Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Oxygen supply of the blood-free perfused guinea-pig brain in normo- and hypothermia measured by the local distribution of oxygen pressure (1989)
    Springer
    Pflügers Archiv 414 (1989), S. 228-234 
    Details
    ISSN: 1432-2013
    Keywords: Brain cortex ; Blood-free perfusion ; $$P_{O_2 }$$ needle electrodes ; Oxygen supply ; Hypothermia ; $$P_{O_2 }$$ histogram of brain tissue ; $$P_{O_2 }$$ histogram of pial surface ; Mean local tissue $$P_{O_2 }$$
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The O2 supply of the blood-free perfused brain cortex of the guinea pig was investigated by measuring polarographically the local distribution of tissue $$P_{O_2 }$$ at 18°C, 24°C, and 37°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 μm in diameter were used and a special puncturing technique was applied. The experimental results indicate the presence of a large variation of local tissue $$P_{O_2 }$$ . Local mean $$P_{O_2 }$$ increased up to a depth of 1000 μm, reached a plateau, and then decreased towards 3000 μm. This demonstrates that the O2 supply changes in dependence of the distance of the brain surface. This may partly becaused by the special vascularization pattern of the brain cortex. As it follows from the $$P_{O_2 }$$ histograms, at 24°C the tissue layer between 0–2000 μm (layer I) was well supplied with oxygen, whereas at the same time the layer between 2001–3000 μm (layer II) was hypoxic. At 37°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°C to sufficiently decrease tissue O2 consumption: at 18°C, there was no sign of hypoxia any more. In comparison with the $$P_{O_2 }$$ histogram of the tissue the $$P_{O_2 }$$ histogram of the pial surface was shifted to higher $$P_{O_2 }$$ values. The experiments show that in the blood-free perfused guinea-pig brain the $$P_{O_2 }$$ histogram of the surface or of the upper tissue layer were not representative for the deeper layers. This has to be taken into account, when comparing results of tissue $$P_{O_2 }$$ measurements with results of biochemical or photometric brain tissue investigations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00580968
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Mikronadelelektroden zur Messung von Ionenaktivitäten in biologischen Geweben (1976)
    Springer
    Naturwissenschaften 63 (1976), S. 40-41 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00768685
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Determination of oxygen gradients in single Ca-alginate beads by means of oxygen-microelectrodes (1989)
    Springer
    Cellular and molecular life sciences 45 (1989), S. 1041-1047 
    Details
    ISSN: 1420-9071
    Keywords: Oxygen gradients ; Ca-alginate ; pO2-microelectrodes ; immobilized microorganisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Oxygen concentrations were measured in single Ca-alginate beads using polarographic microneedle electrodes. To obtain reliable results the effects of mechanical pressure on the electrode as well as the influence of free Ca2+-ions had to be compensated. No oxygen gradients were detectable in cell-free alginate beads, whereas in beads with entrapped cells ofEnterobacter cloacae steep oxygen gradients were observed. The steepness of these gradients depended on the bacterial growth in the gel. At the end of the logarithmic phase of growth the maximum depth of oxygen penetration into a bead of about 3 mm in diameter was in the range of 150 μm; i.e. nearly 70% of the volume of the alginate beads was free of oxygen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01950156
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Kurze Originalmitteilungen (1975)
    Springer
    Naturwissenschaften 62 (1975), S. 572-573 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01166971
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    The oxygen supply of the rat kidney: Measurements of intrarenalpO2 (1969)
    Springer
    Pflügers Archiv 309 (1969), S. 328-349 
    Details
    ISSN: 1432-2013
    Keywords: O2-Microelectrodes ; Measuring of LocalpO2 ; Shunt-Diffusion of O2 ; Critical O2-Supply Pressure ; Oxygen Tension in the Kidney ; Sauerstoff-Mikroelektroden ; LokalepO2-Messung ; O2-Diffusions-Shunt ; Kritischer Sauerstoffdruck ; Sauerstoffdrucke in der Niere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Using a newly developed platinum-O2-microeletrode [30] based on the design ofSilver [37] the construction and properties of which are described,pO2-measurements in the parenchyma of the blood-perfused and the cell-free perfused rat kidney were carried out. By continuous recording of thepO2 during slow (150 μ×min−1) insertion of the O2-electrode into the respiring tissue two regions of distinctly different meanpO2-values were found. In the outer region which extends from the renal surface to a depth of about 3–4 mm (corresponding anatomically with the renal cortex) largepO2-differences exist close to each other. In the blood-perfused kidney the maximum corticalpO2-values lie in the range of arterialpO2 the lowest values at about 10 Torr. In the cortex of the cell-free perfused kidney the maximumpO2-values lie considerably below the arterialpO2. In both the blood perfused and in the cell-free perfused kidney at centripetal movement of the O2-electrode the cortical region of high and fluctuatingpO2 is followed by a narrow zone (≈200 μ radial extension) of a steep decrease of the meanpO2. At further insertion in both preparations thepO2 remains at lowpO2-values of ca. 10 Torr. Anatomically, this latter region of low and constantpO2 corresponds to renal medulla and pelvis. By recording the decrease of parenchymalpO2 after sudden stop of the perfusion attempts were made at measuring the critical local O2-supply pressure. In the cortex of the cell-free perfused kidney critical local O2-supply pressures between 6 and 28 Torr with a maximum abundance at 8 Torr were found. The qualitative and quantitative implications of the presented data on the conditions of parenchymal O2-supply are discussed. The results are interpreted as an indication for the arteriovenous shunt (bypass)-diffusion of considerable amounts of oxygen, especially under the conditions of the cell-free perfusion. Furthermore, it follows from the data presented that even at high venous O2-pressures and high meanpO2-values in the parenchyma regions of local anoxia may exist.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587756
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Lokale pO2- und pH2-Messungen mit Nadelelektroden zum Studium der Sauerstoffversorgung und MikroZirkulation des Innenohres (1976)
    Springer
    European archives of oto-rhino-laryngology and head & neck 213 (1976), S. 439-440 
    Details
    ISSN: 1434-4726
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary For the study of the oxygen supply and the microcirculation of the inner ear we performed local pH2-measurements at the round window membrane of the cochlea in guinea-pigs and cats, using newly developed micro-electrodes. Under normoxia, hypoxia and hypercapnia conditions, oxygen pressure fields in the Sc. tympani and the Sc. media were determined; in addition we carried out some experiments on the problem of the oxygen supply of the Organ of Corti in the area of the base of the cochlea. Two different O2-supply systems seem to be of importance: 1. The oxygen transport per diffusionem and per convectionem via the round window membrane and the perilymph of the Sc. tympani. 2. The capillary system of the delimiting structures of the Sc. tympani. For an analysis of the normal circulatory capacity in the area of the basal cochlear turn, first measurements by means of the H2-clearance-method were conducted. It could be demonstrated that the blood supply of the inner ear can be influenced in various manners.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00455500
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Lokale pO2- und pH2-Messungen mit Mikrokoaxialnadelelektroden an der Basalwindung der Katzencochlea nach akuter oberer zervikaler Sympathektomie (1978)
    Springer
    European archives of oto-rhino-laryngology and head & neck 221 (1978), S. 269-284 
    Details
    ISSN: 1434-4726
    Keywords: Intracochlear pO2 ; Inner ear microcirculation ; Sympathectomy ; Exposure to loud sounds ; Microcoaxial needle electrodes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Oxygen partial pressure (pO2) profiles and microcirculatory parameters were recorded in vivo under standardized conditions in the three scalae of the cat's cochlea after unilateral excision of the upper cervical sympathetic nerve. Experiments were performed both under rest conditions and during exposure to loud sounds. pO2 and pH2 were polarographically measured using microcoaxial needle electrodes with sputtered reference elements according to Baumgärtl and Lübbers (1975). The tip diameter of the complete probe was 0.3–0.7 μm. The oxygen pressure field of the three scalae of the basal winding was recorded through the round window membrane during continuous advance of the needle (150 μm/min). Temporal pO2 changes as well as microcirculatory parameters were measured in the scala media after the electrode was fixed in position. Starting out from the air values at the surface of the round window membrane, pO2 decreased continuously from more than 100 Torr during insertion towards the basilar membrane, where it averaged 25 Torr. When the needle had penetrated the basilar membrane and entered the endolymphic space, an increased pO2 of 35–40 Torr was recorded. After penetrating Reissner's membrane, a slightly decreased pO2 was measured in the scala vestib. Aside from the oxygen reaching the cochlea through the round window, the capillaries of the round window membrane were found to contribute to the oxygen saturation of the perilymph near the window. Under rest condition, unilateral upper cervical sympathectomy did not noticeably influence the oxygen pressure field in the three cochlear scalae. After exposure to loud sounds, however, endolymphic pO2 decreased less and recovered quicker on the sympathectomized side than on the intact one. Ventilation of the animals with pure oxygen or gas mixtures of high CO2-O2 concentrations increased the pO2 level within 1 min. The increase was more pronounced in the endolymphic space than in the other cochlear scalae and also the pO2 decrease in the scala media was particularly distinct in the cat. Under exposure to loud sounds the influence of the sympathetic nerve on the intracochlear pO2 was found to depend on the aortic blood pressure. The advantageous effect of sympathectomy was particularly visible at a low aortic pressure but less distinct at a higher one. In some cases, a long-lasting pO2 decrease was noticed in the endolymphic space even after short (1–2 s) exposure to noise. The hydrogen exchange rate recorded in the endolymphic space after exposure to loud sounds (noise of 115 dB) using the hydrogen clearance method was distinctly delayed and, consequently, the capillary blood flow was diminished. Unilateral acute upper cervical sympathectomy favorably influenced the peripheral circulation during exposure to loud sounds by increasing the blood flow (reduced half life period). The experiments showed that unilateral acute upper cervical sympathectomy did not considerably influence the endolymphic pO2 under rest condition, whereas an advantageous effect on the endocochlear pO2 and blood flow was noticed under exposure to loud sounds. Moreover, there was indication of a correlation between sympathetic effect and mean aortal blood pressure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00491463
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Wirkung einer oberen zervikalen Sympathektomie auf den cochleären Sauerstoffpartialdruck (pO2) unter den Bedingungen einer hämorrhagischen Hypotension (1977)
    Springer
    European archives of oto-rhino-laryngology and head & neck 216 (1977), S. 519-519 
    Details
    ISSN: 1434-4726
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00458942
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Real and pseudo oxygen gradients in Ca-alginate beads monitored during polarographic Po2-measurements using Pt-needle microelectrodes (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 44 (1994), S. 617-625 
    Details
    ISSN: 0006-3592
    Keywords: oxygen profiles ; oxygen microprobe ; Po2-microelectrode ; artifacts ; alginate beads ; Saccharomyces cerevisiae ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Polarographic microcoaxial needle electrodes were used to measure internal profiles of dissolved oxygen tension (Po2) within single Ca-alginate beads of different diameter containing entrapped cells of Saccharomyces cerevisiae. For the investigations, single beads coming from variable growing conditions and distinct cultivation stages were fixed in a special holding device. In dependence on microbial growth steep oxygen gradients were observed. The Oxygen penetration depth at steady state lay between 50 and 100 μm. After 8 h of cultivation time, the anaerobic space within the beads (φ 2 mm; cultivation in a packed bed reactor) is beginning at ∼ 130 μm, whereas the anaerobic space within the beads (φ 2 mm) coming from the shaker flask culture is located ∼440 μm below the bead surface. Surprisingly, steep gradients were also observed, when recording profiles from cell-free Ca-alginate beads of different diameter and alginate concentrations. The steep oxygen gradients apparently had to be interpreted as pseudo-Po2-gradients. These results were borne by several effects, such as formation of artifacts and diffusion barriers in front of the electrode tip or oxygen “availability” at the tip and consumption of oxygen by the electrode itself. These phenomena could be documented by microscopic observation and photography. Thus, to obtain real Po2-profiles it is important to be exactly informed about the physical, chemical, and biological properties of the material to be investigated. Furthermore, it is necessary to apply a special stepwise puncture technique with distinct step-in/step-out movements of the electrode: e.g., unidirectional or contradirectional puncture techniques. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260440508
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Lokale pO2- und pH2-Messungen mit Nadelelektroden zum Studium der Sauerstoffversorgung und Mikrozirkulation des Innenohres (1976)
    Springer
    European archives of oto-rhino-laryngology and head & neck 214 (1976), S. 109-124 
    Details
    ISSN: 1434-4726
    Keywords: O2 supply ; Intracochlear O2 pressure ; Cochlea circulation ; Abnormal vascular plexus ; pO2 and pH2 needle electrodes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The local partial pressure of oxygen (pO2) and the rate of hydrogen elimination were measured in the three scalae of the basal turn of 28 Guinea-pig cochleae under conditions of normoxia, hyperoxia and hypercapnia and with acoustical stimulation with the needle electrodes developed by Baumgärtl and Lübbers. In the scala tympani a pO2 decrease from the round window toward Corti's organ was registered and pO2 values of over 100 mm Hg were measured near the membrane of the round window and of 10–40 mm Hg near the basilar membrane depending on how deeply the electrode penetrated into the scala tympani. The pO2 profiles were changed or reversed when the animal breathed a mixture of 95% oxygen and 5% carbon dioxide and when the round window membrane was covered with agar-agar or paraffine and exteriorly flooded with nitrogen. Acoustical stimulation with a white noise of 85 dB caused a considerable pO2 drop in the perilymph of the scala tympani while in the endolymph of the scala media we observe only a slight decrease. Intravenous application of dextran of low viscosity leads to a pO2 increase when the original oxygen value in the scala tympani was low. The half-life of hydrogen in the scala tympani amounts to about 4 min. The results permit the conclusion that, in the area of the cochlear basis, Corti's organ receives its oxygen supply via the capillary system as well as via the membrane of the round window.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00453607
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...