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PubMed1989

[Prevention of spinal cord ischemia after cross-clamping of the thoracic aorta--monitoring of spinal cord perfusion pressure and somatosensory evoked potentials].

The pressure difference between the mean distal aortic pressure (MDAP) and the cerebrospinal fluid pressure (CSFP), defined as the spinal cord perfusion pressure (SCPP), as well as somatosensory evoked potentials (SEP) were monitored intraoperatively to detect and prevent intraoperative spinal cord ischemia in 24 patients who required cross-clamping of the descending thoracic aorta. A temporary axillo-femoral shunt, utilizing a 10 mm woven Dacron tube graft, was employed in 10 patients and partial cardiopulmonary bypass was employed in fourteen. Ischemic SEP changes were seen in six patients. Two patients, whose SCPPs were 32 and 35 mmHg, showed a complete loss of SEP and subsequently developed paraplegia. In the other four cases, increase of the MDAP and/or withdrawal of cerebrospinal fluid were performed to increase the SCPP to more than 60 mmHg when ischemic SEP changes occurred. The SEP gradually recovered in two of these cases. The ischemic SEP changes seen in one patient, who had the longest aortic cross-clamping time, (175 minutes) returned to normal immediately after unclamping. In another case, who had a thoracoabdominal aortic aneurysm, the intercostal arteries were reimplanted since the ischemic SEP changes did not revert. These four patients recovered without any neurological deficit. In the other 18 cases without ischemic SEP change, SCPP was kept at more than 40 mmHg during aortic cross-clamping. We conclude that the SCPP should be maintained at more than 40 mmHg during aortic occlusion, and increased to more than 60 mmHg when ischemic SEP changes occur, by increasing MDAP and/or withdrawing cerebrospinal fluid in order to prevent postoperative paraplegia.

Adult↗

PubMedDate not supplied

Glucose disposal in obese non-diabetic and diabetic type II patients. A study by indirect calorimetry and euglycemic insulin clamp.

Insulin resistance is a characteristic finding in obesity and in non insulin dependent (Type II) diabetes mellitus. However, the interaction between diabetes and obesity has been poorly characterized and the metabolic disturbances contributing to the defect in insulin-mediated glucose uptake have not been defined. To examine these questions euglycemic and hyperinsulinemic clamp studies (40 mU/m2/min) were performed in 10 control non-obese subjects, 10 non diabetic obese subjects, 8 normal weight Type II diabetics, and 12 obese Type II diabetics. During the insulin clamp study total body glucose uptake in the obese non diabetics (157 +/- 18 mg/m2.min, p less than 0.01), the normal weight diabetics (159 +/- 21, p less than 0.01) and the obese diabetics (125 +/- 11, p less than 0.001) was significantly reduced compared to the non-obese non diabetic control group (249 +/- 22 mg/m2.min). The impairment in total body glucose uptake was the result mainly of a defect in non-oxidative glucose disposal. Indeed non-oxidative glucose disposal was blunted by 50% in the obese groups (p less than 0.01), somewhat less significantly in the non-obese diabetic group (p less than 0.05) but more when obesity and diabetes mellitus were combined (p less than 0.001). Total glucose oxidation was significantly diminished (p less than 0.01) in both diabetic groups but not in the obese non diabetic group when compared to lean control. A significant inverse correlation between the fasting free fatty acids levels and total glucose uptake (r = -0.453, p less than 0.001) and total glucose oxidation (r = -0.446, p less than 0.001) during the clamp was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1988

Cross-clamping the thoracic aorta. Effect on intracranial pressure.

A clinical case is reported indicating that intracranial pressure (ICP) rises with cross-clamping of the thoracic aorta (CCTA) in humans and does not fall if arterial blood pressure (BP) is lowered by nitroprusside. Hantler and Knight (Anesthesiology 1982;56:146-147) also reported a similar case. We investigated this phenomenon prospectively, measuring ICP, aortic arch BP, and right atrial pressure in 10 halothane-anesthetized New Zealand White rabbits ventilated to pH 7.45-7.55. When CCTA was applied, BP and ICP rose significantly (by paired t test, p less than or equal to 0.01), although right atrial pressure did not change. After removal of the cross-clamp and a period of stabilization, BP was elevated to the same level as that attained with CCTA with phenylephrine. Although phenylephrine induced BP elevation, neither ICP nor CVP changed significantly from control or recovery measurements. In six animals, after applying CCTA, BP was lowered to control levels with nitroprusside (in combination with CCTA). Nitroprusside was effective in lowering BP to control level, but ICP remained elevated as long as the cross-clamping continued. With no rise in central venous pressure, venous engorgement is an unlikely mechanism for ICP elevation. Time constants of ICP change are too short to invoke increased cerebral spinal fluid production or decreased absorption. BP does not rise above the expected range for autoregulation, but recruitment of either arterial capacitance vessels or of a neuroreflex arc, or the effects of cord ischemia disrupting cerebral autoregulation may be the cause of an acute increase in cerebral blood volume.

Animals↗

PubMed1987

Voltage-clamp of cut-end skeletal muscle fibre: a diffusion experiment.

Membrane potential and current were studied in cut end fibres of frog skeletal muscle under current and voltage clamp conditions, by the double sucrose gap technique. Similar action potentials were recorded under current clamp conditions with either the microelectrode or the double sucrose gap techniques. Under voltage clamp conditions, the control of the membrane potential was maintained adequately. The early current was sensitive to both TTX and external Na concentration suggesting that the current was carried by Na ions. Sodium current (INa) was subsequently analysed using the Hodgkin-Huxley formulae. INa half-activation and inactivation occurred at -34 mV and -60 mV, respectively. Na-rich solution applied internally by diffusion through cut ends produced a reduction of INa associated with a shift of the sodium current reversal potential (VNa) towards more negative membrane potentials. This suggested that the sodium electromotive force was reduced by the increase in internal Na content of the fibre. Iodate applied externally changed neither the activation nor the inactivation time courses of INa, but reduced the peak current. Conversely, internally applied by diffusion from the cut end of skeletal muscle fibre, iodate slowed down the time course of INa inactivation and decreased the current peak. In conclusion, the double sucrose gap technique adapted to cut end frog skeletal muscle fibre allows a satisfactory analysis of INa.

Action Potentials↗

PubMed1986

Plasma calcitonin response to a calcium clamp in endogenous Cushing's syndrome.

Basal and calcium (Ca) stimulated plasma CT concentrations have been studied in 6 premenopausal females with Cushing's disease and 3 premenopausal females with Cushing's syndrome due to an adrenocortical adenoma. Thirteen healthy premenopausal females served as a reference group. A standardized Ca-stimulus was applied to all subjects by means of the 'calcium clamp' technique. Plasma immunoreactive CT (iCT) was determined by RIA using a carboxyl terminal antiserum with 8 pg-eq/ml as detection limit. The patients with Cushing's disease had normal basal plasma iCT levels and their iCT response during the 2 h calcium clamp was within the reference range in 5 out of 6 patients, the remaining patient showed a slightly exaggerated response. The patients with adrenal adenoma had elevated plasma iCT levels in the basal state but a normal response during the calcium clamp. It is therefore less likely that the bone resorption often seen in Cushing's syndrome is due to CT deficiency.

Adenoma↗

PubMed1985

St. Thomas' Hospital cardioplegia for myocardial preservation during prolonged aortic cross-clamping.

The effectiveness of St. Thomas' Hospital cardioplegia for myocardial preservation during prolonged aortic cross-clamping was analyzed in a clinical series of 100 consecutive cardiac surgical patients identified as having aortic cross-clamp times greater than 120 minutes. Hospital mortality from all causes was 8%, but only one of these 8 patients succumbed from immediate primary failure of the myocardial preservation protocol. Severe but reversible low cardiac output syndrome occurred in 5 patients, and in 4 of them there had obviously been a primary failure in cardiac protection. Peri-operative, clinically "silent" myocardial infarction could be demonstrated in retrospect by electrocardiographic criteria in 3 other patients. Post-operative complications occurred in 26 patients, many of them having several complications at the same time. Paired left ventricular and right ventricular prebypass and post-bypass biopsies processed for cytochemical and biophysical investigation were available from one third of the patients. Only 2 cases showed a severe deterioration. There was lack of correlation between the duration of aortic occlusion and operative mortality rate, incidence of peri-operative infarction, and occurrence of low cardiac output syndrome post-operatively. The results thus indicate that St. Thomas' Hospital cardioplegia is a very effective means of myocardial protection during prolonged periods of aortic cross-clamping.

Adolescent↗

PubMed1979

Cross clamping the lower abdominal aorta during vascular surgery.

The effect of cross clamping the lower abdominal aorta on systemic blood pressure and right and left heart pressure was studied in 17 patients requiring surgical treatment for abdominal aortic aneurysm or aortic occlusive disease, in neuroleptanaesthesia. After cross clamping the systemic systolic blood pressure rose 24 mmHg (p is less than 0.01) and the systemic diastolic blood pressure 8 mmHg (p is less than 0.01). There was no influence of cross clamping on the right (CVP) and and left (PCWP) heart filling pressure even in patients with preexistent readings beyond the normal range.

Aged↗

PubMed1979

Enhancing effect of clamping of the portal vein on the effectiveness of antitumor agents against lymph node metastasis.

An experimental study was made on the suppressive effect on lymph node metastasis of an antitumor agent administered during the clamping of the portal vein. When mitomyaneously clamped, a higher concentration of the drug was detected in the mesenteric lymph nodes compared to the conventional intravenous administration. The growth of mesenteric lymph node metastasis was markedly suppressed by the combined use of mitomycin-C and portal vein clamping. These results suggest that the procedure applied in the present study directs a high concentration of antitumor preparations to the lymph nodes in the portal vein region, and thus is a good method for the suppression of lymph node metastasis.

Animals↗

PubMed1977

Response of delayed (K+) channels to the time-dependent clamping function in squid giant axon. I. Ascending ramps.

Squid giant axons are voltage-clamped with ascending potential ramps whose slopes range from 0.5 mV/msec to 60 mV/msec and delayed (K+) currents are observed. The parametric current-voltage curves exhibit a delay period of minimal current followed by a rapid increase of current toward a final steady state. Both the initial delay and the slope of the subsequent rising phase increase with increasing ramp slope. When the Hodgkin-Huxley equations are used to generate theoretical current-voltage curves, the sharp difference between the delay and rising phases is muted and the ramp slope must be increased to produce an adequate representation of the data. A muted biphasic response is also observed when the current-voltage curves are generated using modified Hodgkin-Huxley parameters and a correction for K+ accumulation in the periaxonal space. These modified equations provide an accurate fit for step-potential clamp current data. Since the ramp experiments include all relevant clamping potentials, the experiments provide a sensitive test for kinetic models of K+ on flow in the delayed (K+) channels of squid giant axon.

Animals↗

PubMed1981

Voltage clamp analysis of inhibitory synaptic action in crayfish stretch receptor neurons.

Abdominal stretch receptor neurons of Procambarus clarkii were voltage clamped with two microelectrodes, and the synaptic currents set up by stimulating the inhibitory axons, or by rapid bath application of gamma-aminobutyric acid (GABA), were recorded. The inhibitory postsynaptic current (IPSC) decay was exponential, the time constant of decay being increased by membrane depolarization. The IPSC decay was prolonged by diphenylhydantoin, whereas the IPSC amplitude was depressed by picrotoxin. It is suggested that these effects may reflect slowing of the channel closing and opening rates, respectively. Step clamps applied in the presence of GABA yield currents that show inactivation in the 100 ms time range. This inactivation was shown to reflect chloride movement across the membrane. Step clamp data were used to construct dose-response curves. Diphenylhydantoin shifts the dose-response curve to the left with little change in the maximum response. Picrotoxin shifts the curve to the right with a small reduction in the maximum response. These effects are consistent with the postulated effects on channel opening and closing rates, if GABA normally opens a large portion of the channels. Suitable combinations of picrotoxin and diphenylhydantoin acting together leave the dose-response curve unmodified, as predicted.

Animals↗

PubMed1984

Use of the Satinsky clamp for excision of anterior tongue lesions.

The use of Satinsky atraumatic vascular clamps in the resection of lesions of the tongue is described. This technique provides for extirpation of tongue lesions in a hemostatically controlled, dry operative field. The application of these clamps does not appear to alter significantly the histopathologic findings at the resected tumor margins, as is found with extensive dissection using electrocautery. In addition, the clamps provide excellent control of the unresected tongue to allow optimal exposure while reapproximating the wound edges.

Constriction↗

PubMed1984

Acid-base equilibrium in umbilical cord blood and time of cord clamping.

The present study was undertaken to determine the influence of the time interval between birth and the clamping of the umbilical cord on the acid-base balance of the newborn. At 30 seconds after birth, arterial blood from the unclamped cord showed a distinct decrease in pH and an increase in PCO2 and base deficit. These changes were not observed in the venous cord blood. The arterial blood changes continue during the first minute following delivery. When the cord is clamped immediately after birth, acid-base equilibrium in arterial and venous blood at 60 seconds after birth oscillates around the values obtained at zero time. When acid-base equilibrium of arterial cord blood is used as a parameter of neonatal well-being, immediate clamping seems mandatory.

Acid-Base Equilibrium↗

PubMed1984

[Influence of pedicle clamping in partial hepatic resection with the Nd YAG laser. Comparative study in a series of 15 pigs].

Liver resection is performed in 15 pigs by means of low divergent Nd YAG laser, the hepatic pedicle being clamped and not. Clamping does not modify the efficiency of laser hemostasis during resection but increases the thickness of the ischemic layer underlying the cut liver edge. The coagulation necrosis and the edematous layer are more thickened. Migration of inflammatory cells and young fibrosis present at day 3 are gaining ground until day 15. During the same period, biliary neoductules and nodules of hepatic regeneration appear. Hepatic inflow being conserved, these reactions are delayed and less intensive. The hyperthermia, the inflammatory cellular reaction and the deepness of parenchymal damages induces by pedicle clamping are suitable for antitumoral surgery. Cooling effects of hepatic inflow are better for traumatic surgery.

Animals↗

PubMedDate not supplied

Myocardial protection in coronary artery bypass surgery. A study comparing cold cardioplegia and intermittent aortic cross clamping.

Twenty patients having elective coronary artery bypass surgery were randomized for myocardial protection during cardiopulmonary bypass with cold cardioplegia and topical deep hypothermia with the Bretschneider solution in one group and intermittent aortic cross clamping at 30 degrees C in another group. The cardioplegic group showed more consistent results with lower CK-MB elevations both in terms of peak values and areas under the time-enzyme activity curves, although no statistical significance was obtained. There were significantly more infarct suspect time-enzyme activity curves in the intermittent cross clamping group (4 vs. O), and therefore, cold cardioplegia is advocated in preference to intermittent cross clamping in coronary artery bypass surgery.

Aorta↗

PubMedDate not supplied

Single clamp technique of Blalock and Taussig's operation.

Subclavian-pulmonary artery shunt is an accepted palliative procedure for severely cyanosed children and is usually performed, opposite to the side of the aortic arch, with a two clamp technique. Same anastomosis, on the side of the aortic arch, with a "Single clamp technique", has been tried on a series of 25 cases with less morbidity, no mortality and better functional results. This technique provides good approximation of the vessels with no tension, twisting or tearing at the anastomotic site and the extra length attained, to apply a single clamp, avoids kinking of the subclavian artery at its origin.

Heart Defects, Congenital↗

PubMed1981

[Clamping of the thoracic aorta in a hypertensive patient with coronary disease. An indication of sodium nitroprusside (author's transl)].

In patients with cardiac failure, coronary disease or arterial hypertension, clamping of the aorta results in increased filling pressure of the left ventricle which may produce or increase subendocardial ischaemia with consequent aggravation of the ventricular insufficiency. And the higher the clamping the greater the risk. This vicious circle can be broken by sodium nitroprusside, which has potent and reversible vasodilator properties. The drug is indicated whenever the left ventricular filling pressure rises above 5 mmHg. These considerations are illustrated by the descriptions of a case where sodium nitroprusside ensured blood circulation in the lower limbs and intra-abdominal organs after clamping of the aorta above the coeliac artery in a high risk cardiac patient.

Aorta, Thoracic↗

PubMed1978

Response of delayed (K+) channels to the time-dependent clamping functions in squid giant axon. II. Descending ramps, hyperbolae, and exponentials.

Squid giant axons are voltage-clamped with decaying ramp, hyperbolic, and exponential potential functions to determine an input potential function that generates parametric current density vs. membrane potential (I-V) plots best approximating the I-V curves generated from the steady state delayed (K+) current densities at a series of step clamp potentials. The optimum potential function must produce consistent I-V plots over an extended range of decay periods. A five-millisecond step clamp at the largest depolarizing potential in the experiment insures identical initial conditions for all potential functions. Although all parametric I-V curves are sensitive to K+ accumulation in the periaxonal space, the alteration of the I-V curves due to this accumulation is minimized for the hyperbolic and exponential decay functions. The advantages of these functions for the rapid generation of I-V curves are discussed.

Animals↗

PubMed1995

[Biomechanical evaluation of cervical stability with Halifax clamp after bilateral facetectomy].

With nine fresh adult cervical spine specimens (C3-T1), the three-dimensional motions of C4-5 segment were analysed to evaluate the immediate stability following bilateral facetectomy, Halifax clamp and wire fixation. The results showed that the stability with Halifax clamp was greater than that of the intact state in flexion, extension and lateral bending, but the same as in axial rotation. The stability with wire fixation was greater than that in flexion and equal to that in extension, lateral bending and axial rotation. The ROMs with Halifax Clamp were less than those with wire fixation in flexion, extension and lateral bending, but close to in axial rotation.

Adult↗