H. Baumgärtl

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 (tcJO2). In this study the sensor was calibrated so that absolute values of tcJO2 could be reported. At rest, tcJO2 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, tcJO2 was recorded at the end of a 5 min suprasystolic occlusion of the forearm. At normal skin surface partial oxygen pressure (163 ± 9 Torr), tcJO2 was 0.53 ± 0.27 ml O2 min−1 m−2. A 5 min interruption of blood flow resulted in an increase of 9.5 ± 6.3 % in tcJO2. The value of tcJO2 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.

Limiting section thickness of guinea pig olfactory cortical slices studied from tissuepO2 values and electrical activities

The relationship between tissue oxygen partial pressure (pO2) values and electrical activities of guinea pig olfactory cortical slices was investigated as the slices were superfused with Krebs-Ringers solution equilibrated with different gas mixtures. ThepO2 values were measured in the slices with oxygen microelectrodes (tip diameter <1 μm). 1. Studies ofpO2 measurements showed the variability of minimumpO2 value of oxygen profiles in the tissue slice. The profile depends on thepO2 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 μm; in thinner slices there was no anoxic area. In our case the limiting section thickness of the slice was ca. 430 μm from the viewpoint of tissuepO2 value. 2. The N potential (extra-cellularly recorded EPSP) showed a tendency to decrease in amplitude, for slices being thicker than ca. 430 μm. 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 tissuepO2 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 tissuepO2 value in the slice. 4. The tissuepO2 value was continuously measured during the electrical stimulation of the lateral olfactory tract. The steady state level of tissuepO2 value obtained during the stimulation diminished as the frequency of stimulation increased from 5–30 Hz.

Lokale pO2- und pH2-Messungen mit Nadelelektroden zum Studium der Sauerstoffversorgung und MikroZirkulation des Innenohres

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 Cortis 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, Cortis organ receives its oxygen supply via the capillary system as well as via the membrane of the round window.SummaryThe 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 Cortis 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, Cortis organ receives its oxygen supply via the capillary system as well as via the membrane of the round window.

Heterogeneity and Stability of Local PO2 Distribution within the Brain Tissue

Heterogeneity of tissue pO2 is a necessary consequence of the fact that in order to supply living tissue with O2, molecular oxygen has to be transported from the arterial blood to the intracellularly situated mitochondria. The O2 delivery of the blood towards the tissue and the diffusional O2 transport within the tissue produce an oxygen pressure field the heterogeneity of which characterizes quantitatively the tissue O2 supply. On the basis of theoretical analyses it could be predicted1,2 that for monitoring this heterogeneity small pO2 sensors having diameters of only a few microns would be necessary. In 1948 using small needle-shaped pO2 electrodes as developed by Davies and Brink3 Remond could measure directly such pO2, profiles between two adjacent small vessels on the brain surface4,5. In a footnote6 it was reported that G. Millikan suggested to use this electrode for intracerebral measurements. Distributions of parameters can be quantitatively presented by a frequency histogram. To our knowlegde Jamieson and van den Brenk7 were the first who used in 1963 pO2 frequency histograms of different organs (included brain tissue) to characterize tissue O2 supply. pO2 histograms are now widely used to describe the O2 supply of the brain under normal and pathological conditions8, but it is still difficult to decide by which means a histogram is measurable which can be considered as representative for the tissue O2 supply. To answer this question a set of pO2 profiles were measured under steady state conditions puncturing the brain cortex with small needle electrodes. It was found that there is a strong local heterogeneity which can be quite different in different punctures, but that by increasing the number of punctures it is possible to obtain a pO2 histogram by which the O2 supply of the brain tissue is characterized.

Evaluation of Po2 profiles to describe the oxygen pressure field within the tissue

Oxygen transport within the tissue occurs by diffusion and produces an oxygen pressure field. To describe its heterogeneity histograms of local PO(2) values are used. PO(2) profiles measured with small polarographic microelectrodes demonstrate that a large heterogeneity of the amplitudes of local PO(2) changes (Delta PO(2)/distance) exists. Therefore, we investigated whether the amplitudes of local PO(2) changes can be used to obtain additional information about the state of oxygen supply. Six PO(2) profiles in the renal cortex of the dog were evaluated. The frequency histograms of the local PO(2) values showed a normal oxygen supply of the kidneys. To analyze the heterogeneity of the amplitudes of the local PO(2) changes every 10 microm the (Delta PO(2)/distance) values were determined. Most of the amplitudes steps are in the range of +/-10 torr. The frequency histogram of the amplitudes steps shows a symmetric form: 100% are between -35 and +49 torr, 90% between -12 and +11 torr. Changes of the amplitude histogram occur if the distances between the selected adjacent points are varied. At distances larger than 100 microm the amplitude histograms became disintegrated. Interestingly, the local PO(2) histograms remained practically unchanged. Therefore we conclude, that by this measuring and evaluation technique histograms of the (Delta PO(2)/microm) values are obtained by which the state of oxygen supply of local structures can be monitored, probably of the microcirculatory unit of capillary oxygen supply. The results demonstrate a well-regulated oxygen pressure field within the kidney. Similar results were obtained from PO(2) profiles measured in the brain cortex (Delta PO(2)/50 microm).

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 μm 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 perilymphaticPO2 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.

Polarographic determination of the oxygen partial pressure field by Pt microelectrodes using the O2 field in front of a Pt macroelectrode as a model.

SummaryThe O2 diffusion field within an agarose medium in front of a 1.5 mm platinum macroelectrode with plane and circular surface was measured by means of a platinum microelectrode (Pt diameter of ca. 0.3 μm). The

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

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