Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “CLAMPS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 793 records · Page 44Linked to original sources
PubMed1995

Increased left ventricular contractility during cross-clamping of the descending thoracic aorta.

OBJECTIVE: To evaluate how left ventricular (LV) dimensions and contractility and proximal systemic hemodynamics respond during and after 30 minutes of cross-clamping of the descending thoracic aorta. DESIGN: The study was prospective and controlled. SETTING: The study was performed in a university animal laboratory. PARTICIPANTS: Ten pigs (bodyweight: 22 to 30 kg). INTERVENTIONS: The pigs were anesthetized with fentanyl and ketamine, and the heart and aorta were exposed through a left thoracotomy. The aortic root pressure and flow and LV dimensions were monitored with a high-fidelity pressure catheter, a precalibrated ultrasonic transit-time flow probe, and by two-dimensional ultrasound imaging, respectively. MEASUREMENTS AND MAIN RESULTS: After 1 minute of cross-clamping, LV end-diastolic and end-systolic diameters were increased 17% and 32% above baseline (both p < 0.001), respectively, whereas LV fiber shortening was decreased by 35% (p < 0.05) corresponding to the 257% increase in wall stress (p < 0.001). After 5 minutes, LV dimensions, fiber shortening, and wall stress had returned to baseline levels. After 10 minutes, fiber shortening was increased 67% (p < 0.05), although wall stress was maintained at baseline levels. Simultaneously, the aortic mean blood pressure, heart rate, and cardiac output peaked 112% (p < 0.001), 81% (p < 0.001), and 125% (p < 0.01) above baseline, respectively. CONCLUSIONS: Cross-clamping grossly increased systemic afterload grossly and was followed by moderate LV dilation, which resolved after 5 minutes owing to the combined effects of proximal vasodilation, increased myocardial contractility, and tachycardia. This hyperdynamic circulatory state was maintained during cross-clamping and decreased after declamping.

Animals↗
PubMed2004

Renal artery clamping and left renal vein division during abdominal aortic aneurysm repair.

OBJECTIVES: To determine whether renal artery clamping and division of the left renal vein affects renal function in the patients who undergo repair of infrarenal abdominal aortic aneurysm (AAA). METHODS: Between 1992 and 2000, 267 patients had open surgery for infrarenal AAA. Of these, 22 (8%) required temporary bilateral (15) or unilateral (7) renal artery clamping. 8 also had the left renal vein divided, three of which were re-anastomosed. RESULTS: Renal artery clamping and/or renal vein divisions did not affect the incidence of complications and long term renal failure. CONCLUSIONS: Clamping of the renal arteries and/or renal vein division during AAA surgery does not in itself compromise short or long term renal function.

Aged↗
PubMed2001

Atomic structure of the clamp loader small subunit from Pyrococcus furiosus.

In eukaryotic DNA replication, replication factor-C (RFC) acts as the clamp loader, which correctly installs the sliding clamp onto DNA strands at replication forks. The eukaryotic RFC is a complex consisting of one large and four small subunits. We have determined the crystal structure of the clamp loader small subunit (RFCS) from Pyrococcus furiosus. The six subunits, of which four bind ADP in their canonical nucleotide binding clefts, assemble into a dimer of semicircular trimers. The crescent-like architecture of each subunit formed by the three domains resembles that of the delta' subunit of the E. coli clamp loader. The trimeric architecture of archaeal RFCS, with its mobile N-terminal domains, involves intersubunit interactions that may be conserved in eukaryotic functional complexes.

Amino Acid Sequence↗
PubMed2003

Clamp-loader-helicase interaction in Bacillus. Leucine 381 is critical for pentamerization and helicase binding of the Bacillus tau protein.

Recently, we revealed the architecture of the clamp-loader-helicase (tau-DnaB) complex in Bacillus by atomic force microscopy imaging and constructed a structural model, whereby a pentameric clamp-loader interacts with the hexameric helicase. Crucial to this model is the assumption that the clamp-loader forms a pentamer in the absence of other components of the clamp-loader complex such as deltadelta'. Here, we show that the Bacillus subtilis tau protein, even in the absence of deltadelta', interacts as a pentamer with the hexameric DnaB and that the L381 of tau is critical for the integrity of the tau oligomer and interaction with DnaB. The effects of the L381A mutation were confirmed by gel filtration, ultracentrifugation, circular dichroism, cross-linking studies, and genetic replacement of the dnaX gene with a mutant L381A dnaX gene in vivo. The L381A protein is able to support growth in vivo only when expressed in high quantities. Finally, despite the fact that a mutation at P465 has been reported to result in a thermosensitive gene in vivo, a P465L mutant protein interacts with DnaB in vitro suggesting that this defect is not a result of a defective tau-DnaB interaction.

Amino Acid Sequence↗
PubMed1998

Clamp subunit dissociation dictates bacteriophage T4 DNA polymerase holoenzyme disassembly.

Clamp proteins confer processivity to the DNA polymerase during DNA replication. These oligomeric proteins are loaded onto DNA by clamp loader protein complexes in an ATP-dependent manner. The mechanism by which the trimeric bacteriophage T4 clamp protein (the 45 protein) loads and dissociates from DNA was investigated as a function of its intersubunit protein-protein interactions. These interactions were continuously monitored using a fluorescence resonance energy transfer (FRET) based assay. A cysteine mutant of the 45 protein was constructed to facilitate site-specific incorporation of a fluorescent probe at the subunit interface. This site was chosen such that FRET was observed between the introduced fluorescent probe and a tryptophan residue located on the opposing subunit. By use of this fluorescently labeled 45 protein, it was possible to obtain an estimate of an apparent trimer dissociation constant from either a cooperative (0.08 +/- 0.04 microM2 at 25 degrees C) or a noncooperative (0.51 microM and 0.17 microM at 25 degrees C) model. Upon mixing the fluorescently labeled 45 protein with a 45 protein containing 4-fluorotryptophan, a nonfluorescent tryptophan analogue, subunit exchange between the two variants of the 45 protein was observed according to a reduction in intersubunit FRET. Subunit exchange rate constants measured in the presence or absence of the clamp loader (44/62 complex), the polymerase (43 protein), and/or a primer template DNA substrate demonstrate (a) that the 45 protein is not loaded onto DNA by subunit exchange and (b) that the disassembly dissociation of a stalled holoenzyme from DNA is dictated by 45 protein subunit dissociation.

Bacteriophage T4↗
PubMedDate not supplied

Patch- and voltage-clamp analysis of cyclic AMP-stimulated inward current underlying neurone bursting.

The second messenger cyclic AMP has been variously reported to affect the electrical activity of different neurones by decreasing outward potassium current, increasing outward current and increasing inward current. The recently developed patch clamp method of recording single ionic channels allows direct measurement of the action of cyclic AMP on membrane conductances. Using the patch clamp, the closure of potassium channels by cyclic AMP has previously been documented on the single channel level. We report here that in a bursting molluscan neurone, intracellular iontophoresis of cyclic AMP under voltage clamp elicits an inward current of maximal amplitude in the pacemaker voltage region. Patch-clamp analysis reveals inward channels whose opening frequency is augmented by cyclic AMP stimulation and whose activity accompanies burst episodes. Channel opening frequency is significantly increased by depolarization of the whole soma, but not by focal depolarization of the patch; this may reflect the action of another second messenger that acts in concert with cyclic AMP to confer voltage sensitivity.

Animals↗
PubMed2000

Placental transfusion: umbilical cord clamping and preterm infants.

OBJECTIVE: To investigate the clinical effects of early versus late cord clamping in preterm infants. STUDY DESIGN: A total of 32 premature infants were prospectively randomized. The following parameters were measured: Initial spun hematocrit (Hct), hemoglobin (Hgb), red blood cell (RBC) counts, frequency of blood transfusions, peak serum bilirubin, mean blood pressure (MBP), oxygen index, intraventricular hemorrhage, and significant patent ductus arteriosus (PDA). RESULTS: Over the 4-week study period, the delayed cord clamping (DCC) group exhibited a decrease in the frequency of blood transfusion (p < 0.001) and also a decrease in albumin transfusions over the first 24 hours (p < 0.03). MBP in the first 4 hours was higher in the DCC group (p < 0.01), and there were statistically significant increases in Hct (21%), Hgb (23%), and RBC count (21%) compared with the early cord clamping group. The risks of patent ductus arteriosus, hyperbilirubinemia, or intraventricular hemorrhage were similar in both groups. Late clamping of the umbilical cord had little or no effect on the oxygen index. CONCLUSION: DCC significantly reduced the requirement for blood and albumin transfusion. It also increased the initial Hct, RBC count, Hgb levels, and MBP.

Blood Component Transfusion↗
PubMed2003

Immediate and delayed cord clamping in infants born between 24 and 32 weeks: a pilot randomized controlled trial.

OBJECTIVE: This pilot study's aim was to establish feasibility of a protocol for delayed cord clamping (DCC) versus immediate cord clamping (ICC) at preterm birth and to examine its effects on initial blood pressure and other outcomes. STUDY DESIGN: A randomized controlled trial recruited 32 infants between 24 and 32 weeks. Immediately before delivery, mothers were randomized to ICC (cord clamped at 5 to 10 seconds) or DCC (30- to 45-second delay in cord clamping) groups. RESULTS: Intention-to-treat analyses revealed that the DCC group were more likely to have higher initial mean blood pressures (adjusted OR 3.4) and less likely to be discharged on oxygen (adjusted OR 8.6). DCC group infants had higher initial glucose levels (ICC=36 mg/dl, DCC=73.1 mg/dl; p=0.02). CONCLUSION: The research design is feasible. The immediate benefit of improved blood pressure was confirmed and other findings deserve consideration for further study.

Blood Pressure↗
PubMed2000

Targeting of single-stranded DNA and RNA containing adjacent pyrimidine and purine tracts by triple helix formation with circular and clamp oligonucleotides.

The aim of this work was to construct an anti-messenger targeted to the pim-1 oncogene transcript, based on circular or clamp oligodeoxyribonucleotides. The formation of bimolecular triplexes by clamp or circular oligonucleotides was investigated using single-stranded targets of both DNA (5'-CCCTCCTTTGAAGAA-3') and RNA type (5'-CCCUCCUUUGAAGAA-3'). The third, 'Hoogsteen' strand of the triplex was represented by G,T-rich sequences. The secondary structures of the complexes were determined by thermal denaturation, circular dichroism and gel mobility shift experiments and shown to depend on the nature of the target strand. With DNA as target, the sequence of a clamp (or circular) oligonucleotide that formed the triple helix was 3'-GGGAGGAAACTTCTTTT-TTGTTGTTT-TT-GGTGGG-5', where the first TT dinucleotide (in italics) is a linker and the second TT (bold) represents the bridge through which the 'Hoogsteen' strand switches from one strand of the Watson-Crick duplex to the other, once the duplex is formed by the corresponding portion of the anti-messenger (underlined). The portion of the 'Hoogsteen' sequence of the triplex between the two TT dinucleotides binds to the 3' extremity of the target strand and runs parallel to it. The portion situated at the 5' end of the oligonucleotide switches to the purine tract of the complementary strand of the duplex and is antiparallel to it. In contrast, with RNA as target, for a branched clamp oligonucleotide that formed a triple helix over its entire length (5'-TTCTTCAAAGGAGGG-3' 3'-GGGTGGTTT-T-GTTGTT-5') the portion of the 'Hoogsteen' sequence that bound to the 3' extremity of the target strand had to be antiparallel to it.

Circular Dichroism↗
PubMed2000

Pulmonary nitric oxide metabolism following infrarenal aortic cross-clamp-induced ischaemia-reperfusion injury.

OBJECTIVES: to investigate endogenous pulmonary nitric oxide metabolism following infrarenal aortic cross-clamp-induced ischaemia-reperfusion injury. METHODS: groups of male Wistar rats (n=6) were subjected to 60 minutes of infrarenal aortic cross-clamping under general anaesthesia. Rats were culled after 0, 60 and 120 minutes>> reperfusion, following release of the aortic clamp. A sham-operated control group was also studied. Acute lung injury (ALI) was quantified by measuring the protein concentration in lung bronchoalveolar lavage (BAL) fluid. Pulmonary myeloperoxidase activity (MPO) was measured as an index of neutrophil infiltration and degranulation in the lung. Plasma tumour-necrosis factor-alpha (TNF-alpha) was measured as an index of the pro-inflammatory cytokine response and pulmonary nitric oxide synthase (NOS) activity was determined by measuring conversion of(3)H L-arginine to(3)H L-citrulline in tissue homogenates. RESULTS: these data show significant ALI with increased pulmonary microvascular permeability and MPO activity in animals subject to 60 minutes>> ischaemia and 60 minutes or 120 minutes of reperfusion compared to control animals (p<0.01). Plasma TNF-alpha levels were significantly increased following 60 minutes of ischaemia compared to controls (p<0.01) and remained significantly increased in animals subject to reperfusion (p<0.01). Pulmonary NOS activity was significantly increased in animals subject to reperfusion (p<0.01). CONCLUSIONS: the reperfusion phase of infrarenal aortic cross-clamping provokes a significant increase in pulmonary NOS metabolism. The increase in plasma TNF-alpha and MPO activity suggests that this response may be secondary to inducible NOS expression. Manipulation of this response may benefit patients at risk of acute injury following infrarenal aortic reconstruction.

Animals↗
PubMed2001

Liver transplantation without venovenous bypass: morbidity and mortality in patients with greater than 50% reduction in cardiac output after vena cava clamping.

OBJECTIVE: To investigate whether a decrease in cardiac output of >or=50% after vena cava clamping is associated with an increase in perioperative morbidity or mortality in patients undergoing orthotopic liver transplantation without venovenous bypass. DESIGN: Retrospective, clinical study. PARTICIPANTS: Patients undergoing elective orthotopic liver transplantation without venovenous bypass (n = 172). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: In 82 patients (group 1), the decrease in cardiac output after vena cava clamping was >or=50%; in 90 patients (group 2), the decrease was <50%. Hemodynamics during surgery and perioperative morbidity and mortality were compared between group 1 and group 2 patients. Mean arterial pressure during the anhepatic phase was not significantly different between groups, but cardiac output and mixed venous oxygen saturation were significantly lower in group 1 patients. Perioperative mortality, need for postoperative renal replacement therapy, postoperative serum creatinine levels, and graft function were not different between groups. CONCLUSION: A >50% reduction in cardiac output after vena cava clamping is not associated with an increase in perioperative morbidity and mortality when compared with patients with a less pronounced reduction in cardiac output. These results question the common practice of basing the indication for venovenous bypass during the anhepatic phase on a reduction in cardiac output of >50% after a trial of vena cava clamping.

Cardiac Output↗
PubMed2002

Cardiac marker responses to coronary artery bypass graft surgery with cardiopulmonary bypass and aortic cross-clamping.

OBJECTIVE: To study several markers of myocardial injury in relation to aortic cross-clamping and cardiopulmonary bypass (CPB) after coronary artery bypass graft (CABG) surgery. DESIGN: Prospective observational study. SETTING: University hospital. PARTICIPANTS: Thirty adult patients who underwent elective CABG surgery with aortic cross-clamping and CPB. MEASUREMENTS AND MAIN RESULTS: Serum levels of interleukin-6 (IL-6), interleukin-8 (IL-8), troponin-T (TnT), myosin light chain I (MLCI), and MB isoenzyme of creatine kinase (CK-MB), as markers of myocardial injury, were measured after induction of anesthesia for baseline values, then again at the end of surgery and on postoperative days 1, 3, and 5. IL-6, IL-8, and CK-MB levels were significantly elevated in the early postoperative stage. TnT significantly increased from the end of surgery to postoperative day 5. MLCI increased also but later than TnT. Aortic cross-clamping time correlated positively with peak TnT (r = 0.51, p < 0.05), TnT level on postoperative day 1 (r = 0.69, p < 0.01), and MLCI level on postoperative day 5 (r = 0.45, p < 0.05). CPB time was correlated only with peak TnT (r = 0.47, p < 0.05). CONCLUSIONS: The increase in TnT level is strongly related to aortic cross-clamping.

Adult↗
PubMed2001

Standardizing nerve crushes with a non-serrated clamp.

Standardized experimental nerve crush attempts should include the number, duration, and intensity (amount of pressure) of crushes. The authors have developed a new crushing device, a clamp with which predetermined forces can be applied to nerves. This allows the exertion of different, standardized forces to crush a nerve within a scale that produces second-degree injuries. The main advantages of the clamp are that it is small, although very robust, is purely mechanical, and is easy to handle. The jaws of the clamp are not serrated, so that pressure on the nerve is uniformly transmitted. To avoid unintended nerve damage, the edges of the jaws are smoothly rounded off. The closure of the clamp is mechanized by a spring. As the spring is exchangeable, any number of different preloads are available. The force can be varied, according to different requirements, and is applicable to variantly thick nerves in any experimental animal, thus enhancing standardization, and making cross-over comparisons of experimental study results possible.

Action Potentials↗
PubMed2002

[Impact of multi-segmental aortic clamping and distal aortic perfusion on the prevention of postoperative paraplegia during thoracoabdominal aortic graft replacement].

OBJECTIVE: We present the impact of multisegmental aortic clamping under distal aortic perfusion and segmental artery reimplantation on the prevention of postoperative paraplegia during thoracoabdominal aortic graft replacement. PATIENTS: During the last 14 years in 47 patients (age range: 22 to 82 years; average: 57,9 +/- 13,2 years; 16 females and 31 males) with thoracoabdominal aortic aneurysm a graft replacement was performed with adjuncts of normothermic partial bypass and multisegmental aortic clamping. As many patent segmental arteries as possible were reimplanted. RESULTS: Five patients died during hospitalization, for an in-hospital mortality rate of 10,6 %. In the elective patients (n = 40), the hospital mortality rate was 7,5 %. The average number of segmental aortic clampings per patient was 2,83 +/- 1,19 times. In 39 patients (82,9 %), 117 segmental arteries were reimplanted or preserved by beveled anastomosis. Eighty-three out of 117 segmental arteries (70,9 %) were located between TH9 and L2. Postoperative paraplegia/paraparesis did not occur in any patient. CONCLUSION: In view of our results reimplantation of as many segmental arteries as possible under multisegmental aortic clamping with adequate distal aortic perfusion can be recommended for effective prevention of spinal cord ischemia in TAAA surgery.

Adult↗
PubMed1985

Estimates of in vivo insulin action in humans: comparison of the insulin clamp and the minimal model techniques.

The insulin clamp technique, which is often assumed to measure the ability of insulin to stimulate glucose uptake, actually measures both insulin-independent and insulin-dependent glucose uptake. In contrast, the minimal model technique, recently introduced by Bergman, Philips and Cobelli (1981), attempts to directly estimate insulin sensitivity (insulin-dependent glucose uptake = S1) by measurement of plasma glucose and insulin values during a 3 hour intravenous glucose tolerance test (IVGTT). In the present study estimates of insulin action derived from the insulin clamp and the minimal model technique were compared in 20 humans with varying degrees of glucose tolerance. The insulin response during the IVGTT was too low to permit calculation of S1 in 5 subjects - 4 with Type II diabetes and 1 with normal glucose tolerance. Although the correlation coefficient between the two tests in the other 15 patients was statistically significant (r = 0.53, P less than 0.05), this statement is somewhat misleading. Thus, S1 in the 4/7 patients with Type II diabetes in whom it could be measured was zero, and the correlation between estimates of insulin action with the two techniques in the 11 non-diabetic patients was not statistically significant (r = 0.41, P = NS) when these 4 patients were removed from the analysis. In conclusion, these data indicate that there was only a weak correlation between estimates of insulin action assessed with the insulin clamp and the minimal model techniques. One explanation for this observation is that the insulin-independent component of total glucose disposal both varies widely among patients and contributes significantly to glucose uptake as assessed by the insulin clamp technique.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1998

[Rivet-like titanium clamps for refixation of bone covers after craniotomy--radiologic identification, safety and image quality in CT and MR studies].

PURPOSE: The MRI and CT compatibility of a new design of metallic fixation implants for cranial bone flaps was investigated experimentally and following clinical application in craniotomy patients. Is imaging quality impaired through implant-induced artifacts? METHODS: Possible induced movement and heating of the clamp implant as well as the magnitude of susceptibility artifacts were assessed experimentally by MRI at 1.5 T. Additionally, implant-induced artifacts were evaluated under clinical conditions for all relevant MRI-sequences in 100 craniotomy patients whose skull flaps were re-affixed using the new clamp implant. RESULTS: In T1-weighted spin echo and fast spin echo sequences the sizes of implant-induced artifacts were equal to the size of the implant or slightly larger; in T2-weighted gradient echo images artifacts were maximally double the size of the implant itself. Induced movement or heating was not observed. CONCLUSIONS: The safety in radiological imaging of titanium clamp implants for fixation of craniotomy bone flaps was established experimentally as well as under clinical conditions. The clamps can be easily identified by radiological imaging, cause no hazards to the patients, and have little effect on image quality.

Artifacts↗
PubMed1983

Aortic cross-clamping for more than 2 hours in open-heart surgery. Early results in 87 patients.

Myocardial protection with cold cardioplegia has made it possible to prolong the time of aortic cross-clamping during open-heart surgery. Myocardial ischemia for up to 120 minutes is considered acceptable under these conditions. Eighty-seven patients operated upon for various heart lesions with cardiopulmonary bypass and aortic cross-clamping for more than 2 hours (mean time 146 minutes) were reviewed. Myocardial protection was achieved with cold cardioplegia, in some cases with additional topical cooling of the heart. Ten patients died and 77 were discharged from the hospital. Perioperative and early postoperative deaths could not be correlated to aortic cross-clamping time or the method of myocardial protection. Aortic cross-clamping can be safely performed for a period far longer than 2 hours with myocardial preservation by cold cardioplegia.

Adult↗
PubMed1980

Glucose clamping using the Biostator GCIIS.

The Biostator GCIIS was used to clamp circulating glucose at hypoglycemic (42 +/- 1 mg/dl), euglycemic (86 +/- 2 mg/dl), and hyperglycemic (142 +/- 1 mg/dl) levels in normal subjects during a concomitant infusion of insulin (0.1 U/kg/h). Because of limitations in maximal glucose infusion (1 g/min) from the Biostator, a supplementary infusion of glucose was required to accomplish euglycemic and hyperglycemic clamps. The coefficients of variation of blood glucose were 7.06 +/- 1.3%, 5.9 +/- 0.5%, and 6.1 +/- 0.9 for 120 minutes of hypoglycemic, euglycemic, and hyperglycemic clamps, respectively. Despite the occasional interruption of blood flow in the double-lumen catheter and the occasional poor correlation between Biostator and reference glucose method, satisfactory glucose clamps could be maintained for 2 hours.

Adult↗