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At least 757 records · Page 42Linked to original sources
PubMed1991

Should tumors be clamped in radiobiological fractionation experiments?

In radiobiological fractionation experiments tumors are often clamped during irradiation. This is done not only to facilitate the interpretation of the data by eliminating the influence of reoxygenation but also to avoid uncontrolled changes in the hypoxic fraction that are caused by anesthesia or stress from physical restraint. In this study it is shown that clamping of tumors during irradiation also affects repair, repopulation, and redistribution. From these results it is concluded that clamping of tumors during fractionated irradiation treatment does not appear to be an adequate measure to elucidate the mechanisms that determine tumor response to radiotherapy. Even some of the fundamental concepts of tumor radiobiology might contain some uncertainties, since they are often based on data resulting from clamped tumors.

Animals↗
PubMed1991

Humoral factors and hemodynamics during cross-clamping of the thoracic aorta.

The present study was designed to test the hypothesis that vasoactive compounds produced in the ischemic part of the body below an occluded aorta are responsible for the hemodynamic changes observed during cross-clamping of the thoracic aorta. The experiments were performed on 32 rabbits anesthetized with halothane that underwent experiments with cross-circulation; the blood from the inferior caval veins of rabbits A was pumped into the inferior caval veins of rabbits B. Simultaneously, exactly the same amount of blood was pumped from the jugular vein of rabbits B into the jugular vein of rabbits A. The aorta and inferior vena cava were exposed and then simultaneously cross-clamped directly below the diaphragm. The cross-clamping of the aorta and inferior vena cava in rabbits A was associated with a 29% to 44% increase in mean arterial pressure in rabbits B. The experiments support the hypothesis and suggest that endogenously produced humoral factors are responsible for at least one third to one half of the arterial hypertension that usually develops during aortic cross-clamping.

Anesthesia, Inhalation↗
PubMed1992

Effects of halothane and isoflurane on transient renal dysfunction associated with infrarenal aortic cross-clamping.

Aortic cross-clamping for reconstructive aortic surgery is associated with impairment of renal function. Halothane or isoflurane was used to assess the influence of volatile anesthesia on renal hemodynamics during aortic surgery. Nineteen patients with normal preoperative creatinine clearances who were scheduled for reconstructive aortic surgery were randomly divided into two groups: halothane group (n = 9) and isoflurane group (n = 10). Induction of anesthesia consisted of midazolam, fentanyl, and pancuronium. Anesthesia was maintained with fentanyl and halothane or isoflurane in nitrous oxide and oxygen (50/50). Systemic hemodynamics were similar in both groups throughout surgery. Before aortic cross-clamping, effective renal plasma flow (ERPF) (131I-hippuran clearance) and glomerular filtration rate (GFR) (99Tc-DTPA clearance) were significantly lower in the halothane group (118.4 +/- 25.6 and 19.7 +/- 5.2 mL/min, respectively) than in the isoflurane group (253.4 +/- 51.5 and 44.9 +/- 8.4 mL/min) (P less than 0.05 for both). During cross-clamping, the renal variables were not markedly affected in either group and remained higher in the isoflurane-anesthetized patients (232.9 +/- 47.1 and 49.5 +/- 1.2 mL/min for ERPF and GFR, respectively) than in the halothane-anesthetized patients (132.4 +/- 31.6 and 14.8 +/- 3.7 mL/min, respectively) (P less than 0.05). After aortic unclamping, ERPF increased markedly in both groups (467.8 +/- 122 and 362.5 +/- 57.7 mL/min in the halothane and isoflurane groups, respectively), as did GFR (74.8 +/- 22 and 71.8 +/- 13.1 mL/min, respectively). These results suggest that anesthesia with halothane is associated with transient renal vasoconstriction during abdominal surgery. In contrast, aortic cross-clamping during isoflurane anesthesia was not associated with renal hemodynamic impairment.

Adult↗
PubMedDate not supplied

Use of an "acetaldehyde clamp" in the determination of low-KM aldehyde dehydrogenase activity in H4-II-E-C3 rat hepatoma cells.

The high-affinity (K(M)<1 microM) mitochondrial class 2 aldehyde dehydrogenase (ALDH2) metabolizes most of the acetaldehyde generated in the hepatic oxidation of ethanol. H4-II-E-C3 rat hepatoma cells have been found to express ALDH2. We report a method to assess ALDH2 activity in intact hepatoma cells that does not require mitochondrial isolation. To determine only the high-affinity ALDH2 activity it is necessary to keep constant low concentrations of acetaldehyde in the cells to minimize its metabolism by high-K(M) aldehyde dehydrogenases. To maintain both low and constant concentrations of acetaldehyde we used an "acetaldehyde clamp," which keeps acetaldehyde at a concentration of 4.2+/-0.4 microM. The clamp is attained by addition of excess yeast alcohol dehydrogenase, 14C-ethanol, and oxidized form of nicotinamide adenine dinucleotide (NAD(+)) to the hepatoma cell culture medium. The concentration of 14C-acetaldehyde attained follows the equilibrium constant of the alcohol dehydrogenase reaction. Thus, 14C-acetate is generated virtually by the low-K(M) aldehyde dehydrogenase activity. 14C-acetate is separated from the culture medium by an anionic resin and its radioactivity is determined. We showed that (1) acetate production is linear for 120 min, (2) addition of 160 microM cyanamide to the culture medium leads to a 75%-80% reduction of acetate generated, and (3) ALDH2 activity is dependent on cell-to-cell contact and increases after cells reach confluence. The clamp system allows the determination of ALDH2 activity in less than one million H4-II-E-C3 rat hepatoma cells. The specificity and sensitivity of the "acetaldehyde clamp" assay should be of value in evaluation of the effects of new agents that modify Aldh2 gene expression, as well as in the study of ALDH2 regulation in intact cells.

Acetaldehyde↗
PubMed2006

Effects of statins on renal function after aortic cross clamping during major vascular surgery.

Ischemic reperfusion injury is an important cause of renal dysfunction after major vascular surgery and increases postoperative morbidity and mortality. The aim of the present study was to assess the effect of statins on renal function in patients at high risk for renal dysfunction, that is, those who underwent suprarenal aortic cross clamping-declamping. Seventy-seven patients (28 statin users, 57 men; mean age 69 +/- 8 years) with normal preoperative renal function requiring suprarenal aortic cross clamping-declamping during vascular surgery from 1995 to 2005 were studied. Creatinine levels were obtained before surgery and on days 1, 2, 3, 7, and 30 after surgery. An analysis-of-variance model for repeated measurements was applied to compare creatinine levels between statin users and nonusers, with adjustment for clamping time and blood loss. There were no differences in baseline clinical characteristics, preoperative creatinine levels (0.93 vs 0.96 mg/dl, p = 0.59), and glomerular filtration rate (79 vs 73 ml/min, p = 0.1). Postoperative creatinine levels during the 30 days after surgery were significantly lower in statin users than in nonusers (analysis-of-variance p <0.01, 1.17 vs 1.98 mg/dl). Postoperative hemodialysis was required (temporarily) in 7 patients (9.1%), all statin nonusers. These findings suggest an association between statin use and preserved renal function after suprarenal aortic clamping.

Aged↗
PubMed2005

Comparison between 4-hour clamping drainage and nonclamping drainage after total knee arthroplasty.

A prospective randomized trial of postoperative drainage-clamping practice was performed in 89 knees undergoing total knee arthroplasty. In group 1 (43 knees), drainage was clamped for the first 4 postoperative hours. In group 2 (46 knees), drainage was not clamped. The average bloody drainage was significantly less in group 1 than group 2 (514.85 +/- 378.0 vs 843.4 +/- 366.4 mL). The decrease of hemoglobin and hematocrit after surgery was also significantly less in group 1. Group differences between postoperative range of motion and narcotics requirements, length of stay, immediate wound problems, and deep vein thrombosis were nonsignificant. These results suggested that clamping the drainage in the first 4 postoperative hours reduces postoperative blood loss without causing excess morbidity after total knee arthroplasty.

Aged↗
PubMed2005

Does cross-clamping the arch increase the risk of descending thoracic and thoracoabdominal aneurysm repair?

BACKGROUND: Descending thoracic and thoracoabdominal aortic aneurysms may arise in the distal aortic arch. Repair of these aneurysms has been associated with increased morbidity and operative mortality. Complex surgical and endovascular techniques have reduced the risks for this cohort. We examined outcomes utilizing an approach based on simple cross-clamping of the arch. METHODS: From July 1997 to January 2004, 272 consecutive patients had aneurysm repair through the left chest. Twenty-nine requiring profound hypothermic circulatory arrest (PHCA) were excluded. Two hundred and forty-three were divided into two groups: group I (n = 60) had distal arch involvement and required cross-clamping proximal to the left subclavian artery. Group II (n = 183) were cross-clamped distal to the subclavian. Adjuncts for neurologic and renal protection were utilized as needed. RESULTS: In-hospital mortality for all 243 patients was 3.7%. There was no difference in mortality between groups (I, 3.3% vs II, 3.8%). Group I patients also had similar rates of paraplegia (I, 0% vs II, 2.2%), stroke (I, 1.2% vs II ,1.1%), and renal failure (I, 1.7% vs II, 5.5%). Group I patients had significantly more recurrent nerve palsies (I, 33% vs II, 4.9%) although this did not translate into a higher incidence of respiratory failure. CONCLUSIONS: Repair of thoracic aneurysms arising in the distal arch can be repaired with a technique based on simple cross-clamping without an increase in mortality or major neurologic injury. Recurrent nerve palsy is much more common with this approach but is well-tolerated without increasing the need for tracheostomy.

Acute Kidney Injury↗
PubMed2005

Video and robotic-assisted minimally invasive mitral valve surgery: a comparison of the Port-Access and transthoracic clamp techniques.

BACKGROUND: In order to assess different surgical techniques for video-assisted minimally invasive mitral valve surgery, a retrospective study was undertaken comparing the Port-Access system (Cardiovations, Ethicon Inc, Somerville, NJ) and the transthoracic clamp technique. METHODS: In 120 patients mitral valve surgery was performed through a small right minithoracotomy using either the Port-Access endovascular cardiopulmonary bypass system (Port-Access, n = 60) or the transthoracic clamp technique (MICRO, n = 60). Mean patient age was 61.5 +/- 10.5 years (81 patients with isolated mitral valve insufficiency, 39 patients with combined mitral valve disease). RESULTS: Eighty-one (67.5%) patients underwent mitral valve repair and 39 (32.5%) patients had valve replacement. Mean time of surgery was 4.5 +/- 3.5 and 4.1 +/- 3.2 hours (p = 0.07), aortic cross-clamp time 89 +/- 69 and 78 +/- 65 minutes (p = 0.08), mean intensive care unit stay 1.5 +/- 2.1 and 1.6 +/- 2.5 days (p = ns), and hospital stay 9.0 +/- 10.5 and 9.2 +/- 9.7 days (p = ns) in the Port-Access and MICRO groups, respectively. In the Port-Access group, there were 6 reexplorations for bleeding, one perforation of the right ventricle with the endopulmonary vent, and 2 reconstructions of the femoral artery necessary after femoral cannulation, compared to one reexploration for bleeding in the MICRO group. There was only one minor paravalvular leak after replacement and 2 cases of residual greater than or equal to grade II mitral valve regurgitation after mitral valve repair in the Port-Access group, necessitating reoperation. In both groups, there was no mortality, no cerebrovascular accident, no aortic dissection, and no conversion to sternotomy. CONCLUSIONS: Minimally invasive mitral valve surgery has become a standard approach for isolated mitral valve operations at our institution. The MICRO technique tends to shorten the time of surgery and aortic cross-clamping and reduces perioperative costs by simplifying the operative procedure.

Cardiopulmonary Bypass↗
PubMed2006

Transcerebral platelet activation after aortic cross-clamp release is linked to neurocognitive decline.

BACKGROUND: Neurocognitive decline after cardiac surgery requiring cardiopulmonary bypass (CPB) may be caused in part by highly prothrombotic atheroemboli to the brain; the source of these emboli is likely the ascending aorta and aortic arch. We examined transcerebral platelet activation gradients using simultaneous measurements in arterial and jugular venous blood and then compared gradients with post-CPB-associated neurocognitive injury. METHODS: Eighty-one patients undergoing elective coronary artery bypass graft surgery requiring CPB were studied. Neurocognitive function was measured preoperatively and again at 6 weeks postoperatively. Paired arterial and jugular venous blood samples were drawn before surgery, immediately before and after aortic cross-clamp removal (an event previously linked to embolic showers), and at the end of the operation. Transcerebral platelet activation gradients (venous minus arterial values) were compared in patients with and without cognitive deficit. RESULTS: Immediately after aortic cross-clamp removal, there was a significant increase in the transcerebral platelet activation gradient (increased % P-selectin-positive platelets during transcerebral passage) in the subset of patients who subsequently developed post-CPB cognitive deficit; this platelet activation gradient did not occur in patients without cognitive injury. In contrast, there was no transcerebral gradient of platelet activation in CPB patients as an entirety, nor was there a gradient at all other time points in the patient subset who went on to have cognitive deficit develop. This fleeting gradient of transcerebral platelet activation after cross-clamp removal was also significantly correlated with the overall change in cognitive injury score. CONCLUSIONS: Transient intracerebral platelet activation after removal of the aortic cross-clamp is associated with post-CPB neurocognitive injury.

Aged↗
PubMed2006

Outcomes of the Fontan procedure using cardiopulmonary bypass with aortic cross-clamping.

BACKGROUND: Avoidance of cardiopulmonary bypass (CPB) and aortic cross-clamping during the Fontan procedure has been advocated to improve outcomes. We continue to use CPB with aortic cross-clamping for the Fontan procedure. METHODS: We performed a review of patients undergoing the Fontan procedure between January 1, 2000 and December 31, 2004. RESULTS: The Fontan procedure was performed in 160 patients. The median age was 2.2 years (range, 1.0 to 29.1 years). Hypoplastic left heart syndrome or a variant was present in 114 patients (71%), and heterotaxy was present in 19 (12%). CPB and modified ultrafiltration were used in all patients. Aortic cross-clamping was used in 154 (96%) of 160 patients and deep hypothermic circulatory arrest (DHCA) in 132 (83%). A lateral tunnel Fontan was performed in 69 patients (43%) and an extracardiac Fontan in 91 (57%). A fenestration was created in 144 patients (90%). Two patients died. Freedom from death or takedown was 98% (157/160). Median duration of pleural drainage was 2 days (range, 1 to 44 days) and was more than 14 days in 16 patients. Median duration of hospitalization was 6 days (range, 3 to 55 days). The small number of deaths precluded assessment of risk factors for mortality. By multivariable analysis, risk factors for pleural drainage longer than 3 days were extracardiac connection (p < 0.001) and increasing mean pulmonary artery pressure before the Fontan procedure (p = 0.033). By multivariable analysis, risk factors for hospitalization for more than 7 days were extracardiac connection (p = 0.003), increasing duration of total support (CPB and DHCA, p = 0.027), and decreasing systemic oxygen saturation before the Fontan procedure (p = 0.048). CONCLUSIONS: The Fontan procedure can be performed using CPB and aortic cross-clamping with low morbidity and mortality.

Adolescent↗
PubMed2006

The development of molecular clamps as drugs.

Some enzymes catalyze the modification of an ensemble of substrates in vivo and, as a consequence, are not ideal targets for active-site-directed drugs. One solution to inhibiting such multisubstrate enzymes would be a drug that binds tightly to only one substrate, which prevents the binding of that substrate to the enzyme. Ideally, such a drug (called a molecular clamp, a molecular forcep or a molecular tweezer) would prevent the enzymatic processing of only the targeted substrate. This would enable the enzyme to function normally on all other substrates. Here, we review the unique steady-state kinetic features of molecular clamp inhibition, identify potential targets for molecular clamp inhibition, and discuss problems for the therapeutic use of molecular clamps.

Drug Delivery Systems↗
PubMed2005

Immediate ischemic preconditioning based on somatosensory evoked potentials seems to prevent spinal cord injury following descending thoracic aorta cross-clamping.

OBJECTIVE: Delayed ischemic preconditioning has demonstrated neuroprotective effects in spinal cord ischemia. We investigated the effects of immediate ischemic preconditioning based on somatosensory evoked potentials monitoring in a model of spinal cord injury due descending thoracic aorta occlusion in dogs. METHODS: Twenty-one dogs were submitted to spinal cord ischemia induced by descending thoracic aorta cross-clamping for 45 min. Control group underwent only the aortic cross-clamping (n=7), group A underwent one cycle of ischemic preconditioning (n=7) and group B underwent three equal cycles of ischemic preconditioning (n=7), immediately before the aortic cross-clamping. Ischemic preconditioning cycles were determined by somatosensory evoked potentials monitoring. Neurologic evaluation was performed according to the Tarlov score at 72 h of follow-up. The animals were then sacrificed and the spinal cord harvested for histopathology. RESULTS: Aortic pressures before and after the occluded segment were similar in the three groups. Ischemic preconditioning periods corresponded to a mean ischemic time of 3+/-1 min and a mean recovery time of 7+/-2 min. Severe paraplegia was observed in three animals in Control group, in four in group A and in none in group B. Tarlov scores of group B were significantly better in comparison to the Control group (P=0.036). Histopathologic examination showed severe neuronal necrosis in the thoracic and lumbar gray matter in animals who presented paraplegia. CONCLUSIONS: Immediate repetitive ischemic preconditioning based on somatosensory evoked potentials monitoring seems to protect spinal cord during descending aorta cross-clamping, reducing paraplegia incidence.

Animals↗
PubMed2006

Endovascular clamping of porcelain aorta in aortic valve surgery using Foley Catheter.

Unclampable calcified aorta is an uncommon condition that all cardiac surgeons may encounter and performing aortic valve surgery in this condition with a non cross-clamping technique of using Foley Catheter has rarely been reported. Aortic valve surgery invariably becomes a high-risk, challenging procedure to cardiac surgeon or even a contraindication to surgery when the ascending aorta cannot be clamped due to extensive calcification precluding safe dissection and clamping. We describe and recommend a non cross-clamping technique of using Foley Catheter and report it successful use in two patients who underwent aortic valve replacement with "porcelain" unclampable aorta.

Aorta, Thoracic↗
PubMed2004

Major liver resection without clamping: a prospective reappraisal in the era of modern surgical tools.

BACKGROUND: Hemorrhage and transfusions remain the main causes of mortality and morbidity from liver resection. In cases of extended resection, especially performed on diseased liver, ischemia-reperfusion injury related to pedicle clamping may be a significant risk factor of postoperative liver dysfunction. The ideal alternative would be to perform major hepatectomy without clamping and without significant bleeding. STUDY DESIGN: This prospective study aimed to reconsider the risk of major hepatectomy performed without pedicle clamping and under low venous pressure in the light of modern surgical tools. Inclusion criteria were adults requiring a resection of more than three segments on healthy or pathologic livers but not on preoperative documented cirrhosis. RESULTS: Fifty patients, with a mean age of 53 +/- 15 years were included. Twenty-two patients had underlying liver disease. The main indications were colorectal metastases, primary liver tumors, and living donation. Twenty-six right hepatectomies, 17 extended right hepatectomies, and 7 extended left hepatectomies were performed. Unclamping method was successful in 96% of patients on an intention-to-treat basis. Seventy-four percent of patients were not transfused and no patients died. Surgical complication rate was 16% but no complication led to reoperation. Medical complication rate was 20%, including three transient liver dysfunctions. CONCLUSIONS: Major hepatectomy without clamping can be performed safely. The low rate of postoperative liver dysfunction, especially in cases of underlying liver disease, suggests good preservation of the small and diseased remnant liver.

Adult↗
PubMed2006

Immobility response elicited by clamping the neck induces antinociception in a "tonic pain" test in mice.

Clamping the neck followed by body inversion to a supine position in mice elicits an immobility response called immobility by clamping the neck (ICN). The noxious pinch to the scruff of the neck produces antinociception in "phasic pain" models (e.g. tail-flick test). Here, a "tonic pain" model was used to test the antinociception associated with the ICN, and naloxone was used to determine the role of opioids in such antinociception. Mice were injected intraperitoneally with 0.3 mL of 0.4% acetic acid to produce writhing responses that were measured for one hour. ICN was induced every five minutes for one hour. Naloxone (5 mg/kg ip) was injected 10 min before acetic acid administration. There was a control group, sham clamping (SCLA). These mice were handled and restricted every five minutes as in the ICN but without real clamping. The repetitive inductions of ICN were able to reduce the writhing behavior; this antinociception was blocked by the naloxone pretreatment. In the SCLA group antinociception was not observed. These findings indicate that as in the "phasic pain" model, ICN also was able to elicit antinociception in this "tonic pain" model, and such antinociception seems to be mediated by opioids.

Acetic Acid↗
PubMed2006

Clamp loaders and replication initiation.

Clamp loaders are ATP-driven multiprotein machines that couple ATP hydrolysis to the opening and closing of a circular protein ring around DNA. This ring-shaped clamp slides along DNA, and interacts with numerous proteins involved in DNA replication, DNA repair and cell cycle control. Recently determined structures of clamp loader complexes from prokaryotic and eukaryotic sources have revealed exciting new details of how these complex AAA+ machines perform this essential clamp loading function.

Adenosine Triphosphate↗
PubMed2007

High intensity ultrasound clamp for bloodless partial nephrectomy: In vitro and in vivo experiments.

In some patients at risk of disease recurrence of renal cancers, maximum conservation of the kidney is possible through partial nephrectomy. However, bloodless surgery is difficult to achieve. The article describes an ultrasonic clamp, which optimises energy deposition and monitors lesion development with an echo-based technique. Using this novel apparatus, coagulation necroses have been obtained in vitro on substantial thicknesses (23 to 38 mm) over exposure durations ranging from 10 s to 130 s, and with acoustic intensities of less than 15 W/cm(2) per transducer. When used for coagulation purposes, two transducers situated on opposite arms of the clamp are driven, while for monitoring, only one is used. Lesions are monitored in real time by analysing the echo signal returned by the opposite arm of the clamp. The presence of a lesion is evaluated on the basis of energy changes and echo phase as a function of time. Both kidneys of two pigs (30 to 36 mm thick) were treated in vivo with the clamp, and the partial nephrectomies performed proved to be bloodless.

Animals↗
PubMed2006

Open partial nephrectomy with selective renal parenchymal control: a new reliable clamp.

We describe our experience of open partial nephrectomy with a parenchymal clamp, the Reni-Clamp, in 30 patients from January 2002 to May 2005. The mean operative and clamping time was 150 and 27 minutes, respectively, and the blood loss was 150 mL. The Reni-Clamp enabled us to perform partial nephrectomy safely in all cases of polar or external edge renal tumor.

Adult↗