Characterization of the iron oxide phases formed during the synthesis of core-shell FexOy@C nanoparticles modified with Ag.

Core-shell FexOy@C nanoparticles (NPs) modified with Ag were studied with x-ray diffraction, transmission electron microscopy, energy dispersive elemental mapping, Mössbauer spectroscopy, static magnetic measurements, and optical magnetic circular dichroism (MCD). FexOy@C NPs synthesized by the pyrolysis process of the mixture of Fe(NO3)3 · 9H2O with oleylamine and oleic acid were added to a heated mixture of oleylamine and AgNO3 in different concentrations. The final product was a mixture of iron oxide crystalline NPs in an amorphous carbon shell and Ag crystalline NPs. The iron oxide NPs were presented by two magnetic phases with extremely close crystal structures: Fe3O4 and γ-Fe2O3. Ag is shown to form crystalline NPs located very close to the iron oxide NPs. An assumption is made about the formation of hybrid FexOy@C-Ag NPs. Correlations were obtained between the Ag concentration in the fabricated samples, their magnetic properties and the MCD spectrum shape. Introducing Ag led to a approximately linear decrease of the NPs saturation magnetization depending upon the Ag concentration, it also resulted into the MCD spectrum shift to the lower light wave energies. MCD was also studied for the Fe3O4@C NPs synthesized earlier with the same one-step process using different heat treatment temperatures, and MCD spectra were compared for two series of NPs. A possible contribution of the surface plasmon excitation in Ag NPs to the MCD spectrum of the FexOy@C-Ag NPs is discussed.

Flow dynamics using high-frequency jet ventilation in a model of bronchopleural fistula.

BACKGROUND: Positive pressure ventilation in patients with a bronchopleural fistula (BPF) is associated with variable, unpredictable gas leaks that can impair gas exchange. The optimum settings for high-frequency jet ventilation in this scenario are unclear. We investigated flow dynamics with BPFs of 2 and 10 mm, at various positions and with different jet ventilator settings in a bench-top model. METHODS: A 2 or 10 mm length fistula was created at proximal, middle, or distal sites in standard artificial ventilator 'test' lungs and cadaveric porcine lungs. The effects of alterations in frequency, applied pressure, and on entrained, expired, and leak volumes were determined using gauge and differential pressure sensors. RESULTS: Entrained, delivered, and leak volumes were affected markedly by ventilator settings, particularly frequency: leaks were much greater at frequencies <100 min(-1). The leak/expired volume ratio varied between 0% and 92%. Leak and entrained volumes increased progressively with more proximally situated fistulae, whereas the measured expired volume decreased. Leak volumes with a 2 mm fistula were approximately half that of a 10 mm fistula across all ventilator frequencies. All volumes increased with increased driving pressure. The optimum injection time varied depending on BPF position and the accepted compromise between leak and expired volumes. Entrained volume contributed up to 50% of the total tidal volume. CONCLUSIONS: These data suggest that gas leak will be minimized and ventilator volumes maintained during jet ventilation using frequencies >200 min(-1) and lower driving pressures, but confirmatory clinical studies are required. Values displayed by the jet ventilator are unreliable.

Air entrainment during high-frequency jet ventilation in a model of upper tracheal stenosis.

BACKGROUND: Previous work has demonstrated that when high-frequency jet ventilation (HFJV) is applied above an airway stenosis, higher distal airway pressures are produced compared with when the same ventilation is delivered below the stenosis (BSV). This study aimed to investigate the mechanisms underlying this finding. METHODS: HFJV was applied to a model of laryngo-tracheal stenosis with the jet located above the stenosis (ASV), with a catheter passed through the stenosis (TSV) or with HFJV delivered by a side port BSV. For each configuration and over a range of diameters of stenosis (2.5-8.5 mm), distal tracheal pressures and delivered minute volume were measured and air entrainment estimated. Experiments were repeated using the same model with the addition of a simulated 'pharynx' around the stenosis. RESULTS: Distal airway pressures, minute volumes, and air entrainment were consistently higher during ASV compared with BSV and TSV. The presence of the 'pharynx' made no significant difference to airway pressures or air entrainment. Delivered minute volumes varied between ASV, TSV, and BSV, and were also dependent on the stenosis diameter. With ASV, there appeared to be a range of stenosis diameters (4.0-5.5 mm) which 'maximized' minute volumes. CONCLUSIONS: The results suggest that the high airway pressures generated during ASV are the consequence of air entrainment and this effect, although reduced slightly, is maintained in the presence of the model pharynx. In contrast to the previous work, no significant entrainment occurred during BSV. If applicable to patients, these data suggest that ASV HFJV should be avoided in small diameter stenoses, but provides more efficient gas delivery and greater distending pressures with larger stenoses. BSV HFJV produces lower distal pressures and more consistent oxygen concentrations of injected gas across a range of stenosis diameters.

Nucleotide binding and sulfation catalyzed by phenol sulfotransferase.

The sulfation of a nucleotide is an indispensable step for the sulfuryl group transfer in a biological system. The product and cosubstrate of sulfotransferase in physiological condition are adenosine 3',5'-bisphosphate (PAP) and 3'-phospho adenosine 5'-phosphosulfate (PAPS), respectively. We find that ribose and adenine, two major parts of the adenosine nucleotide, bind tightly to phenol sulfotransferase (PST) separately, and various nucleotides also bind tightly to PST. We determine the dissociation constants of a variety of nucleotides and examine their potential as cofactors or cosubstrates of PST. Using 4-nitrophenyl sulfate as the sulfuryl group donor, three nucleotides, adenosine 5'-monophosphate (AMP), adenosine 2',5'-bisphosphate (2',5'-PAP), and adenosine 2':3'-cyclic phosphate 5'-phosphate (2':3'-cyclic PAP), are shown here for the first time to be sulfated at 5'-phopho position by a PST catalyzed reaction. Spectrophotometry, HPLC, and (31)P NMR are used to determine the activity of PST and identify the sulfated nucleotides. The V(max) of PST and K(m) of these nucleotides are determined when they are used as cofactors or cosubstrates for the sulfuryl group transfer. The existence and possible physiological significance of these newly reported binding and sulfation of nucleotides by PST in biology is yet to be discovered.

Colorimetric determination of the purity of 3'-phospho adenosine 5'-phosphosulfate and natural abundance of 3'-phospho adenosine 5'-phosphate at picomole quantities.

This work presents novel colorimetric methods not only to measure 3'-phospho adenosine 5'-phosphate (PAP) and 3'-phospho adenosine 5'-phosphosulfate (PAPS) in the range of picomoles, but also to determine the purity of PAPS or PAP contaminants in PAPS in the range of nanomoles. These methods exploit the availability of overexpressed phenol sulfotransferase (PST) and the fact that sulfuryl group transfer requires the use of PAP or PAPS as a cofactor or cosubstrate. Experimental results indicate that absorption at 400 nm due to the production of 4-nitrophenol (pNP) is catalyzed by PST when the sulfuryl group transfers from 4-nitrophenylsulfate (pNPS) to PAP or to 2-napthol. In the absence of an acceptor substrate, PAPS is hydrolyzed to PAP by PST and is determined by sulfation with pNPS before and after this reaction. The change of absorption of pNP at 400 nm corresponds to the amount of PAP that is hydrolyzed from PAPS. Moreover, a standard curve is constructed using authentic PAP and PAP-free PST. Furthermore, this curve is used to determine the amount of PAP in extracts of pig liver, rat liver, and Escherichia coli.

Effects of 3'-phosphoadenosine 5'-phosphate on the activity and folding of phenol sulfotransferase.

Known spectroscopic and kinetic data are used to formulate pathways of the physiological and transfer reactions and the substrate inhibition of phenol sulfotransferase. Kinetic mechanisms indicate that release of PAP from enzyme complex is required for the physiological reaction but not for the transfer reaction. The pathways explain rate difference between the physiological and transfer reactions since the release of PAP is the rate-limiting step of the former reaction. Two enzyme species of phenol sulfotransferase which distinguish the physiological and transfer reaction were found to involve the binding of PAP. Differences between two forms of phenol sulfotransferase, alpha and beta, indicate that they assemble through different folding process. It is demonstrated that only alpha enzyme renatures in the presence of PAP and beta enzyme renatures only in the absence of PAP in vitro. In the over-expressed system, formation of alpha and beta phenol sulfotransferase is also dependent on the availability of PAP in Escherichia coli. It is concluded that folding of phenol sulfotransferase is assisted by PAP to form alpha enzyme. In the absence of PAP, beta form of phenol sulfotransferase is produced.

Configuration of the SCOTI device with different tracheal tubes.

We have evaluated the Sonomatic Confirmation of Tracheal Intubation device (SCOTI) by testing its ability to be correctly configured with a variety of tracheal tubes of differing internal diameter and length. The device only configured correctly for RAE tubes with internal diameter of 7.0 mm or greater and for armoured tubes of internal diameter 8.5 mm. For conventional tubes of varying internal diameter cut to different lengths, configuration was only successful with certain dimensions. The inability to configure the device correctly with all types and lengths of tracheal tubes limits its usefulness as a indicator of tracheal intubation.

Leukotriene B4 as a marker of cerebral dysfunction.

It has been postulated that leukotriene B4 is involved in the pathogenesis of postischaemic cerebral oedema. We set out to determine if a relationship exists between jugular bulb leukotriene B4 and other indicators of cerebral ischaemia. No association could be demonstrated for either intracranial pressure, jugular bulb blood oxygen saturation or lactate oxygen index. Our results provide insufficient evidence to suggest that measurement of leukotriene B4 has any place in the management of head-injured patients.

Resistance and additional inspiratory work imposed by the laryngeal mask airway. A comparison with tracheal tubes.

Laryngeal mask airways and tracheal tubes were studied to determine both their resistance to constant gas flows and additional inspiratory work during simulated inspiration. Laryngeal mask airways imposed less resistance and required lower additional inspiratory work compared with the corresponding sized tracheal tubes. If inspiratory loading during anaesthesia is an important consideration, then the laryngeal mask airway may be preferable to a tracheal tube.

Intra-arterial blood sampling for clotting studies. Effects of heparin contamination.

Prothrombin time and activated partial thromboplastin time were measured in two groups of 30 patients each. Blood sampled from an arterial line after various discard volumes and from a central venous line were compared with direct venipuncture control samples. The arterial line flushing solution contained 1 unit of heparin per ml in group 1 and 2 units per ml in group 2. Our results confirmed that clotting studies carried out on blood samples from an arterial line or central venous line correlate well with those obtained from a venipuncture sample. The only exception was activated partial thromboplastin time in group 2 patients when the discard volume from the arterial line is only 2.5 ml above the deadspace volume of the connecting line. At least 5 ml of discard volume must be withdrawn before sampling, to obtain reliable results.

Inspiratory work imposed by demand valve ventilator circuits.

The inspiratory work (WI) imposed by three commonly used demand valve ventilator circuits was studied using a lung model to simulate spontaneous ventilation. The CPU-1 and Engstrom Erica circuits recorded WI of 379 mJ/l and 190 mJ/l respectively. A negative WI of -32 mJ/l was recorded for the Servo 900C, denoting that the circuit performed work on the lung. The demand valves recorded a time delay between inspiratory effort and onset of gas flow, of 300 ms (CPU-1), 190 ms (Servo 900c) and 160 ms (Engstrom Erica). Both the Servo 900C and Engstrom Erica demand valves were able to generate a high inspiratory gas flow response, but the CPU-1 lacked such a flow compensation. Expiratory work was also greatest with the CPU-1 (156 mJ/l) with 141 mJ/l and 90 mJ/l recorded for the Servo 900C and Engstrom Erica. Of the three ventilators studied, the Servo 900C appears to be the ventilator circuit of choice for spontaneous ventilation.

Systems analysis applied to intracranial pressure waveforms and correlation with clinical status in head injured patients.

Intracranial pressure waveforms (ICPWF) in head injured patients vary with the nature and severity of injury. Clinical interpretation of ICPWF shape is not defined. Spectral analysis provides an objective method of measuring changes in waveform shape, but the indices most suitable for clinical use remain unknown. Spectral analysis has been applied to ICPWF recorded from 30 patients with head injury, classified on clinical grounds into good, poor and intermediate groups. Normalized indices derived from ratios of certain characteristics of the ICP waveform to those of the arterial pressure (AP) waveform, were different (P less than 0.05) in all groups. A simple index examined was the harmonic count ratio (Nc:Na) which decreased with increasing severity of injury. ICP/AP harmonic transfer functions were derived, and demonstrated a peaked response in the range 10-12 Hz. Increasing attenuation of this peaked response occurred with increasing severity of injury. These results suggest that transfer functions may be a clinically useful index of intracranial conditions.

Resistance of humidifiers, and inspiratory work imposed by a ventilator-humidifier circuit.

The pressures and resistances of a bubble humidifier (Bennett Cascade) and a blow-by humidifier (Fisher and Paykel) were measured and computed at gas flow rates from 4.5 to 100 litre min-1. Pressures increased with flows, with the Bennett pressures being greater at all flows. The resistance of the Fisher-Paykel increased with flows, but remained less than that of the Bennett. An inverse resistance-flow relationship was seen with the Bennett up to a flow of 35 litre min-1. The work of breathing through a Servo 900C ventilator-humidifier circuit was computed, using a lung model. Work was performed by the Servo 900C on the lung, especially with the Fisher-Paykel circuit. The Bennett circuit required considerably greater (3.7 times more) inspiratory work. Thus the Bennett Cascade humidifier may present an unacceptable inspiratory load during spontaneous breathing.

Plasma catecholamines and oxygen consumption during weaning from mechanical ventilation.

Previous studies on oxygen consumption (VO2) during weaning from mechanical ventilation assumed that an increase in VO2 (delta VO2) reflected oxygen consumption by respiratory muscles (VO2RESP), and proposed delta VO2 as a weaning predictor. We measured VO2 CO2 production (VCO2) and plasma catecholamines in 20 short-term ventilated patients during weaning by SIMV and CPAP. delta VO2 as a percentage of VO2 during spontaneous ventilation (delta VO2%) ranged from 4.8% to 41.5%. VCO2 also increased and correlated with VO2. Plasma adrenaline and noradrenaline increased significantly to levels known to produce considerable increases in metabolic rate. Mean arterial pressure and heart rate concomitantly increased, but spontaneous minute ventilation decreased. Thus, since the increased plasma catecholamines are calorigenic, the assumption that delta VO2 represents VO2RESP is incorrect. Although mean delta VO2% of successfully weaned patients was significantly less than that of failure-to-wean patients, the wide scatter of individual values in the latter group excludes delta VO2% as an accurate weaning predictor.

Measurement of entrainment ratio during high frequency jet ventilation.

We have measured tidal (VT), entrained (Ve) and "blowback" (Vbb) volumes during high frequency jet ventilation (HFJV) through a Mallinckrodt Hi-Lo Jet tracheal tube in anaesthetized patients. The above volumes were calculated by digital integration of the appropriate regions of flow curves derived from a pneumotachograph placed between the bias flow tubing and the tracheal tube. At a driving pressure of 1 bar, lung minute ventilation increased with increasing ventilatory frequency, whilst tidal volumes decreased. The contribution of entrainment to tidal volume (Ve/VT) remained constant, although the volumes entrained were relatively small and varied widely from subject to subject. Blowback volumes were considerable, especially at ventilatory frequencies used clinically (1-2 Hz). We conclude that it is not possible to entrain predictable concentrations of volatile agents from the low pressure bias flow during HFJV.

Factors influencing humidification in high-frequency jet ventilation.

A new method of water nebulization for high-frequency jet ventilation (HFJV) using a coaxial saline infusion is described. A bench study was performed to investigate how alteration of the HFJV variables affects humidity using this method of humidification. The variables examined included the water flow rate (0.1, 0.25, 0.5, and 1.0 ml/min), cannula OD 2.1 mm (14 ga) and 1.4 mm (17 ga), ventilation rate (60, 80, 100, and 120 beat/min), inspiratory/expiratory (I/E) ratio (0.25, 0.67, and 1.5), and driving pressure (600, 900, 1200, and 1500 torr). Increasing water flow rate increased humidity. Humidity decreased with increased driving pressure, I/E ratio, and cannula OD. Humidity is not much affected by ventilation rate.

Relationship between resonance and gas exchange during high frequency jet ventilation.

We have studied the relationship between gas exchange and mechanical frequency response during high frequency jet ventilation (HFJV) at 0.5-5.0 Hz in anaesthetized pigs. The mechanical gain curve showed a minimal "anti-resonant" response at 0.8 Hz (f1) and a maximal "resonant" response at 5.0 Hz (f2). This finding may be explained by modelling the thorax and abdomen as a system of coupled masses and compliances which undergo two different modes of forced oscillation in the frequency range studied. Gas exchange was optimal in the frequency range between the minimal and maximal responses. The tidal volumes produced were greater than anatomical deadspace, suggesting that gas transport was mainly convective in this range.

Resonance in the mechanical response of the respiratory system to high frequency jet ventilation.

Eight normal domestic pigs (Large White breed) of body weights 17 kg to 62 kg were subjected to high frequency jet ventilation (HFJV) at frequencies of 1 to 10 Hz (60-600 breaths/min). Six animals survived the study. The gain response curves and phase shift response curves obtained for these animals indicate that respiratory system resonance can be excited at HFJV frequencies. Post-mortem examinations of the nonsurvivors' lungs suggested pulmonary barotrauma. These findings and their clinical implications are discussed.

Transcription of the celE gene in Thermomonospora fusca.

The steady-state level of celE mRNA (coding for cellulase E5) in Thermomonospora fusca YX was measured by Northern (RNA blot) hybridization under conditions causing induction or repression of cellulase synthesis. A good correlation was found between the mRNA level and the level of cellulase E5, suggesting that the T. fusca celE gene is regulated at the level of mRNA and, most likely, at the level of transcription. The 5' and 3' ends of the celE gene transcription unit were determined by S1 mapping with single-stranded DNA probes. These results showed that there were three species of celE mRNA in T. fusca YX with closely spaced 5' ends and identical 3' ends. The size of each mRNA was about 1.5 kilobases, from both the Northern and S1 data. This size is only slightly longer than that required to code for the 45-kilodalton E5 protein. In Escherichia coli D318 (celE), the 5' ends of the celE mRNAs are identical to those in T. fusca, but the 3' ends are located ca. 300 base pairs upstream of the T. fusca 3' end. The region where the putative celE promoters were located had some interesting features, including a 60-base-pair A + T-rich sequence and sequences resembling sigma 60 promoters.