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Biomedical subjects

R Sauter

Publications and source records attributed to R Sauter.

At least 55 records · Page 3Linked to original sources
PubMed1989

Cerebral metabolism in man after acute stroke: new observations using localized proton NMR spectroscopy.

Localized proton NMR spectroscopy at 1.5 T using stimulated echoes has been applied to study metabolic alterations in the postischemic phase of patients with acute cerebral infarction. A complete depletion of N-acetyl aspartate in the area of infarction has been observed in a patient studied 4 days after stroke. This finding was paralleled by a dramatic increase in the concentration of lactic acid to about 16 mM within the lesion, indicating continued anaerobic glycolysis. The diluting effect of the edema has been estimated to reduce average metabolite concentrations by about a factor of 3.

Adult↗
PubMed1989

Localized proton NMR spectroscopy in different regions of the human brain in vivo. Relaxation times and concentrations of cerebral metabolites.

High-resolution proton NMR spectra of normal human brain in vivo have been obtained from selected 27- and 64-ml volumes-of-interest (VOI) localized in the insular area, the occipital area, the thalamus, and the cerebellum of normal volunteers. Localization was achieved by stimulated echo (STEAM) sequences using a conventional 1.5-T whole-body MRI system (Siemens Magnetom). The proton NMR spectra show resonances from lipids, lactate, acetate, N-acetylaspartate (NAA), gamma-aminobutyrate, glutamine, glutamate, aspartate, creatine and phosphocreatine, choline-containing compounds, taurine, and inositols. While T1 relaxation times of most of these metabolites were about 1100-1700 ms without significant regional differences, their T2 relaxation times varied between 100 and 500 ms. The longest T2 values of about (500 +/- 50) ms were observed for the methyl protons of NAA in the white matter of the occipital lobe compared to (320 +/- 30) ms in the other parts of the brain. No significant regional T2 differences were found for choline and creatine methyl resonances. The relative concentrations of NAA in gray and white matter were found to be 35% higher than those in the thalamus and cerebellum. Assuming a concentration of 10 mM for total creatine the resulting NAA concentrations of 13-18 mM are by a factor of 2-3 higher than previously reported using analytical techniques. Cerebral lactate reached a maximum concentration of about 1.0 mM.

Brain↗
PubMed1989

Noninvasive differentiation of tumors with use of localized H-1 MR spectroscopy in vivo: initial experience in patients with cerebral tumors.

A recently developed method for image-selected localized hydrogen-1 magnetic resonance (MR) spectroscopy was assessed in the differential diagnosis of nine primary and secondary cerebral tumors, including four gliomas, two meningiomas, one neurilemoma, one arachnoid cyst, and one metastasis of breast cancer. Well-resolved H-1 MR spectra of these tumors were obtained in vivo with a conventional 1.5-T whole-body MR imaging system. All tumor spectra were remarkably different from spectra from normal brain tissue. Spectra obtained from different tumors exhibited reproducible differences, while histologically similar tumors yielded characteristic spectra with only minor differences. The observed spectral alterations reflect variations in concentrations and relaxation times of the H-1 MR sensitive pool of free (mobile) metabolites within the tissues. In most cases, the concentrations of N-acetyl-aspartate and creatine/phosphocreatine are reduced below detectability, whereas choline-containing compounds are generally enhanced. The spectral differences between the tumors are mainly due to the differing concentrations of lipids, lactic acid, and carbohydrates. Localized H-1 MR spectroscopy may become an important clinical tool for the differentiation of tumors as well as for therapeutic control.

Adult↗
PubMed1989

Bioequivalence studies: single vs multiple dose.

Bioequivalence of different preparations of the same drug substance has gained considerable importance over the last few years due to increasing generic substitution. The procedure that the manufacturer of the generic test preparation has to show bioequivalence with an appropriate reference preparation is scientifically accepted and laid down in international regulations. However, the necessity of single- vs multiple-dose bioequivalence studies has not been discussed in detail with the exception of the Dutch and US guidelines on sustained-release theophylline formulations, where multiple-dose studies are specifically required. This paper compares the conclusions drawn from single- and multiple-dose studies in the same subjects and recommends appropriate pharmacokinetic characteristics.

Adult↗
PubMed1988

A novel approach to the specification of in-vitro dissolution boundaries based on regulatory requirements for bioequivalence.

Although bioequivalence between products has gained considerable importance over the last few years, the concept has not yet been transferred to "within product bioequivalence", i.e. "batch-to-batch bioequivalence". Two different formulations of an active substance are considered bioequivalent if they differ by not more than 20% in rate and extent of absorption. This regulatory requirement should also be satisfied for two different batches of the same formulation ("within product bioequivalence"). Euphylong pellets appear to be the first sustained-release theophylline formulation for which data on the "within product bioequivalence" can be presented. The upper and lower limits of the in-vitro dissolution were specified so that even the most extreme batches within these specifications, which normally do not occur among production batches, are bioequivalent. This novel procedure requires that the in-vitro method used is suitable to detect in-vivo differences. Furthermore, it should be able to predict the in-vivo absorption kinetics on the basis of in-vitro data, at least insofar as a discriminatory ranking is concerned. It has been shown how this approach has lead to the in-vitro specifications of Euphylong pellets and how specially manufactured experimental batches representing the upper and lower specification limits were tested for bioequivalence. Finally, it is shown that a typical production batch conforms well with the specification limits and does not reach the extremes of the experimental batches which were specially manufactured for the purpose of this study.

Absorption↗
PubMed1988

Pharmacokinetic profile of a new sustained-release theophylline pellet formulation for once-daily evening administration.

Euphylong is a new anhydrous theophylline sustained-release pellet formulation developed for once-daily administration in the evening in normal and slow metabolizers, and unequally divided twice-daily administration in fast metabolizers. Its pharmacokinetics have been investigated with respect to bioavailability, peak-trough fluctuation, nocturnal plateau profile, food effects, predictability and reproducibility between subjects and from day to day. To this end, 7 single-dose and 4 multiple-dose, randomized, cross-over studies were performed in a total of 168 healthy, normal, male volunteers. In order to match the dosage strengths of three reference products, capsules containing different amounts of pellets--also referred to as Euphylong pellets--have been used. Absolute bioavailability of theophylline from Euphylong was 88 and 100%, depending on the rate and the total dose of the intravenous reference infusions. Relative bioavailability ranged between 85 and 112%, depending on the reference formulations. The peak-trough fluctuation was reduced for Euphylong pellets in comparison with other once-daily theophyllines, by more than 30% in the case of a reference tablet. In contrast to another once-daily theophylline capsule, Euphylong pellets seem to be hardly affected by meals. Moreover, in view of the known variability of theophylline pharmacokinetics both between subjects and from day to day, the nocturnal plateau profile, which is characteristic of Euphylong, is extremely reproducible. The nocturnal excess is consistently 30-40% and the plateau time is consistently 11-12 h in normal metabolizers. The long nocturnal plateau profile together with the high reproducibility of Euphylong pharmacokinetics enable an easy and safe adjustment of the dose tailored to the needs of the individual patient. In addition, the time of the evening dose and its relationship to meals is not critical in the case of Euphylong pellets. Particularly patients presenting with nocturnal asthma, which is one of the major areas of theophylline therapy, should have a clinically relevant benefit from Euphylong.

Absorption↗
PubMed1988

Theophylline therapeutic drug monitoring in the case of a new sustained-release pellet formulation for once-daily evening administration.

In view of the large interindividual differences in theophylline clearance and the narrow therapeutic range it is essential to individualize the theophylline dose. In order to do so, estimation of minimum and maximum serum theophylline concentrations during one dosing interval from one or two blood samples is desirable, particularly in the case of once-daily administration. Whereas the minimum (trough) concentration can be readily estimated from the pre-dose level, the maximum (peak) concentration occurs at night. For Euphylong, a new sustained-release theophylline pellet formulation, administered once-daily in the evening, for example between 7 p.m. and 8 p.m., the nocturnal maximum concentration can be calculated as 110-120% of the serum theophylline concentration determined from a blood sample taken in the early morning, for example between 7 a.m. and 8 a.m. This procedure works not only for mean data but also on an individual basis. The procedure is based on the extended nocturnal plateau profile of Euphylong with its high reproducibility and cannot be transferred to other formulations.

Delayed-Action Preparations↗
PubMed1987

Cartilage disorders: comparison of spin-echo, CHESS, and FLASH sequence MR images.

Magnetic resonance (MR) imaging is known to be a suitable modality for the visualization of the hyaline cartilage and the fibrocartilage joint structures. To compare standard spin-echo (SE) images with water images obtained with the chemical shift selective (CHESS) sequence and with the fast low angle shot (FLASH) sequence, examinations were performed with all three sequences in eight volunteers and 28 patients with inflammatory degenerative and traumatic alterations of the knee, hip, and sacroiliac joints. Arthroscopic and/or surgical correlation were available in 16 patients; bone scanning and computed tomography of the sacroiliac joints were performed in four patients. CHESS-water and FLASH images proved superior to SE images in demonstrating hyaline cartilage disorders. There was no difference between SE, CHESS, and FLASH in the detection of fibrocartilage disorders. Short imaging times and satisfactory depiction of cartilage alterations make FLASH a promising method.

Adult↗
PubMed1986

[Nuclear magnetic resonance tomographic diagnosis of joint changes. Value of chemical shift imaging].

Chemical shift imaging permits separate demonstration of water and fat-bound protons in a selected plane. Compared with normal spin-echo sequences, specific information can be obtained in the investigation of internal joint structures. A pilot study was carried out on the possibility of showing normal and abnormal structures, using normal controls, and 16 patients with various joint abnormalities.

Arthritis, Rheumatoid↗
PubMed1986

MR imaging of the normal shoulder.

Magnetic resonance (MR) images of the shoulders of a healthy volunteer were obtained in axial, sagittal, and coronal orientations using a 0.5-T imaging system. Multiple high-resolution spin-echo images were generated using an off-center zoom technique and a specially designed surface coil. Several anatomic structures, including the rotator cuff, long biceps tendon, articular capsule, muscles, and bones, were visualized. The coronal and sagittal views were the most useful for demonstrating the rotator cuff. MR imaging has potential as a new non-invasive tool for the evaluation of the shoulder region.

Adult↗
PubMed1986

Temporal bone region: high-resolution MR imaging using surface coils.

Specially designed surface coils for the region of the temporal bone enable high-resolution magnetic resonance (MR) imaging of the structures of the inner ear. Eight healthy volunteers and 21 patients (six with cholesteatomas, five with acoustic neuromas, five with glomus tumors, and five with mastoiditis) were examined using a 0.5-T MR imager. The demarcation of tumor extent with MR imaging was better than with computed tomography because of improved soft-tissue contrast and because the surrounding bony tissue did not generate any signal. High-resolution MR imaging is particularly useful for small acoustic neuromas because of its higher specificity compared with gas cisternography.

Brain Neoplasms↗
PubMed1985

[Nuclear spin tomography of the petrous bone and cerebellopontiLe angle. Methods and normal anatomy].

Proton nuclear resonance tomography, also called magnetic resonance imaging, is a new imaging procedure which makes it possible to obtain tomographic cuts of the petrous bone in three planes. It is complementary to CT and is able to demonstrate the small structures of the inner ear and of the cerebello-pontine angle, without bone artefacts and without overlap or distortion. By using special surface coils combined with thin sections and a gradient-zoom technique, it is possible to obtain high resolution images which equal those of modern CT. By choosing suitable exposure parameters and a multi-echo technique, one can obtain excellent tissue contrast without using positive or negative contrast media.

Cerebellopontine Angle↗
PubMed1985

[Proton spin tomography in diseases in the petrous bone region].

Magnetic resonance tomography (MRI = magnetic resonance imaging) can provide sectional images of the petrous bones in all planes. It is complementary to computed tomography (CT) and can demonstrate inflammatory changes in the petrous bones and mastoids, and cholesteatomas, with accuracy and without artifacts. MRI is inferior to CT for the demonstration of bone destruction and this this limits its use in the diagnosis of glomus tumours. The use of special surface coils combined with thin sections and a gradient-zoom technique provides high resolution images which approach the quality of modern CT examinations. This opens new possibilities for the diagnosis of small acoustic neuromas; because of the excellent tissue contrast, they can be well demonstrated without using intravenous contrast media or intrathecal air (CT-air meatography).

Adult↗
PubMed1978

Immunoglobulin abnormalities in relatives of IgA deficient epileptics.

Serum levels of IgA were found to be reduced in some patients with epilepsy. Further studies revealed that only epileptics with constitutional factors for seizures showed, if ever, IgA deficiency, particularly those treated with hydantoins (up to 25%). In order further to substantiate the association of immunoglobulin alterations with epilepsy nine families in whom the disease was clustered were investigated. An IgA deficiency was detected in 16 of the 19 epileptics (three without hydantoin medication), but in none of their 45 non-epileptic relatives. However, four of the relatives had a low IgM. Seven other families were tested in each of which only one IgA deficient epileptic was known. No other family members were found with a low IgA, but 24 of 58 such relatives had increased IgM serum concentrations. The association of IgA deficiency and epilepsy with IgM imbalances in relatives of IgA deficient epileptics gives additional support for the hypothesis that immune imbalances and certain forms of epilepsy might be linked.

Epilepsy↗
PubMed1976

IgA deficiency, epilepsy, and hydantoin medication.

Serum-immunoglobulin concentrations were measured in 364 patients with epilepsy. On dividing the patients into those treated with or without hydantoins, and according to possible aetiological factors, a characteristic pattern emerged. Irrespective of the treatment given, the mean values of IgA were significantly reduced in patients in whom constitutional factors were apparent, including those with familial prevalence of seizures. While IgA was rarely found below 0-6 mg/ml, a limit chosen to define IgA deficiency in patients not treated with hydantoins, the IgA level was subnormal in 20-25% of the patients treated with such drugs. In contrast, the mean concentration of IgA was normal and no individual subnormal values were observed in epileptic patients treated with or without hydantoins whose disease was thought to be secondary to traumatic or infectious events or to metabolic disturbances. The data suggest that epilepsy with constitutional characteristics might predispose to low IgA, but that IgA deficiency only occurs when hydantoins are given. Whether this postulated predisposition is relevant to the aetiology or pathogenesis of epilepsy remained unresolved.

Child↗