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PubMed2006

On-pump beating-heart mitral valve plasty without aortic cross-clamping.

Patients with ischemic cardiomyopathy often have mitral regurgitation, which should be corrected for better long-term survival. Mitral valve surgery is usually performed during cardiopulmonary bypass under the arrested heart condition. The ascending aorta is cross-clamped and the heart is arrested using a cardioplegic solution. However, because ischemic cardiomyopathy patients often have a severely atherosclerotic ascending aorta and low cardiac function, aortic cross-clamping and cardiac arrest increase the risk of postoperative thromboemboli and low cardiac output syndrome. Under the on-pump beating-heart condition, we performed mitral valve plasty concomitant with coronary artery bypass grafting, tricuspid annuloplasty, left ventricular aneurysmectomy, and the maze procedure without aortic cross-clamping for a patient with ischemic dilated cardiomyopathy and bradycardial atrial fibrillation. The patient had no postoperative complications and re covered rapidly. Thus, to prevent serious postoperative complications, on-pump beating-heart mitral valve surgery without aortic cross-clamping may be a suitable surgical option for patients with ischemic cardiomyopathy.

Aged↗
PubMed1990

Reduction of myocardial injury with verapamil before aortic cross-clamping.

The effect of verapamil administered before aortic cross-clamping was assessed in 40 patients undergoing elective coronary artery bypass grafting. Myocardial protection consisted of cold blood potassium cardioplegia, topical ice slush, and moderate (28 degrees C) systemic hypothermia. Patients were randomly divided into two groups: group 1 (18 patients) received verapamil (0.1 mg/kg up to 10 mg) intravenously three to five minutes before aortic cross-clamping; group 2 (22 patients) did not (control). Myocardial injury was assessed by cumulative release of the cardiac-specific isoenzyme of creatine kinase (CK-MB) after release of the aortic cross-clamp. Release of CK-MB was significantly lower in the verapamil group (44.9 +/- 6.2 versus 72.2 +/- 9.0 IU at 24.5 hours, p = 0.005). Calculated total infarct size was also lower in the verapamil group (6.0 +/- 0.9 versus 8.9 +/- 1.0 g-Eq, p = 0.035). Individual CK-MB release curves showed either one or two peaks. The two-peak pattern was more frequent in control patients (18 of 21 control patients versus 6 of 18 verapamil patients, p = 0.001) and was associated with a larger infarct size. Atrioventricular pacing was not required in any verapamil patient, but was needed in 1 control patient. We conclude that verapamil administered before aortic cross-clamping protects against myocardial injury during coronary artery bypass grafting with no increase in the incidence of atrioventricular block.

Aged↗
PubMed1994

Regional deep hypothermia of the spinal cord protects against ischemic injury during thoracic aortic cross-clamping.

We tested in pigs the hypothesis that regional deep hypothermia of the spinal cord achieved by cerebrospinal fluid cooling will protect against ischemic injury during thoracic aortic cross-clamping. Eight control animals underwent aortic cross-clamping at the distal aortic arch and just above the diaphragm for 30 minutes. Eight experimental animals had placement of two subarachnoid perfusion catheters through laminectomies at T4 and the lower lumbar region. The subarachnoid space was perfused with normal saline solution at 6 degrees C delivered by gravity infusion, with infusion rates adjusted to maintain cord temperatures at less than 20 degrees C. After 30 minutes of aortic cross-clamping, the infusion was stopped and the cord allowed to warm to body temperature. Hind limb neurologic function was graded by Tarlov's scale. All of the animals in the control group had complete hind limb paraplegia (Tarlov grade 0) postoperatively. Seven of the 8 animals in the experimental group had preservation of hind limb motor function (Tarlov grade 2), and 1 animal had complete hind limb paraplegia (Tarlov grade 0) (p = 0.002, Fisher's exact test). We conclude that regional deep hypothermia of the spinal cord in pigs does provide some protection from ischemic injury during thoracic aortic cross-clamping. Clinically this may be a useful adjunct for prevention of paraplegia during thoracic aortic operations.

Animals↗
PubMed1996

Intermittent aortic cross-clamping and cold crystalloid cardioplegia for low-risk coronary patients.

BACKGROUND: Blood cardioplegic strategies have been shown to increase myocardial oxygen uptake, replenish depleted energy stores, and improve myocardial function and survival in the high-risk subset of patients. However, the superiority of these techniques over intermittent aortic cross-clamping and crystalloid cardioplegia in low-risk patients is still controversial. METHODS: This study consisted of two parts. In the first part, we assessed the results of a recent cohort of 399 consecutive low-risk patients undergoing their first coronary artery bypass grafting between 1993 and 1995 using cold crystalloid cardioplegia (n = 128) and intermittent aortic cross-clamping (n = 271). In the second part of the study, 40 consecutive low-risk patients undergoing elective first time coronary artery bypass grafting were randomly divided into two equal groups. One group received cold crystalloid cardioplegia and the other group had myocardial management with intermittent aortic cross-clamping. The two groups were compared with respect to hemodynamic, biochemical and ultrastructural changes. RESULTS: The overall mortality rate, the perioperative myocardial in the need for intraaortic balloon pumps, and the need for inotropic agents were 0.25%, 1.5%, 1%, and 5.8%, respectively. No significant differences were observed between the groups with respect to these clinically defined end points. CONCLUSIONS: Both intermittent aortic cross-clamping and cold crystalloid cardioplegia techniques may be used safely in low-risk patients undergoing first-time coronary artery bypass grafting.

Aged↗
PubMed1988

Effects of basolateral ouabain, amphotericin B, cyanide and potassium on amiloride noise during voltage clamp of Rana pipiens skin support sodium-amiloride competition.

In a previous study, the amiloride-induced corner frequency (fc) was found to decrease as apical sodium was increased. This effect was small or absent when the basolateral surface was exposed to high potassium. It has been suggested that the apical sodium effect may be indirect, due either to increased intracellular [Na+] which repelled amiloride or to an increased potential at the apical surface which reduced amiloride affinity. High basolateral K+ might then suppress the sodium effect either by preventing intracellular [Na+] from increasing or by allowing a better clamp of the apical membrane potential by reducing basolateral membrane resistance and potential. We checked the effects of basolateral [K+], of cyanide and of ouabain at concentrations known to increase intracellular [Na+]. We found only negligible effects on fc. In addition, amphotericin B added to the basolateral bathing solution either in 115 mM Na+ or in 120 mM K+ had no significant effect on fc. We found that relatively wide variation in clamp potential under all conditions, even with active transport severely inhibited, left fc virtually constant. Since the amiloride kinetics were independent of clamp potential, we were able to measure paracellular and transcellular conductances separately by examining the voltage dependence of clamp current (linear) and amiloride noise power (quadratic). This made possible estimation of channel density and single-channel current.

Amiloride↗
PubMed1993

The ultrastructure of the tegument and clamp attachment organ of Gotocotyla bivaginalis (Monogenea, Polyopisthocotylea).

The tegument of Gotocotyla bivaginalis consists of a syncytium, perikarya and four kinds of secretory bodies, viz. electron-dense granules, moderately electron-dense vesicles, electron-lucent vesicles and large multivesicular bodies occurring in the ratio of 83:50:40:1. Microvillus-like structures, finger-like projections and a thin coat of glycocalyx occur on the In contrast, the syncytium of the clamp is relatively thin and irregularly folded, containing only three kinds of secretory bodies, viz. electron-dense granules, a few moderately electron-dense granules and several large electron-lucent vacuole-like structures in the ratio of 15:2:5. Exocytosis of the electron-dense and -lucent vesicles is apparently prevalent both in the syncytium of the haptor and general body surface. Tegumental damages induced by natural mechanical forces appear to occur in some regions of the syncytium of the clamps/haptor. Sclerites of the clamp are electron-dense and they are interconnected by the basal lamina, tendon and radial muscle fibres. Interstitial space is absent between the sarcolemma of adjacent muscle fibres of the clamp. Groups of neurons and non-myelinated nervous processes can be seen in the vicinity of the clamps. The axon is subdivided by invaginations of the neurolemma. Presumed non-ciliated mechano-receptors occur on the body surface.

Animals↗
PubMed1985

The metabolic response to the euglycemic insulin clamp in type I diabetes and normal humans.

The euglycemic insulin clamp has been utilized extensively to measure in vivo tissue sensitivity to insulin under various circumstances. Insulin sensitivity is determined from the amount of glucose metabolized under steady state conditions. To assess the effect of abnormalities in other insulin responsive metabolic pathways on glucose metabolism and thus insulin sensitivity as measured by the glucose clamp, the concentration of lactate, pyruvate, 3-hydroxybutyrate, glycerol, alanine, and free fatty acids were measured at baseline and during a two-hour euglycemic clamp in 13 nonobese subjects with type I diabetes. The observed responses were compared to 11 normal controls. Insulin sensitivity as measured by M (glucose metabolized), MCRg (metabolic clearance of glucose), and M/I ratio (glucose metabolized per unit insulin) were all significantly decreased in the diabetic subjects (P less than 0.005). Free fatty acids (FFA) and 3-hydroxybutyrate were significantly elevated at baseline in the diabetic subjects (P less than 0.05) and decreased significantly at 60 and 120 minutes in both groups. Baseline blood pyruvate and lactate concentrations were similar in the control and diabetic subjects. Pyruvate increased significantly at 60 minutes in both groups (P less than 0.05) and returned to baseline in the control subjects but remained elevated at 120 minutes in the diabetic subjects (P less than 0.001). Lactate increased similarly in both groups and remained elevated at 60 and 120 minutes. In summary, insulin sensitivity as assessed by the euglycemic insulin clamp is decreased in type I diabetes. However, specific differences in the concentration of several other metabolites both at baseline and in response to hyperinsulinemia were also identified in the diabetic subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxybutyric Acid↗
PubMed1987

Changes in plasma growth hormone in diabetic and nondiabetic subjects during the glucose clamp.

A group of 22 newly diagnosed noninsulin-dependent diabetic subjects and seven nondiabetic subjects underwent a glucose clamp at plasma glucose 100 mg/dL with insulin infusion rates of 1.0 and 10 mU/kg/min. During both insulin infusion rates, there was a sustained rise in plasma growth hormone (GH) above basal in 18 of the 22 diabetic subjects. Basal GH values were 2.37 +/- 0.67 ng/mL, rising above basal during the lower insulin infusion (6.1 +/- 3.3 ng/mL, P = 0.05) with a further rise at the higher insulin level (8.58 +/- 2.0 ng/mL, P less than 0.001). There was no rise in GH in any of the nondiabetic subjects. In neither group was there any rise above basal in cortisol, prolactin, glucagon, or somatostatin (SRIH). In a group of three nondiabetic subjects, a rise in GH similar to that seen in the diabetic group was induced by elevating the plasma glucose to 200 mg/dL for 60 minutes prior to the euglycemic clamp procedure. However, it is unlikely that changes in plasma glucose account totally for the changes in plasma GH described in the diabetic subjects since a rise in plasma GH was also seen in four diabetic subjects clamped at their fasting plasma glucose. We conclude that in newly diagnosed noninsulin-dependent diabetic subjects there is a rise in plasma GH during the euglycemic clamp procedure, which may be due to both the prior lowering of plasma glucose and the high plasma insulin levels.

Adult↗
PubMed1987

Studies of high and low insulin responders with the hyperglycemic clamp technique.

We have investigated insulin responsiveness in relation to insulin sensitivity during sequential hyperglycemic clamping in low insulin responders (LIR), high insulin responders (HIR) and in women with a history of gestational diabetes (GD). Designation of HIR and LIR was done on the basis of mathematical modeling of the insulin response to a glucose infusion test. Insulin sensitivity was determined by a somatostatin-insulin-glucose infusion test (SIGIT) according to which LIR were subdivided into groups with higher or lesser sensitivity. Hyperglycemic clamping (60 min, 11 mmol/L of glucose) induced diphasic insulin and C-peptide responses in all groups. Insulin and C-peptide responses were significantly higher in HIR than in other groups. The ratio of first phase to total insulin response was higher in HIR v GD but did not differ between other groups. A second identical clamp was performed after a 60-minute rest period. Except in HIR, insulin levels attained were then moderately but significantly higher than during the first clamp. Conversely, the glucose utilization (mg/kg/min) to insulin (mU/L) = M/L ratio was markedly increased in LIR with high insulin sensitivity but not in other groups. We conclude that (1) large and consistent differences exist in glucose-induced insulin secretion from the pancreas between nondiabetic subjects; (2) time dynamics of insulin secretion and priming effects of glucose are similar in LIR with lesser and higher sensitivity; and (3) in the latter group a glucose stress affects insulin sensitivity more markedly than insulin responsiveness.

Blood Glucose↗
PubMed1995

Potentiation of the immobility response elicited by bandaging and clamping in mesencephalic rats.

In earlier work, we showed that adult rats exhibit immobility response (IR) if a clamp is fastened to the skin of the nape of the neck, but not at other areas of the body, and not by bandaging. The present study characterizes IR in adult rats with complete mesencephalic transections. In the mesencephalic rats, the duration of the IR not only increased, but the stimuli capable of eliciting it were more diverse. All head and body areas clamped or bandaged were capable of inducing a profound IR. In contrast, the IR in intact rats was of shorter duration, and was only induced by clamping the neck, or by bandaging the upper or the lower torso. Furthermore, unlike the mesencephalic rats the ability of the bandaging to induce IR is reduced after the first trial and finally disappears. Only clamping the neck was able to persistently induce IR in intact rats. These data support the hypothesis that the IR control system is in the midbrain, hindbrain or spinal cord, and that systems above the mesencephalon modulate the IR. Such modulation appears to involve the ability to discriminate amongst tactile stimuli, and to integrate previous experience.

Animals↗
PubMed1993

Calcium clamp in single nerve cells.

Free calcium concentration in isolated single neurons was clamped using a new technical approach based on a feed-back connection between the Fura-2 fluorescence signal measuring the intracellular Ca2+ concentration ([Ca2+]i) and iontophoretic current injecting Ca2+ into the cell. Beginning of [Ca2+]i clamping at a level above the basal one triggered fast (few seconds) current transients equal to injection of 36 +/- 20 microM Ca2+ (for a 0.1 microM change of [Ca2+]i), representing the filling of a fast cytosolic buffer. Continuation of clamping required very small clamping currents (corresponding to injection of 0.39 +/- 0.20 microM.s-1 Ca2+). This value increased proportionally to the magnitude of the change of [Ca2+]i above basal level, indicating the activation of calcium-dependent mechanisms for Ca2+ removal from the cytosol. The described approach allowed measurement, under physiological conditions, of the capacitative and kinetic properties of different Ca-regulating systems functioning in a single nerve cell as well as other types of cells.

Animals↗
PubMed1984

Theory and operation of a single microelectrode voltage clamp.

The theory of operation of a discontinuous single-electrode voltage clamp using an ideal microelectrode (infinite response speed) and fixed (current-passing) duty cycle has been previously described. In this paper, the theory is extended by considering a microelectrode which has a finite response speed, by allowing the duty cycle to be variable, and by considering the clamp noise. Formulate are derived for the relationships between the step response, the steady-state error, the steady-state ripple, and the stability, in terms of the cycling frequency, the duty cycle, the open loop gain, and the electrical resistance and capacitance of the microelectrode and the cell membrane. In addition, the amplification of the microelectrode noise by aliasing is analysed, the error due to incomplete decay of the microelectrode voltage is described, and the accuracy of averaging the peak current measurement is established. To achieve the fastest dynamic response and the smallest steady-state error, the cycling period should be made as small as possible, and the open-loop gain should be as large as possible, consistent with stability. Incomplete decay of the microelectrode voltage destabilizes the clamp, and can introduce a significant clamp error. The choice of duty cycle is a compromise between reducing the noise and the step response time while avoiding design problems in the current output circuit. The output noise is amplified by aliasing. It can be minimized for a given output filter cutoff frequency by keeping the cycling frequency as high as possible, and by the use of an anti-aliasing filter whose cutoff frequency must be set for each microelectrode.

Animals↗
PubMed1988

Technical aspects of voltage-clamping the cut-open squid giant axon.

The design of a voltage-clamp system dedicated to recording the fluctuation of sodium currents under non-stationary conditions from a leaflet of cut-open squid axon is presented. The membrane leaflet is mechanically sandwiched between the apices of two finely machined plexiglass cones which enable fluid access to each side of the membrane and a known area of membrane to be voltage-clamped. The design requirements necessary to achieve satisfactory signal resolution have been assessed in terms of the overall digitising resolution of the ADC hardware and the intrinsic and extrinsic components of the clamp-system noise. Good agreement between the predicted and measured noise performance was found. The clamp system has enabled simultaneous estimates of the single-channel conductance and channel density to be made over a much wider range of experimental conditions than previously possible.

Animals↗
PubMed1989

A hybrid patch clamp amplifier.

The current-to-voltage convertor used in patch clamping is analyzed for noise generation and the major noise sources determined. A hybrid patch clamp amplifier design is theoretically analyzed. Here it is shown that by differentiation and recombining of signals the original input signal can be reconstructed. Several circuits of this design are described and their performance compared. The optimal signal detection obtained for a 1 ms current pulse width with a signal-to-noise ratio of 1 is 0.025 pA. In these circuits, high frequency attenuation is readily accomplished with a single control. In addition, compensation for the transients which occur with step control voltages is effectively accomplished. With this circuitry, it is shown that for most patch clamp situations, the minimum pulse width and current which can be detected is determined by the patch clamp seal resistance.

Amplifiers, Electronic↗
PubMed1996

The differential haloperidol effect on the immobility response elicited by clamping, grasping, bandaging and inversion in guinea pig, hamster and rat.

The induction and modification by haloperidol of inhibitory responses, by 4 inducing stimuli (inversion, clamping, bandaging and grasping) were studied and compared in guinea pig, hamster and rat. When undrugged, all 4 stimuli induced immobility responses in guinea pig; only clamping, bandaging and grasping, but not inversion, induced immobility responses (IR) in hamsters; only clamping and grasping, but not inversion and bandaging induced IR in rats. Haloperidol significantly potentiated the occurrence and duration of the IR by clamping, grasping and bandaging in rats. In hamsters haloperidol only potentiated the IR induced by bandaging, and in guinea pigs, haloperidol had no effect on IR produced by any of the stimuli. These findings suggest an inverse relationship between susceptibility to IR and the potentiation of IR by haloperidol.

Animals↗
PubMed1991

A multi-arterial clamping method with arterial hypotension does not bring about complete brain ischemia in dogs.

The completeness of brain ischemia with a multi-arterial clamping method in dogs was examined using EEG, evoked potentials (EPs) and vessel staining with Evans blue. EEG was monitored by bipolar parietal lead. EPs stimulating electrodes were inserted into the first thoracic (T1) epidural space and recording electrodes into the C2 epidural space, brain stem and cerebral cortex. EPs were measured at 30 s intervals with 50 measurements each time using 3.0 mA current of 100 microseconds duration. In dogs in which brain ischemia was brought about by ventricular fibrillation (VF group, n = 5) EEG disappeared within 40 s in all dogs and the amplitudes of EPs at the C2 spinal cord, brain stem and cerebral cortex after 10 min ischemia were 57%, 0% and 0%, respectively. In the dogs in which a multi-arterial clamping method (clamping internal thoracic arteries, brachiocephalic trunk and left subclavian artery while lowering systolic arterial pressure (AP) below 50 Torr) was used (AC group, n = 5) EEG was still recognizable at 5 min in 2 dogs and the amplitudes of EPs at the C2, brain stem and cerebral cortex at 10 min ischemia were 103%, 53% and 0%, respectively. Stainings with Evans blue were observed in all soft tissue at and below thoracic level, entire intervertebral venous plexus, venous sinuses of cranial dura mater and spinal cord below the lower part of cervical region. Bright red fluorescence by Evans blue was observed microscopically in the vessels of the spinal cord, brain stem and cerebrum (1 dog only). In conclusion a multi-arterial clamping method with arterial hypotension brings about only incomplete brain ischemia.

Animals↗
PubMed1992

Whole-cell patch-clamp recordings from respiratory neurons in neonatal rat brainstem in vitro.

Whole-cell recordings were obtained from respiratory neurons by applying patch-clamp techniques in the en bloc medulla of in vitro neonatal rat brainstem-spinal cord preparations. Stable voltage-clamp recordings of excitatory or inhibitory synaptic drive currents and current-clamp recordings of spike discharge of inspiratory and expiratory neurons could be maintained for periods of 1-2 h. Parameters of whole-cell recording, including membrane seal resistances and series resistances, obtained in the en bloc medulla were similar to those obtained in corresponding regions of thin slices where neurons were directly visualized to optimize conditions for whole-cell patch clamp.

Animals↗
PubMed1993

Patch-clamp recording from Müller (glial) cell endfeet in the intact isolated retina and acutely isolated Müller cells of mouse and guinea-pig.

Müller cells span through the entire retina and terminate with the formation of endfeet at the vitreous body. These endfeet are thought to be specialized for maintaining the K+ homeostasis in the retina based on the assumption that voltage signals can passively spread from the cell body to the endfeet. We employed the patch-clamp technique to study the physiological properties of these endfeet in a retinal wholemount preparation from guinea-pig or mouse. After assessing one endfoot with the patch pipette and establishing the whole cell recording configuration, a membrane area which approximately matched the size of one endfoot and proximal process could be voltage-clamped. This morphological correlation could be established by filling the cytoplasm with the fluorescent dye Lucifer Yellow via the patch-pipette. The morphological, immunocytochemical and ultrastructural inspection of the recorded cells revealed that mouse Müller cell endfeet were connected by only a thin stalk to the proximal process. In contrast, guinea-pig endfeet were connected by thick stalks. The endfoot current in the mouse was dominated by a voltage and time-independent K+ conductance. In contrast, in some of the recordings from guinea-pig, delayed and inwardly rectifying K+ currents were observed. These voltage-gated currents were more frequently observed or were facilitated when the membrane area under voltage clamp was increased, blocking the passive K+ currents by Ba2+ in both, mouse and guinea-pig. We thus assume that the voltage-gated currents were not in the endfeet membrane, but rather in the proximal process and could thus be better activated in the guinea-pig with its thicker stalk or after increasing the membrane area under voltage clamp control. Similar results were obtained in freshly isolated Müller cells; in contrast to the cells from the wholemount the voltage-gated currents were more frequently observed. These studies demonstrate that the Müller cell endfoot of the mouse with its vascularized retina is an electrically isolated unit and that voltage signals do not spread to the proximal process. Such a property would, however, be required for the redistribution of K+ via spatial buffer currents. In contrast, guinea-pig Müller glial cells with their stout morphological connection between endfoot and proximal process are better suited to fulfil this task.

Animals↗