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H Baumgärtl

Publications and source records attributed to H Baumgärtl.

At least 19 recordsLinked to original sources
PubMed2002

The cutaneous uptake of atmospheric oxygen contributes significantly to the oxygen supply of human dermis and epidermis.

It has been known since 1851 that atmospheric oxygen is taken up by the human epidermis. The contribution to total respiration is negligible. Until now the significance for the local oxygen supply of the skin has remained unknown. With a newly developed sensor, the oxygen fluxoptode, it has become possible to make local measurements of the transcutaneous oxygen flux (tcJ(O2)). In this study the sensor was calibrated so that absolute values of tcJ(O2) could be reported. At rest, tcJ(O2) was determined on normal, humidified skin on the volar forearm of 20 volunteers of different age groups. In order to evaluate the contribution of the blood flow to the oxygen supply of the skin, tcJ(O2) was recorded at the end of a 5 min suprasystolic occlusion of the forearm. At normal skin surface partial oxygen pressure (163 +/- 9 Torr), tcJ(O2) was 0.53 +/- 0.27 ml O2 min(-1) x m(-2). A 5 min interruption of blood flow resulted in an increase of 9.5 +/- 6.3 % in tcJ(O2). The value of tcJ(O2) was unaffected by the age of the subject. Published data on the oxygen diffusion properties of skin and simulations of intracutaneous profiles of oxygen partial pressure indicated that under these conditions, the upper skin layers to a depth of of 0.25-0.40 mm are almost exclusively supplied by external oxygen, whereas the oxygen transport of the blood has a minor influence. As a consequence, a malfunction in capillary oxygen transport cannot be the initiator of the development of superficial skin defects such as those observed in chronic venous incompetence and peripheral arterial occlusive disease.

Adult↗
PubMed2001

Nephron pO2 and renal oxygen usage in the hypertensive rat kidney.

BACKGROUND: The kidney has a high rate of oxygen usage (QO2) that is closely dependent on tubular Na+ transport (TNa). However, little is known concerning the regulation of the cortical partial pressure of oxygen (pO2). METHODS: First, the pO2 was measured in the outer cortical proximal (PT) and distal tubules (DT), efferent arterioles (EA), and superficial (SC) and deep cortical (DC) tissues in normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHRs) using an ultramicrocoaxial O2 electrode. We next assessed the determinants of QO2 and tubular reabsorption of sodium (TNa) for whether they could account for any differences in renal cortical pO2 in SHRs. RESULTS: The pO2 in the EA was reduced 40 to 50% compared with arterial values but was similar in the two strains (WKY rats 45 +/- 2 vs. SHRs 41 +/- 1 mm Hg, P = NS). The pO2 value in the PT, DT, and SC did not differ within strains. All were significantly (P < 0. 001) lower in SHRs (for example, pO2 in PT of WKY rats 39 +/- 1 vs. SHRs, 30 +/- 1 mm Hg). The pO2 in the renal vein was above that at any site in the EA or the cortex, implying a precapillary shunting of O2 from the artery to vein. SHRs had reduced renal blood flow (RBF) leading to a reduced (P < 0.05) rate of O2 delivery (WKY rats 42 +/- 6 vs. SHRs 30 +/- 1 micromol. min-1. g-1) and a reduced glomerular filtration rate, leading to a lower (P < 0.001), TNa (WKYs 115 +/- 9 vs. SHRs 66 +/-8 micromol. min-1. g-1). However, despite the 43% reduction in TNa, the renal O2 usage was not significantly different between strains (WKY rats 7.6 +/- 0.8 vs. SHRs 9.0 +/- 1.0 micromol. min-1. g-1). Therefore, the SHRs had a sharp reduction (P < 0.001) in the O2 efficiency for Na+ reabsorption (TNa/QO2; WKY rats 15.1 +/- 1.6 vs. SHRs 7.3 +/-1.0 micromol-1). CONCLUSIONS: A precapillary O2 shunt reduces the pO2 of cortical nephrons. The pO2 is reduced further in SHRs because of less efficient O2 usage for Na+ transport.

Absorption↗
PubMed1997

Effects of experimental cochlear thrombosis on oxygenation and auditory function of the inner ear.

To elucidate the etiology and pathogenesis of sudden hearing loss, the effect of experimental cochlear thrombosis on oxygenation and the auditory function of the inner ear was investigated in anesthetized guinea pigs. Impairment of cochlear blood flow (CBF) was induced by ferromagnetic obstruction of cochlear blood vessels at lowered body temperature. Perilymphatic oxygen partial pressure (PO2) in the basal scala tympani (about 200 microm below the round window membrane) was measured polarographically using micro-coaxial needle electrodes. Auditory function was examined by recording cochlear microphonic (CM) frequency responses, compound action potentials (CAP) and auditory evoked brainstem responses (ABR). Findings demonstrated a considerable decrease in the mean perilymphatic PO2 of 40%, 2 h after the start of the experiment. Mean CM and N1 CAP amplitudes were reduced by about 25% each and ABR by 18%. No significant changes were observed in the latencies of either CAP or ABR. Mean basal CBF was found to decrease by 35%, as measured by laser Doppler flowmetry in a parallel study. The present findings demonstrate that vascular impairment in the inner ear results in a considerable drop in intracochlear oxygenation, causing a significant loss in the auditory response.

Action Potentials↗
PubMed1994

Investigation of oxygen transfer through the membrane of polymer hollowspheres by oxygen micro-electrodes.

Estimation of oxygen transfer from an aqueous solution into polymer hollow spheres, as used for encapsulation of microorganisms, requires detection of the dissolved oxygen concentration inside the hollow sphere. Using microcoaxial needle electrodes, oxygen kinetics in different penetration depths within single cellulose-sulfate hollow spheres loaded with and without living yeast cells could be measured. Based on the reaction kinetics the diffusion coefficient for oxygen and the oxygen-uptake rate have been calculated. The diffusion coefficient DO2 within the thin membrane of cell-free spheres was in the order of 10(-10)m2s-1. Due to the liquid core of the hollow sphere the corresponding diffusion coefficient DO2 is in the range of the value for water. The oxygen-uptake rate QO2 in cell containing spheres could be estimated to 90 mmol l-1 h-1, which corresponds to a specific oxygen-uptake rate qO2 of 10 mmol g-1 h-1. It is to conclude that oxygen supply of the microorganisms inside the hollow spheres was, in this case, not critically influenced by the thin polymeric wall of the capsules.

Diffusion↗
PubMed1993

Investigations of the oxygen supply in Ca-alginate beads and microcapsules loaded with Penicillium raistrickii using a microelectrode.

The oxygen supply of free, Ca-alginate entrapped and microencapsulated mycelia of Penicillium raistrickii i 477 capable of 15 alpha-hydroxylation of 13-ethyl-gon-4-en-3,17-dione was investigated. Using an oxygen microelectrode distinct gradients of oxygen within the Ca-alginate beads as well as the microcapsules were detected. Slope and width of the gradients were investigated in dependence on the kind of immobilization, the culture age and the cell density on or in the carrier as well as the different forms of the oxygen supply in the medium. So it could be shown that large parts of immobilizates, approximately 96% of the diameter of both types, were oxygen-free. In comparison with free mycelia, the lower oxygen supply of the immobilized mycelia led to a metabolic shift to fermentative catabolism.

Alginates↗
PubMed1990

Evidence for a preglomerular oxygen diffusion shunt in rat renal cortex.

Although blood flow to the renal cortex is high and oxygen extraction is low, the renal cortex is remarkably susceptible to hypoxia. Because erythropoietin production has been localized mainly to the renal cortex, the aim of this study was to find a common denominator for both the high susceptibility to hypoxia and oxygen sensing within the renal cortex. By direct measurement of oxygen pressure with microcoaxial needle sensors at superficial glomeruli of the in situ kidney of anesthetized Munich-Wistar-Frömter rats, we obtained mean partial pressure of O2 (PO2) values of 46 +/- 13 (SD) mmHg (n = 71). The simultaneously measured systemic PO2 in arterial blood was 90 +/- 8 mmHg (n = 54). Changing the respirator gas from air to pure oxygen enhanced systemic arterial PO2 to 593 +/- 27 mmHg, whereas PO2 at the superficial glomeruli increased only to a mean of 80 +/- 28 mmHg (n = 71). These data suggest significant preglomerular shunting of oxygen within the cortical vasculature, most likely between interlobular vessels, which are arranged in a countercurrent fashion and represent quantitatively the largest contact area between arteries and veins within the renal cortex.

Air↗
PubMed1989

Oxygen supply of the blood-free perfused guinea-pig brain in normo- and hypothermia measured by the local distribution of oxygen pressure.

The O2 supply of the blood-free perfused brain cortex of the guinea pig was investigated by measuring polarographically the local distribution of tissue PO2 at 18 degrees C, 24 degrees C, and 37 degrees C. The perfusion was performed in situ, using a medium equilibrated by a gas mixture of 95% O2 and 5% CO2. Papaverine was added to prevent vasoconstriction during hypothermia. To avoid measuring artefacts thin micro electrodes with a small sharpened tip of ca. 4 microns in diameter were used and a special puncturing technique was applied. The experimental results indicate the presence of a large variation of local tissue PO2. Local mean PO2 increased up to a depth of 1000 microns, reached a plateau, and then decreased towards 3000 microns. This demonstrates that the O2 supply changes in dependence of the distance of the brain surface. This may partly be caused by the special vascularization pattern of the brain cortex. As it follows from the PO2 histograms, at 24 degrees C the tissue layer between 0-2000 microns (layer I) was well supplied with oxygen, whereas at the same time the layer between 2001-3000 microns (layer II) was hypoxic. At 37 degrees C, both layers were hypoxic, but layer III showed the more pronounced tissue hypoxia. To obtain a sufficient oxygen supply the temperature had to be reduced below 24 degrees C to sufficiently decrease tissue O2 consumption: at 18 degrees C, there was no sign of hypoxia any more. In comparison with the PO2 histogram of the tissue the PO2 histogram of the pial surface was shifted to higher PO2 values.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Oxygen transfer from gas bubble into liquid.

Oxygen transfer from a gas bubble into the surrounding liquid is examined by measuring oxygen pressure with Po2-needle electrodes at different distances from the bubble. From there, the mass transfer coefficient can be calculated. First measurements yielded results in the range to be expected.

Ethylene Glycol↗
PubMed1984

Oxygen profiles and structure of Penicillium chrysogenum pellets.

Oxygen profiles were measured polarographically with micro-needle electrodes in single fixed pellets of Penicillium chrysogenum. The oxygen concentration, the grade of turbulence and the flow conditions of the outer medium were varied. Pellets were then histologically investigated. Under our experimental conditions the pellets were found to contain a 200 micrometers thick active outer zone with intact cells. In this zone, the oxygen partial pressure decreased from the initial values to zero. The results show that the Po2 profile within the pellet is strongly influenced by the Po2 of the outer medium. Apart from molecular diffusion, surface turbulence as well as a convective flow through the pellets are of importance for the oxygen transport.

Diffusion↗
PubMed1982

Limiting section thickness of guinea pig olfactory cortical slices studied from tissue pO2 values and electrical activities.

The relationship between tissue oxygen partial pressure (pO2) values and electrical activities of guinea pig olfactory cortical slices were investigated as the slices were superfused with Krebs-Ringer's solution equilibrated with different gas mixtures. The pO2 values were measured in the slices with oxygen microelectrodes (tip diameter less than 1 micrometer). 1. Studies of pO2 measurements showed the variability of minimum pO2 value of oxygen profiles in the tissue slice. The profile depends on the pO2 value of the superfusate and on the thickness and the oxygen consumption of the slice. With our experimental conditions an anoxic area developed in the middle layers of the slice when the thickness of the slice exceeded ca. 430 micrometers; in thinner slices there was no anoxic area. In our case the limiting section thickness of the slice was ca.430 micrometers from the viewpoint of tissue pO2 value. 2. The N potential (extra-cellularly recorded EPSP) showed a tendency to decrease in amplitude, for slices being thicker than ca 430 micrometers. It would seem reasonable to think that the decrement of the N potential was brought about by the existence of the anoxic area. 3. When the slice was bubbled with 25, 45 or 95% O2, the tissue pO2 value changed, and the N potential height also changed. The N potential was higher in amplitude when bubbled with 95% O2 than with 25% O2. On the other hand, the amplitude of the IS potential (the lateral olfactory tract potential) was not influenced as much as that of the N potential by the change of tissue pO2 value in the slice. 4. The tissue pO2 value was continuously measured during the electrical stimulation of the lateral olfactory tract. The steady state level of tissue pO2 value obtained during the stimulation diminished as the frequency of stimulation increased from 5-30 Hz.

Animals↗