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PubMed1993

Use of neuroanesthesia adjuncts (hyperventilation and mannitol administration) improves neurological outcome after thoracic aortic cross-clamping in dogs.

BACKGROUND AND PURPOSE: Using a canine model of thoracic aortic cross-clamping, we compared the incidence and severity of paraplegia with and without standard neuroanesthesia adjuncts (mannitol administration and deliberate hyperventilation). Better outcome was predicted for animals treated with mannitol and hyperventilation. METHODS: Nineteen dogs (mean +/- SD weight, 21 +/- 3 kg) were anesthetized with methohexital to an isoelectric electroencephalogram. Animals were randomized to group C (control; n = 9) or group M (mannitol administration and deliberate hyperventilation; n = 10). In group C, animals were maintained normocapnic (PaCO2, 38 to 42 mm Hg). In group M, animals were hyperventilated to a PaCO2 of 28 to 32 mm Hg and received mannitol 2 g.kg-1 during surgical preparation, then 1 g.kg-1.h-1 by continuous infusion. The thoracic aorta was cross-clamped for 30 minutes. Systemic hemodynamics, cerebrospinal fluid pressure, and arterial blood gases were measured at (1) baseline, (2) 2 minutes after cross-clamp, (3) 20 minutes after cross-clamp, (4) 5 minutes after cross-clamp release, and (5) 30 minutes after resuscitation. No attempt was made to control the hemodynamic consequences of cross-clamping in either group. With release of the cross-clamp, PaCO2 was not controlled in group C; in group M the minute ventilation was further increased to maintain PaCO2 constant. At precisely 24 hours after cross-clamp the animals were assessed for incidence and severity of paraplegia, using the Tarlov score, by an observer unaware of the experimental protocol. The animals were killed, and the entire spinal cord was removed for histological assessment. Multiple sections of the lumbar spinal cord were processed and stained with hematoxylin and eosin. RESULTS: With application of the cross-clamp, cerebrospinal fluid pressure and central venous pressure increased significantly in both groups. However, in group M the maximal mean cerebrospinal fluid pressure never exceeded baseline values in group C. With cross-clamp release, spinal cord perfusion pressure (distal mean aortic pressure minus mean cerebrospinal fluid pressure) was significantly greater in group M (86 +/- 23 vs 65 +/- 17 mm Hg; P = .0017 between groups). Acid-base balance was better maintained in group M. The incidence and severity of paraplegia were significantly lower in group M (P = .043; Mann-Whitney rank-sums test, two-tailed). In this group 10 of 10 animals could walk and 4 of 10 had complete recovery. In group C 4 of 9 animals were paraplegic. There was a strong negative correlation between the Tarlov score and the ratio of dead to total anterior spinal cord neurons in the lumbar region as assessed by light microscopy (P = .0004; Spearman's rank test). CONCLUSIONS: We conclude that a protocol using standard neuroanesthesia adjuncts (mannitol administration and deliberate hyperventilation) is associated with improved neurological outcome after thoracic aortic cross-clamping of 30 minutes' duration in dogs anesthetized with methohexital.

Anesthesia↗
PubMed2001

Fenoldopam infusion associated with preserving renal function after aortic cross-clamping for aneurysm repair.

BACKGROUND: Cross-clamping of the descending aorta during operative repairs causes sudden, significant reductions in renal function that may persist well beyond arterial clamp release. Commonly used agents, such as dopamine and mannitol, have not consistently affected renal outcome in these high-risk patients. Fenoldopam mesylate is a novel, highly selective dopamine type-1 agonist that preferentially dilates the renal and splanchnic vasculature, but has not been investigated in patients undergoing prolonged aortic clamping for whom adverse renal outcomes should be more likely. METHODS AND RESULTS: Twenty-two adult patients without significant pre-existing renal dysfunction and presenting for elective repairs of abdominal aortic aneurysms were studied. Fenoldopain mesylate was infused after obtaining baseline values ranging from 0.1 to 1.0 microg/kg/min for the first 24 hours postoperatively to maintain mean arterial pressure +/-25% baseline. Serial renal function indices, including creatinine clearance and electrolyte fractional excretions, were measured at baseline, at aortic clamping and unclamping, and post-clamp release, and were estimated through hospital discharge. Creatinine clearance fell during abdominal exploration and clamping, reaching a nadir with clamp removal. Partial recovery occurred by 2 hours after clamp removal, and returned to baseline values by postoperative day 1 and thereafter. Fractional excretions rose rapidly throughout the operative phase. Total fenoldopam dose was directly related to the baseline creatinine clearance; after clamp removal, creatinine clearance was directly related to the mean arterial pressure at the lowest dose of fenoldopam, and inversely related to the mean arterial pressure at clamp release. CONCLUSIONS: In elderly patients with severe vascular disease undergoing aneurysmal repairs, the use of a fenoldopam infusion in this open-label, uncontrolled trial was associated with a relatively rapid return of renal function to baseline values, despite profound decreases during aortic cross-clamping. Further studies will be necessary to investigate how fenoldopam infusions compare with traditional therapies.

Adult↗
PubMed2006

Comparison between 3 aortic clamps for video-assisted cardiac surgery: a histological study in a pig model.

OBJECTIVES: To assess histological traumatic effects of aortic clamps used in video-assisted surgery, an experimental study was undertaken in a pig model, comparing the Portaclamp, Endoclamp, and a metallic clamp. MATERIAL AND METHODS: In 3 groups of 5 pigs each, the descending aorta was exposed through a posterolateral left thoracotomy. External clamps (Portaclamp and metallic clamp) were positioned at the middle of the aorta. Endoclamps were inserted at the top of the descending aorta through a small purse and inflated lower. After 60 minutes of clamping, the clamp was removed and the animal reperfused for 60 minutes. It was then sacrificed and the descending aorta was harvested for blind histological study using hemotoxylin-eosin staining of 4 samples per animal: A, before the clamping spot; B, at the clamping spot; C, after the clamping spot; D, a remote sample as control. RESULTS: In the Portaclamp and metallic clamp groups, there were no lesions of the intima in all aortic samples. In the Endoclamp group, severe lesions of the intima were observed on the clamping spot: endothelium crushing with flattening of cell nucleus (3/5) or endothelium stripping with vanishing of cell nucleus all gathered in 1 point (2/5). Only spongy lesions (clearance between fibers) located on the external third of the media and moderate inflammatory lesions of the adventice were observed with a random distribution in aortic samples without difference between groups. CONCLUSIONS: This study reveals the impressive lesions of the aortic intima due to the Endoclamp. The nonspecific lesions observed in media or adventice may be related to the surgical trauma of the procedure.

Animals↗
PubMedDate not supplied

[Vascular clamping in cirrhotic liver surgery].

Different vascular clamp methods in liver surgery have led to less complications. The aim of this study was to evaluate the results after hepatic resection involving different vascular clamping methods and liver function outcome. Our study examined 46 patients who underwent surgery for liver lesions, developed on cirrhotic and noncirrhotic livers, applying the technique of selective clamping and pedicular clamping. There was one death (1/17; 5.9%) due to postoperative liver failure which occurred in a cirrhotic liver patient who underwent left hepatectomy with pedicular clamping. Complication rate was higher, but not significant (4/7; 57.1%) in the group with selective clamping compared to those with pedicular clamping (3/10; 30%). Hemorrhagic complications were observed in a higher rate among patients with selective clamping (3/7; 42.9%) compared to those with pedicular clamping (1/10; 10%). Selective clamping seems to find major indications in patients with chronic liver disease undergoing minimal hepatic resections. Intermittent pedicular clamping seems to be more effective in regards to blood loss and postoperative hepatic function.

Adult↗
PubMed1975

Voltage clamp simulation.

The voltage clamp experiment on the squid giant axon is successful because of the special characteristics of the preparation: cylindrical shape, large diameter, and so on. The method is much more difficult to apply to small cells and to networks of cells because voltage gradients and unwanted stray impedances are not readily eliminated. Simulation of the voltage clamp experiment is proposed as a method for determining when these factors and the characteristics of the clamp electronics affect the experimental results, for evaluating experimental techniques for improving the quality of the clamp, and as a possible method of learning something about the membrane when no experimental improvement is feasible. The numerical methods for including one spatial variable in the analysis are reviewed briefly. Several examples of voltage clamp simulations are discussed: double sucrose gap clamp of axons, clamp of the giant synapse, single sucrose gap clamp of cardiac muscle bundles, point clamp of the end of a fiber bundle, and the steady-state three-microelectrode clamp of a cable with nonlinear membrane. The results indicate that the quality of a clamp cannot be evaluated from the voltage and current records as commonly measured.

Action Potentials↗
PubMed1989

Results of supraceliac aortic clamping in the difficult elective resection of infrarenal abdominal aortic aneurysm.

We have used clamping of the aorta above the celiac axis (SC) in 30 of 431 elective resections of infrainguinal abdominal aortic aneurysms (AAA) during the past five years as an alternative to a difficult aortic cuff dissection. The results of SC clamping in these 30 patients are compared with the results of 379 routine aneurysm resections with infrarenal (IR) clamping and 22 additional aneurysm resections where the clamp was placed immediately above the renal arteries. These difficult cuff dissections occurred in 12 patients with inflammatory AAA, in 11 patients with juxtarenal AAA, and in seven patients with recurrent or noninfected false AAA of the proximal cuff. Patients with ruptured or suprarenal aneurysms and those undergoing combined operation for a visceral ischemic syndrome and an aneurysm were excluded from this study. Patients with SC clamping had similar operative mortality rates, comparable renal function, and frequency of cardiac events as patients with IR clamping. Blood loss was slightly higher in the SC group (p = 0.07) and serum aspartate amino transferase (AST) levels were three times higher than in the IR group; however, this was of no clinical significance. In contrast, those 22 patients whose aortas were clamped immediately above the renal arteries (AR) had higher perioperative mortality rates (2% IR, 3% SC vs 32% AR) and a higher incidence of kidney failure requiring dialysis (1% IR, 3% SC vs 23% AR). The mean values of serum creatinine and blood urea nitrogen were also significantly higher in the AR group when compared with both the IR and the SC groups (IR: 25 and 1.5 mg/dl, respectively; SC: 27 and 1.8 mg/dl; AR: 41 and 3.5 mg/dl). The single most important risk factor accounting for the differences between clamping above the celiac artery and clamping above the renal arteries was the presence of atherosclerotic debris in the nonaneurysmal, juxtarenal aortic segment. Clamping the aorta with juxtarenal atherosclerosis caused either atheroembolization to kidneys, legs, and intestine or injury to the aorta, renal arteries, or both; it was the cause of morbidity in all five cases of kidney failure requiring dialysis and accounted for all seven of the deaths in the AR group. SC clamping does not add risk to the patient undergoing resection of an infrarenal AAA and is the preferred method of achieving proximal control of the infrarenal aorta when a a hazardous cuff dissection is likely.(ABSTRACT TRUNCATED AT 400 WORDS)

Aorta, Abdominal↗
PubMed1986

The effect of renin-angiotensin system blockade on visceral blood flow during and after thoracic aortic cross-clamping.

Surgical procedures necessitating clamping of the thoracic aorta are associated with a high incidence of postoperative renal dysfunction. Plasma renin activity is elevated during and after thoracic aortic occlusion in animals. The pathophysiology of the renal dysfunction may involve the renin-angiotensin system. Blockade of the renin-angiotensin system was studied in a canine model during occlusion of the thoracic aorta. Saralasin, a competitive blocker of angiotensin II, and the converting enzyme inhibitor MK422 were studied. Sixteen animals were separated into three treatment groups: control (five animals), saralasin (five), and MK422 (six). All dogs underwent clamping of the thoracic aorta for 60 minutes. In control animals, plasma renin activity increased from 0.16 +/- 0.04 to 6.41 +/- 1.57 ng/ml/hr at 30 minutes after thoracic aortic occlusion (p less than 0.05). Thirty minutes after cross-clamp release, plasma renin activity remained 10 times greater than baseline, 1.47 +/- 0.20 ng/ml/hr (p less than 0.05). Renal blood flow was measured with 15 micron microspheres before, during, and after thoracic clamping. In control animals, renal cortical blood flow decreased during cross-clamping and remained below baseline after clamp release: baseline, 7.05 +/- 0.98 ml/gm/min (standard error of the mean); 30 min after clamp release, 3.77 +/- 0.43 ml/gm/min (standard error of the mean) (p less than 0.05). In the MK422 group, renal cortical blood flows returned to baseline after cross-clamp release: baseline, 6.38 +/- 0.49 ml/gm/min; 30 minutes after clamp release, 7.30 +/- 1.6 ml/gm/min. Infusion of MK422 after placement of the thoracic aortic cross-clamp resulted in normal renal blood flow after clamp release. This protective effect was not seen with saralasin. The resumption of normal renal cortical blood flow after the administration of the converting enzyme inhibitor MK422 suggests that elevated plasma renin activity may contribute to renal dysfunction after thoracic aortic occlusion.

Angiotensin II↗
PubMed1982

Arteriographic and ultrasonic evaluation of vascular clamp injuries using an in vitro human experimental model.

A new experimental model was developed for dynamic in vitro evaluation of clamp effects in normal and atherosclerotic human arteries. Five normal and 25 atherosclerotic arteries obtained at autopsy were perfused by a pulsatile blood pump. Five vascular clamps--DeBakey, Satinsky, Fogarty, bulldog and Potts--were applied separately to 150 arterial segments, 30 each. The arterial segments were examined by single exposure arteriography and real time ultrasonography. The arteries were opened longitudinally and examined for traumatic lesions and atherosclerotic plaques. Except for a single intimal tear, there were no lesions produced by the clamps applied to normal arteries. In atherosclerotic arteries, the number of traumatic lesions, intimal tears and flaps, was comparable for all five clamps except the bulldog clamp which caused no intimal flaps. Intimal tears and flaps were observed in 14 and 26 per cent of all atherosclerotic vessels, respectively. The occurrence of clamp trauma in atherosclerotic arteries was independent of the age, sex and direct clamp application to plaques. Sensitivity of intimal tears by arteriography and ultrasonography was comparable low. Intimal flap sensitivity and accuracy of ultrasonography were greater than that of arteriography, p less than 0.01. It is concluded that the occurrence of important trauma by vascular clamps in atherosclerotic arteries is high and occurs whether or not discrete plaques are clamped. Clamp trauma is minimal in normal arteries. Imaging ultrasonography is superior to arteriography in detecting intimal flaps and can demonstrate the majority of intimal flaps produced by vascular clamps.

Adolescent↗
PubMed1996

Clamping stiffness and its influence on load distribution between paired internal spinal fixation devices.

The load distribution between two internal spinal fixation devices depends, besides other factors, on their stiffness. The stiffness ranges were determined experimentally for the clamps of the AO internal fixator with lateral nut and with posterior nut as well as for the clamps of the SOCON fixator. The stiffness of eight devices each differed by a factor of 3.1 for the clamp with lateral nut, by a factor of 1.5 for the clamp with posterior nut, and by a factor of 1.4 for the clamp of the SOCON fixator. For the AO clamp with lateral nut, the influence of the nut-tightening torque on the stiffness was determined. Using instrumented internal spinal fixation devices mounted to plastic vertebrae and simulating a corpectomy, the load distribution between the implants was measured for different tightening torques. It could be shown that, for the AO internal fixator whose clamps have a lateral nut, a nut-tightening torque > 5 Nm has only a negligible influence on load-sharing between the implants. Tooth damage occurs when the teeth of the clamp body and clamping jaw of the clamp with lateral nut do not gear together exactly, which leads to changes in the clamping stiffness and load-sharing between the two implants.

Humans↗
PubMed2000

The hyperinsulinaemic-euglycaemic glucose clamp: reproducibility and metabolic effects of prolonged insulin infusion in healthy subjects.

To examine the reproducibility of the hyperinsulinaemic-euglycaemic clamp technique at mid-physiological hyperinsulinaemia, seven healthy subjects ¿age 50 (25, 59) years [median (range)], body mass index 23.1 (20.8, 25.5) kg.m(-2)¿ were investigated with three 2 h hyperinsulinaemic (60 micromol.l(-1))-euglycaemic (4.5 mmol.l(-1)) clamps performed 48 h and 14 days apart respectively. The third clamp was prolonged to 8 h in order to examine effects on glucose disposal during prolonged clamps. The glucose infusion rates (GIRs) during the three 2 h clamps were 7.41 (4.28, 10.96), 7.26 (5.38, 11. 02) and 6.63 (4.42, 10.3) mg.kg(-1).min(-1), with a median intra-individual coefficient of variation of 5.8 (2.6, 22) %. During the 8 h clamp a highly variable gradual increase in GIR was observed, reaching a plateau between 4 and 5 h at 32 (5, 101) % above the GIR between 1 and 2 h (P<0.05). This increase was correlated inversely with the GIR between 1 and 2 h (r=-0.82; P<0.05), and directly with age (r=0.86; P<0.05). Carbohydrate oxidation measured by indirect calorimetry was stable during the repeated 2 h clamps and the 8 h clamp. Endogenous glucose production measured by infusion of [6, 6-(2)H(2)]glucose was suppressed during the 8 h clamp. The 2 h hyperinsulinaemic-euglycaemic clamp is reproducible at a mid-physiological range of hyperinsulinaemia. If prolonged, it results in a delayed increase in non-oxidative glucose disposal, which is most pronounced in subjects with low insulin sensitivity. The findings underline the importance of selecting age-matched controls in studies of insulin resistance.

Adult↗
PubMed1996

Computer simulations of voltage clamping retinal ganglion cells through whole-cell electrodes in the soma.

1. Computer simulations of voltage-clamp experiments in retinal ganglion cells were implemented to better understand the insights that can be obtained with this physiological approach. 2. Simulation studies of voltage clamping were based on the contemporary approach of using whole-cell recordings with low resistance electrodes attached to the soma. Realistic ganglion cell morphologies were provided by cell staining experiments in the mudpuppy retina; selected cells included small-, medium-, and large-field neurons whose morphologies were entered into a computer through a neuron tracing program. 3. Values for the specific membrane resistance (Rm) varied from 5,000 to 100,000 omega/cm2 to conform to the range of Rm values obtained with intracellular sharp electrodes and whole-cell recordings. 4. Synaptic input currents were simulated by injecting current with and without an underlying conductance change into different regions of the dendritic tree. The time-variant waveform of the current included a combined transient and sustained component similar to the waveform of ON-bipolar activation. 5. Simulations were base on 1) intact structures, which included the soma and the entire dendritic tree, and 2) a more limited cell geometry that included representation of the soma, but only part of the dendritic tree, to represent the restricted morphology that might be rendered after cutting the retina into 150-microns cross sections for retinal slice experiments. 6. The results of this study indicate that voltage clamping from the soma, with optimal, low resistance electrodes and series resistance compensation, provides an error-free voltage clamp for slow signals that are generated within a small electrotonic distance from the soma (approximately 0.1 lambda). 7. The ideal voltage-clamp conditions are optimized when synaptic conductances are small and nonlinear membrane elements are minimally activated: small-field neurons best approximate these conditions, but clamping errors are evident in these cells when more distal branches are activated. The degree of error in voltage clamping was much greater when medium-and large-field neurons were evaluated. 8. It was not possible to clamp action potentials (nonpropagating) even when they were generated near the soma in any of the three model cells examined. 9. Experimental paradigms were developed to demonstrate that inadequate voltage clamping can lead to errors in the interpretation of experimental data when relevant variables are not taken into consideration. Suggestions are made for determining and optimizing favorable clamp conditions.

Action Potentials↗
PubMed2002

Indices of insulin action, disposal, and secretion derived from fasting samples and clamps in normal glucose-tolerant black and white children.

OBJECTIVE: To validate fasting indices of insulin sensitivity and secretion in a diverse pediatric population against gold standard estimates from euglycemic and hyperglycemic clamps. RESEARCH DESIGN AND METHODS: A total of 31 children (mean BMI 25.1 +/- 4.9 kg/m(2), mean age 8.7 +/- 1.4 years, 15 girls and 16 boys, 12 black and 19 white) underwent euglycemic and hyperglycemic clamps 2-6 weeks apart to derive insulin sensitivity indices (SI (Eug clamp) and SI (Hyper clamp)). Fasting samples were used to derive the homeostasis model assessment of insulin resistance index (HOMA-IR), HOMA of percent beta-cell function (HOMA-B%), quantitative insulin sensitivity check index (QUICKI), insulinogenic index, antilipolytic insulin sensitivity index (ISI-FFA), and C-peptide-to-insulin ratio. RESULTS: The QUICKI correlated best with SI (Eug clamp) (r = 0.69, P < 0.05) and had greater correlations to SI (Eug clamp) than did either SI (Hyper clamp) (r = 0.45, P < 0.05) or the HOMA-IR (r = -0.51, P < 0.05). Both fasting insulin and the insulinogenic index correlated well with first- and steady-phase insulin secretion (r's from 0.79 to 0.86, P < 0.05). HOMA-B% was not as highly correlated (r = 0.69-0.72, P < 0.05). Fasting C-peptide-to-insulin ratio was not significantly correlated with clamp-derived metabolic clearance rate of insulin. ISI-FFA was not correlated with the degree of free fatty acid suppression obtained from the clamps. CONCLUSIONS: The QUICKI, fasting insulin, and the insulinogenic index all closely correlate with corresponding clamp-derived indices of insulin sensitivity and secretion in this diverse pediatric cohort. These results, if replicated in similarly diverse populations, suggest that estimates based on fasting samples can be used to rank order insulin secretion and sensitivity in pediatric cohorts.

Black or African American↗
PubMed2004

Early versus delayed umbilical cord clamping in preterm infants.

BACKGROUND: Optimal timing for clamping of the umbilical cord at birth is unclear. Early clamping allows for immediate resuscitation of the newborn. Delaying clamping may facilitate transfusion of blood between the placenta and the baby. OBJECTIVES: To delineate the short- and long-term effects for infants born at less than 37 completed weeks' gestation, and their mothers, of early compared to delayed clamping of the umbilical cord at birth. SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group trials register (2 February 2004), the Cochrane Neonatal Group trials register (2 February 2004), the Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 1, 2004), PubMed (1966 to 2 February 2004) and EMBASE (1974 to 2 February 2004). SELECTION CRITERIA: Randomized controlled trials comparing early with delayed (30 seconds or more) clamping of the umbilical cord for infants born before 37 completed weeks' gestation. DATA COLLECTION AND ANALYSIS: Three reviewers assessed eligibility and trial quality. MAIN RESULTS: Seven studies (297 infants) were eligible for inclusion. The maximum delay in cord clamping was 120 seconds. Delayed cord clamping was associated with a higher hematocrit four hours after birth (four trials, 134 infants; weighted mean difference 5.31, 95% confidence interval (CI) 3.42 to 7.19), fewer transfusions for anaemia (three trials, 111 infants; relative risk (RR) 2.01, 95% CI 1.24 to 3.27) or low blood pressure (two trials, 58 infants; RR 2.58, 95% CI 1.17 to 5.67) and less intraventricular haemorrhage (five trials, 225 infants; RR 1.74, 95% CI 1.08 to 2.81) than early clamping. REVIEWERS' CONCLUSIONS: Delaying cord clamping by 30 to 120 seconds, rather than early clamping, seems to be associated with less need for transfusion and less intraventricular haemorrhage. There are no clear differences in other outcomes.

Blood Transfusion↗
PubMed1977

Influences of ulcerogenic stimulations in the stomach with the clamping ulcers in rats.

Ulcerogenic stimulations such as histamine and restraint water immersion stress were given to rats after the gastric ulcers were made by the clamping method. Development of the stress and histamine ulcers were distinctly inhibited after the clamping ulcers were made, and this inhibition reached a maximum at the 7th clamping ulcer day and lowered gradually thereafter. In control rats, the stress and histamine ulcers usually develop in the lesser curvature, but in animals with the clamping ulcers they develop in the greater curvature where the clamping ulcer was made. The histological changes of the stress ulcers in the stomach with the clamping ulcer were slighter compared with those of the control (without clamping ulcers) rats. Furthermore, the relationships between the development of the stress ulcers and the changes of the uronic acid content in the stomach were observed. The uronic acid content increased after the clamping ulcer was made and reached a maximum at the 7th clamping ulcer day. Thereafter it began to decrease and returned to the normal level. From the results of the studies, it was strongly suggested that the mechanism of inhibition to development of the stress ulcers might be attributed to an increase of acid mucopolysaccharide in the gastric wall after the clamping ulcer was induced.

Animals↗
PubMed2003

Examination of the role of the clamp-loader and ATP hydrolysis in the formation of the bacteriophage T4 polymerase holoenzyme.

Transient kinetic analyses further support the role of the clamp-loader in bacteriophage T4 as a catalyst which loads the clamp onto DNA through the sequential hydrolysis of two molecules of ATP before and after addition of DNA. Additional rapid-quench and pulse-chase experiments have documented this stoichiometry. The events of ATP hydrolysis have been related to the opening/closing of the clamp protein through fluorescence resonance energy transfer (FRET). In the absence of a hydrolysable form of ATP, the distance across the subunit interface of the clamp does not increase as measured by intramolecular FRET, suggesting gp45 cannot be loaded onto DNA. Therefore, ATP hydrolysis by the clamp-loader appears to open the clamp wide enough to encircle DNA easily. Two additional molecules of ATP then are hydrolyzed to close the clamp onto DNA. The presence of an intermolecular FRET signal indicated that the dissociation of the clamp-loader from this complex occurred after guiding the polymerase onto the correct face of the clamp bound to DNA. The final holoenzyme complex consists of the clamp, DNA, and the polymerase. Although this sequential assembly mechanism can be generally applied to most other replication systems studied to date, the specifics of ATP utilization seem to vary across replication systems.

Adenosine Triphosphate↗
PubMed2003

The Cutler-Beard clamp for lid reconstruction.

PURPOSE: To analyze the use of the Cutler-Beard transmarginal rotation entropion clamp (Karl Ilg & Co., St. Charles, IL) in patients undergoing the Cutler-Beard procedure for repair of eyelid defects after tumor excision or trauma. DESIGN: Prospective, noncomparative case series. PARTICIPANTS: Twenty-five patients undergoing the Cutler-Beard procedure. RESULTS: The Cutler-Beard clamp (Karl Ilg & Co., St. Charles, IL) helps avoid the problems of a commonly used chalazion clamp. The clamp allows a skin orbicularis muscle incision to be combined with a conjunctival tarsal incision without the need to remove the clamp. It is also helpful in creating each of these incisions 4 mm from the eyelid margin to spare the marginal artery, which, if injured, could lead to loss of the eyelid margin. The clamp blades have multiple teeth to stabilize the eyelid and avoid slippage of the clamp. MAIN OUTCOME MEASURES: The incidence of intraoperative or postoperative complications. CONCLUSIONS: The transmarginal rotation clamp or Cutler-Beard clamp allows for the creation of a precise incision 4 mm from the eyelid margin with a high probability of avoiding injury to the marginal artery and is superior to traditional chalazion clamps.

Eyelids↗
PubMed1999

The internal workings of a DNA polymerase clamp-loading machine.

Replicative DNA polymerases are multiprotein machines that are tethered to DNA during chain extension by sliding clamp proteins. The clamps are designed to encircle DNA completely, and they are manipulated rapidly onto DNA by the ATP-dependent activity of a clamp loader. We outline the detailed mechanism of gamma complex, a five-protein clamp loader that is part of the Escherichia coli replicase, DNA polymerase III holoenzyme. The gamma complex uses ATP to open the beta clamp and assemble it onto DNA. Surprisingly, ATP is not needed for gamma complex to crack open the beta clamp. The function of ATP is to regulate the activity of one subunit, delta, which opens the clamp simply by binding to it. The delta' subunit acts as a modulator of the interaction between delta and beta. On binding ATP, the gamma complex is activated such that the delta' subunit permits delta to bind beta and crack open the ring at one interface. The clamp loader-open clamp protein complex is now ready for an encounter with primed DNA to complete assembly of the clamp around DNA. Interaction with DNA stimulates ATP hydrolysis which ejects the gamma complex from DNA, leaving the ring to close around the duplex.

Adenosine Triphosphate↗
PubMedDate not supplied

Biomechanical evaluation of a crimp clamp system for loop fixation of monofilament nylon leader material used for stabilization of the canine stifle joint.

OBJECTIVE: To test a crimp clamp system designed to secure monofilament nylon leader (MNL) material commonly used as lateral fabellotibial sutures (LFS) in extra-articular stabilization of the canine stifle joint. STUDY DESIGN: In vitro biomechanical tests of MNL loops secured with either the crimp clamp system or knots were performed. Suture loops (n = 94) were created from 27.3 kg tensile strength MNL and fastened with knots or crimp clamps. Tests were conducted on steam-sterilized, ethylene-oxide-sterilized, and nonsterilized MNL sutures. Loops were evaluated in single load tests and cycled tests. Values for load to failure, initial loop tension, loop elongation, mode of failure, and point of failure were determined. RESULTS: Crimp-clamped loops were superior to knotted loops in all parameters tested in both cycled and noncycled tests. Loop failure generally occurred by breaking within 3 mm of the fixation in both clamped and knotted tests. Loop elongation after cycling was greater in the knotted loops compared with clamped loops (P < .001). Load to failure was greater in clamped tests than in knotted tests (P < .001), regardless of sterilization technique used. Significantly higher initial loop tension could be achieved with the clamp system compared with knot fixation (P < .001). CONCLUSIONS: The crimp clamp system provides superior in vitro loop fixation characteristics compared with knot fixation in 27.3 kg test MNL. CLINICAL RELEVANCE: Based on the results of biomechanical testing and the known biocompatibility of the system's implant components, clinical trials using the crimp clamp system are warranted.

Animals↗