Effect of CO 2 on the Perilymphatic Oxygen Tension in Cats

A microelectrode with a tip of 100μ permitting recording of the oxygen tension in the perilymphatic space according to the polarographic principle and having a minimal drift of 1–2.5% per hour has been developed. The effects of apnea, hypo- and hyperventilation as well as those of inhalation of pure oxygen, and CO₂ upon the perilymphatic P_o2 have been measured by placing the electrode in the perilymph through the fenestrated stapedial footplate of 87 adult cats. The correlation between the arterial P_co2 and the perilymphatic P_o2 is so close that even hypo- or hyperventilation in presence of air does influence the oxygen content of the perilymphatic space. In view of the effect of the smallest accumulation of alveolar CO₂, particular attention has to be paid to the system used for respiration of the experimental animal, when determining the action of drugs or inhaled gas mixtures on the oxygenation of the inner ear fluids. The measurement of the perilymphatic oxygen tension also indicates that the rate of blood flow cannot be used to deduct with accuracy the actual degree of oxygenation of the inner ear fluids.