Effect of thermal interface on heat flow in carbon nanofiber composites

The thermal transport process in carbon nanofiber (CNF)/epoxy composites is addressed through combined micromechanics and finite element modeling, guided by experiments. The heat exchange between CNF constituents and matrix is studied by explicitly accounting for interface thermal resistance between the CNFs and the epoxy matrix. The effects of nanofiber orientation and discontinuity on heat flow and thermal conductivity of nanocomposites are investigated through simulation of the laser flash experiment technique and Fourier's model of heat conduction. Our results indicate that when continuous CNFs are misoriented with respect to the average temperature gradient, the presence of interfacial resistance does not affect the thermal conductivity of the nanocomposites, as most of the heat flow will be through CNFs; however, interface thermal resistance can significantly alter the patterns of heat flow within the nanocomposite. It was found that very high interface resistance leads to heat entrapment at the interface near to the heat source, which can promote interface thermal degradation. The magnitude of heat entrapment, quantified via the peak transient temperature rise at the interface, in the case of high thermal resistance interfaces becomes an order of magnitude more intense as compared to the case of low thermal resistance interfaces. Moreover, high interface thermal resistance in the case of discontinuous fibers leads to a nearly complete thermal isolation of the fibers from the matrix, which will marginalize the contribution of the CNF thermal conductivity to the heat transfer in the composite.

Effect of twist and porosity on the electrical conductivity of carbon nanofiber yarns

This study focuses on the effect of twist and porosity on the electrical conductivity of carbon nanofiber (CNF) yarns. The process of fabrication of CNF yarns included the synthesis of aligned ribbons of polyacrylonitrile (PAN) nanofibers via electrospinning. The PAN ribbons were twisted into yarns with twist levels ranging from zero twist to high twists of 1300 turn per meter (tpm). The twist imposed on the ribbons substantially improved the interactions between nanofibers and reduced the porosity. The PAN yarns were subsequently stabilized in air, and then carbonized in nitrogen at 1100 °C for 1 h. Compressive stresses developed between the PAN nanofibers as a result of twist promoted interfusion between neighboring nanofibers, which was accelerated by heating the yarns during stabilization to temperatures above the glass transition of PAN. The electrical conductivity of the yarns was measured with a four point probe measurement technique. Although increasing the twist promotes electrical conductivity between nanofibers by forming junctions between them, our results indicate that the electrical conductivity does not continuously increase with increasing twist, but reaches a threshold value after which it starts to decrease. The causes for this behavior were studied through experimental techniques and further explored using a yarn-equivalent electrical circuit model.

Tension pneumocephalus: a life-threatening complication of septoplasty and septorhinoplasty

PROBLEMS/ OBJECTIVES: Septoplasty and septorhinoplasty are two important surgical operations in otorhinolaryngology. Tension pneumocephalus is a rare, but potentially fatal, intracranial complication of these operations.

METHODOLOGY

We present two cases of tension pneumocephalus following nasal surgery. Both patients had tension pneumocephalus, meningitis, and defects in the skull base.

RESULTS

One patient underwent endoscopic repair of the defect, while the second case expired despite medical and neurosurgical management.

Association between the functional polymorphism C-159T in the CD14 promoter gene and nasal polyposis: potential role in asthma

BACKGROUND

Nasal polyposis (NP) is a chronic inflammatory disease that is frequently associated with allergy and asthma. Corticosteroid therapy and surgical removal of polyps are the 2 most common treatment strategies for NP. Various allergic and inflammatory mediators are thought to play a major role in the pathophysiology of this disorder. The CD14 gene is located on chromosome 5q31-32, which is considered a critical region for several allergic and atopic diseases, including asthma. Consequently, variations in CD14 could have functional effects on the etiology and severity of allergy and asthma. The aim of this study was to investigate the association between the polymorphism C-159T in the CD14 gene of patients with NP and controls.

METHODS

The study population comprised 106 patients with NP diagnosed based on computed tomography scan of the paranasal sinus, endoscopy, and histological examination. Findings were compared with those from 87 controls. The frequency of C-159T was determined using polymerase chain reaction-restriction fragment length polymorphism analysis. DNA was extracted using the salting out technique.

RESULTS

A significant association was observed between C-159T and NP (P = .04). Patients with the CC genotype at position -159 of the CD14 promoter region had an increased risk of asthma (OR, 3.83, 95% CI, 0.99-13.91; P < .02). However, we did not find an association between the distribution of C-159T and serum immunoglobulin E level.

CONCLUSIONS

A genetic variation in the CD14 promoter might play a role in the pathogenesis of NP and in the incidence of asthma.

Two-dimensional determination of the cellular Ca2+ binding in bovine chromaffin cells

The spatiotemporal profile of intracellular calcium signals is determined by the flux of calcium ions across different biological membranes as well as by the diffusional mobility of calcium and different calcium buffers in the cell. To arrive at a quantitative understanding of the determinants of these signals, one needs to dissociate the flux contribution from the redistribution and buffering of calcium. Since the cytosol can be heterogeneous with respect to its calcium buffering property, it is essential to assess this property in a spatially resolved manner. In this paper we report on two different methods to estimate the cellular calcium binding of bovine adrenal chromaffin cells. In the first method, we use voltage-dependent calcium channels as a source to generate calcium gradients in the cytosol. Using imaging techniques, we monitor the dissipation of these gradients to estimate local apparent calcium diffusion coefficients and, from these, local calcium binding ratios. This approach requires a very high signal-to-noise ratio of the calcium measurement and can be used when well-defined calcium gradients can be generated throughout the cell. In the second method, we overcome these problems by using calcium-loaded DM-nitrophen as a light-dependent calcium source to homogeneously and quantitatively release calcium in the cytosol. By measuring [Ca2+] directly before and after the photorelease process and knowing the total amount of calcium being released photolytically, we get an estimate of the fraction of calcium ions which does not appear as free calcium and hence must be bound to either the indicator dye or the endogenous calcium buffer. This finally results in a two-dimensional map of the distribution of the immobile endogenous calcium buffer. We did not observe significant variations of the cellular calcium binding at a spatial resolution of approximately 2 micron. Furthermore, the calcium binding is not reduced by increasing the resting [Ca2+] to levels as high as 1.1 microM. This is indicative of a low calcium affinity of the corresponding buffers and is in agreement with a recent report on the affinity of these buffers (Xu, T., M. Naraghi, H. Kang, and E. Neher. 1997. Biophys. J. 73:532-545). In contrast to the homogeneous distribution of the calcium buffers, the apparant calcium diffusion coefficient did show inhomogeneities, which can be attributed to restricted diffusion at the nuclear envelope and to rim effects at the cell membrane.

Two dye two wavelength excitation calcium imaging: results from bovine adrenal chromaffin cells

We tested a mixture of Calcium-Green-1 (CG-1) and Brilliantsulfaflavine (BS) for dual excitation ratiometric measurements of the intracellular free calcium concentration ([Ca2+]i) in bovine adrenal chromaffin cells. Dyes were coloaded (without being molecularly linked to each other) in the whole-cell configuration of the patch clamp technique. We compared the loading time-courses of CG-1 and BS, investigated their intracellular distribution patterns and studied the time course of photobleaching. We determined the apparent dissociation constant of CG-1, both optically and by potentiometric titration. Our findings indicate that: (i) with excitation at 420/488 nm, calibrated fluorescence signals could be derived using a Grynkiewicz-type equation; (ii) BS is an ideal reference dye that displayed no interaction with CG-1 or cellular constituents; and (iii) that calibration requires diffusional equilibration between pipette and the accessible volume of the cell. Spatially resolved recordings of fluorescence excitation spectra revealed elevated fluorescence of CG-1 in the nucleus such that reported [Ca2+]i levels seemed 25% higher compared to cytosolic values. Comparing fluorescence emission from in vitro dye solutions with in vivo values, we could estimate the accessible volume fraction and amount of Ca(2+)-insensitive dye.

T-jump study of calcium binding kinetics of calcium chelators

Recent experimental studies have investigated the kinetic competition between calcium chelators and the secretion apparatus at a fast central synapse. Simultaneously, mathematical modelling studies indicate the importance of a quantitative knowledge of the binding kinetics of the chelators in studying fast physiological processes operating on a millisecond time scale. Using the temperature-jump relaxation method, I have studied the in vitro kinetics of Bis-Fura-2, Furaptra, Fluo-3, Calcium-Green-1, Calcium-Green-5N, Calcium-Orange-5N as well as EGTA, BAPTA and H-EDTA in conditions which are identical to those implemented in our patch clamp recordings, i.e. 100-140 mM CsCl, 20-40 mM Cs-HEPES, 8 mM NaCl, pH = 7.2 at 22 degrees C. The results can be summarized as follows: all fluorescent indicators have on rates in the range of 10(8)-10(9) M-1s-1. They differ significantly with respect to their off-rates from each other according to their affinities, ranging from 100 s-1 up to 26,000 s-1. BAPTA is kinetically almost indistinguishable from Fura-2. EGTA and H-EDTA have small binding rate constants for calcium in the range of 3 x 10(6) M-1s-1 since, at pH 7.20, protons need to be dissociated from the chelators before they can bind calcium ions.

Linearized buffered Ca2+ diffusion in microdomains and its implications for calculation of [Ca2+] at the mouth of a calcium channel

Immobile and mobile calcium buffers shape the calcium signal close to a channel by reducing and localizing the transient calcium increase to physiological compartments. In this paper, we focus on the impact of mobile buffers in shaping steady-state calcium gradients in the vicinity of an open channel, i.e. within its "calcium microdomain." We present a linear approximation of the combined reaction-diffusion problem, which can be solved explicitly and accounts for an arbitrary number of calcium buffers, either endogenous or added exogenously. It is valid for small saturation levels of the present buffers and shows that within a few hundred nanometers from the channel, standing calcium gradients develop in hundreds of microseconds after channel opening. It is shown that every buffer can be assigned a uniquely defined length-constant as a measure of its capability to buffer calcium close to the channel. The length-constant clarifies intuitively the significance of buffer binding and unbinding kinetics for understanding local calcium signals. Hence, we examine the parameters shaping these steady-state gradients. The model can be used to check the expected influence of single channel calcium microdomains on physiological processes such as excitation-secretion coupling or excitation-contraction coupling and to explore the differential effect of kinetic buffer parameters on the shape of these microdomains.

Kinetic studies of Ca2+ binding and Ca2+ clearance in the cytosol of adrenal chromaffin cells

The Ca2+ binding kinetics of fura-2, DM-nitrophen, and the endogenous Ca2+ buffer, which determine the time course of Ca2+ changes after photolysis of DM-nitrophen, were studied in bovine chromaffin cells. The in vivo Ca2+ association rate constants of fura-2, DM-nitrophen, and the endogenous Ca2+ buffer were measured to be 5.17 x 10(8) M-1 s-1, 3.5 x 10(7) M-1 s-1, and 1.07 x 10(8) M-1 s-1, respectively. The endogenous Ca2+ buffer appeared to have a low affinity for Ca2+ with a dissociation constant around 100 microM. A fast Ca2+ uptake mechanism was also found to play a dominant role in the clearance of Ca2+ after flashes at high intracellular free Ca2+ concentrations ([Ca2+]), causing a fast [Ca2+]i decay within seconds. This Ca2+ clearance was identified as mitochondrial Ca2+ uptake. Its uptake kinetics were studied by analyzing the Ca2+ decay at high [Ca2+]i after flash photolysis of DM-nitrophen. The capacity of the mitochondrial uptake corresponds to a total cytosolic Ca2+ load of approximately 1 mM.

Effect of esmolol given during cardiopulmonary bypass on fractional area of contraction from transesophageal echocardiography

The infusion of esmolol during hypothermic cardiopulmonary bypass (CPB) has no negative myocardial effects after CPB, despite increased esmolol levels during CPB due to hypothermia. The purpose of this randomized, double-blind, prospective study was to measure the effects of esmolol infused during CPB on cardiac function as measured by calculated indices of cardiac work and by transesophageal echocardiography (TEE). Patients scheduled for CPB were randomized to receive intravenous esmolol (300 micrograms.kg-1.min-1 during CPB after bolus of 2 mg/kg prior to CPB) or placebo. Infusion was stopped at 10 min after release of aortic cross-clamp. Hemodynamics and TEE were recorded during the procedure. Fractional area of contraction (FAC), an approximation of left ventricular ejection fraction, was calculated from end-diastolic and end-systolic areas. Esmolol was administered to 15 patients and placebo to 14. Heart rates in the esmolol group were lower during infusion and prior to CPB (P < 0.05). Stroke volume index and left ventricular stroke work index were higher in the esmolol group at 15 min post-CPB (P < 0.05). FAC was higher in the esmolol group at 15 and 30 min post-CPB (P < 0.05), but no difference was observed between groups at 1 h post-CPB. Esmolol infused during CPB in this series of patients was associated with better left ventricular function during the first 0.5 h post-CPB.

Leak rate of latex gloves after tearing adhesive tape

Anesthesiologists use latex gloves to provide barrier protection against infectious disease or contamination while providing anesthetic services. The performance of these services often involves tearing tape. The purpose of this study was to test the effect of tearing adhesive tape on permeability of latex examination gloves and to test the effect of an adhesive-sparing moisturizing cream on permeability of latex gloves used to tear adhesive tape. In a blinded, randomized, controlled laboratory experiment, 48 nonsterile latex examination gloves (24 pairs) were randomized to 1 of 2 groups. Adhesive-sparing moisturizing cream, 0.1 mL, was applied to 12 glove pairs; the remaining 12 pairs served as controls. Each of the 24 pairs of gloves were used to tear five 4-cm strips of cloth adhesive tape from a standard 1 1/2-inch roll. After initial inspection for obvious tears, each glove was tested for leaks using the watertight test as specified by the American Society for Testing and Materials (ASTM). Data recorded included the identity of the investigator tearing tape, number of holes initially observed, number of holes observed from the ASTM test, location of holes, glove classification as right or left hand, and treatment group. Based on the study, the authors concluded that health care providers who tear adhesive tape while wearing latex gloves should be aware that there is a high probability that the gloves no longer form a protective barrier and that adhesive-sparing moisturizing cream applied before tape is torn increases barrier protection.

Treatment of the cutaneous pain of acute herpes zoster with 9% lidocaine (base) in petrolatum/paraffin ointment

BACKGROUND

Treatment of the pain of acute herpes zoster by local anesthetic injections has drawbacks. Topical percutaneous local anesthesia (TPLA) may offer another strategy of providing regional analgesia in affected patients.

OBJECTIVE

We evaluate the analgesic efficacy and safety of 9% (wt/vol) lidocaine (base) in petrolatum/paraffin ointment in patients with acute herpes zoster.

METHODS

Ointment was applied to the affected skin of 22 patients. Pain, tenderness, sensitivity to pinprick and cold, and blood lidocaine concentration were measured repeatedly during a 20-hour interval and intermittently thereafter.

RESULTS

Mean pain, tenderness, and cutaneous sensation scores were reduced at measurements taken from 4 to 20 hours after ointment application (p < 0.05), but not every patient obtained relief. No patient had local skin irritation or systemic toxic effects related to the local anesthetic.

CONCLUSIONS

TPLA is a promising therapy for control of cutaneous pain of acute herpes zoster. Controlled studies should be performed to prove efficacy, determine optimal TPLA formulation, and define dosage limits.

Odorant-induced oscillations in the mushroom bodies of the locust

Kenyon cells are the intrinsic interneurons of the mushroom bodies in the insect brain, a center for olfactory and multimodal processing and associative learning. These neurons are small (3-8 microns soma diameter) and numerous (340,000 and 400,000 in the bee and cockroach brains, respectively). In Drosophila, Kenyon cells are the dominant site of expression of the dunce, DC0, and rutabaga gene products, enzymes in the cAMP cascade whose absence leads to specific defects in olfactory learning. In honeybees, the volume of the mushroom body neurophils may depend on the age or social status of the individual. Although the anatomy of these neurons has been known for nearly a century, their physiological properties and the principles of information processing in the circuits that they form are totally unknown. This article provides a first such characterization. The activity of Kenyon cells was recorded in vivo from locust brains with intracellular and local field potential electrodes during olfactory processing. Kenyon cells had a high input impedance (approximately 1 G omega at the soma). They produced action potentials upon depolarization, and consistently showed spike adaptation during long depolarizing current pulses. They generally displayed a low resting level of spike activity in the absence of sensory stimulation, despite a large background of spontaneous synaptic activity, and showed no intrinsic bursting behavior. Presentation of an airborne odor, but not air alone, to an antenna evoked spatially coherent field potential oscillations in the ipsilateral mushroom body, with a frequency of approximately 20 Hz. The frequency of these oscillations was independent of the nature of the odorant. Short bouts of oscillations sometimes occurred spontaneously, that is, in the absence of odorant stimulation. Autocorrelograms of the local field potentials in the absence of olfactory stimulation revealed small peaks at +/- 50 msec, suggesting an intrinsic tendency of the mushroom body networks to oscillate at 20 Hz. Such oscillatory behavior could not be seen from local field potential recordings in the antennal lobes, and may thus be generated in the mushroom body, or via feedback interactions with downstream neurons in the protocerebrum. During the odor-induced oscillations, the membrane potential of Kenyon cells oscillated around the resting level, under the influence of excitatory inputs phase-locked to the field activity. Each phasic wave of depolarization in a Kenyon cell could be amplified by intrinsic excitable properties of the dendritic membrane, and sometimes led to one action potential, whose timing was phase-locked to the population oscillations.(ABSTRACT TRUNCATED AT 400 WORDS)

Outpatient spinal opiate analgesia: a case report

Outpatient spinal opiate analgesia for relief of cancer pain has been well-described in the literature. We report a case of a patient with metastatic disease who received epidural morphine using a subcutaneous epidural catheter via home injections. The patient and his family administered the medications. There are several options to choose from when using epidural morphine, and each patient's needs must be evaluated for the appropriate system.

Fatal cardiac perforation caused by the dilator of a central venous catheterization kit

We report a case of cardiac perforation and tamponade caused by the dilator of a central venous catheterization kit. Standards for dilator manufacture and guidelines for safe use of these instruments are suggested.

Elective transtracheal jet ventilation for bronchoscopic removal of tracheal foreign body

We have shown that transtracheal jet ventilation can be used safely and effectively when removing a foreign body from the airway. In some cases, it may be wise to choose this method of ventilation initially, thus avoiding the difficulties associated with more conventional modes of controlled ventilation. This is especially true when the potential for loss of the airway during the procedure is significant. This technique also allows the bronchoscopist the benefit of unimpeded access to the airway and adequate uninterrupted time for his operative procedure.

Complications of endotracheal intubation

Tracheal intubation for airway control, once done only by anesthesiologists during surgical procedures, is now being done by physicians in other specialties and by nurses, technicians, and paramedics in areas other than the operating room. Intubation, however, does not always assure a patent airway. Unrecognized esophageal placement of endotracheal tubes is the major cause of cardiac arrest and brain damage associated with intubation. Though auscultation for breath sounds is the universally accepted method of verifying proper tube placement, recent studies indicate that it is reliable only approximately two thirds of the time in situations in which verification of proper placement is needed most and is least obvious. The usefulness of this technique merits reassessment. Identification of carbon dioxide in end-expired air is the most reliable method for verification, but instruments to detect carbon dioxide are usually immediately available only in special care and surgical suites. Mouth-to-tube insufflation with a two-way disposable microbial filter differentiates immediately between esophageal and tracheal placement and can be used in any area. Malpositioned and malfunctioning tubes cause partial or complete obstruction accompanied by varying degrees of hypoxemia and hypercapnia. Respiratory and circulatory derangements and brain damage ensue if the problem is not promptly recognized and corrected. We discuss the most common causes of tube malfunction.

Chronic neuralgia incidence following local anesthetic therapy for herpes zoster

We treated 72 patients, referred to a pain clinic for acute herpes zoster neuralgia, with local anesthetics administered by nerve block and infiltration. Only those patients with severe pain initially proved to be at risk for the development of chronic postherpetic neuralgia (defined as pain in the involved dermatomes lasting at least six months). Although local anesthetic injections effectively relieved the acute pain of active herpes zoster, they did not prevent the development of chronic postherpetic neuralgia.

Adverse effects of pancuronium in patients with hemorrhagic shock

Thirty-five patients with hemorrhagic shock had surgical repair of trauma to the great vessels using a ketamine-pancuronium-nitrous oxide sequence for anesthesia. The data of the cardiovascular and respiratory changes occurring during anesthesia and the operation were tabulated and subjected to multifactorial computer analysis. Fifteen patients died during or after operation because the injury was beyond repair. Twenty survived the oepration. Profound hypotension associated with mild tachycardia occurred with surprising regularity each time incremental doses of pancuronium were administered in nearly all patients. This hypotension was not associated with the administration of any other drug or with any other parameter and strongly implicates pancuronium as the causative factor. Pancuronium should be used cautiously and administered in small increments to this type of patient if it is used as a muscle relaxant.

Complications from unrecognized defects in endotracheal tubes

Considerable effort has been made to improve endotracheal tubes and make them safer than they have been in the past; yet complications continue to occur, due, in most instances, to inherent defects in the tube. It is not possible to identify these defects in a routine preoperative examination. Three cases are presented illustrating how defects in anode endotracheal tubes almost caused fatalities during anesthesia. Other possible complications and contributing factors causing obstruction of endotracheal tubes are also reviewed. Until some way is devised for the automatic compensation of the increases in volumes and pressures in endotracheal tube cuffs, hourly deflation is recommended to prevent complications.

Acute systemic toxicity from bupivacaine during epidural anesthesia in obstetric patients

Convulsions occurred within 30 seconds after the injection of bupivacaine through the epidural catheter in four obstetric patients in labor, and mild excitation without convulsions occurred in three others. Since the time between injection and the reaction was so short and since the dose was so small, the response probably was due to intravenous injection resulting from lodgement of the catheter in a vein, rather than to absorption from the epidural space itself. It is not generally known that the epidural veins become thin-walled and engorged during labor; thus, inadvertent placement of a cathether in a vein can occur readily. Convulsions, therefore, may follow even injection of a test dose of a drug. Other colleagues have had similar though unreported experiences. Physicians performing epidural blocks should be aware that such an occurrence is possible and that the catheter may be within a vein without blood returning on aspiration.