Cochlear action potentials threshold and systemic arterial

A progressive decrease in arterial pO₂ was induced in Hartley guinea pigs (GP) by having them rebreathe the air entrapped in a closed circuit from which the CO₂ was continuously absorbed. Following this slow-developing hypoxemia, a sequence of events concerning the ear could be observed. Firstly, a fluctuation in cochlear action potentials (CAP) was noted. This appeared only at stimulus intensities near the threshold and was not evident at higher intensities. At a mean arterial pO₂ level of 30 mm Hg, this phenomenon was observed in 60% of the GP. At a mean pO₂ of 24.66 mm Hg, a shift in threshold occurred in all GP. Finally, when the blood pO₂ reached an average of 14.92 mm Hg, no CAP response could be elicited, even at click intensity of 120 dB SPL. The 30 mm Hg oxygen concentration in the arterial blood was considered as a “critical level” at which the cochlear function starts to deteriorate in guinea pigs.