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H Baumgärtl

Publications and source records attributed to H Baumgärtl.

13 recordsLinked to original sources
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↗
PubMed1979

[The effect of sympathectomy on the cochlear oxygen pressure (pO2) under conditions of haemorrhagic hypotension (author's transl)].

Oxygen partial pressure was measured in the endolymph area of the cat cochlea under conditions of hemorrhagic hypotension. The experiments took place after unilateral upper cervical sympathectomy and under control conditions. The pO2-measurements were carried out with the aid of polarographic micro-coaxial needle electrodes according to Baumgärtl and Lübbers (1, 2, 3). In animals which had not been sympathectomized, the cochlear pO2 decreased continuously parallely to blood pressure, with the beginning of bleeding. After sympathectomy pO2-decrease in cochlea only occurred at substantially lower aortal blood pressure. This allows the following conclusions: 1. Under conditions of hemorrhagic shock the blood flow of the inner ear is not as much included in central circulation as brain and heart. 2. The blood pressure dependence of the inner ear blood flow depends on the sympathetic innervation, it can practically be abolished up to a blood pressure of 65 mm Hg by denervation. 3. It is being discussed, which therapeutic consequences can be drawn from the evident influence of the sympathetic innervation on the inner ear blood flow.

Animals↗
PubMed1976

[Local pO2- and pH2-measurements with needle electrodes for the examination of the hydrogen maintenance and microcirculation of the cochleae (author's transl)].

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.

Acoustic Stimulation↗
PubMed1976

Oxygen pressure in small lymphatics.

Oxygen tension of the small lymph vessels (PLO2) of the rabbit hind limb was measured with both a flow-through micro chamber and a polarographic catheter-tip oxygen electrode to obtain experimental data on the source of oxygen in the lymph. The following processes may influence PLO2: 1. Since the structure of the lymphatic capillaries allows a free diffusion of small molecules from the interstitial fluid into the lymphatics the lymph within its capillaries can mirror the oxygen supply of the tissue, i.e., probably a mean interstitial PO2. 2. PLO2 might be influenced by the oxygen content of the tissue surrounding the lymph vessels. Measurement with the catheter electrode showed that PLO2 rose after superfusing vessel with O2-saturated saline. After occlusion of the artery running paralled to the lymph vessel, a decrease in PLO2 was recorded. PLO2 in the absence of lymph flow increased rapidly after O2 inhalation. This reaction could be impeded by occluding the artery running parallel with the lymph vessel. 3. The mean oxygen tension of the prenodal (afferent) lymph measured with the flow-through chamber was 28.1 +/- 12.0 torr, whereas that measured with the catheter electrode was 42.0 +/- 12.18 torr. This difference may be attributed to the oxygen consumption of the lymph cells. The lymph containing a large number of cells has a stronger oxygen consumption than that with a lower number of cells. These observations suggest that PLO2 is influenced not only by the oxygen tension of the tissues drained by the lymph but also by the oxygen consumption of lymph cells as well as by the oxygen content of the surrounding tissues and perhaps by that of the blood vessels which are located at different distances from the collecting lymphatic vessels.

Animals↗