Short Chorus Wave Packets: Generation Within Chorus Elements, Statistics, and Consequences on Energetic Electron Precipitation.

Short and intense lower-band chorus wave packets are ubiquitous in the Earth's outer radiation belt. In this article, we perform various Vlasov hybrid simulations, with one or two triggering waves, to study the generation of short chorus packets/subpackets inside long rising tone elements. We show that the length of the generated short wave packets is consistent with a criterion of resonance non-overlap for two independent superposed waves, and that these chorus packets have similar characteristics as in Van Allen Probes observations. We find that short wave packets are mainly formed near the middle/end of long rising tones for moderate linear growth rates, and everywhere for stronger linear growth rates. Finally, we analyze an event characterized by Time History of Events and Macroscale Interactions during Substorms spacecraft measurements of chorus rising tones near the equator and simultaneous measurements by low altitude ELFIN CubeSats of precipitating and trapped electron fluxes in the same sector. The measured precipitating electron fluxes are well recovered by test particle simulations performed using measured plasma and wave properties. We show that short chorus wave packets of moderate amplitudes (160-250 pT) essentially lead to a more diffusive-like transport of 50-200 keV electrons toward the loss cone than long packets. In contrast, long chorus packets are found to produce important nonlinear effects via anomalous trapping, which significantly reduces electron precipitation below 150 keV, especially for higher wave amplitudes.

Randomized clinical trial of fluid and salt restriction compared with a controlled liberal regimen in elective gastrointestinal surgery.

BACKGROUND: Excessive intravenous fluid prescription may play a causal role in postoperative complications following major gastrointestinal resectional surgery. The aim of this study was to investigate whether fluid and salt restriction would decrease postoperative complications compared with a more modern controlled liberal regimen. METHODS: In this observer-blinded single-site randomized clinical trial consecutive patients undergoing major gastrointestinal resectional surgery were randomized to receive either a liberal control fluid regimen or a restricted fluid and salt regimen. The primary outcome was postoperative complications of grade II and above (moderate to severe). RESULTS: Some 240 patients (194 colorectal resections and 46 oesophagogastric resections) were enrolled in the study; 121 patients were randomized to the restricted regimen and 119 to the control (liberal) regimen. During surgery the control group received a median (interquartile range) fluid volume of 2033 (1576-2500) ml and sodium input of 282 (213-339) mmol, compared with 1000 (690-1500) ml and 142 (93-218) mmol respectively in the restricted group. There was no significant difference in major complication rate between groups (38·0 and 39·0 per cent respectively). Median (range) hospital stay was 8 (3-101) days in the controls and 8 (range 3-76) days among those who received restricted fluids. There were four in-hospital deaths in the control group and two in the restricted group. Substantial differences in weight change, serum sodium, osmolality and urine : serum osmolality ratio were observed between the groups. CONCLUSION: There were no significant differences in major complication rates, length of stay and in-hospital deaths when fluid restriction was used compared with a more liberal regimen. REGISTRATION NUMBER: ISRCTN39295230 (http://www.controlled-trials.com).

Anaesthetic specialisation leads to improved early- and medium-term survival following major vascular surgery.

OBJECTIVE: Vascular surgical specialisation is associated with improved outcomes. We aimed to assess the effect of anaesthetic specialisation on outcome following major vascular surgery. DESIGN: Retrospective cohort study. METHODS: Patients undergoing major vascular surgery (lower limb revascularisation, elective and ruptured abdominal aortic aneurysm repair, endovascular aneurysm repair and carotid endarterectomy) over a five-year period were identified from a prospective database. The primary outcomes were death within 30 days and death within two years of surgery. Potential risk factors for mortality were assessed using multivariate logistic regression modelling. RESULTS: The analysis cohort comprised 1155 patients followed up for a median of 583 days. Mortality within two years of surgery was 16%. For the overall cohort, care from vascular anaesthetists was independently associated with reduced 30-day (odds ratio 0.22; 95% CI 0.12-0.62) and medium-term mortality (0.31; 95% CI 0.18-0.55). For elective patients (n=851), vascular anaesthesia reduced two-year mortality (odds ratio 0.29; 95% CI 0.15-0.58; P=0.0004) though not 30-day mortality (odds ratio 0.55; 95% CI 0.15-1.95; P=0.35). For emergency patients, care by a vascular anaesthetist influenced neither 30-day mortality (odds ratio 0.33; 95% CI 0.08-1.41; P=0.13) nor medium-term mortality (odds ratio 0.45; 95% CI 0.17-1.21; P=0.11). CONCLUSIONS: Anaesthetic specialisation reduced early- and medium-term mortality rates following major vascular surgery. If replicated by prospective studies, these results suggest that vascular surgery services would benefit from specialised anaesthetic support.

LipC, a second lipase of Pseudomonas aeruginosa, is LipB and Xcp dependent and is transcriptionally regulated by pilus biogenesis components.

We have isolated cosmids that complement a Pseudomonas aeruginosa export-impaired mutant by increasing growth on lipid agar, a medium that requires lipase expression and export. These cosmids encode a previously unidentified lipase, LipC, which has high homology to the P. aeruginosa lipA gene product. Like LipA, LipC activity requires the chaperone activity of the lipB gene product and a functional xcp gene cluster for export. However, expression of LipC is barely detectable in a wild-type background. Transposon insertions that increase lipC promoter activity have been obtained that inactivate two pilus biogenesis genes, pilX and pilY1. This suggests that these proteins either directly or indirectly repress the expression of LipC and may be involved in transducing an extracellular signal that regulates this lipase.

Bacterial type II protein export and pilus biogenesis: more than just homologies?

Protein export by Gram-negative bacteria requires devoted machineries to allow for the passage of hydrolytic enzymes and toxins through the cell envelope. The Type II export machinery has a number of distinct characteristics, which include its role as an extension of Sec-dependent secretion, its ability to recognize and export fully folded substrates efficiently and, perhaps most significantly, the relationship between a subset of its gene products with the Type IV pilus-biogenesis apparatus. An important question is whether we can extrapolate our knowledge, albeit limited, of Type IV pilus biogenesis to understand the structure and function of the Type II export apparatus. This and other questions relating to the energetics of assembly and specificity of the apparatus are addressed in this article.

Structural failure of Dacron arterial grafts.

The ultimate test of a Dacron (polyethylene terephthalate or PET) arterial prosthesis depends on its ability to retain sufficient strength and durability to function properly for the life of the patient. Because graft recipients appear to be living longer, primarily because of improved medical and surgical treatment of cardiovascular disease, strength and durability of arterial prostheses have become increasingly important. From the time of implantation, all PET prostheses are continuously subjected to the cyclic stresses of pulsatile blood flow with mechanical fatiguing of yarns, as well as chemical and physical alterations associated with biodegradation. Notwithstanding the overall successful use of currently available prostheses, structural failure continues to occur sporadically and is especially noteworthy because of its potentially serious nature and usual occurrence 5 or more years after implantation, when the diagnosis may be overlooked or delayed. A review of the subject is provided based on the premise that timely recognition and appropriate management require a basic understanding of PET prostheses with respect to various fabric constructions and physical properties, graft healing, postoperative dilation, and known causes of structural failure.

Characterization of type IV pilus genes in Pseudomonas syringae pv. tomato DC3000.

Many strains of Pseudomonas syringae produce retractile pili that act as receptors for lytic bacteriophage phi 6. As these are also characteristics of type IV pili, it was postulated that P. syringae may possess genes for type IV pilus biogenesis. A cosmid clone bank of P. syringae pv. tomato DC3000 genomic DNA was used to complement a mutant of Pseudomonas aeruginosa defective in the PilD (XcpA) prepilin peptidase gene by selection for restoration of extracellular protein secretion, a function also known to require PilD. A cosmid able to complement this mutant was also able to complement mutations in the pilB and pilC genes, suggesting that, if the organization of these genes is similar to that of P. aeruginosa, the cosmid may contain the P. syringae pilA. This was confirmed by sequencing a region from this plasmid that was shown to hybridize at low stringency to the P. aeruginosa pilA gene. The deduced P. syringae PilA polypeptide possesses the characteristic properties of the type IV pilins. Heterologous expression of the P. syringae pilA in P. aeruginosa was also shown, conferring not only phi 6 phage sensitivity to P. aeruginosa pilA mutants but also sensitivity to PO4, a lytic bacteriophage specific for the pilus of P. aeruginosa. This suggests that additional components might be present in the mature pilus of P. aeruginosa that are the true receptors for this phage. Chromosomal mutations in P. syringae pv. tomato DC3000 pilA and pilD genes were shown to abolish its sensitivity to bacteriophage phi 6. To determine the importance of P. syringae pilus in plant leaf interactions, these mutations were tested under laboratory and field conditions. Although little effect was seen on pathogenicity, culturable leaf-associated population sizes of the pilA mutant were significantly different from those of the wild-type parent. In addition, the expression of the DC3000 pilA gene appears to contribute to the UV tolerance of P. syringae and may play a role in survival on the plant leaf surface.

Impairment of gas exchange due to alveolar oedema during xylazine sedation in sheep; absence of a free radical mediated inflammatory mechanism.

We studied the mechanism of impairment of gas exchange following sedation with the alpha2 adrenoreceptor agonist, xylazine, in Suffolk cross-bred sheep spontaneously breathing room air. Xylazine caused a significant fall in PaO2 from a mean (pre-xylazine) of 97.9 mm Hg (6.7 mm Hg SEM) to a mean of 38.1 mm Hg (3.2 mm Hg SEM) one minute after injection with a transient increase in PaCO2 from a mean (pre-xylazine) of 32.6 mm Hg (1.9 mm Hg SEM) to a mean of 40.2 mm Hg (3.0 mm Hg SEM). There was no significant fall in mean arterial pressure or in white cell count. There was no significant change in a number of indices of free radical release which included ascorbyl radical, plasma antioxidant potential and alpha-tert-butyl phenyl nitrone (PBN) spin adduct measured simultaneously in both arterial and venous blood. In all sheep given xylazine there was no histological evidence of platelet emboli but lung histopathology showed evidence of pulmonary oedema and intense microvascular congestion with red cells extravasated into alveoli. No such histological changes were seen in the lungs of normal sheep. The impaired gas exchange during sedation with xylazine in sheep is caused, not by an oxidant mediated inflammatory mechanism or by platelet emboli, but by intense alveolar oedema which is probably due to pulmonary venospasm.

Identification of an additional member of the secretin superfamily of proteins in Pseudomonas aeruginosa that is able to function in type II protein secretion.

Pseudomonas aeruginosa is a prolific exporter of virulence factors and contains three of the four protein secretion systems that have been described in gram-negative bacteria. The P. aeruginosa type II general secretory pathway (GSP) is used to export the largest number of proteins from this organism, including lipase, phospholipase C, alkaline phosphatase, exotoxin A, elastase and LasA. Although these exoproteins contain no sequence similarity, they are specifically and efficiently transported by the secretion apparatus. Bacterial homologues of XcpQ (GspD), the only outer membrane component of this system, have been proposed to play the role of gatekeeper, by presumably interacting and recognizing the exported substrates to allow their passage through the outer membrane. While determining the phenotype of nonpolar deletions in each of the xcp genes, we have shown that a deletion of the P. aeruginosa strain K xcpQ does not completely abolish protein secretion. As the proposed function of XcpQ should be requisite for secretion, we searched for additional factors that could carry out this role. A cosmid DNA library from a PAK strain deleted for xcpP-Z was tested for its ability to increase protein secretion by screening for enhanced growth on lipid agar, a medium that selects for the secretion of lipase. In this manner, we have identified an XcpQ homologue, XqhA, that is solely responsible for the residual export observed in a deltaxcpQ strain, although it is not required for efficient secretion in wild-type P. aeruginosa. We have also demonstrated that this protein is capable of recognizing all of the exoproteins of P. aeruginosa, arguing against the proposed role of members of the secretin family as determinants of specificity.

Type II protein secretion by Pseudomonas aeruginosa: genetic suppression of a conditional mutation in the pilin-like component XcpT by the cytoplasmic component XcpR.

Pseudomonas aeruginosa exports a number of hydrolytic enzymes and toxins using the type II or general secretion pathway, found in a variety of Gram-negative bacteria and requiring the functions of at least 12 gene products (XcpP-Z and PilD/XcpA in P. aeruginosa). A number of these gene products are homologues of components of the type IV pilus biogenesis system, including four proteins, XcpT-W, which are highly similar to the pilin subunit in their size, localization and post-translational modifications. These proteins, in addition to the pilin subunit, are cleaved and methylated by the PilD/XcpA prepilin peptidase, but their interactions with other components of the export apparatus are unclear. Using a medium developed for the selection of export-proficient P. aeruginosa strains, we have isolated temperature-sensitive mutations in the xcpT gene and extragenic suppressors for one of the mutants. These suppressors fall into two classes, one that maps outside of the xcpP-Z gene cluster and may define additional cellular functions that are required for export, and a second that maps to the xcpR gene product and indicates a potential protein-protein interaction connecting two different cellular compartments and required for the assembly or function of the export apparatus.

Intrinsic Dacron graft failure 19 years post-implantation.

Intrinsic failure of a knitted Dacron aortic bifurcation graft 19 years after implantation is reported. Failure was due to inability of the dilated and deteriorated left graft limb to hold anastomotic sutures. Numerous transverse cracks and breaks were detected in the Dacron filaments, in addition to small holes throughout the fabric structure, and a severe reduction in the yarn's tensile strength. Criteria are defined for establishing a correct diagnosis, and causative factors, incidence, and clinical management are discussed.

Characterization of genes required for pilus expression in Pseudomonas syringae pathovar phaseolicola.

Nonpiliated, phage phi 6-resistant mutants of Pseudomonas syringae pv. phaseolicola were generated by Tn5 transposon mutagenesis. A P. syringae pv. phaseolicola LR700 cosmid library was screened with Tn5-containing EcoRI fragments cloned from nonpiliated mutants. The cosmid clone pVK253 complemented the nonpiliated mutant strain HB2.5. A 3.8-kb sequenced region spanning the Tn5 insertion site contained four open reading frames. The transposon-inactivated gene, designated pilP, is 525 bp long, potentially encoding a 19.1-kDa protein precursor that contains a typical membrane lipoprotein leader sequence. Generation of single mutations in each of the three remaining complete open reading frames by marker exchange also resulted in a nonpiliated phenotype. Expression of this gene region by the T7 expression system in Escherichia coli resulted in four polypeptides of approximately 39, 26, 23, and 18 kDa, in agreement with the sizes of the open reading frames. The three genes upstream of pilP were designated pilM (39 kDa), pilN (23 kDa), and pilO (26 kDa). The processing of the PilP precursor into its mature form was shown to be inhibited by globomycin, a specific inhibitor of signal peptidase II. The gene region identified shows a high degree of homology to a gene region reported to be required for Pseudomonas aeruginosa type IV pilus production.

Dilative characteristics of Microvel and Vasculour-II aortic bifurcation grafts.

Dilation is inherent to all knitted Dacron arterial prostheses. Insufficient clinical data regarding the usual dilative characteristics of specific grafts confound its significance and management. Alterations in size of all parts of knitted aortic bifurcation grafts (43 Microvel and 37 Vasculour-II) were evaluated by CT scanning in 80 patients; 76 scans were obtained in those with Microvel and 69 in those with Vasculour-II grafts. The mean dilation values were Microvel 54% +/- 16% SD at a mean follow-up of 21 months and Vasculour-II 48% +/- 21% SD with a mean follow-up of 73 months. Serial scans and a linear correlation study indicated that the rate of progressive dilation for both grafts was relatively low. The wide range of dilation values among patients with the same graft type, and even the same implantation time, operated upon by the same surgeon, suggests that multiple etiologic mechanisms are involved. Consequently, all patients must be evaluated individually, preferably with serial scans that evaluate all parts of the graft.

The effect of very early cleft palate closure on the need for ventilation tubes in the first years of life.

The otologic consequences associated with cleft palates are well known. Closure of palatal clefts within the first weeks of life has many potential benefits, including improved feeding and cosmesis. The potential otologic benefits of very early closure are not known. Eighteen newborns have undergone closure of their palatal clefts within the first month of life with subsequent otolaryngology follow-up through our craniofacial center. Thirteen (72%) of the 18 still required placement of ventilation tubes during their first 3 years of life because of persistent effusion (for more than 120 days) or recurrent infection (more than four episodes in 6 months or more than six episodes in 12 months). Very early cleft palate closure may not significantly alter the need for ventilation tubes in children with palatal clefts.