Effect of flow on an array of Helmholtz resonators: Is Kevlar a "magic layer"?

The effects of flow on the acoustic behavior of metamaterials can be very significant and possibly destructive. To avoid these detrimental effects, it would be a good idea to have a "magic layer" that allows acoustics to pass through while suppressing the sound-flow interactions. A possible realization of this layer based on Kevlar fabric is tested in this paper. It is shown that, in the presence of Kevlar, flow-sound interactions that can lead to acoustic amplification and whistling phenomena are avoided. Thus, Kevlar will permit liner designs including large slits. However, it adds large acoustic losses, which limits interesting resonance effects in applications.

Metabolic clearance of the antioxidant ascorbic acid in surgical patients

BACKGROUND

A reduction of plasma ascorbic acid concentration in the post-operative period has been well documented and is associated with an increase in post-operative complications. The underlying reason for the decreased concentration of ascorbic acid in the plasma is not clear. However, only an increased post-operative requirement for ascorbic acid would justify a substitution. Therefore, we investigated the pre-operative and post-operative metabolic clearance of ascorbic acid.

MATERIALS AND METHODS

We calculated the metabolic clearance subsequent to intravenous bolus injection of 6 mg ascorbic acid/kg body weight in 15 patients before and after they underwent major maxillofacial surgery. Blood samples were taken before and 5, 15, 30, 45, 60, 90, 120, and 240 min after administration of ascorbic acid before and after the operation. Urine was collected. Ascorbic acid in plasma and urine was analyzed using a high performance liquid chromatographic technique.

RESULTS

The pre-operative metabolic clearance was 7.6 +/- 2.22 l/h (mean +/- SD), increasing significantly to 12.1 +/- 4.87 l/h on the first post-operative day (P < 0.001). Doses of approximately 1150 mg ascorbic acid would be necessary to compensate for the observed loss and to raise plasma ascorbic acid to high normal values.

CONCLUSIONS

There is a significantly increased post-operative metabolic clearance of ascorbic acid that might be considered when framing future dose recommendations in post-operative patients.

Ceftazidime determination in serum by high-pressure liquid chromatography

A rapid and sensitive high-pressure liquid chromatographic method with simple sample preparation was developed for the quantitative analysis of the beta-lactam antibiotic ceftazidime (CAS 78439-06-2, Fortum). A good linear relationship was established between the peak area and the amount of ceftazidime injected over a concentration range of 1 to 200 microg/ml. The detection limit of the method was calculated to be 0.9 microg/ml. Stability was shown at 4 degrees C and at -196 degrees C for time periods of 2 h and 84 days, respectively.

Determination of alpha-tocopherol in plasma by high performance liquid chromatography with fluorescence detection and stability of alpha-tocopherol under different conditions

In order to study the clinical effects of the antioxidant alpha-tocopherol (tocofersolan, CAS 30999-06-5) a simple, robust, sensitive and reliable high performance liquid chromatography (HPLC) method using fluorescence detection for the daily measurement of alpha-tocopherol concentration in plasma is described. Several methods of HPLC analysis using fluorescence techniques are published, however, investigations of the stability of alpha-tocopherol during sample preparation under different conditions are relevant in the routine measurements and have to date not been reported. Therefore a modified method, both sensitive and robust, qualified for the day-by-day measurement of alpha-tocopherol in plasma was established and the stability of alpha-tocopherol during sample preparation was analysed under different conditions. This method enables the complete separation of alpha-tocopherol from other compounds within 14 min. In addition, investigations on the stability of alpha-tocopherol during sample preparation showed the necessity of rapid sample preparation without delay. Prepared samples can be stored in liquid nitrogen for at least 56 days.

Neurophysiology of orthostatic tremor. Influence of transcranial magnetic stimulation

A 74-year-old patient suffers from painful muscle cramps when he stands since 30 years. He has no visible tremor but 16 Hz burst activity on EMG, indicating orthostatic tremor. Previous diagnosis was hysteria, stiff person syndrome or dystonia. This shows that EMG during standing should be part of the examination of patients with stiff muscles or muscle cramps. Tremor was not strictly orthostatic. It appeared in back muscles while sitting, when the patient supported a weight with outstretched arms. Phase between muscles differed between normal standing and standing on heels. Subthreshold transcranial magnetic stimulation modulated timing of the tremor bursts and inhibited them at higher intensity stimulation.

Pilot investigation of thyrotropin-releasing hormone-induced thyrotropin and prolactin release in anxious patients treated with diazepam

Benzodiazepines have been reported to inhibit thyrotropin (TSH) and prolactin (PRL) secretion in response to stressful and pharmacologic stimuli in experimental animals. The current study investigates basal and thyrotropin-releasing hormone (TRH)-stimulated TSH and PRL release in anxious patients treated with diazepam. Six hospitalized patients having generalized anxiety or adjustment disorder with anxious mood (DSM III-R criteria) were treated during 1 week with diazepam (mean daily dose 33.3 mg). TRH testing was performed comparatively before and after 7 days of diazepam administration (with 250 micrograms protirelin and blood sampling at 15-min intervals over 60 min). Steady-state plasma levels of diazepam and its metabolite nordazepam (desmethyldiazepam) were determined by high-performance liquid chromatography. After 7 days of diazepam treatment, basal plasma levels of TSH and PRL were not affected compared with pretreatment values. Similarly, the time-course of TRH-induced TSH release was not modified by the treatment. By contrast, there was a trend to decrease in the TRH-induced PRL release, and the decrease in the PRL response to TRH on day 7 was significantly correlated with plasma nordazepam concentrations (rs = 0.943, p = 0.02). These preliminary results suggest that benzodiazepines, at therapeutic doses for the treatment of anxiety, may alter TRH-induced PRL release in humans.

Impairment of visuospatial function in idiopathic spasmodic torticollis

We studied visuospatial function in 15 patients with idiopathic spasmodic torticollis (ST) and 15 age- and sex-matched controls. All subjects underwent a battery of visuospatial tests, assessing different functional components of spatial ability. The performance of ST patients on tasks of spatial perception did not significantly differ from that of normal subjects, but patients performed significantly worse on spatial tasks requiring mental manipulation of personal space. This distinct pattern of visuospatial impairment may result from basal ganglia dysfunction.

Immunological changes in a case of Marchiafava Bignami disease: response to amineptine treatment

Marchiafava-Bignami disease (MBD) is a rare complication of chronic alcoholism. We describe a regressive form of MBD in which a primary decrease in CD4(+) cells was improved by amineptine treatment. No significant change in the CD4 : CDS ratio was observed in a few major depressed subjects receiving this drug.

Heterogeneous distribution of a fatty acid analogue uptake in the myocardium of aged rats

The aim of this study was to determine the extent and location of damaged myocardial areas in senescent rats. The viability of myocardial cells was evaluated in virgin young (4 months old) and aged (29 months old) female Wistar rats by analysing the uptake of a slowly metabolisable radiolabelled fatty acid analogue, 15-p-iodophenyl-beta-methylpentadecanoic acid (IMPPA). The biodistribution of IMPPA was measured in various organs, and regional myocardial uptake was specifically assessed using quantitative autoradiography. Myocardial enzymatic activity and DNA content were also evaluated with nitro blue tetrazolium (NBT) and propidium iodide (PI) staining, respectively. In senescent rats, cardiac and renal IMPPA uptake showed a significant (50%) reduction compared with young adult rats and the uptake was not significantly changed in the liver, spleen, lungs, and skeletal muscle. Total ventricular NBT staining and IMPPA uptake were almost homogeneous in young adult rats, whereas they were very heterogeneous in aged rats. In the latter, approximately 11% of the total ventricular volume showed a significantly decreased (by 60% or more) IMPPA uptake compared with normal values, and this reduction was greater in ventricle base than in apex. The myocardial areas unlabelled or poorly labelled by IMPPA represented 4, 5, 6, and 21% of the right ventricular, left ventricular epicardial, septal, and left ventricular endocardial volume, respectively, and were poorly stained with NBT. In some of these areas, PI staining indicated the presence of living cells unable to pick up NBT staining. In conclusion, in young adult rats, no myocardial lesions were observed using three different labelling techniques.(ABSTRACT TRUNCATED AT 250 WORDS)

[Neuroendocrine effects of benzodiazepines]

After presenting some general aspects of psychoneuroendocrinology, pharmaco-endocrinology and benzodiazepine receptor molecular pharmacology, the author reviews the neuro-endocrine effects of the benzodiazepines both in experimental animals and in humans. While benzodiazepines produce inconsistent effects on basal hormone secretion, they have potent effects on inhibition of ACTH, cortisol, TSH and prolactin secretion in response to stressful and pharmacological stimuli. Acute diazepam administration causes stimulation of GH secretion, but patients taking this drug regularly over periods of years have an impaired GH response or no response at all (tolerance). The mechanisms of action by which the benzodiazepines produce their effects on neuroendocrine functions are complex. The BZD may act at GABA-coupled BZD receptors in hypothalamus, or other brain regions to potentiate the effects of endogenous GABA. Nevertheless, some neuro-endocrine effects of BZD are mediated through actions on BZD receptors in the pituitary gland: we reported an inhibition of TRH induced PRL release by diazepam (treatment of 7 days) in anxious patients.

[Contribution of single photon emission computerized tomography (SPECT-HMPAO) to the study of schizophrenia]

The authors studied a group of thirteen schizophrenic patients with functional brain imaging, using single-photon-emission-computed tomography (S.P.E.C.T.). The radiotracer was the H.M.P.A.O. labelled with 99 m Technetium. All were being given neuroleptic drug. Forty-one lesions demonstrated decreased perfusion. These functional abnormalities are mainly located in the left hemisphere and this asymmetry is more pronounced in positive-symptom schizophrenics. However, at rest, these correlations are limited and finally we demonstrated a wide spectrum of metabolic dysfunctions in the same subtype of schizophrenia.

Marchiafava-Bignami disease. A case studied by structural and functional brain imaging

Marchiafava-Bignami disease (MBD) is a rare complication of chronic alcoholism. The clinical features, X-ray, CT and MRI findings are well documented. However, functional brain imaging has not been used in cases of MBD. We used single-photon emission computed tomography (SPECT) to monitor the regional cerebral blood flow in a patient suffering from a acute form of MBD, from which he subsequently recovered. Several abnormalities were found. A more frequent use of functional brain imaging in MBD could improve our knowledge of pathogenesis and prognosis for MBD.

Evaluation of cellular viability by quantitative autoradiographic study of myocardial uptake of a fatty acid analogue in isoproterenol-induced focal rat heart necrosis

Previous studies led us to hypothesize that a fatty acid analogue, 15-p-iodophenyl-beta-methyl pentadecanoic acid (IMPPA or BMIPP), which is taken up but not quickly metabolized by heart cells, would be a more suitable tracer of cellular viability than thallium-201. Biodistribution studies of 1-14C-IMPPA in conscious, freely moving rats showed that the concentration ratio of radioactivity in the heart with respect to the blood was about 8 for at least 60 min after intravenous administration, permitting its use as a putative tracer in these conscious, freely moving rats. Thereafter, the myocardial uptake of 14C-IMPPA was studied in isoproterenol-treated rats (daily treatment for 10 days in order to induce cardiac hypertrophy and necrotic foci) with respect to control ones. Comparison of myocardial localizations by quantitative autoradiography of the uptake of 201Tl and 14C-IMPPA with that of triphenyltetrazolium chloride (TTC) staining enabled comparative evaluation of nutritional blood flow, localization and uptake of 14C-IMPPA and necrotic foci size. Distributions of 14C-IMPPA and 201Tl in control rats' hearts were homogeneous, like TTC staining. In infarcted hearts, areas of decreased 14C-IMPPA uptake were nearly the same (100% +/- 5%) as those unstained by TTC. These areas were larger than those showing a decrease in thallium uptake (about 70% +/- 5% of the total scar size). Therefore, IMPPA seems to be a more accurate and sensitive indicator of necrosis localization compared with thallium. It may be a useful agent for assessment of myocardial viability by single photon emission tomography (SPET) imaging.

Influence of the presence of a methyl group on the myocardial metabolism of 15-(paraiodophenyl)-3 methyl pentadecanoic acid (IMPPA)

The objective of the present study was to determine the mechanism of accumulation of myocardial activity following i.v. injection of 15-(paraiodophenyl)-3 methyl pentadecanoic acid (IMPPA). IMPPA and 15 phenyl-3 methyl pentadecanoic acid (MPPA) were labeled with 14C at position 1 and used to perfuse isolated rat hearts in a closed system. After 5 min of perfusion, IMPPA reached 2/3 of its value at 45 min. 14CO2 production was low. Most of the myocardial activity was in the form of free IMPPA. Analysis of IMPPA activation by CoA SH revealed that it was very strongly inhibited. The retention of myocardial activity is thus due to intracellular accumulation of free IMPPA following inhibition of activation. Comparison of results obtained with IMPPA and MPPA showed that the presence of iodine in the molecule accentuates the inhibition of activation.

Intramyocardial fate of 15-p-iodophenyl-beta-methylpentadecanoic acid (IMPPA): is it a good tracer of fatty acid myocardial uptake?

Iodinated fatty acids (FAs) are now used in Nuclear Medicine to assess, by external detection, myocardial metabolism. Methylated FAs have been proposed as tracers of FA myocardial uptake. IMPPA is a new FA analogue in which a methyl group have been introduced in beta position to inhibit beta-oxidation and a terminal phenyl group prevents a possible omega oxidation. We have compared the intramyocardial behaviour of this FA with the 15-p-iodophenyl-pentadecanoic acid (IPPA), the straight chain analogue, and with the 15-phenyl-beta-methylpentadecanoic acid (MPPA), the 3 of them being labelled with C14 on the carboxyl group, in isolated rat hearts perfused in a recirculating system. When IMPPA is compared to IPPA (influence of the methyl group), we observe 1--an inhibition of beta-oxidation (no significant production of labelled CO2 and very low radioactivity in the aqueous phase) leading to a reduced uptake, 2--a lower radioactivity in the organic phase due to a hindrance to the esterification process both into TGs and PLs, the free FAs level being higher. When IMPPA is compared to MPPA (influence of the iodine atom), we observe 1--the same inhibition of beta-oxidation, 2 - a higher myocardial radioactivity due to a much higher level of free FAs, the esterification into TGs and PLs being reduced. This study with IMPPA indicates that it is taken up by the heart and trapped there, as it is not oxydized. This long retention time, apart from giving good scintigraphic images, should make IMPPA useful to study the regional myocardial uptake of FAs.