implantation. Electropolishing clearly reduced the thrombogenicity of the stents.

TEACHING NOTES

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The Endosquid, a New Device for Laparoscopic Pomeroy Tubal Ligation

The Pomeroy method is a most widely practiced and most familiar form of tubal ligation. It traditionally requires laparotomy or multiple-puncture laparoscopic suturing, which is not a realistic option for the average endoscopist. We designed a 5-mm device, the Endosquid, to reproduce Pomeroy tubal ligation laparoscopically using a single 5-mm accessory puncture site. It is able to ligate, transect, and remove a loop of isthmic tube. We tested the Endosquid in a porcine model by ligating 25 bicornuate uterine horns and aortas. Ligation times averaged less than 5 minutes for each application. Gross and histologic evaluation of ligation specimens performed at necropsy confirmed correct placement. Blood loss was negligible and there were no operative complications.

Two-Dimensional Simulations of Valveless Pumping Using the Immersed Boundary Method

Flow driven by pumping without valves is examined, motivated by biomedical applications: cardiopulmonary resuscitation (CPR) and the human fetus before the development of the heart valves. The direction of flow inside a loop of tubing which consists of (almost) rigid and flexible parts is investigated when the boundary of one end of the flexible segment is forced periodically in time. Despite the absence of valves, net flow around the loop may appear in these simulations. The magnitude and even the direction of this flow depend on the driving frequency of the periodic forcing.

Incompatibility between human blood and isolated islets of Langerhans: a finding with implications for clinical intraportal islet transplantation?

The remarkable difference in success rates between clinical pancreas transplantation and islet transplantation is poorly understood. Despite the same histocompatibility barrier and similar immunosuppressive treatments in both transplantation procedures, human intraportal islet transplantation has a much inferior success rate than does vascularized pancreas transplantation. Thus far, little attention has been directed to the possibility that islets transplanted into the blood stream may elicit an injurious incompatibility reaction. We have tested this hypothesis in vitro with human islets and in vivo with porcine islets. Human islets were exposed to nonanticoagulated human ABO-compatible blood in surface-heparinized polyvinyl chloride tubing loops. Heparin and/or the soluble complement receptor 1 (sCR1) TP10 were tested as additives. Adult porcine islets were transplanted intraportally into pigs, and the liver was recovered after 60 min for immunohistochemical staining. Human islets induced a rapid consumption and activation of platelets. Neutrophils and monocytes were also consumed, and the coagulation and complement systems were activated. Upon histological examination, islets were found to be embedded in clots and infiltrated with CD11+ leukocytes. Furthermore, the cellular morphology was disrupted. When heparin and sCR1 were added to the blood, these events were avoided. Porcine islets retrieved in liver biopsies after intraportal islet allotransplantation showed a morphology similar to that of human islets perifused in vitro. Thus, exposure of isolated islets of Langerhans to allogenic blood resulted in significant damage to the islets, a finding that could explain the unsatisfactory clinical results obtained with intraportal islet transplantation. Because administration of heparin in combination with a soluble complement receptor abrogated these events, such treatment would presumably improve the outcome of clinical islet transplantation by reducing both initial islet loss and subsequent specific immune responses.

Chamber-Specific Cardiac Expression of Tbx5 and Heart Defects in Holt–Oram Syndrome

To further define the role of a T-box transcription factor, Tbx5, in cardiac development, we have examined its expression in the developing mouse and chick heart and correlated this pattern with cardiac defects caused by human TBX5 mutations in Holt–Oram syndrome. Early in the developing heart, Tbx5 is uniformly expressed throughout the entire cardiac crescent. Upon formation of the linear heart tube, Tbx5 is expressed in a graded fashion, stronger near the posterior end and weaker at the anterior end. As the heart tube loops, asymmetric Tbx5 expression continues; Tbx5 is expressed in the presumptive left ventricle, but not the right ventricle or outflow tract. This pattern of expression is maintained in more mature hearts. Expression in the ventricular septum is restricted to the left side and is contiguous with left ventricular free wall expression. Trabeculae, vena cavae (inferior and superior), and the atrial aspect of the atrioventricular valves also express high levels of Tbx5. These patterns of Tbx5 expression provide an embryologic basis for the prevalence of atrial septal defects (ostium primum and secundum), ventricular muscular septal defects, and left-sided malformations (endocardial cushion defects, hypoplastic left heart, and aberrant trabeculation) observed in patients with Holt–Oram syndrome.

Tube loop (seton) drainage treatment of recurrent extrasphincteric perianal fistulae

Tube loop seton drainage treatment of multiply recurring high-spreading extrasphincteric perianal fistulae in 19 patients is reported in this study. The drainage loop setons make possible the rinsing of the wound following fistulectomy and also the bidirectional drainage of the wound discharge. Strangulation of the wound and an early closure of the fistula and hence the development of recurrence is prevented by means of controlled formation of scarred tissue. The sphincteral musculature of the anus is also protected from damage. Thirty-five recurring fistulae of 19 patients included in the present study were treated successfully by this method. Two fistula recurred. None of these patients developed incontinence. The use of tube loop setons was found to have advantages over the pull-out method in cases of high-spreading multiply recurring extrasphincteric or suprasphincteric perianal fistulae.

Embryological basis for cardiac left–right asymmetry

Asymmetric heart tube looping and chamber morphogenesis is a complex process that is just beginning to be understood at the genetic level. Rightward looping is the first embryological manifestation of consistently oriented, left–right asymmetric development of nearly all visceral organs. Intuitively, invariant anatomical asymmetry must derive from a novel mechanism capable of integrating dorsoventral and anteroposterior information. The details of this process are emerging for several vertebrates and reveal that overall left–right asymmetry, once polarized with respect to dorsoventral and anteroposterior axes, unfolds through distinct left- and right-sided programs of gene expression. These, in turn, regulate expression of cardiac and chamber-specific genes which guide heart morphogenesis and differentiation

Use of an extracorporeal arteriovenous tubing loop to measure cardiac output in intensive care unit patients by ultrasound velocity dilution.

Thermodilution cardiac output (CO) measurement requires heart catheterization and is known as a risk factor. The existing cannula in the radial artery in intensive care unit (ICU) patients can be used to measure CO by ultrasound dilution (COus). An arteriovenous shunt between the radial artery and cubital vein was created using a 25 cm tubing loop. An ultrasound flow dilution sensor was clamped on the tubing and connected to a modified HD01 monitor (Transonic Systems, Inc., Ithaca, NY). Calibration injections of 1 ml 0.9% NaCl were injected into the tubing. An intravenous bolus injection consisted of 10-20 ml 0.9% NaCl. Simultaneously, CO was measured by thermal dilution (COth; MI 166A, Hewlett Packard, Andover, MA). Each value for COth or COus was based on the average of three to five injections. Blood flow through the shunt was 10 to 26 ml/min. The comparison was made on 14 patients. In 33 measurements, the regression equation was COth = -0.08 + 1.02 COus (r = 0.97). In 22 cases, the difference between COth and COus was less than 5%, in 9 cases it was in the range of 5-10%, and in 2 cases it was in the range of 10-20%. The presence of arterial and venous lines in an ICU setting obviates the need for cardiac catheterization for the determination of CO.

The expression pattern of nodal and lefty in the mouse mutant Ft suggests a function in the establishment of handedness

We have investigated the expression of left/right ( L R ) asymmetry markers, nodal and lefty, in the situs inversus mouse mutant Fused toes (Ft). Both genes exhibited bilateral expression in the lateral plate mesoderm (LPM) at developmental stages whereas in wildtype embryos these genes were found to be expressed exclusively in the left LPM. Inspection of tail location and primitive heart tube looping, structures known to be handed in their orientation, documented a random orientation of these structures. Crossing of the Ft mutation into a different genetic background resulted in a strong reduction of this random orientation. Although the major fraction of these individuals still displayed nodal and lefty on both sides of the LPM, expression was almost always found to be weaker in the right LPM. These results suggest that the establishment of asymmetry is independent of nodal or lefty signals. However, handed asymmetry, which means consistent L R differences, such as the dextral looping of the primitive heart tube or the right-oriented tail, is directed by differences in the L R expression pattern of these two genes.

CARP, a cardiac ankyrin repeat protein, is downstream in the Nkx2-5 homeobox gene pathway.

To identify the molecular pathways that guide cardiac ventricular chamber specification, maturation and morphogenesis, we have sought to characterize factors that regulate the expression of the ventricular myosin light chain-2 gene, one of the earliest markers of ventricular regionalization during mammalian cardiogenesis. Previously, our laboratory identified a 28 bp HF-la/MEF-2 element in the MLC-2v promoter region, which confers cardiac ventricular chamber-specific gene expression during murine cardiogenesis, and showed that the ubiquitous transcription factor YB-1 binds to the HF-la site in conjunction with a co-factor. In a search for interacting co-factors, a nuclear ankyrin-like repeat protein CARP (cardiac ankyrin repeat protein) was isolated from a rat neonatal heart cDNA library by yeast two-hybrid screening, using YB-1 as the bait. Co-immunoprecipitation and GST-CARP pulldown studies reveal that CARP forms a physical complex with YB-1 in cardiac myocytes and immunostaining shows that endogenous CARP is localized in the cardiac myocyte nucleus. Co-transfection assays indicate that CARP can negatively regulate an HF-1-TK minimal promoter in an HF-1 sequence-dependent manner in cardiac myocytes, and CARP displays a transcriptional inhibitory activity when fused to a GAL4 DNA-binding domain in both cardiac and noncardiac cell context. Northern analysis revealed that carp mRNA is highly enriched in the adult heart, with only trace levels in skeletal muscle. During murine embryogenesis, endogenous carp expression was first clearly detected as early as E8.5 specifically in heart and is regulated temporally and spatially in the myocardium. Nkx2-5, the murine homologue of Drosophila gene tinman was previously shown to be required for heart tube looping morphogenesis and ventricular chamber-specific myosin light chain-2 expression during mammalian heart development. In Nkx2-5(-/-)embryos, carp expression was found to be significantly and selectively reduced as assessed by both whole-mount in situ hybridizations and RNase protection assays, suggesting that carp is downstream of the homeobox gene Nkx2-5 in the cardiac regulatory network. Co-transfection assays using a dominant negative mutant Nkx2-5 construct with CARP promoter-luciferase reporter constructs in cardiac myocytes confirms that Nkx2-5 either directly or indirectly regulates carp at the transcriptional level. Finally, a carp promoter-lacZ transgene, which displays cardiac-specific expression in wild-type and Nkx2-5(+/-) background, was also significantly reduced in Nkx2-5(-/-) embryos, indicating that Nkx2-5 either directly or indirectly regulates carp promoter activity during in vivo cardiogenesis as well as in cultured cardiac myocytes. Thus, CARP is a YB-1 associated factor and represents the first identified cardiac-restricted downstream regulatory gene in the homeobox gene Nkx2-5 pathway and may serve as a negative regulator of HF-1-dependent pathways for ventricular muscle gene expression.

Hepatic Influence on Pulmonary Neutrophil Sequestration Following Intestinal Ischemia–Reperfusion

Intestinal ischemia–reperfusion (I/R) causes a myriad of systemic physiologic derangements including pulmonary neutrophil (PMN) sequestration, increased microvascular permeability, and adult respiratory distress syndrome. It has been suggested that the observed lung injury is mediated by transhepatic passage of portal venous blood from ischemic intestine resulting in hepatic Kupffer cell activation and cytokine secretion. The purpose of this investigation was to test the hypothesis that PMN sequestration and microvascular permeability reflect Kupffer cell activity and/or portal venous blood flow. Experiments were designed to independently test the contribution of (1) Kupffer cell activity and (2) portal venous blood flow. In the first set of experiments, Kupffer cells were eliminated by treatment with gadolinium chloride 10 mg/kg iv (KC-ablated,n= 11). Control rats were treated with saline (KC-intact,n= 10). Intestinal ischemia was induced by SMA occlusion for 2 hr followed by 2 hr of reperfusion. In additional studies, the liver was excluded from the circulation by creation of a complete portosystemic shunt (portal vein to right femoral vein; shunt,n= 23). Control rats were treated by insertion of a loop of tubing within the intact portal vein (sham,n= 23). Intestinal ischemia was induced by SMA occlusion for 15 min followed by reperfusion for 1–3 hr. In both models, lung PMN accumulation and pulmonary microvascular permeability were assessed by myeloperoxidase (MPO) activity and125I-albumin lung/blood ratio (AL/BR), respectively. Kupffer cell elimination had no effect on PMN accumulation (MPO: KC-intact 29 ± 8 vs KC-ablated 26 ± 5 ΔÅ/min/g;P= NS) or microvascular permeability (AL/BR: KC-intact 0.22 ± 0.01 vs KC-ablated 0.23 ± 0.03;P= NS). Hepatic exclusion also had no effect on either PMN accumulation or permeability after reperfusion for 1 hr (MPO: sham 38 ± 12 vs shunt 42 ± 14 ΔÅ/min/g; AL/BR: sham 0.24 ± 0.02 vs shunt 0.23 ± 0.03;P= NS), 2 hr (MPO: sham 27 ± 5 vs shunt 29 ± 7 ΔÅ/min/g; AL/BR: sham 0.29 ± 0.02 vs shunt 0.26 ± 0.05;P= NS), or 3 hr (MPO: sham 24 ± 12 vs shunt 32 ± 7 ΔÅ/min/g; AL/BR: sham 0.33 ± 0.03 vs shunt 0.33 ± 0.01;P= NS). In this animal model, pulmonary PMN sequestration and microvascular permeability following intestinal I/R are independent of hepatic portal blood flow and Kupffer cell activity.

The saturated vapor pressure of desflurane at various temperatures.

The saturated vapor pressure of desflurane at various temperatures.

An Investigation of Household Refrigerator Cabinet Thermal Loads

The thermal load on a refrigerator cabinet during closed door conditions was investigated. The area of focus was the door and wall gasket region. Conduction heat transfer into the refrigerator cabinet was quantified using experimental techniques and numerical computer models. The specific loads for each of the various pathways, as well as the overall cabinet load were determined. Both the simulations and experiments showed that the edge losses account for approximately 30% of the overall cabinet load. In addition to this primary finding, percentages were determined for heat leakage directly through the door gaskets, along the steel casing at the wall and door flanges, and along the steel skin in the mullion section. The energy loading from antisweat electrical heaters and condenser tube loops is illustrated in this paper.

A recirculating-flow fluorescent oxygen sensor

An immersible oxygen sensor was constructed by circulating small quantities of ruthenium tris-(2,2′-bipyridyl) II dichloride oxygen-sensitive fluorescent dye through a loop of oxygen-permeable silicone tubing immersed in test medium. The fluorescence intensity of the dye was subsequently measured as it exited the flow loop and related to oxygen tension. This method of measuring the oxygen tension, through diffusive transport to a flowing stream of dye and recirculating it in the sensor, has been found to give a stable response and relatively long sensor lifetime without major recalibration. The sensor showed good stability over at least a week's duration and showed no degradation due to leaching of the dye through membranes or photobleaching that commonly affects fluorescent sensors with immobilized chemistries.

Direct Measurement of Dilute Nitric Oxide in Solution with an Ozone Chemiluminescent Detector

Nitric oxide can be rapidly extracted from dilute aqueous solutions into the gas phase by diffusion through hydrophobic membranes, permitting direct measurement of nitric oxide and observation of its reactions by a commercial chemiluminescent nitric oxide detector. Nitric oxide is a hydrophobic gas, crossing membranes much as oxygen and carbon dioxide do in blood gas analyzers. A loop of hydrophobic tubing made from microporous polypropylene was passed through a solution containing nitric oxide. One end of the tubing was connected to the inlet of the nitric oxide detector and maintained under vacuum. A continuous stream of carrier gas is passed through the other end of the tubing to sweep the nitric oxide from the inside of the tubing walls into the chemiluminescent detector. The device can measure nitric oxide at final concentrations as low as 10 nM with a time response of under 1 s. When the gas flow through the tubing is transiently diverted for periods up to several minutes, nitric oxide continues to accumulate within the tubing. The accumulated nitric oxide is rapidly washed out upon return of gas flow, resulting in a single peak which increases the sensitivity by one to two orders of magnitude. This method of measuring nitric oxide can be used to follow kinetics of nitric oxide formation or reactions with biological molecules. It is substantially faster and more selective than commercial electrochemical probes for nitric oxide.