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Notizen: 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.

Notizen: 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.

Notizen: Zusammenfassung 1. Zur Absolutmessung des Sauerstoffdruckes in beliebigen Medien wird eine neuartige membranüberzogene Kammer-Pt-Elektrode beschrieben, die nach dem Prinzip von Davies u. Brink (1942) arbeitet. 2. Um über Tage konstante Eichkurven zu bekommen, muß ein bestimmtes Meßschema eingehalten werden, bei dem kontinuierliches Messen, Aufsättigungszeit und die Messung selbst in einem festgelegten zeitlichen Abstand aufeinanderfolgen. 3. Die Empfindlichkeit der Elektrodenanordnung für Sauerstoff hängt von der Größe des Pt-Drahtes ab; sie betrug z.B. 1 nA/mm Hg bei einem Pt-Durchmesser von 0,5 mm. 4. Die mittlere quadratische Abweichung der Einzelmessung betrug je nach benutzter Verstärkeranordnung zwischen σ=±1% und σ=±2,0%. 5. Die Temperaturabhängigkeit der Eichkurve ist in verschiedenen Temperaturbereichen unterschiedlich. 6. Durch Kombination einer gewöhnlichen kontinuierlich messenden Pt-Elektrode mit einer Kammer-Pt-Elektrode läßt sich die gewöhnliche Pt-Elektrode mit der Kammer-Pt-Elektrode eichen. Auf diese Art wurden absolute und kontinuierliche pO2-Messungen, z.B. auf dem Gehirn und im Blut durchgeführt.

Notizen: Zusammenfassung 1. Durch die Beseitigung des Spaltes und Trennung des Reaktionsraumes (vor dem Platin) von dem Raum, in dem sich die Bezugselektrode befindet, gelingt es, eine Pt-Elektrode zu bauen, die erlaubt, Sauerstoff-drucke über 200 mm Hg in kleinen Flüssigkeitsmengen mit geringem α zu messen (Kugelschliffelektrode). 2. Aufbau und Arbeitsweise der Kugelschliffelektrode werden beschrieben. 3. Die Standardabweichung betrug im Routinebetrieb bei Messungen über 9 Tage σ=±1,0 bis ±1,5%. 4. Die Eichkurve ist linear und geht durch den Nullpunkt des Koordinatensystems. Sie wird durch CO2 nicht beeinflußt. Der Einfluß der Temperatur zwischen 10 und 37°C wurde untersucht. Die Einstellzeit (auf 100%) in Gas beträgt 15 sec.