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Biomedical subjects

G Hahn

Publications and source records attributed to G Hahn.

At least 73 records · Page 4Linked to original sources
PubMed1991

Comparison of chromogenic and fluorogenic substances for differentiation of coliforms and Escherichia coli in soft cheese.

In food hygiene the differentiation of Escherichia coli and coliforms as index resp. indicator organisms is very important as a basis for the assessment of good manufacturing practice (gmp). Using a fluorogenic (MUG) and chromogenic (X-gal) substrate the laborious methods have become more simple and reliable. A new German DIN standard method (10.183, part 3) was used as a base to examine 200 soft cheese samples for coliforms and Escherichia coli comparing different media, parameters and incubation times. It could be shown that an incubation of 48 h is absolutely necessary for E. coli and coliforms in both media, that X-gal is a quicker and more sensitive parameter for total coliforms than gas production and that the combination of fluorescence and indole is slightly superior to fluorescence and gas for the identification of E. coli. To sum up, the new fluorescence principle, integrated in new standard methods will be an excellent tool to simplify the differentiation of E. coli and coliforms in food hygiene. Additionally, X-gal as a chromogenic substrate for all coliforms, including E. coli, may be integrated in further standard methods.

Bacteriological Techniques↗
PubMed1991

[Quantitative and qualitative MRI changes in temporal lobe epilepsy. A comparison with normal parameters of nuclear magnetic resonance tomography].

Magnetic resonance imaging (MRI) often reveals no pathology in patients with temporal lobe epilepsy (TLE) who are candidates for surgery, even though post-surgery histology reveals atrophy or sclerosis. To differentiate these pathologies in MRI, we performed a standardized acquisition and a quantitative analysis of MRI data (qMRI). The standard values of 43 healthy subjects (both sex, left and right handed) were compared with those of 10 patients with TLE and unilateral EEG focus. A reduced estimated total brain extension, a significant atrophy of both temporal lobes with accentuation on the focus side and a significant hippocampal atrophy on focus-side were seen even in patients with no visually detectable pathology. The analysis of the signal intensities did not give additional information. Thus, qMRI is a helpful additional tool in the course of presurgical evaluation for focus lateralization.

Adolescent↗
PubMed1991

Acute and chronic hypothermia in a man with spinal cord injury: environmental and pharmacologic causes.

It is well known that people with spinal cord injuries can develop hypothermia when exposed to an unusually cold environment. Hypothermia can also develop during inpatient rehabilitation, particularly as a side effect of certain medications. We present a patient with C4 incomplete spinal cord injury whose core body temperature was chronically subnormal, and who developed acute hypothermia on several occasions during inpatient rehabilitation. The results of tests of his autonomic function were abnormal. Acute hypothermia (core temperature approximately 34C) was induced when he was challenged with nifedipine. The serum level of phenytoin became elevated to toxic levels during two episodes of acute hypothermia, but the serum level of carbamazepine did not change appreciably. This case demonstrates that people with spinal cord injuries are at risk for hypothermia, that hypothermia can be induced by nifedipine, and that significant thermal challenges can occur during routine inpatient rehabilitation. In addition, hypothermia appears to affect the metabolism of phenytoin.

Adult↗
PubMed1990

Multiple breath washout of He and SF6 in panting dogs.

Pulmonary gas transport mechanisms in panting were studied by multiple breath washout of two poorly soluble inert gases of similar solubility but different diffusivity (He and SF6). The experiments were performed in 6 chronically tracheotomized conscious dogs (mean body weight 31.0 kg) which, upon exposure to elevated room temperature, were enforced to thermal panting (mean breathing frequency 288/min). After equilibration of lung gas with 1% He and 1% SF6 followed by changeover to test gas-free air, end-tidal gas concentrations during multiple breath washout were recorded by mass spectrometry. The washout time course was analyzed into 3 exponential components. The initial fast component was considered to be in part determined by the transient response of the measuring system, whereas the intermediate and the slow component could be attributed to lung washout. The mean He/SF6 ratio of medium and slow rate constants was 1.06 and 1.13, respectively (both values differing from 1.0 at P less than 0.001). It is concluded that gas transport in dog lungs during panting was mainly determined by convection, diffusion-dependent processes being discernible but playing a minor role.

Animals↗
PubMed1990

Resonant frequency of the chest-lung system by analysis of the respiratory flow curve.

1. Resonant frequency of the chest-lung system in six tracheotomized, spontaneously breathing dogs was determined by analyzing the shape of the respiratory flow curve. 2. The resonant frequency was calculated from the periodic deviations from a sinusoidal flow pattern observed in the inspiratory phase of the breathing cycle. 3. Mean (+/- S.D.) resonant frequency was 6.1 +/- 0.9 Hz which was very close to the panting frequency (5.7 Hz) of the same dogs. 4. Resonant frequencies of the respiratory system in various species are compared.

Animals↗
PubMed1990

Adolescents' first and most recent use situations of smokeless tobacco and cigarettes: similarities and differences.

This study compared first and most recent use situations of adolescent smokeless tobacco experimenters with those of adolescent cigarette experimenters. Structured, open-ended interviews were conducted with 320 seventh and tenth grade youths in 16 Southern California schools. Students were categorized as nonusers (those who had never experimented with any tobacco product), minimal experimenters (those who had experimented with smokeless tobacco or cigarettes between 1 and 9 times), and persistent experimenters (those who had experimented with smokeless tobacco or cigarettes 10 or more times). The situations reported by smokeless tobacco were similar to those reported by cigarette experimenters. The most important differences between the two groups are highlighted. In particular, smokeless tobacco users seemed less concerned about negative social consequences of use than cigarette smokers. In addition, nonusers' observations of use and implications for prevention and cessation are discussed.

Adolescent↗
PubMed1989

Differential immunological response of patients with rheumatoid arthritis towards two different Epstein-Barr virus strains: inhibition of interleukin-1 release by the B95-8, but not the P3HR-1 virus strain.

An abnormal immune response towards the Epstein-Barr virus (EBV) has been documented in patients with rheumatoid arthritis (RA). To investigate whether these findings are due to the transformation event caused by EBV, RA blood mononuclear cells and monocyte-enriched preparations were incubated with two different EBV strains: the transforming virus secreted by the cell line B95-8 and the virus released by the P3HR-1 cell line that is not able to transform due to a small deletion in the U2 region of the virus genome. Immunological response was determined by the production of interleukin-1 (IL-1) and tumor necrosis factor (TNF) using ELISA and bioassay systems. There was a striking difference in cytokine measurements with a strong inhibition of IL-1 and TNF production after incubation with the B95-8 virus, but not the P3HR-1 virus. These data indicate that the disturbed reaction of the immune system towards EBV is either dependent on the full transformation of B cells in RA patients or alternatively due to the secretion of a cytokine inhibitor by the B95-8 cell line.

Arthritis, Rheumatoid↗
PubMed1989

Pulmonary gas exchange in panting dogs: a model for high frequency ventilation.

Panting in animals can be expected to represent a naturally occurring physiological counterpart to today's techniques of mechanical high-frequency ventilation. To analyze the mechanisms underlying the gas exchange inefficiency during ventilation with high frequencies, steady-state pulmonary gas exchange was studied in seven conscious dogs (32 kg mean body weight) during panting elicited by mild thermal stress. The animals had a chronic tracheostomy and an exteriorized carotid artery loop and were exposed to 27.5 degrees C ambient temperature for 2 h (65% relative humidity). Open-circuit techniques were used and PO2 and PCO2 from the tracheostomy tube were continuously monitored by mass spectrometry using a special sample-hold phase-locked gas sampling technique. PO2 and PCO2 were determined in arterial blood collected from the carotid artery. During the exposure, the following variables of steady-state gas exchange were determined (means +/- SD): breathing frequency 313 +/- 19 min-1; tidal volume, 167 +/- 21 ml; total ventilation, 52 +/- 9 l.min-1; effective alveolar ventilation, 5.5 +/- 1.3 l.min-1; partial pressures (torr; a, arterial; E', end-tidal): PaO2, 106.2 +/- 5.9; PaCO2, 27.2 +/- 3.9; (PE'-Pa)O2, 26.0 +/- 5.3; (Pa-PE')CO2, 14.9 +/- 2.5. According to the conventional lung model, parallel-dead space ventilation (ventilation of unperfused lung regions) would account for about 55% of the alveolar ventilation and for 2/3 of the (PE'-Pa)O2 difference. However, the lack of an 'alveolar plateau' in the CO2 and O2 expirograms suggests that incomplete serial mixing in peripheral airways contributes to the enhanced gas exchange inefficiency during panting as reflected in the increased blood/gas differences for O2 and CO2.

Animals↗
PubMed1989

Pulmonary gas exchange in panting dogs.

Pulmonary gas exchange during panting was studied in seven conscious dogs (32 kg mean body wt) provided with a chronic tracheostomy and an exteriorized carotid artery loop. The animals were acutely exposed to moderately elevated ambient temperature (27.5 degrees C, 65% relative humidity) for 2 h. O2 and CO2 in the tracheostomy tube were continuously monitored by mass spectrometry using a special sample-hold phase-locked sampling technique. PO2 and PCO2 were determined in blood samples obtained from the carotid artery. During the exposure to heat, central body temperature remained unchanged (38.6 +/- 0.6 degrees C) while all animals rapidly switched to steady shallow panting at frequencies close to the resonant frequency of the respiratory system. During panting, the following values were measured (means +/- SD): breathing frequency, 313 +/- 19 breaths/min; tidal volume, 167 +/- 21 ml; total ventilation, 52 +/- 9 l/min; effective alveolar ventilation, 5.5 +/- 1.3 l/min; PaO2, 106.2 +/- 5.9 Torr; PaCO2, 27.2 +/- 3.9 Torr; end-tidal-arterial PO2 difference [(PE' - Pa)O2], 26.0 +/- 5.3 Torr; and arterial-end-tidal PCO2 difference, [(Pa - PE')CO2], 14.9 +/- 2.5 Torr. On the basis of the classical ideal alveolar air approach, parallel dead-space ventilation accounted for 54% of alveolar ventilation and 66% of the (PE' - Pa)O2 difference. But the steepness of the CO2 and O2 expirogram plotted against expired volume suggested a contribution of series in homogeneity due to incomplete gas mixing.

Acepromazine↗
PubMed1988

Universal immuno-stick test for direct rapid identification of microbial antigens within 5 minutes. Preliminary report.

Based on experiences with ELISA and biochemical fluorescence assays we have developed a new serologic identification system for detecting all conceivable particle and soluble antigens within 5 min using a very simple, sensitive procedure. This assay represents a sandwich ELISA that has been modified with regard to the sorbent, the enzyme substrate and the identification step. The test is performed as follows: 10 microliter aliquots of antigen dilution, specific or control antibody, respectively, and a phosphatase-conjugated anti-antibody are consecutively mixed. A small strip of special indicator sorbent paper (test stick) is moistened with this mixture for one minute. Subsequently it is dipped 3-5 times alternately in 0.1 M NaOH and a solution of the enzyme-substrate 4-methylumbelliferyl phosphate and immediately evaluated under a UV lamp. Positive samples instantaneously show brilliant light blue fluorescence and decolorization from dark red to white. Although the principle behind the reaction is not yet fully understood, the test works specifically and sensitively within a pg range. Thus far, for example, we have been able to identify Salmonella from suspended milk powder and streptococci from milk (3-5 cells/ml) without previous incubation, enterotoxins from staphylococcal colonies, Aflatoxin M1 and organ-phosphates. Results from examinations of staphylococcal enterotoxins are presented in more detail. Moreover, using a defined antigen, antibodies from different sera could be identified in the same rapid, sensitive and specific manner. Thus, we are convinced that the usual time-consuming enrichment methods for isolating pathogenic bacteria and other immunogenic substances as also current serologic assays will turn out to be superfluous.

Antigens, Bacterial↗
PubMed1988

Sample-hold technique for analysis of respiratory gas composition at high breathing frequencies.

A gas sampling device is described for continuous monitoring of respiratory gas composition that is applicable to experimental conditions when the breathing frequency is very high (greater than 2 Hz) and the response time of conventional gas analyzers becomes a critical limiting factor. The system utilizes the principle of discontinuous gas collection at any selected point of the respiratory cycle facilitated by ultraspeed piezoelectric valves and includes provision for sample-hold characteristics. Two distinct modes of operation are supported. In phase-locked mode gas sampling is synchronous with breathing frequency. In scanning mode gas collection is asynchronous with breathing frequency. Phase-locked mode may be used for continuous monitoring of end-tidal gas concentrations, whereas scanning mode is intended for assessing the gas concentration profile throughout the respiratory cycle. The system may be applied to steady breathing encountered in mechanical ventilation at high frequency or during quasi-steady breathing observed in panting animals. Combined with a respiratory mass spectrometer, the system has been used for measurement of gas concentrations in alveolar gas mixtures at breathing frequencies ranging from 3 to 30 Hz that were otherwise not amenable to rapid measuring techniques.

Animals↗
PubMed1985

Haemodialysis in 'hepatorenal syndrome': report on two cases.

We report two patients with hepatorenal syndrome who recovered from oliguria and renal failure after temporary treatment with haemodialysis. Hepatorenal syndrome developed under diuretic treatment in both patients. Volume expansion, dopamine, and prostaglandin I2 did not improve renal function. In the one patient with alcoholic cirrhosis, renal biopsy showed only minimal alterations of glomeruli, tubuli, and arterial vessels. In the other case, the deterioration and improvement in renal function parallelled changes in acute alcohol-toxic hepatic function. We conclude that haemodialysis should be considered for treatment of hepatorenal syndrome in selected patients where reversal of liver failure can be expected.

Acute Kidney Injury↗