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

Abstract

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.

Noise-Induced Cochlear Hypoxia Is Intensity Dependent, Correlates with Hearing Loss and Precedes Reduction of Cochlear Blood Flow

“…Since cochlear hypoxia occurs before evidence of reduced CoBF at exposure to 101-, 106-and 115-dB SPL broad-band noise, we suppose that cochlear oxygen deficiency measured during acoustic overstimulation with pure tones [11-13, 15, 18-20], broad-band noise [14,15,18,20], impulse noise [16] or gun shots [17] did not result from reduction in CoBF, as has been suggested so far. An important question asked here is why noise results in cochlear hypoxia and whether this induces hearing loss or is merely an epiphenomenon occuring at the same time as the hearing loss.…”

Sudden Deafness – A Critical Evaluation of Pathogenesis and ‘Cure’

“…Several indirect ways of measuring CBF were used during the 60s and 70s with the aim of measuring metabolism and the influence of drugs and adrenergic control [9][10][11][12][13][14].…”

Gas Permeability of Round Window Membrane

“…Maass et al [12] measured the peri lymphatic oxygen tension by penetrating the round window membrane with an oxygen sensing microelectrode. They found that the perilymphatic oxygen tension was higher near the round window membrane and lower in the deeper parts of the tympanic peri lymph.…”

“…Furthermore, oxygen was found to pass from the middle ear to the inner ear through the round window membrane [12][13][14].…”