Biomedical subjects

A W Miller

Publications and source records attributed to A W Miller.

At least 19 recordsLinked to original sources

PubMed2001

Lidocaine increases the proarrhythmic effects of monophasic but not biphasic shocks.

INTRODUCTION: Lidocaine increases monophasic shock defibrillation energy requirement (DER) values but does not alter biphasic shock DER values. However, the mechanism of this drug/shock waveform interaction is unknown. It may be that lidocaine increases the proarrhythmic actions of monophasic shocks but not biphasic shocks. Thus, lidocaine may increase monophasic shock DER values by increasing myocardial vulnerability to shock-induced ventricular fibrillation. METHODS AND RESULTS: Area of myocardial vulnerability (AOV), defined by a two-dimensional grid according to shock strength (y-axis) and shock coupling interval (x-axis), was assessed for biphasic shocks (n = 11) and monophasic shocks (n = 13) in intact swine hearts. Shocks were randomly delivered during right ventricular pacing at 10 shock strengths (50 to 500 V) and five coupling intervals (160 to 240 msec). AOV was defined as the number of points within the test grid that induced ventricular fibrillation. AOV, upper limit of vulnerability (ULV), and DER values were determined at baseline and during systemic infusion of lidocaine (10 mg/kg/hour). Lidocaine increased AOV, ULV, and DER values by 35%, 23%, and 36%, respectively, for monophasic shocks. However, lidocaine did not alter AOV, ULV, or DER values for biphasic shocks. CONCLUSION: Lidocaine increases the AOV to monophasic shocks, which is directly related to changes in ULV and DER values. This implies that lidocaine increases the proarrhythmic activity of monophasic shocks but not biphasic shocks. This may explain why lidocaine increases monophasic shock DER values.

Animals↗

PubMed2001

Implant abutment screw rotations and preloads for four different screw materials and surfaces.

STATEMENT OF PROBLEM: Chronic implant screw loosening remains a problem in restorative practices. Some implant manufacturers have introduced abutment screws with treated surfaces in an effort to increase preload and reduce potential loosening. Purpose. This study evaluated the materials and surfaces of 4 commercially available abutment screws on preload generation. MATERIAL AND METHODS: Twenty of each of the following abutment screws-Gold-Tite (Gt), TorqTite (Tt), gold alloy (Ga), and titanium alloy (Ta)-were divided into 2 groups. Measurements were recorded for each abutment screw on a mounted 3.75 x 18 mm external hex implant with a titanium abutment. Rotational angle measurements were conducted on the 4 abutment screws at 20 and 32 Ncm. Removal torque values were recorded and used to indirectly generate preload values. Random implant block specimens were sectioned and qualitatively evaluated with an SEM. RESULTS: At 20 and 32 Ncm, the largest rotational angles were recorded for the Tt groups: 21.2 +/- 3.1 degrees and 38.1 +/- 8.7 degrees, respectively. The greatest preload values at 20 and 32 Ncm were calculated for the Gt groups: 596.8 +/- 101.2 N and 1015.3 +/- 191.2 N, respectively. SEM analysis of the 4 implant block specimens revealed mating thread contacts located in the middle portion of the superior surface of the abutment screw thread. The greatest number of mating thread contacts were seen in the Gt implant block specimen (14 of 20 possible thread contacts). CONCLUSION: The Gt and Tt abutment screws with enhanced surfaces that help reduce the coefficient of friction produced greater rotational angles and preload values than the conventional gold alloy and titanium alloy screws.

Algorithms↗

PubMed2001

Defibrillation energy requirements and electrical heterogeneity during total body hypothermia.

OBJECTIVE: Determine the effects of hypothermia on defibrillation energy requirements and cardiac electrophysiology. DESIGN: Prospective randomized acute intervention trial. SETTING: Medical center animal laboratory. SUBJECTS: Fifteen domestic farm swine. INTERVENTIONS: Swine were randomized to a hypothermia group (n = 8) or a control group (n = 7). All animals were instrumented with a transvenous defibrillation system connected to a defibrillator that delivers a biphasic-truncated waveform. Values for defibrillation energy requirements were measured at baseline (normothermia, 38-40 degrees C) and during treatment with total body hypothermia (30 degrees C) or no temperature change (sham). Hypothermia was induced by circulating ice-water through anterior and posterior surgical thermal blankets. MEASUREMENTS AND MAIN RESULTS: Defibrillation energy requirement values at 20%, 50%, and 80% were determined by using an up/down method. In the hypothermia group, defibrillation energy requirement values at baseline did not significantly change during hypothermia (defibrillation energy requirements 50% = 14 +/- 2 J vs. 15 +/- 2 J, respectively). Similarly, the defibrillation energy requirement values in the control group did not change from baseline to sham phase (defibrillation energy requirements 50% = 12 +/- 1 J vs. 13 +/- 1 J, respectively). Hypothermia profoundly affected cardiac electrophysiology, decreasing ventricular fibrillation threshold by 72%, conduction velocity by 25% (p < .01), and tissue excitability, while it prolonged ventricular repolarization and refractoriness by 7.5% to 15%, respectively (p < .05). CONCLUSIONS: Total body cooling to 30 degrees C was highly arrhythmogenic, although this unstable electrophysiological state did not alter ventricular defibrillation energy requirements. These data suggest that hypothermia may be used to slow metabolic processes without concern over the ability to successfully defibrillate and treat hypothermia-induced arrhythmias.

Animals↗

PubMed2001

Enhanced endothelin-1 response and receptor expression in small mesenteric arteries of insulin-resistant rats.

Hyperinsulinemia, a primary feature of insulin resistance, is associated with increased endothelin-1 (ET-1) activity. This study determined the vascular response to ET-1 and receptor binding characteristics in small mesenteric arteries of insulin-resistant (IR) rats. Rats were randomized to control (C) (n = 32) or IR (n = 32) groups. The response to ET-1 was assessed (in vitro) in arteries with (Endo+) and without (Endo-) endothelium. In addition, arteries (Endo+) were pretreated with the ET(B) antagonist A-192621 or the ET(A) antagonist A-127722. Finally, binding characteristics of [(125)I]ET-1 were determined. Results showed that in Endo+ arteries the maximal relaxation (E(max)) to ET-1 was similar between C and IR groups; however, the concentration at 50% of maximum relaxation (EC(50)) was decreased in IR arteries. In Endo- arteries, the E(max) to ET-1 was enhanced in both groups. Pretreatment with A-192621 enhanced the E(max) and EC(50) to ET-1 in both groups. In contrast, A-127722 inhibited the ET-1 response in all arteries in a concentration-dependent manner; however, a greater ET-1 response was seen at each concentration in IR arteries. Maximal binding of [(125)I]ET-1 was increased in IR versus C arteries although the dissociation constant values were similar. In conclusion, we found the vasoconstrictor response to ET-1 is enhanced in IR arteries due to an enhanced expression of ET receptors and underlying endothelial dysfunction.

Animals↗

PubMed2001

Epoxyeicosatrienoic acid-induced relaxation is impaired in insulin resistance.

We assessed the effect of epoxyeicosatrienoic acids (EETs) in intact mesenteric arteries and Ca(2+)-activated K(+) (BK(Ca)) channels of isolated vascular smooth muscle cells from control and insulin-resistant (IR) rats. The response to 11,12-EET and 14,15-EET was assessed in small mesenteric arteries from control and IR rats in vitro. Mechanistic studies were performed in endothelium intact or denuded arteries and in the presence of pharmacological inhibitors. Moreover, EET-induced activation of the BK(Ca) channel was assessed in myocytes in both the cell-attached and the inside-out (I/O) patch-clamp configurations. In control arteries, both EET isomers induced relaxation. Relaxation was impaired by endothelium denudation, N(omega)-nitro-L-arginine, or iberiotoxin (IBTX), whereas it was abolished by IBTX + apamin or charybdotoxin + apamin. In contrast, the EETs did not relax IR arteries. In control myocytes, the EETs increased BK(Ca) activity in both configurations. Conversely, in the cell-attached mode, EETs had no effect on BK(Ca) channel activity in IR myocytes, whereas in the I/O configuration, BK(Ca) channel activity was enhanced. EETs induce relaxation in small mesenteric arteries from control rats through K(Ca) channels. In contrast, arteries from IR rats do not relax to the EETs. Patch-clamp studies suggest impaired relaxation is due to altered regulatory mechanisms of the BK(Ca) channel.

8,11,14-Eicosatrienoic Acid↗

PubMed2000

Bladder cancer: race differences in extent of disease at diagnosis.

BACKGROUND: Blacks are less likely than whites to develop bladder cancer; although once diagnosed, blacks experience poorer survival. This study sought to examine multiple biological and behavioral factors and their influence on extent of disease. METHODS: A population-based cohort of black bladder cancer patients and a random sample of frequency-matched white bladder cancer patients, stratified by age, gender, and race were identified through cancer registry systems in metropolitan Atlanta, New Orleans, and the San Francisco/Oakland area. Patients were ages 20-79 years at bladder cancer diagnosis from 1985-1987, and had no previous cancer history. Medical records were reviewed at initial diagnosis. Of the patients selected for study, a total of 77% of patients was interviewed. Grade, stage, and other variables (including age, socioeconomic status, symptom duration, and smoking history) were recorded. Extent of disease was modeled in 497 patients with urothelial carcinoma using logistic regression. RESULTS: Extent of disease at diagnosis was significantly greater in Blacks than in Whites. Older age group, higher tumor grade, larger tumors, and presence of carcinoma in situ were related to greater extent of disease in blacks and in whites. Large disparities between blacks and whites were found for socioeconomic status and source of care. Blacks had greater symptom duration and higher grade. Black women were more likely to have invasive disease than white women; this difference was not seen among men. Blacks in unskilled occupational categories, perhaps reflecting socioeconomic factors, were at much higher risk for muscle invasion than whites. CONCLUSIONS: While specific relationships between variables were noted, an overall pattern defining black and white differences in stage did not emerge. Future studies should examine the basis upon which occupation and life style factors operate by using biochemical and molecular methods to study the genetic factors involved.

Adult↗

PubMed2000

DNA sequencing up to 1300 bases in two hours by capillary electrophoresis with mixed replaceable linear polyacrylamide solutions.

This paper presents results on ultralong read DNA sequencing with relatively short separation times using capillary electrophoresis with replaceable polymer matrixes. In previous work, the effectiveness of mixed replaceable solutions of linear polyacrylamide (LPA) was demonstrated, and 1000 bases were routinely obtained in less than 1 h. Substantially longer read lengths have now been achieved by a combination of improved formulation of LPA mixtures, optimization of temperature and electric field, adjustment of the sequencing reaction, and refinement of the base-caller. The average molar masses of LPA used as DNA separation matrixes were measured by gel permeation chromatography and multiangle laser light scattering. Newly formulated matrixes comprising 0.5% (w/w) 270 kDa and 2% (w/w) 10 or 17 MDa LPA raised the optimum column temperature from 60 to 70 degrees C, increasing the selectivity for large DNA fragments, while maintaining high selectivity for small fragments as well. This improved resolution was further enhanced by reducing the electric field strength from 200 to 125 V/cm. In addition, because sequencing accuracy beyond 1000 bases was diminished by the low signal from G-terminated fragments when the standard reaction protocol for a commercial dye primer kit was used, the amount of these fragments was doubled. Augmenting the base-calling expert system with rules specific for low peak resolution also had a significant effect, contributing slightly less than half of the total increase in read length. With full optimization, this read length reached up to 1300 bases (average 1250) with 98.5% accuracy in 2 h for a single-stranded M13 template.

Acrylic Resins↗

PubMed2000

Endotoxemia alters splanchnic capacitance.

The splanchnic circulation constitutes a major portion of the total capacitance vasculature and may affect venous return and subsequently cardiac output during low output states. This study assessed the effects of rapid (10 microg/kg over 5 min) and slow (10 microg/kg over 60 min) induction of endotoxin (Escherichia coli) shock on splanchnic blood volume in 8 farm swine. Blood volume was measured by using Tc99m-labeled erythrocytes and radionuclide imaging. Baseline arterial pressure (MAP), central venous pressure (CVP), and liver, splenic, mesenteric and total splanchnic volumes were stable during the 30-min baseline. Approximately 30 min after the rapid endotoxin infusion, splenic volume decreased by 45%, whereas liver volume increased by 40% and MAP decreased by 60% (P < 0.01). The reduction in splenic volume occurred within 10 min of the endotoxin infusion, whereas liver volume changes occurred after MAP reduction. The slow endotoxin infusion also reduced splenic volume by approximately 50% (P = 0.05), whereas MAP declined by 30% (P < 0.05). However, the slow endotoxin infusion lowered liver volume (P < 0.05). Mesenteric volume was unaffected by the fast or slow endotoxin infusion. Total splanchnic volume was unaffected by the fast infusion but decreased by 37% in the slow infusion group (P < 0.05). In summary, E. coli endotoxin reduces splenic blood volume and increases liver blood volume after acute hypotension ensues. Endotoxin does not increase total splanchnic blood volume and may actually decrease total splanchnic volume in the absence of circulatory collapse. This endotoxin shock model is not associated with blood volume pooling in the splanchnic capacitance circulation.

Animals↗

PubMed2000

A maximum-likelihood base caller for DNA sequencing.

The procedures used to sequence the human genome involve the electrophoretic separation of mixtures of dioxyribonucleic acid (DNA) fragments tagged with reporting groups, usually fluorescent dyes. Each fluorescent pulse which arrives from an optical detector corresponds to a nucleotide (base) in the DNA sequence, and the subsequent process of base detection is known as base calling. Generating longer and more accurate sequences in the base-calling process will reduce the high cost of DNA sequencing. This paper presents an automated base-calling algorithm, referred to as maximum-likelihood base caller (MLB), which is based on maximum likelihood equalization for digital communication channels. Based on 125 experimental datasets, MLB averaged up to 40% fewer errors than the widely used ABI base caller from the Applied Biosystems Division of PE Corporation. MLB's accuracy rivaled that of another well-known base caller, Phred, surpassing it on datasets with high background noise.

Algorithms↗

PubMed2000

Regional hyperkalemia increases ventricular defibrillation energy requirements: role of electrical heterogeneity in defibrillation.

INTRODUCTION: Increased spatial electrical heterogeneity has been associated with impaired defibrillation efficacy. The current study investigated the relationship between electrical heterogeneity and defibrillation efficacy by manipulating spatial electrical heterogeneity. METHODS AND RESULTS: We increased spatial electrical heterogeneity by infusing potassium chloride (2 to 4 mEq/hour) or placebo in the left anterior descending artery in 13 pentobarbital anesthetized swine. Electrophysiologic measurements at five myocardial sites and defibrillation energy requirement (DER) values were determined at baseline and during regional hyperkalemia (n = 7) or placebo (n = 6). Regional potassium infusion was titrated to a 20% reduction in action potential duration in the perfused region. Regional hyperkalemia increased biphasic DER values by 87% (P = 0.02), whereas infusion of placebo did not alter defibrillation efficacy. Regional hyperkalemia decreased myocardial repolarization and refractoriness in the perfused region by 21% (P < 0.001) and 18% (P = 0.01), respectively. However, regional hyperkalemia increased ventricular fibrillation cycle length (VFCL) by 39% (P = 0.008). Consequently, dispersions of repolarization, refractoriness, and VFCL were significantly increased by 169%, 92%, and 200%, respectively. Regional hyperkalemia also increased ventricular conduction time to the perfused region by 54% (P = 0.006), indicating conduction velocity dispersion, while not affecting local pacing threshold or local voltage gradient. CONCLUSION: Regional hyperkalemia increased DER values. Regional hyperkalemia likely impairs defibrillation by increasing myocardial electrical heterogeneity, which supports the theory that electrical heterogeneity promotes nonuniform propagation of early postshock activations, thereby inhibiting defibrillation.

Animals↗

PubMed2000

Metformin improves vascular function in insulin-resistant rats.

This study assessed the effect of metformin treatment on insulin, mean arterial pressure (MAP), and endothelial function in insulin-resistant (IR) rats. In addition, we assessed the direct effect of metformin in vitro. Sprague-Dawley rats were randomized to control (n=28) or IR (n=28) groups. Rats were further randomized to receive metformin (300 mg/kg) or placebo for 2 weeks. MAP and insulin were measured. Subsequently, a third-order branch of the superior mesenteric artery was isolated, and endothelial function was assessed. Specifically, dose-response experiments of acetylcholine (ACh) with or without N-nitro-L-arginine (LNNA) were performed. For in vitro experiments, mesenteric arteries were removed from untreated control and IR rats and treated with metformin (100 micromol/L) before ACh+/-LNNA. MAP and insulin levels were improved in IR-metformin compared with IR-placebo rats. Maximal relaxation (E(max)) to ACh was enhanced in IR-metformin (92+/-2%) compared with IR-placebo rats (44+/-4%) (P<0.05). Relaxation in response to ACh+LNNA was greater in IR-metformin (33+/-4%) than in IR-placebo rats (12+/-4%) but remained depressed compared with control rats (E(max)=68+/-5%). The control group was not affected by metformin. In vitro treatment of arteries with metformin in response to ACh produced results similar to those in the experiments with metformin-treated rats. Although metformin improves metabolic abnormality in IR rats, this action does not appear to mediate its effect on vascular function. Both in vivo and in vitro metformin improved ACh-induced relaxation in IR rats to control levels, apparently through nitric oxide-dependent relaxation. These data suggest that metformin improves vascular function through a direct mechanism rather than by improving metabolic abnormalities.

Acetylcholine↗

PubMed1999

Marginal gap of crowns made with a phosphate-bonded investment and accelerated casting method.

STATEMENT OF PROBLEM: Numerous materials and methods have been used for complete crown fabrication. Conventional investing and casting procedures for phosphate-bonded investments require a 2- to 4-hour process before completion. Accelerated laboratory techniques have been used, but may not result in castings with equal marginal accuracy. PURPOSE: This study measured the marginal gap and determined the clinical acceptability of single castings invested in a phosphate-bonded investment with the use of conventional and accelerated methods. MATERIAL AND METHODS: Forty-four individual stone casts were poured from impressions made from a master die. Conventional and accelerated methods of investing and casting were followed in the fabrication of 44 single-unit castings. Twenty-two casts were used in each of the 2 groups. Each casting and its respective stone die were examined with a microscope at 4 predetermined sites. Perpendicular and 25-degree tilted measurements of marginal gap were documented for each. Evidence of marginal gap was then evaluated by t test. RESULTS: Measurements recorded on the perpendicular and on a 25-degree tilt showed no statistically significant difference between conventional and accelerated groups. All gap measurements except one were within the range of clinical acceptability. The measurements revealed that conventional and accelerated perpendicular gap means were 13.2 and 13.6 microm, respectively, and the average tilted gap means were 31.6 and 32.2 microm, respectively. CONCLUSIONS: A phosphate-bonded investment (Ceramigold) selected for an accelerated casting technique produced single castings within 30 minutes with marginal gaps comparable to those found that used conventional methods.

Crowns↗

PubMed1999

In vitro investigation of the wear of human enamel by dental porcelain.

STATEMENT OF PROBLEM: Metal ceramic systems are advocated when both esthetics and strength are required. A major drawback to many porcelains is their wear and destruction of opposing natural dentition. PURPOSE: This study evaluated the wear of enamel opposing 1 traditional and 2 recently introduced low-fusing feldspathic dental porcelains. MATERIAL AND METHODS: Six blocks of Ceramco II, Finesse, and Omega 900 feldspathic porcelain materials were fabricated and fired according to manufacturer recommendations. Porcelain blocks were polished through 0.25 microm diamond polishing paste. Thirty-six enamel specimens were obtained and milled to a 2 mm (+0.5 mm) diameter. Enamel specimens were attached to an offset cam motor operating at 60 Hz. Enamel specimens were in constant contact with the stationary porcelain blocks under a load of 600 g and traversed a distance of 8 mm. Diameter and height of enamel specimens were measured at times of 0, 6, 12, 24, and 48 hours and subsequent determination of enamel volume loss recorded. Profilometric surface roughness of the ceramic blocks was also measured for the corresponding times. RESULTS: Statistical analysis revealed that both Finesse and Omega 900 feldspathic porcelains caused significantly less enamel volume loss when compared with Ceramco II porcelain at all time intervals. Surface roughness revealed no consistent significant differences among porcelains. CONCLUSION: Both Finesse and Omega 900 porcelains were not as destructive to human tooth structure as Ceramco II porcelain. These results suggest an advantage of the new, lower-fusing porcelains in conditions where natural dentition wear is a concern.

Aluminum Silicates↗

PubMed1999

Impaired vagal reflex activity in insulin-resistant rats.

Insulin resistance, without frank diabetes, is associated with sudden cardiac death. We postulated that a potential mechanism for this association is autonomic dysfunction. Male Sprague-Dawley rats were randomized into one of two groups: (a) insulin resistant (IR; n = 15), or (b) control (n = 11). Animals were made insulin resistant with a fructose-rich diet, whereas control animals received standard rat chow. Four weeks after randomization, arterial pressure and baroreceptor reflex were assessed. Baroreflex sensitivity was defined as the heart-rate response to acute blood pressure changes caused by nitroprusside (0.5-18 micrograms) or phenylephrine (0.2-3 micrograms). To determine the role of vagal stimulation specifically, each animal was randomized to receive atropine sulfate (1 mg/kg) or vehicle (normal saline) before administration of phenylephrine. Mean arterial pressure and fasting insulin concentrations were increased in the insulin-resistant group, whereas there were no differences in body weight, fasting glucose concentrations, or resting heart rate. Phenylephrine increased arterial blood pressure to a maximum of 54 +/- 2 mm Hg for control and 45 +/- 6 mm Hg for IR, p = 0.7. The maximal heart-rate change response to the increased blood pressure was markedly blunted in IR as compared with control (-88 +/- 12 beats/min for IR vs. -238 +/- 18 beats/min for control; p < 0.001). Thus the baroreflex sensitivity (BRS) was threefold less in IR versus the control group (-1.8 +/- 0.2 vs. -4.6 +/- 0.7 beats/min/mm Hg; p = 0.001). Pretreatment with atropine sulfate decreased the BRS in both groups, eliminating the difference between groups (-0.96 +/- 0.5 beats/min/mm Hg for control and -0.56 +/- 0.3 beats/min/mm Hg for IR; p = 0.2). Thus atropine sulfate caused the phenylephrine-induced heart rate and arterial blood pressure response to be equal between groups. On the other hand, BRS to nitroprusside-induced blood pressure changes were similar between groups. Insulin resistance, without the confounding factors of obesity, diabetes, and significant hypertension, is associated with a large reduction in vagal activity, which occurs via attenuation in reflex activity. In contrast, the insulin-resistant syndrome does not affect baroreflex sensitivity via sympathetic reflex.

Animals↗

PubMed1999

EDHF-mediated relaxation is impaired in fructose-fed rats.

Insulin resistance (IR) is associated with endothelial dysfunction. A defect in endothelium-dependent relaxation via outward potassium conductance has been observed in mesenteric arteries from IR rats. The purpose of this study was to assess whether this defect in endothelium-dependent relaxation was due to impaired endothelium-derived hyperpolarizing factor (EDHF) and to determine which specific potassium channel(s) are involved in relaxation. This was accomplished by using specific potassium channel inhibitors in the presence of nitric oxide synthase and cyclooxygenase inhibition. In addition, we sought to assess the function of smooth muscle cell adenosine triphosphate (ATP)-dependent potassium (K(ATP)) channels. Sprague-Dawley rats were randomized to control or IR. To determine EDHF-mediated relaxation, acetylcholine (ACh)-induced (10(-9)-10(-5) M) relaxation was measured (in vitro) in mesenteric arteries in the presence of indomethacin (10(-5) M) and N-nitro-L-arginine (L-NNA) (10(-4) M). Subsequently the combination of charybdotoxin (CTX) (0.1 microM) and apamin (0.5 microM) or glibenclamide (Glib) (10 microM) was added to the bath to inhibit KCa or K(ATP), respectively. In separate experiments, relaxation to pinacidil (10(-13)-10(-5) M), a K(ATP) activator, was assessed in vessels with intact endothelium, endothelium denuded, or with L-NNA. Maximal relaxation to ACh in the presence of L-NNA and indomethacin was 68+/-6% for control and 12+/-3% for IR (p<0.01). The addition of CTX + apamin almost abolished EDHF-mediated relaxation in control (Emax, 8+/-5% vs. 68+/-6%; p<0.01), whereas Glib had little affect. Neither CTX + apamin nor Glib had any affect on IR. Additionally, IR arteries were less sensitive to pinacidil than were controls (EC50, 1.5+/-0.9 microM vs. 5x10(-4)+/-3x10(-4) microM, respectively; p<0.01). Endothelial removal or L-NNA pretreatment of control arteries decreased the response to pinacidil similar to IR, whereas IR vessels were unaffected. EDHF-mediated relaxation is impaired in IR arteries. In addition, the K(Ca) channel appears to be imperative for activity of EDHF in rat small mesenteric arteries. Moreover, activation of K(ATP) channels by pinacidil is impaired in IR, and this appears to be a result of endothelial dysfunction.

Animals↗

PubMed1998

Routine DNA sequencing of 1000 bases in less than one hour by capillary electrophoresis with replaceable linear polyacrylamide solutions.

Long, accurate reads are an important factor for high-throughput de novo DNA sequencing. In previous work from this laboratory, a separation matrix of high-weight-average molecular mass (HMM) linear polyacrylamide (LPA) at a concentration of 2% (w/w) was used to separate 1000 bases of DNA sequence in 80 min with an accuracy close to 97% (Carrilho, E.; et al. Anal. Chem. 1996, 68, 3305-3313). In the present work, significantly improved speed and sequencing accuracy have been achieved by further optimization of factors affecting electrophoretic separation and data processing. A replaceable matrix containing a mixture of 2.0% (w/w) HMM (9 MDa) and 0.5% (w/w) low-weight-average molecular mass (50 kDa) LPA was employed to enhance the separation of DNA sequencing fragments in CE. Experimental conditions, such as electric field strength and column temperature, as well as internal diameter of the capillary column, have been optimized for this mixed separation matrix. Under these conditions, in combination with energy-transfer (BigDye) dye-labeled primers for high signal-to-noise ratio and a newly developed expert system for base calling, the electrophoretic separation of 1000 DNA sequencing fragments of both standard (M13mp18) and cloned single-stranded templates from human chromosome 17 could be routinely achieved in less than 55 min, with a base-calling accuracy between 98 and 99%. Identical read length, accuracy, and migration time were achieved in more than 300 consecutive runs in a single column.

Acrylic Resins↗

PubMed1998

Marginal fit and surface roughness of crowns made with an accelerated casting technique.

STATEMENT OF PROBLEM: Conventional investing and casting techniques following the manufactures' recommendations are time-consuming. Accelerated casting techniques have been reported, but their accuracy has not been adequately studied for complete crown castings. PURPOSE: This study evaluated the marginal fit and surface roughness of complete crowns made with a conventional and an accelerated casting technique. MATERIALS AND METHODS: Part I of the study determined the mean time interval required for each investment to reach its maximum exothermic setting reaction temperature. Part II determined the marginal discrepancy of standardized complete crowns cast in a high noble metal ceramic alloy, with the use of four phosphate-bonded investments. A conventional technique (as recommended by the manufacturer) was compared with an accelerated technique that used 13- to 17-minute bench set time (as determined in part 1 for each investment)_ and 15-minute wax elimination cycle in a 815 degrees C (1500 degrees F) preheated furnace. Part III evaluated the surface roughness of castings made with the same techniques as in part II. RESULTS: For the marginal discrepancy and surface roughness, crowns fabricated with the accelerated casting technique were not significantly (P > 0.05) different from those fabricated with the conventional technique. CONCLUSION: The accelerated casting technique described in this study could be a vital alternative to the time-consuming conventional techniques.

Crowns↗

PubMed1998

High-dose lidocaine does not affect defibrillation efficacy: implications for defibrillation mechanisms.

This study assessed the effect of low (10 mg.kg-1.h-1) and very high (18 mg.kg-1.h-1) doses of lidocaine on defibrillation energy requirements (DER) to relate changes in indexes of sodium-channel blockade with changes in DER values using a dose-response study design. In group 1 (control; n = 6 pigs), DER values were determined at baseline and during treatment with 5% dextrose in water (D5W) and with D5W added to D5W. In group 2 (n = 7), DER values were determined at baseline and during treatment with low-dose lidocaine followed by high-dose lidocaine. In group 3 (n = 3), DER values were determined at baseline and high-dose lidocaine. Group 3 controlled for the order of lidocaine treatment with the addition of high-dose lidocaine after baseline. DER values in group 1 did not change during D5W. In group 2, low-dose lidocaine increased DER values by 51% (P = 0.01), whereas high-dose lidocaine added to low-dose lidocaine reduced DER values back to within 6% of baseline values (P = 0.02, low dose vs. high dose). DER values during high-dose lidocaine in group 3 also remained near baseline values (16.2 +/- 2.7 to 12.9 +/- 2.7 J), demonstrating that treatment order had no impact on group 2. Progressive sodium-channel blockade was evident as incremental reduction in ventricular conduction velocity as the lidocaine dose increased. Lidocaine also significantly increased ventricular fibrillation cycle length as the lidocaine dose increased. However, the greatest increase in DER occurred when ventricular fibrillation cycle length was minimally affected, demonstrating a negative correlation (P = 0.04). In summary, lidocaine has an inverted U-shaped DER dose-response curve. At very high lidocaine doses, DER values are similar to baseline and tend to decrease rather than increase. Increased refractoriness during ventricular fibrillation may be the electrophysiological mechanism by which high-dose lidocaine limits the adverse effects that low-dose lidocaine has on DER values. However, there is a possibility that an unidentified action of lidocaine is responsible for these effects.

Animals↗