Feasibility of pulse oxymetry to measure arterial O2 saturation in studies on cochlear blood circulation

Abstract

To understand the characteristics of oxygen transport to the inner ear, the relationship between arterial O2 saturation and cochlear microcirculation was investigated under different respiratory condition in guinea pigs. To monitor arterial O2 saturation a pulse oxymeter instead of an arterial blood gas analyzer was used. When the arterial O2 saturation was measured in the foot pad by a pulse oxymeter under different respiratory conditions, the data showed a close correlation with the results of blood gas analysis. For the measurement of cochlear microcirculation, a pulse oxymeter was found to be a feasible respiratory monitor for animal experiments. With this apparatus our study demonstrated a slower reaction in the decrease of perilymphatic oxygen tension than of cochlear blood flow during stepwise induction of hypoventilation monitored by a pulse oxymeter. Under certain conditions of hyperventilation in which arterial O2 saturation and perilymphatic oxygen tension increased gradually, cochlear blood flow was found to decrease. This decrease of cochlear blood flow could be attributed to chemical controls which are regulated, as in the cerebral blood circulation, by the content of CO2 and H+ in the vascular bed in the cochlea.