Biomedical subjects

C Bäumer

Publications and source records attributed to C Bäumer.

6 recordsLinked to original sources

PubMed2006

Gamow-Teller strengths in the A = 14 multiplet: a challenge to the shell model.

A new experimental approach to the famous problem of the anomalously slow Gamow-Teller (GT) transitions in the beta decay of the A=14 multiplet is presented. The GT strength distributions to excited states in 14C and 14O were studied in high-resolution (d,2He) and (3He,t) charge-exchange reactions on 14N. No-core shell-model calculations capable of reproducing the suppression of the beta decays predict a selective excitation of Jpi=2+ states. The experimental confirmation represents a validation of the assumptions about the underlying structure of the 14N ground state wave function. However, the fragmentation of the GT strength over three 2+ final states remains a fundamental issue not explained by the present no-core shell model using a 6homega model space, suggesting possibly the need to include cluster structure in these light nuclei in a consistent way.

Journal Article↗

PubMed2004

Crater landscape: two-dimensional oxygen gradients in the circulatory system of the microcrustacean Daphnia magna.

Oxygen transport processes in millimetre-sized animals can be very complex, because oxygen molecules do not exclusively follow the pathway predetermined by the circulating fluid but may also simultaneously move from the respiratory surfaces to the tissues along different paths by diffusion. The present study made use of the oxygen-sensitive phosphorescence probe Oxyphor R2 to analyze the internal oxygen pathway in the transparent microcrustacean Daphnia magna. Oxyphor R2 was injected into the circulatory system and the distribution of oxygen partial pressure (P(O(2))) in the haemolymph was measured by phosphorescence lifetime imaging in the P(O(2)) range 0-6 kPa (0-30% air saturation). There were substantial differences in the shape of the two-dimensional P(O(2)) profiles depending on the concentration of haemoglobin (Hb) in the haemolymph. A steep global gradient, from posterior to anterior, occurred in animals with low concentrations of Hb (90-167 micromol l(-1) haem). In contrast, animals with a five- to sixfold higher concentration of Hb showed flat internal P(O(2)) gradients which, however, were only present under reduced ambient oxygen tensions (P(O(2)amb)=3-1 kPa), when Hb was maximally involved in oxygen transport. Under these conditions, the presence of Hb at high concentrations stabilized the unloading P(O(2)) in the central body to 0.9-0.4 kPa. Independent of Hb concentration and body size, the loading P(O(2)) was always 0.5 kPa below the P(O(2)amb). From these P(O(2)) profiles, it was possible (i) to follow the track of oxygen within the animal, and (ii) to visualize the shift from a diffusion-dominated to a convection-dominated transport as a result of increased Hb concentration.

Analysis of Variance↗

PubMed2002

Circulatory oxygen transport in the water flea Daphnia magna.

To determine the contribution of circulatory convection to tissue oxygen supply in animals of Daphnia magna, heart rate ( f(H)), in-vivo Hb oxygen-saturation ( S(Hb)) and NADH fluorescence intensity ( I(NADH)) as a measure of the tissue oxygenation state were simultaneously measured using digital motion analysis, microabsorption spectroscopy and fluorescence microscopy. In addition, the relationship between stroke volume and body size was established. Groups of differently sized animals (small: 1.4-1.6 mm, medium: 2.7-2.9 mm, large: 3.3 mm) with either low (Hb-poor) or high Hb concentration (Hb-rich) in the hemolymph were exposed to a gradual decrease in ambient oxygen partial pressure ( P(O2amb)) between normoxia and anoxia. In all groups, f(H) increased in response to progressive hypoxia. The hypoxic maximum in f(H) was highest in medium-sized Hb-poor animals, whereas perfusion rate increased continuously with increasing body size in Hb-poor and Hb-rich animals. The P(O2amb) at which Hb in the heart region was half-saturated (in-vivo P(50)) was higher in medium-sized (Hb-poor: 3.2 kPa, Hb-rich: 2.0 kPa) than in small (Hb-poor: 2.1 kPa, Hb-rich: 1.5 kPa) and large animals (Hb-poor: 1.9 kPa). The in-vivo P(50) was always lower in Hb-rich than in Hb-poor animals. The I(NADH) indicated an impairment of tissue oxygenation starting at higher critical P(O2amb) with increasing body size and with lower Hb concentration. Model calculations suggest that at the respective critical P(O2amb), circulatory convection delivers less than half of the oxygen demand in Hb-poor animals. In contrast, in Hb-rich animals, the contribution of circulatory convection to tissue oxygen supply at respective critical P(O2amb) was much greater due to the higher concentration of Hb.

Animals↗

PubMed2001

Benefits of haemoglobin in the cladoceran crustacean Daphnia magna.

To determine the contribution of haemoglobin (Hb) to the hypoxia-tolerance of Daphnia magna, we exposed Hb-poor and Hb-rich individuals (2.4-2.8 mm long) to a stepwise decrease in ambient oxygen partial pressure (P(O(2)amb)) over a period of 51 min from normoxia (20.56 kPa) to anoxia (<0.27 kPa) and looked for differences in their physiological performance. The haem-based concentrations of Hb in the haemolymph were 49 micromol l(-1) in Hb-poor and 337 micromol l(-1) in Hb-rich animals, respectively. The experimental apparatus made simultaneous measurement of appendage beating rate (fA), NADH fluorescence intensity (I(NADH)) of the appendage muscles, heart rate (fH) and in vivo Hb oxygen-saturation possible. In response to progressive, moderate hypoxia, both groups showed pronounced tachycardia and a slight decrease in fA. The fA and fH of Hb-rich animals were generally 4-6 % lower than those of Hb-poor animals. In addition, Hb-rich animals showed a significant decrease in the P(O(2)amb) at which the Hb in the heart region was half-saturated and a striking reduction in the critical P(O(2)amb) of appendage-related variables. In Hb-poor animals, the I(NADH) signal indicated that the oxygen supply to the limb muscle tissue started to become impeded at a critical P(O(2)amb) of 4.75 kPa, although the high level of fA was largely maintained until 1.77 kPa. The obvious discrepancy between these two critical P(O(2)amb) values suggested an anaerobic supplementation of energy provision in the range 4.75-1.77 kPa. The fact that I(NADH) of Hb-rich animals did not rise until P(O(2)amb) fell below 1.32 kPa strongly suggests that the extra Hb available to Hb-rich animals ensured an adequate oxygen supply to the limb muscle tissue in the P(O(2)amb) range 4.75-1.32 kPa. This finding illustrates the physiological benefit of Hb in enabling the animal to sustain its aerobic metabolism as the energetically most efficient mode of fuel utilization under conditions of reduced oxygen availability.

Animals↗

PubMedDate not supplied

[Software and system-induced errors in isokinetic force measurements].

In the literature a good reliability of isokinetic measurements is reported. In spite of these reports high variations of the peak torque and work values were registered when testing 24 patients with low back pain, using a CYBEX TR isokinetic trunk rotation apparatus. After a 3 week's training the patients force (peak torque) increased in the average between 10.7 p.c. (SD +/- 26.4) and 23.2 p.c. (SD +/- 63.8), corresponding to the test-velocity. Seven of the 24 patients improved or deteriorated more than 30 p.c. Analysing the parameters which could interfere with the results there was found a discrepancy between the original CYBEX software and the German Iso-Kin 4.0 software. The Isokin 4.0 does not warm up and calibrate the isokinetic apparatus daily. Investigations with definite weights showed that the values for peak torque are 40-50 m higher when using the Iso-Kin 4.0 software in comparison to the original CYBEX software. Furthermore there are a lot of other parameters such as acceleration of the body, psychological alterations, pain, motivation, learning effects, and artificial oscillations of the registered curve, which can affect the results even when using the original CYBEX software.

Adult↗

PubMedDate not supplied

Respiratory adaptations to running-water microhabitats in mayfly larvae Epeorus sylvicola and Ecdyonurus torrentis, Ephemeroptera.

The mayfly larvae Epeorus sylvicola and Ecdyonurus torrentis inhabit either fast-flowing or, for the latter species, calm zones of running water. We studied (1) mechanisms and limitations of oxygen transport in single individuals (oxygen consumption rate, occurrence and rate of gill movements, and heartbeats) in running water of different oxygen concentrations and (2) capacities for anaerobiosis (L-lactate production). Our aim was to look for specific adaptations in the two species to slightly different microhabitats. Epeorus sylvicola, whose immovable gills are not able to generate ventilatory convection, proved to be an oxyconformer at both test temperatures (11 degrees and 15 degrees C). Ecdyonurus torrentis showed a progressively stronger oxyregulatory behavior at higher temperatures. In this species an onset of gill beating was found at moderate hypoxia (below 16 kPa). Ventilating individuals reached maximum rates (300 min-1) of 5-14 kPa. In the case of a further reduction of oxygen partial pressure, the ventilatory rate started to decrease. Ventilatory activity, however, was maintained down to very low oxygen concentrations. Neither in E. sylvicola nor in E. torrentis was experimental evidence found to confirm the hypothesis of a respiratory function of hindgut movements. During hypoxia, the heart rate was constant in both species (E. sylvicola: 80 min-1; E. torrentis: 60 min-1): bradycardia occurred either below 1.5 kPa or below 4 kPa. Anaerobiosis, that is, lactate production, was not detected in either species.

Adaptation, Physiological↗