Unfavorable mechanical effects of heat and moisture exchangers in ventilated patients

OBJECTIVE: To investigate the mechanical effects of artificial noses. SETTING: A general intensive care unit of a university hospital. PATIENTS: 10 patients in pressure support ventilation for acute respiratory failure. INTERVENTIONS: The following three conditions were randomly tested on each patient: the use of a heated humidifier (control condition), the use of a heat and moisture exchanger without filtering function (HME), and the use of a combined heat and moisture exchanger and mechanical filter (HMEF). The pressure support level was automatically adapted by means of a closed-loop control in order to obtain constancy, throughout the study, of patient inspiratory effort as evaluated from airway occlusion pressure at 0.1 s (P0.1). Patient's ventilatory pattern, P0.1, work of breathing, and blood gases were recorded. MEASUREMENTS AND MAIN RESULTS: The artificial noses increased different components of the inspiratory load: inspiratory resistance, ventilation requirements (due to increased dead space ventilation), and dynamic intrinsic positive end-expiratory pressure (PEEP). The additional load imposed by the artificial noses was entirely undertaken by the ventilator, being the closed-loop control of P0.1 effective to maintain constancy of patient inspiratory work by means of adequate increases in pressure support level. CONCLUSIONS: The artificial noses cause unfavorable mechanical effects by increasing inspiratory resistance, ventilation requirements, and dynamic intrinsic PEEP. Clinicians should consider these effects when setting mechanical ventilation and when assessing patients' ability to breathe spontaneously.     

Ceramic Composites Fabricated by Selective Laser Sintering

Selective laser sintering (SLS) uses a computer controlled laser beam to create objects directly from the CAD data without part-specific tooling. In this paper, the effect of material and processing parameters on the microstructure and mechanical properties of an alumina/aluminum phosphate composite fabricated by SLS is described. The precursor material is a blend of alumina and ammonium phosphate powder. This paper deals primarily with the effect of alumina particle size and material composition on the strength of the composite. A constitutive equation is also proposed to relate the mechanical properties of the composite to its microstructural characteristics.     

Evidence for disturbed S-adenosylmethionine : S-adenosylhomocysteine ratio in patients with end-stage renal failure: a cause for disturbed methylation reactions?

BACKGROUND: Elevated homocysteine concentrations have been associated with premature arteriosclerosis and with impairment of key methylation reactions through accumulation of the homocysteine metabolite S-adenosylhomocysteine. In end-stage renal failure high homocysteine concentrations are commonly found but thus far the concentrations of related adenosylated metabolites in plasma have not been assessed. METHODS: In this prospective study we determined plasma homocysteine and related metabolites in 25 patients on regular haemodialysis, and in 40 healthy volunteers. Blood samples from patients were drawn immediately before and in 10 patients additionally after the dialysis session. RESULTS: Folic acid and vitamin B12 in plasma were similar in patients (mean +/- SEM 25+/-2 nmol/l and 400+/-41 pmol/l respectively) and controls (24+/-3 and 324+/-23 respectively). In patients plasma homocysteine, S-adenosylmethionine and S-adenosylhomocysteine were markedly elevated (36.6+/-3.6 micromol/l, 381+/-32nmol/l and 1074+/-55 nmol/l respectively) compared to the control values (6.8+/-0.4 micromol/l, 60+/-3 nmol/l and 24.4+/-1.1 nmol/l respectively) whereas the molar ratio of plasma S-adenosylmethionine and S-adenosylhomocysteine was significantly decreased (0.36+/-0.02 and 2.7+/-0.2 in patients and controls respectively). Haemodialysis failed to normalize the abnormal levels of these metabolites. CONCLUSION: Since the ratio of S-adenosylmethionine : S-adenosylhomocysteine is closely linked to the activity of numerous enzymatic methylation reactions, these results suggest that methylation may be impaired in these patients.     

The protease-protected 30 kDa domain of SecA is largely inaccessible to the membrane lipid phase

SecA binds to the inner membrane of Escherichia coli through low affinity lipid interactions or with high affinity at SecYEG, the integral domain of preprotein translocase. Upon addition of preprotein and nucleotide, a 30 kDa domain of SecYEG-bound SecA is protected from proteolysis via membrane insertion. Such protection could result from some combination of insertion into the lipid phase, into a proteinaceous environment or across the membrane. To assess the exposure of SecYEG-bound SecA to membrane lipids, a radiolabeled, photoactivatable and lipid-partitioning crosslinker, 3-trifluoromethyl-3-(m[125I]iodophenyl) diazirine benzoic acid ester, was incorporated into inner membrane vesicles. The 30 kDa domain of SecYEG-bound SecA, inserted into the membrane in response to translocation ligands, is 18-fold less labeled than SecY, which is labeled effectively. In contrast, incorporation of the purified 30 kDa SecA fragment into crosslinker-containing detergent micelles or addition of detergent to crosslinker-containing membranes bearing the protease-protected SecA domain readily allows for labeling of this domain. We propose that the protease-inaccessible 30 kDa SecA domain is shielded from the fatty acyl membrane phase by membrane-spanning SecYEG helices and/or is largely exposed to the periplasm.     

Generation of chromosome fragment specific bovine DNA sequences by microdissection and DOP-PCR

Trends in causative organisms and sources of infection were studied in a series of 288 episodes of bacteremia in neutropenic cancer patients observed in a single institution from 1986 to 1993. The incidence of bacteremia increased significantly from 20 episodes per 1000 admissions in 1986 to 50 episodes per 1000 admissions in 1993 (p = 0.00001). Over the study period, a continuous increment in gram-positive bacteremia, which reached 81% of episodes in 1993 (p = 0.000001), was observed. Conversely, the incidence of gram-negative bacteremia remained stable. Coagulase-negative staphylococci and viridans group streptococci were the most commonly isolated pathogens. Bacteremia caused by coagulase-negative staphylococci increased from 3 episodes per 1000 admissions to 19 episodes per 1000 admissions (p = 0.0001), and viridans group streptococci bacteremia increased from 0 episodes per 1000 admissions to 19 episodes per 1000 admissions (p = 0.000001). The upward trend in gram-positive bacteremia appeared to be related to a significant increase in both intravascular catheters (p = 0.003) and oral mucositis (p = 0.003) as sources of infection. Specific strategies to prevent chemotherapy-induced mucositis and catheter-related bacteremia merit further investigations.     

Path integral Monte Carlo simulations of the melting of molecular hydrogen surfaces

We have used Path Integral Monte Carlo to study the surface melting of molecular hydrogen. Density profiles perpendicular and parallel to the bare H₂ surface are computed showing the formation of a liquid adlayer at 6 K, less than half the bulk melting temperature of para-hydrogen, 13.8 K. To estimate the onset temperature and depth of H₂ surface melting we determine the static structure factor within the individual H₂-layers for wave vectors in the plane and find no crystalline order down to 3 K in a partially filled H₂ adlayer at the free surface. We find quantum effects amplify the melting point depression at the free H₂ surface compared to bulk by a factor of five over classical Lennard-Jones solids and find that the zero-point fluctuations of molecules at the surface are much enhanced over their bulk values. We see vacancy formation in the solid before melting.     

Convergence of simultaneous perturbation stochastic approximation for nondifferentiable optimization

We consider simultaneous perturbation stochastic approximation for function minimization. The standard assumption for convergence is that the function be three times differentiable, although weaker assumptions have been used for special cases. However, all work that we are aware of at least requires differentiability. We relax the differentiability requirement and prove convergence using convex analysis.     

Bodies, antibodies, and neighborhood-density effects in masked form priming.

Facilitatory priming effects due to similarity of orthographic form are obtained for high-N target words provided that they have low-frequency bodies and the body is shared between the prime and target (e.g., perd-HERD). Conversely, it is shown that low-N target words show priming regardless of the frequency of the body, provided that the prime and target do not share the same body (e.g., drice-DRIVE). If the body is shared, then priming occurs only for targets with low-frequency bodies. These results suggest that neighborhood density should be defined in terms of both individual letter units and subsyllabic units and that both types of density jointly determine priming. (PsycINFO Database Record (c) 2010 APA, all rights reserved)