Analytic Reviews : Radiological Assessment of Central Vascular Volume Status in an Intensive Care Unit Setting

We studied the chest radiographs of 126 patients under going pulmonary artery catheterization. An experienced radiologist, unaware of the patient's clinical condition and results of pulmonary artery catheterization and without review of prior films, evaluated each radiograph focusing exclusively on fluid status, and assigned each one to one of the following four categories: definitely or probably elevated central vascular volume status, or definitely or probably nonelevated central vascular vol ume status. This assessment was then compared with the "official" reading, performed with knowledge of the patient's clinical status and with availability of previous chest radiographs. The radiologist's prediction was more accurate than the official report (65% proportion of correct classification vs. 59% ) ( p < 0.05). Patients with actual high pulmonary artery wedge pressure read ings were more difficult to diagnose correctly than pa tients with low or normal pulmonary artery wedge pres sure. In those patients in whom the radiologist felt more confident of his prediction (25% of patients), diagnostic accuracy improved considerably for both the high and normal pulmonary artery wedge pressure groups of pa tients to a proportion of correct classification of 71% and 80%, respectively. Although the radiological assess ment was not accurate enough to replace pulmonary artery catheterization, the official reading can be im proved by focusing on specific radiological features to estimate central vascular volume status.

Plasticity of fimbrial genotype and serotype within populations of Bordetella pertussis: analysis by paired flow cytometry and genome sequencing

The fimbriae of Bordetella pertussis are required for colonization of the human respiratory tract. Two serologically distinct fimbrial subunits, Fim2 and Fim3, considered important vaccine components for many years, are included in the Sanofi Pasteur 5-component acellular pertussis vaccine, and the World Health Organization recommends the inclusion of strains expressing both fimbrial serotypes in whole-cell pertussis vaccines. Each of the fimbrial major subunit genes, fim2, fim3, and fimX, has a promoter poly(C) tract upstream of its −10 box. Such monotonic DNA elements are susceptible to changes in length via slipped-strand mispairing in vitro and in vivo, which potentially causes on/off switching of genes at every cell division. Here, we have described intra-culture variability in poly(C) tract lengths and the resulting fimbrial phenotypes in 22 recent UK B. pertussis isolates. Owing to the highly plastic nature of fimbrial promoters, we used the same cultures for both genome sequencing and flow cytometry. Individual cultures of B. pertussis contained multiple fimbrial serotypes and multiple different fimbrial promoter poly(C) tract lengths, which supports earlier serological evidence that B. pertussis expresses both serotypes during infection.

Bordetella pertussis fimbriae (Fim): relevance for vaccines

Bordetella pertussis produces two serologically distinct fimbriae, Fim2 and Fim3. Expression of these antigens is governed by the BvgA/S system and by the length of a poly(C) tract in the promoter of each gene. Fim2 and Fim3 are important antigens for whole cell pertussis vaccines as clinical trials have shown an association of anti-fimbriae antibody-mediated agglutination and protection. The current five component acellular pertussis vaccine contains co-purified Fim2/3 and provided good efficacy in clinical trials with the anti-Fim antibody response correlating with protection when pre and post exposure antibody levels were analysed. The predominant serotype of B. pertussis isolates has changed over time in most countries but it is not understood whether this is vaccine-driven or whether serotype is linked to the prevailing predominant genotype. Recent studies have shown that both Fim2 and Fim3 are expressed during infection and that Fim2 is more immunogenic than Fim3 in the acellular vaccine.

Treatment of an extracapsular post-renal biopsy pseudoaneurysm with ultrasound-guided thrombin injection

Percutaneous renal biopsy is a convenient method to obtain allograft tissue for histologic evaluation. Vascular complications, such as arteriovenous (AV) fistula and pseudoaneurysm, following renal biopsy are well known, and they usually resolve without further intervention. When symptomatic, they should be treated. We present a patient on chronic anticoagulation who developed a pseudoaneurysm after percutaneous renal biopsy. Applying techniques learned in the management of femoral artery pseudoaneurysm, we treated our patient with ultrasound-guided thrombin injection.

Proteomic analysis of Neisseria lactamica and N eisseria meningitidis outer membrane vesicle vaccine antigens

Vaccines to prevent meningococcal disease have been developed from the outer membrane vesicles (OMVs) of Neisseria meningitidis and the related commensal organism Neisseria lactamica. In addition to lipopolysaccharide and the major porins, these vaccines contain a large number of proteins that are incompletely characterised. Here we describe comparative proteomic analyses of the N. lactamica OMV vaccine and OMVs from a serogroup B strain of N. meningitidis. Tandem mass-spectrometry data for trypsinised N. lactamica OMV vaccine were matched to an incompletely assembled genome sequence from the same strain to give 65 robust protein identifications and a further 122 single- or two-peptide matches. Fifty-seven N. meningitidis K454 proteins were identified robustly (and a further 68 from single- or two-peptide matches) by inference from the N. meningitidis MC58 genome. The results suggest that OMVs have a hitherto unappreciated complexity and pinpoint novel candidate antigens for further characterisation.

Microfabrication of individual 200 microm diameter transdermal microconduits using high voltage pulsing in salicylic acid and benzoic acid

We describe an extension of semiconductor fabrication methods that creates individual approximately 200 microm diameter aqueous pathways through human stratum corneum at predetermined sites. Our hypothesis is that spatially localized electroporation of the multilamellar lipid bilayer membranes provides rapid delivery of salicylic acid to the keratin within corneocytes, leading to localized keratin disruption and then to a microconduit. A microconduit penetrating the isolated stratum corneum supports a volumetric flow of order 0.01 ml per s with a pressure difference of only 0.01 atm (about 10(2) Pa). This study provides a method for rapidly microengineering a pathway in the skin to interface future devices for transdermal drug delivery and sampling of biologically relevant fluids.

Biological sensing of small field differences by magnetically sensitive chemical reactions

There is evidence that animals can detect small changes in the Earth's magnetic field by two distinct mechanisms, one using the mineral magnetite as the primary sensor and one using magnetically sensitive chemical reactions. Magnetite responds by physically twisting, or even reorienting the whole organism in the case of some bacteria, but the magnetic dipoles of individual molecules are too small to respond in the same way. Here we assess whether reactions whose rates are affected by the orientation of reactants in magnetic fields could form the basis of a biological compass. We use a general model, incorporating biological components and design criteria, to calculate realistic constraints for such a compass. This model compares a chemical signal produced owing to magnetic field effects with stochastic noise and with changes due to physiological temperature variation. Our analysis shows that a chemically based biological compass is feasible with its size, for any given detection limit, being dependent on the magnetic sensitivity of the rate constant of the chemical reaction.

Mechanism of transdermal drug delivery by electroporation

Human skin is a complex system, providing a formidable obstacle to drug delivery Fig. 1 (1-3). In particular, the stratum corneum (SC) is the primary barrier to transdermal drug delivery. The stratum corneum is made up of corneocytes, which are flattened remnants of cells, surrounded by lipid bilayer membranes (2,3). Because lipid-based structures tend to exclude charged species, the multilamellar arrangement acts as a "brick wall" (4) to prevent ionic and molecular transport. Fig. 1. 1. Key features of skin, skin barriers (104) and hypothetical aqueous pathways. The stratum corneum (SC) is the dead outermost layer (≈ 20 μm hydrated thickness) that is the main barrier to transport, particularly for charged molecules (1-3,5). Appendages (sweat ducts and hair follicles) penetrate the SC, but are lined with a double cell layer with tight junctions (105), which prevents significant transport. Hypothetical transport sites are labeled: LV (low voltage): Iontophoresis involves transport through preexisting aqueous pathways associated with appendages or around corneocytes within the SC (7,8,53,55,106). MV (moderate voltage) pulses: A relatively fast (>10 ms) process of "macropore activation" is followed by cell lining electroporation, which is hypothesized to create new aqueous pathways at appendages ("appendageal electroporation") (40,107). HV (high voltage) pulses: A very fast (<10 μs) process is hypothesized to involve a primary event of aqueous pathway creation based on electroporation of multilamellar lipid bilayers separating corneocytes (27,61,63,91,108), and secondary processes such as localized heating, or pathwayenlarging chemical introduction. Lower right: The original "brick wall model" of the SC (the largest area skin feature) intended to treat permeation of lipophilic molecules through the continuous "mortar" (4).

Retrobulbar hematoma and blepharoplasty

Retrobulbar hematoma leading to visual impairment is a rare but serious complication associated with elective blepharoplasty. A review of the literature addressing etiology, prevention, and management is presented. Removal of anterior orbital fat associated with traction and rupture of vessels within posterior orbital fat is currently most strongly supported as the cause of retrobulbar hematoma after blepharoplasty. Optic nerve ischemia is identified as the likely cause of visual impairment. Specific recommendations for avoidance and management of acute retrobulbar hematoma are offered. Recent background animal and human research is summarized.

Spatially constrained skin electroporation with sodium thiosulfate and urea creates transdermal microconduits

Controlled transport of molecules through the skin's main barrier, the stratum corneum (SC), is a long standing goal of transdermal drug delivery. Traditional, needle-based injection provides delivery of almost any water soluble compound, by creating a single large aqueous pathway in the form of the hollow core of a needle, through which drug is delivered by pressure-driven flow. We extend previous work to show that SC-spanning microconduits (here with diameters of about 200 microm) can be created in vivo by skin electroporation and low-toxicity, keratolytic molecules (here sodium thiosulfate and urea). A single microconduit in isolated SC can support volumetric flow of the order of 0.01 ml s(-1) by a pressure difference of only 0.01 atm (about 10(2) Pa), demonstrating that the SC barrier has been essentially eliminated within this microscopic area.

Spatially constrained localized transport regions due to skin electroporation

Rapid, controlled molecular transport across human skin is of great interest for transdermal drug delivery and minimally invasive chemical sensing. Short, high-voltage pulses have been shown previously to create localized transport regions in the skin. Here, we show that these regions can be constrained to occur at specific sites using electrically insulating masks that restrict the field lines. The increase in total ionic and molecular transport per area was comparable to the levels observed in unconstrained electroporation of human skin. Constraining the area of intervention to encompass small areas of interest, a primary feature in the design of microdevices for transdermal drug delivery, can provide the same levels of flux as the unconstrained case.

Biological effects due to weak electric and magnetic fields: the temperature variation threshold

A large number of epidemiological and experimental studies suggest that prolonged (>100 s) weak 50-60-Hz electric and magnetic field (EMF) exposures may cause biological effects(NIEHS Working Group, NIH, 1998; Bersani, 1999). We show, however, that for typical temperature sensitivities of biochemical processes, realistic temperature variations during long exposures raise the threshold exposure by two to three orders of magnitude over a fundamental value, independent of the biophysical coupling mechanism. Temperature variations have been omitted in previous theoretical analyses of possible weak field effects, particularly stochastic resonance (Bezrukov and Vodyanoy 1997a. Nature. 385:319-321; Astumian et al., 1997 Nature. 338:632-633; Bezrukov and Vodyanoy, 1997b. Nature. 338:663; Dykman and McClintock, 1998. Nature. 391:344; McClintock, 1998;. Gammaitoni et al., 1998. Rev. Mod. Phys. 70:223-287). Although sensory systems usually respond to much shorter (approximately 1 s) exposures and can approach fundamental limits (Bialek, 1987 Annu. Rev. Biophys. Biophys. Chem. 16:455-468; Adair et al, 1998. Chaos. 8:576-587), our results significantly decrease the plausibility of effects for nonsensory biological systems due to prolonged, weak-field exposures.

The strategies and autonomy of university hospitals in competitive environments

University-owned hospitals face increasingly threatening and unstable environments. This article examines the strategies that university-owned hospitals are using, and can use, to respond to their changing environments. Further, it examines factors that can hinder or promote the effective development of university-owned hospital strategies.

Theoretical limits on the threshold for the response of long cells to weak extremely low frequency electric fields due to ionic and molecular flux rectification

Understanding exposure thresholds for the response of biological systems to extremely low frequency (ELF) electric and magnetic fields is a fundamental problem of long-standing interest. We consider a two-state model for voltage-gated channels in the membrane of an isolated elongated cell (Lcell = 1 mm; rcell = 25 micron) and use a previously described process of ionic and molecular flux rectification to set lower bounds for a threshold exposure. A key assumption is that it is the ability of weak physical fields to alter biochemistry that is limiting, not the ability of a small number of molecules to alter biological systems. Moreover, molecular shot noise, not thermal voltage noise, is the basis of threshold estimates. Models with and without stochastic resonance are used, with a long exposure time, texp = 10(4) s. We also determined the dependence of the threshold on the basal transport rate. By considering both spherical and elongated cells, we find that the lowest bound for the threshold is Emin approximately 9 x 10(-3) V m-1 (9 x 10(-5) V cm-1). Using a conservative value for the loop radius rloop = 0.3 m for induced current, the corresponding lower bound in the human body for a magnetic field exposure is Bmin approximately 6 x 10(-4) T (6 G). Unless large, organized, and electrically amplifying multicellular systems such as the ampullae of Lorenzini of elasmobranch fish are involved, these results strongly suggest that the biophysical mechanism of voltage-gated macromolecules in the membranes of cells can be ruled out as a basis of possible effects of weak ELF electric and magnetic fields in humans.

Theory of skin electroporation: implications of straight-through aqueous pathway segments that connect adjacent corneocytes

Previous in vitro experiments have shown that transdermal high-voltage pulses (Uskin approximately 100 V; duration approximately 1 ms) create local transport regions (LTR) away from appendages in human skin. Quantitative interpretation of the associated ionic and molecular transport led to the view that a large number of aqueous pathways were created, and these connect the corneocytes within an LTR. Here we use the "brick wall" model of the stratum corneum, modified so that morphology important to understanding electrical behavior is emphasized. In this model a minimum-size LTR is regarded as an idealized stack of corneocytes in which the 5-6 multilamellar lipid bilayer membranes between adjacent corneocytes are electroporated. As in artificial planar bilayer and cell membrane electroporation, a distribution of pathway sizes is expected during pulsing, and during recovery after pulsing individual pathway segments are expected to shrink and close randomly, with a time constant tau(seg) that depends on temperature and on lipid composition. Numerical simulations based on stochastic closure of individual segments were used to predict the electrical conductance G(LTR)(t) of a minimum-size LTR after pulsing stops. These theoretical results show that simple exponential decay, G(LTR)(t) = G(LTR)(0)exp(-t/tau(seg)), occurs with minimal fluctuations if the number of pathways is large (np > 10(2)), but for much smaller values the conduction decreases erratically. A "stochastic bottleneck" leading to complete closure is reached only at about np < 3. Thus, for the same number of electrically created pathways, the stratum corneum will remain "open" longer if the pathways are located within an LTR than if the same number of pathways are distributed sparsely over the skin. These predictions are relevant to postpulse transport, including the trapping of linear macromolecules that can hold pathway segments open for prolonged intervals.

Results of the 1997 survey of the American Association of Academic Chief Residents in Radiology

RATIONALE AND OBJECTIVES

The American Association of Academic Chief Residents in Radiology annually surveys residency programs on a variety of issues related to residency training. The survey results allow individual programs to compare features of their programs with national averages and to gauge trends in radiology residency training.

MATERIALS AND METHODS

Questionnaires were mailed to the chief residents in 180 accredited radiology residency programs in the United States. A variety of demographic and common-interest questions were asked. The 1997 survey focused on American Board of Radiology (ABR) examination preparation, residency curriculum, and socioeconomic issues relevant to graduating radiology residents.

RESULTS

Completed surveys from 73 programs (41%) were returned. Areas of curriculum concern among chief residents reflected primarily current turf issues. A higher than expected percentage of residents considered their training to be inadequate in nonneurologic magnetic resonance imaging and chest, musculoskeletal, and genitourinary radiology. Job security is a major emerging concern for radiology residents who are considering careers in private practice. The practice of remembering and transcribing questions from the ABR written examination is common, and these questions are a valued resource in preparing for the diagnostic section of the written examination. Most residents attend a commercial review course before the oral examination, and the majority of programs also provide internal review courses.

CONCLUSION

A higher than expected percentage of chief residents expressed concern regarding training in subspecialties of radiology that are neither areas of turf dispute nor areas where certificate of additional qualification examinations are offered. Radiology programs and residents expend substantial resources on preparation for the ABR examinations in addition to the usual 4-year curriculum. The most valued resource for the diagnostic section of the examination is almost certainly not equally available. Radiology residents are increasingly concerned about future job security.

Heparin alters transdermal transport associated with electroporation

Short, high-voltage (HV; U(skin,max) approximately 100 V) pulses have been shown to increase rates of transdermal transport by several orders of magnitude via a mechanism hypothesized to involve electroporation. We show that heparin, a linear, highly charged macromolecule, significantly alters the molecular transport capacity and lifetime of aqueous pathways across human stratum corneum (SC) created by such pulses. If co-transported during pulsing, heparin molecules can interact with the SC and other molecules, thereby altering ionic and molecular transport. We also observed an increase in post-pulse skin permeability and persistent lower skin resistance. Because most heparin molecules are long enough to span the five to six lipid bilayer membranes that separate corneocytes within the SC, these results can be explained by the hypothesis that heparin molecules were trapped within the skin, holding open pathway segments connecting adjacent corneocytes. These results support the skin electroporation hypothesis and provide the first demonstration of a chemical enhancer effect for transdermal transport by HV pulsing.

Energetic constraints on the creation of cell membrane pores by magnetic particles

Naturally occurring and contaminant ferromagnetic and ferrimagnetic particles have been found within or near cells, and might allow pulsed magnetic fields to create transient cell membrane opening ("pores"). We show that this possibility is significantly constrained by the maximum rotational energy that can be transferred to the cell membrane. For single biologically synthesized magnetosomes (radius rmag approximately 10(-7) m, magnetic moment mu approximately 2 x 10(-15) A m2) and typical cell membranes, the estimated pulse magnitude must exceed Bo approximately 6 x 10(-3) to 7 x 10(-2) T, and the optimal pulse durations are in the range 10(-5) s < tpulse < 10(-1) s. For larger contaminant particles with larger net magnetic moments, the pulse magnitudes could be only somewhat smaller, and the optimal durations are about the same. Very large pulses that exceed the coercive force of a particle are predicted to have a smaller effective magnitude and shorter effective duration.

Endogenous digoxin-like immunoreactivity in blood is increased during prolonged strenuous exercise

Digoxin-like immunoreactive factors (DLIFs) in serum may represent endogenous cardiotropic agents. We determined if blood levels of these endogenous factors changed during prolonged strenuous exercise. Total and loosely protein-bound (LPB) DLIF were measured by radioimmunoassay in the serum of nine healthy subjects during prolonged exercise to exhaustion. Mean total and LPB serum levels of DLIF increased by 72% (580 to 945 pg/mL) and 63% (53 to 91 pg/mL) over baseline values in digoxin equivalents (p less than 0.01), respectively, after three hours of exercise at 70% of VO2max. The prevalent serum nonesterified fatty acids (arachidonic, linoleic, oleic, palmitic, and stearic acids) as well as hydrocortisone did not account for the observed elevations in DLIF. Percent left ventricular fractional shortening (%FS) and mean velocity of left ventricular circumferential fiber shortening (mVCF) measured echocardiographically were lower (-18.0% and -16.4%, respectively, p less than 0.05) after exercise as compared to prior to exercise. Cardiac left ventricular dysfunction as measured by %FS did correlate with blood levels of DLIF (r = -0.680, p less than 0.02). These observations may suggest a relationship between serum levels of DLIF and cardiac fatigue.