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Biomedical subjects

David M Eckmann

Publications and source records attributed to David M Eckmann.

At least 19 recordsLinked to original sources
PubMed2006

High throughput modular chambers for rapid evaluation of anesthetic sensitivity.

BACKGROUND: Anesthetic sensitivity is determined by the interaction of multiple genes. Hence, a dissection of genetic contributors would be aided by precise and high throughput behavioral screens. Traditionally, anesthetic phenotyping has addressed only induction of anesthesia, evaluated with dose-response curves, while ignoring potentially important data on emergence from anesthesia. METHODS: We designed and built a controlled environment apparatus to permit rapid phenotyping of twenty-four mice simultaneously. We used the loss of righting reflex to indicate anesthetic-induced unconsciousness. After fitting the data to a sigmoidal dose-response curve with variable slope, we calculated the MAC(LORR) (EC50), the Hill coefficient, and the 95% confidence intervals bracketing these values. Upon termination of the anesthetic, Emergence timeRR was determined and expressed as the mean +/- standard error for each inhaled anesthetic. RESULTS: In agreement with several previously published reports we find that the MAC(LORR) of halothane, isoflurane, and sevoflurane in 8-12 week old C57BL/6J mice is 0.79% (95% confidence interval = 0.78-0.79%), 0.91% (95% confidence interval = 0.90-0.93%), and 1.96% (95% confidence interval = 1.94-1.97%), respectively. Hill coefficients for halothane, isoflurane, and sevoflurane are 24.7 (95% confidence interval = 19.8-29.7%), 19.2 (95% confidence interval = 14.0-24.3%), and 33.1 (95% confidence interval = 27.3-38.8%), respectively. After roughly 2.5 MAC(LORR) x hr exposures, mice take 16.00 +/- 1.07, 6.19 +/- 0.32, and 2.15 +/- 0.12 minutes to emerge from halothane, isoflurane, and sevoflurane, respectively. CONCLUSION: This system enabled assessment of inhaled anesthetic responsiveness with a higher precision than that previously reported. It is broadly adaptable for delivering an inhaled therapeutic (or toxin) to a population while monitoring its vital signs, motor reflexes, and providing precise control over environmental conditions. This system is also amenable to full automation. Data presented in this manuscript prove the utility of the controlled environment chambers and should allow for subsequent phenotyping of mice with targeted mutations that are expected to alter sensitivity to induction or emergence from anesthesia.

Journal Article↗
PubMed2006

A guest molecule-host cavity fitting algorithm to mine PDB for small molecule targets.

Inhaled anesthetic molecule occupancy of a protein internal cavity depends in part on the volumes of the guest molecule and the host site. Current algorithms to determine volume and surface area of cavities in proteins whose structures have been determined and cataloged make no allowance for shape or small degrees of shape adjustment to accommodate a guest. We developed an algorithm to determine spheroid dimensions matching cavity volume and surface area and applied it to screen the cavities of 6,658 nonredundant structures stored in the Protein Data Bank (PDB) for potential targets of halothane (2-bromo-2-chloro-1,1,1-trifluoroethane). Our algorithm determined sizes of prolate and oblate spheroids matching dimensions of each cavity found. If those spheroids could accommodate halothane (radius 2.91 A) as a guest, we determined the packing coefficient. 394,766 total cavities were identified. Of 58,681 cavities satisfying the fit criteria for halothane, 11,902 cavities had packing coefficients in the range of 0.46-0.64. This represents 20.3% of cavities large enough to hold halothane, 3.0% of all cavities processed, and found in 2,432 protein structures. Our algorithm incorporates shape dependence to screen guest-host relationships for potential small molecule occupancy of protein cavities. Proteins with large numbers of such cavities are more likely to be functionally altered by halothane.

Algorithms↗
PubMed2006

Dextran functionalized surfaces via reductive amination: morphology, wetting, and adhesion.

Dextran surface grafting density was systematically varied via a two-step process involving SiO(2) amination by aminopropyltriethoxy silane (APTES) followed by oxidized dextran (M(w) = 110 kDa) chemisorption. Dextran oxidation kinetics with sodium metaperiodate (NaIO(4)) were quantified by (1)H NMR and pH measurements. Aldehyde group formation increased with increasing oxidation time. For 0.5 h oxidation time, dried film ellipsometric thickness was constant for solution concentrations ranging from 1 to 4 mg/mL. Dextran layers with the lowest grafting density wetted fastest and displayed the lowest contact angle (theta(APTES) > theta(1 h) > theta(2,4 h) > theta(0.5 h)). Under aqueous conditions, AFM force versus displacement measurements on 0.5 and 4.0 h surfaces exhibited a single displacement jump upon retraction. The 1.0 and 2.0 h surfaces showed two jumps consistent with two populations of chains, namely, loosely and strongly bound dextran. Overall, film morphology and wetting behavior were relatively invariant with grafting density, confirming the method's robustness for preparing biomimetic coatings with consistent properties.

Amination↗
PubMed2006

Influence of endothelial glycocalyx degradation and surfactants on air embolism adhesion.

BACKGROUND: Microbubble adherence to endothelial cells is enhanced after damage to the glycocalyx. The authors tested the hypothesis that exogenous surfactants delivered intravascularly have differential effects on the rate of restoration of blood flow after heparinase-induced degradation of the endothelial glycocalyx. METHODS: Air microbubbles were injected into the rat cremaster microcirculation after perfusion with heparinase or saline and intravascular administration of either saline or one of two surfactants. The surfactants were Pluronic F-127 (Molecular Probes, Eugene, OR) and Perftoran (OJSC SPC Perftoran, Moscow, Russia). Embolism dimensions and dynamics were observed using intravital microscopy. RESULTS: Significant results were that bubbles embolized the largest diameter vessels after glycocalyx degradation. Bubbles embolized smaller vessels in the surfactant treatment groups. The incidence of bubble dislodgement and the magnitude of distal displacement were smallest after glycocalyx degradation alone and largest after surfactant alone. The time to bubble clearance and restoration of blood flow was longest with heparinase alone and shortest with Pluronic F-127 alone. CONCLUSIONS: Degradation of the glycocalyx causes air bubbles to adhere to the endothelium more proximally in the arteriolar microcirculation. Surfactants added after glycocalyx degradation and before gas embolization promotes bubble lodging in the distal microcirculation. Surfactants may have a clinical role in reducing embolism bubble adhesion to endothelial cells undergoing glycocalyx disruption.

Animals↗
PubMed2006

Dose- and time-dependent liquid sclerosant effects on endothelial cell death.

BACKGROUND: Intravenous sclerotherapy solutions can induce endothelial cell death. OBJECTIVE: The objective was to determine the relationship between sclerosant concentration and minimum contact time required for in endothelial cell death. METHODS: Cultured bovine aortic endothelial cells were exposed to a broad range of concentrations of two liquid sclerosants, polidocanol and sodium tetradecyl sulfate. Fluorescence microscopy was used to study cells using dyes specifically indicating changes in intracellular calcium levels, nitric oxide production, and loss of cell membrane integrity after sclerosant exposure. Fluorescence intensity measurements were used to identify the timing of cell death. RESULTS: Calcium signaling and nitric oxide pathways were activated by the administration of the sclerosants and were followed by cell death. The time to the activation and the cell death was dependent on the concentration of sclerosants. At 0.3% polidocanol or 0.1% sodium tetradecyl sulfate, cell death occurred within 15 minutes. At less than 0.003% polidocanol and at 0.005% sodium tetradecyl sulfate, cells remained alive after 60 minutes. CONCLUSION: Both sclerosants rapidly led to cell death at sufficiently high concentrations. At low sclerosant concentrations, cell viability was maintained beyond the recording time of the experiment. The timing of endothelial cell death is predictable based on sclerosant concentration during exposure.

Animals↗
PubMed2006

Gas embolism and surfactant-based intervention: implications for long-duration space-based activity.

Intravascular gas embolism can occur with decompression in space flight, and it commonly occurs during cardiac and vascular surgery. Intravascular bubbles may be deposited into any end organ such as the heart or the brain. Surface interactions between the bubble and the endothelial cells lining the vasculature result in serious impairment of blood flow and can lead to heart attack, stroke, or even death. Surfactant-based intervention is a novel treatment for gas embolism. Intravascular surfactant can adsorb onto the gas-liquid interface and compete with blood-borne macromolecules for interfacial occupancy. Surfactants can retard the progress of pathophysiological molecular and cellular events stimulated by the bubble surface, including endothelial cell injury and initiation of blood clotting. Bulk and surface transport of a surfactant to provide competition for interfacial occupancy is a therapeutic strategy because surfactant adsorption can dominate protein (or other macromolecule) adsorption. The presence of surfactant along the gas-liquid interface also induces variation in the interfacial tension, which in turn affects the blood flow and the bubble motion. We describe the interplay between biological transport processes and physiological events occurring and the cellular and molecular level in vascular gas embolization. Special consideration is given to modeling the transport and hydrodynamic interactions associated with surfactant-based intervention.

Adsorption↗
PubMed2006

Numerical modeling of the transport to an intravascular bubble in a tube with a soluble/insoluble surfactant.

Using a newly developed algorithm in conjunction with the front tracking scheme, we have evaluated the transport associated with a deformable bubble moving in a tube in the presence of a soluble or an insoluble surfactant. Such evaluations are useful to the understanding of gas embolism--a common syndrome for decompression sickness. Decompression sickness may be encountered in performing extravehicular activity during space exploration. The numerical evaluations indicate that as the location of the adsorptive interface gets closer to the vessel wall, the surfactant amount on the wall gets depleted. The implication is that the process by which a bubble occluding a vessel dislodges may depend both on the strength of the diffusivity of the surfactant and the adsorption process. More detailed study is needed to clarify this observation. The numerical results evaluated include Marangoni flow, which causes a bubble to propel out of its initial static location, and bubble motion in Poiseuille flow. The presence of a soluble/insoluble surfactant slows down the bubble motion. For identical surface concentrations of the surfactant, the effect of the presence of a soluble surfactant is more severe on the retardation of the bubble motion than that of an insoluble surfactant.

Algorithms↗
PubMed2005

A quantitative and selective chromatography method for determining coverages of multiple proteins on surfaces.

Competitive protein adsorption plays a key role in the surface hemocompatibility of biological implants. We describe a quantitative chromatography method to measure the coverage of multiple proteins physisorbed to surfaces. In this method adsorbed proteins are displaced by CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate) and then analyzed by high performance liquid chromatography to separate and quantify the individual proteins, in this case bovine serum albumin (BSA) and bovine fibrinogen (Fg). CHAPS displaced over 95% of the adsorbed proteins and was easily removed from solution by dialysis. This method was tested by measuring the coverage of BSA, 66 kDa, and Fg, 340 kDa, simultaneously adsorbed from solutions with concentration of 20 microg/ml, on bare and dextranized silicon. Relative to silicon, the dextranized surfaces were found to strongly inhibit protein adsorption, decreasing BSA and Fg coverages by 76 and 60%, respectively.

Adsorption↗
PubMed2005

Surfactants reduce platelet-bubble and platelet-platelet binding induced by in vitro air embolism.

BACKGROUND: The effect of gas bubbles on platelet behavior is poorly characterized. The authors assessed platelet-bubble and platelet-platelet binding in platelet-rich plasma in the presence and absence of bubbles and three surface-active compounds. METHODS: Platelet-rich plasma was prepared from blood drawn from 16 volunteers. Experimental groups were surfactant alone, sparging (microbubble embolization) alone, sparging with surfactant, and neither sparging nor surfactant. The surfactants were Pluronic F-127 (Molecular Probes, Eugene, OR), Perftoran (OJSC SPC Perftoran, Moscow, Russia), and Dow Corning Antifoam 1510US (Dow Corning, Midland, MI). Videomicroscopy images of specimens drawn through rectangular glass microcapillaries on an inverted microscope and Coulter counter measurements were used to assess platelet-bubble and platelet-platelet binding, respectively, in calcium-free and recalcified samples. Histamine-induced and adenosine diphosphate-induced platelet-platelet binding were measured in unsparged samples. Differences between groups were considered significant for P < 0.05 using analysis of variance and the Bonferroni correction. RESULTS: Sixty to 100 platelets adhered to bubbles in sparged, surfactant-free samples. With sparging and surfactant, few platelets adhered to bubbles. Numbers of platelet singlets and multimers not adherent to bubbles were different (P < 0.05) compared both with unsparged samples and sparged samples without surfactant. No significant platelet-platelet binding occurred in uncalcified, sparged samples, although 20-30 platelets adhered to bubbles. Without sparging, histamine and adenosine diphosphate provoked platelet-platelet binding with and without surfactants present. CONCLUSIONS: Sparging causes platelets to bind to air bubbles and each other. Surfactants added before sparging attenuate platelet-bubble and platelet-platelet binding. Surfactants may have a clinical role in attenuating gas embolism-induced platelet-bubble and platelet-platelet binding.

Adenosine Diphosphate↗
PubMed2005

Microvascular embolization following polidocanol microfoam sclerosant administration.

BACKGROUND: Intravenous microfoam sclerotherapy solutions can potentially cause cerebrovascular arterial embolization. OBJECTIVE: To determine the relationship between polidocanol microfoam formulation and arteriolar embolization bubble lodging and clearance in vivo. METHODS: Three polidocanol microfoams (one made by the double-syringe method using air and two Varisolve (Provensis, Inc., West Conshohocken, PA, USA) formulations using different physiologic gas mixtures composed primarily of oxygen and carbon dioxide and dispensed from a proprietary canister mechanism) were mixed with venous blood and injected into the rat cremaster arterial microcirculation. Bubble dimensions and dynamics were recorded using intravital microscopy. RESULTS: Bubble entry frequency, size, and dynamics depended on microfoam formulation. Air-based bubbles (2.72 1.38 nL; n = 21) lodged, obliterating blood flow. Varisolve bubbles (0.20 0.02 nL; n = 2 and 0.53 0.27 nL; n = 27 for the two gas compositions) entered but either did not lodge or cleared within seconds. Bubble size and number were different among these microfoams. CONCLUSIONS: Both Varisolve formulations produced smaller embolism bubbles than occurred with air-based microfoam. Rapid clearance of Varisolve bubbles suggests that they are so small that they do not have adequate surface area available for significant binding interactions with arteriolar endothelium. Larger air-based bubbles obstruct arteriolar vessels and block blood flow.

Animals↗
PubMed2004

Surfactants attenuate gas embolism-induced thrombin production.

BACKGROUND: There are no pharmacologic strategies to prevent embolism bubble-induced blood clot formation. The authors conducted experiments to measure thrombin production in sheared whole blood in the presence and absence of bubbles and three surface-active compounds. METHODS: Blood samples were obtained from six volunteers seven times. The thrombin-specific substrate Boc-VPR-MCA was added to citrated blood diluted with HEPES-buffered saline. Experimental groups were as follows: sparging (air microbubble embolization) with surfactant present; sparging alone; surfactant alone; and neither surfactant nor sparging. The surfactants were Dow Corning Antifoam 1510US, Perftoran, and Pluronic F-127. Blood was sheared by a cone-plate viscometer at 100 and 500 s-1 for 5, 10, and 20 min at 37 degrees C, pipetted into excess stop buffer, and evaluated fluorimetrically. Mean values of fluorescence intensity +/- SDs for each group were compared using ANOVA. Differences were considered significant at P < 0.05 using the Bonferroni correction. RESULTS: For fixed shear rate, thrombin production increased 2.3- to 5.7-fold (P < 0.05) as shear duration lengthened. For fixed shear duration, thrombin production increased 1.9- to 3.9-fold (P < 0.05) with increasing shear rate. For fixed shear rate and duration, sparging increased thrombin production 2.1- to 3.7-fold (P < 0.05). Surfactant addition without sparging did not change thrombin production (P > 0.05). Surfactants attenuated thrombin production in sparged samples 31.8-70.9% (P < 0.05). CONCLUSIONS: Thrombin production is shear rate and duration-dependent. Sparging increases thrombin production. Surfactants added before sparging attenuate thrombin production. Surfactants may have a clinical application to attenuate gas embolism-induced clotting.

Blood Platelets↗
PubMed2004

Surfactant reduction in embolism bubble adhesion and endothelial damage.

BACKGROUND: Surfactants may reduce the adhesion force holding bubbles to the vessel wall in gas embolism. The authors measured bubble adhesion force using excised microvessels. They assessed endothelial damage by measuring vessel reactivity and with microscopy. METHODS: Microbubbles injected into arterioles resided for 5, 10, or 30 min, with intact or damaged endothelium. Perfusion was with rat serum alone (control) or with 1% Perftoran (OJSC SPC Perftoran, Moscow, Russia) or 1% Pluronic F-127 (Molecular Probes, Eugene, OR) added. Pressure across the bubble, bubble length, and bubble diameter were measured, and adhesion force per unit surface area, K = deltaPD/4 l, was calculated. Vessel reactivity was assessed using topical application of phenylephrine and acetylcholine. RESULTS: With the endothelium intact, K was higher in controls than with Perftoran at 10 and 30 min or Pluronic F-127 at 10 min (P < 0.05). With surfactant added after air perfusion to damage the endothelium, K was lower (P < 0.05) at all times for both Perftoran and Pluronic F-127. With surfactant in the perfusate before air perfusion, K was lower at 10 and 30 min for Perftoran and at 10 min for Pluronic F-127 than for controls (P < 0.05). Phenylephrine-induced vasoconstriction was identical among groups. Acetylcholine-induced vasodilatation was the same among groups with an intact endothelium but was found to be lower in controls after air perfusion that followed surfactant exposure than in either surfactant group (P < 0.05). CONCLUSIONS: Surfactants reduced bubble adhesion force and preserved basic endothelial structure and vasodilatory function despite attempts to damage the endothelium. Surfactants seem to protect the endothelium from mechanically induced injury in addition to decreasing bubble adhesion forces.

Adhesiveness↗
PubMed2003

Embolism bubble adhesion force in excised perfused microvessels.

BACKGROUND: The mechanics of gas embolism bubble adhesion to the vessel wall is poorly understood. New strategies to treat gas embolism may result from an understanding of adhesion forces, including the molecular determinants of bubble adhesion. The authors conducted experiments to measure the adhesion force of bubbles contacting the vessel wall. METHODS: Microbubbles were injected into excised arterioles. Bubbles resided for 5, 10, 20, or 30 min with the endothelium intact or damaged and with a physiologic salt solution, physiologic salt solution with 5% bovine serum albumin, or rat serum as the perfusate. Inflow pressure was raised until the bubble dislodged. The differential pressure across the microbubble, deltaP, was recorded at the moment of bubble movement. Bubble diameter, D, and length, L, were determined by videomicroscopy. The adhesion force per unit surface area of a bubble contacting the vessel wall, K = deltaPD/4 L, was calculated for each experiment. RESULTS: K at 10 min contact time (physiologic salt solution, 141 +/- 29; serum, 153 +/- 57 dyne/cm2) was higher than at 5 min (physiologic salt solution, 56 +/- 22; serum, 71 +/- 29 dyne/cm2), 20 min (physiologic salt solution, 46 +/- 29) and 30 min (physiologic salt solution, 14 +/- 5) (P < 0.05). Endothelium removal reduced K at 10 min (physiologic salt solution, 68 +/- 46; serum, 60 +/- 14 dyne/cm2) (P < 0.05). K was higher with 5% bovine serum albumin present at 10 min (349 +/- 149, P < 0.05), correlating with in vivo estimates. CONCLUSIONS: The adhesion force developed between a microbubble and the vessel wall depends on multiple factors, including bubble residence time, presence of the endothelium, and perfusion solution.

Acetylcholine↗
PubMed2003

Model predictions of gas embolism growth and reabsorption during xenon anesthesia.

BACKGROUND: It is not readily obvious whether an intravascular bubble will grow or shrink in a particular tissue bed. This depends on the constituent gases initially present in the bubble, the surrounding tissue, and the delivered gas admixture. The authors used a computational model based on the physics of gas exchange to predict cerebrovascular embolism behavior during xenon anesthesia. METHODS: The authors estimated values of gas transport parameters missing from the literature. The computational model was used with those parameters to predict bubble size over time for a range of temperatures (18 degrees -39 degrees C) used during extracorporeal circulation. RESULTS: Bubble size over time is highly nonlinearly dependent on multiple factors, including diffusivity, solubility, gas partial pressures, magnitude of concentration gradients, vessel diameter, and temperature. Xenon- and oxygen-containing bubbles continue to grow during xenon delivery. Bubble volume doubles from 50 to 100 nl in approximately 3-68 min, depending on initial gas composition and bubble shape. Bubble growth and reabsorption are relatively insensitive to temperature in the physiologic and surgical range. CONCLUSIONS: Xenon anesthesia results in gas exchange conditions that favor bubble growth, which may worsen neurologic injury from gas embolism. The concentration gradients can be manipulated by discontinuation of xenon delivery to promote reabsorption of xenon-containing bubbles. Estimated growth and reabsorption rates at normothermia can be applied to temperature extremes of cardiopulmonary bypass.

Algorithms↗
PubMed2002

Microvascular gas embolization clearance following perfluorocarbon administration.

Effective treatment of vascular gas embolism may be possible with emulsified fluorocarbon compounds. We tested the hypothesis that a fluorocarbon emulsion delivered before gas embolization would enhance bubble motion through the vasculature, favoring more rapid clearance. Air microbubbles were injected into the rat cremaster microcirculation in six groups of rats receiving Perftoran, an emulsified fluorocarbon, or saline immediately before, 2 h before, or after bubble injection. Embolism dimensions and dynamics were observed by using intravital microscopy. Surface area at lodging was equal between groups. Bubbles having smaller volume embolized smaller diameter vessels in the Perftoran pretreatment groups. A higher incidence of bubble dislodgement and larger distal displacement occurred in these two groups, with a 36% decrease in the time to bubble clearance and restoration of blood flow. Intravascular emulsified fluorocarbon administration before gas embolization affected initial bubble conformation, increased bubble dislodgement, and resulted in bubble displacement further into the periphery of the microcirculation. These dynamic events did not occur if embolization preceded fluorocarbon administration.

Algorithms↗
PubMed2002

Clinical application of acoustic reflectometry in predicting the difficult airway.

UNLABELLED: Acoustic reflectometry, a noninvasive test that produces a length versus cross-sectional area map of the airway, has been used to identify difficult-to-tracheally intubate patients in a small retrospective case-control study. A critical airway volume of 40.2 mL separated those patients whose tracheas were impossible to intubate from those who were easily intubated. To determine if this technology was applicable for prospectively predicting difficult intubation and difficult ventilation in routine clinical practice, we performed a double-blinded, prospective cohort study. Our a priori hypothesis was that small airway volumes in adults (<40.2 mL) would predict absolute inability to intubate. We conclude that by use of acoustic reflectometry, there was no relationship between inability to intubate, poor glottic visualization, and multiple laryngoscopies with airway volume. IMPLICATIONS: Acoustic reflectometry, a noninvasive test that uses sound to produce a length versus cross-sectional area map of the airway, was not able to predict inability to intubate, poor glottic visualization, and multiple laryngoscopies.

Adult↗