Auditory nerve-brain stem potentials in man and cat under hypoxic and hypercapnic conditions.
In order to study the effects of hypoxic and hypercapnic respiratory gas mixtures on brain activity, the auditory nerve brain stem evoked potentials (ABP) were recorded in 6 human volunteers and in 12 cats while they were breathing various gas mixtures. In humans, no effect of gas mixtures containing 9-13% O2 or 7.5-10% CO2 was observed on the wave form, latency and amplitude of the ABP. The cats were exposed to up to 25% CO2 and down to 5.5% O2 or to combined hypoxic and hypercapnic gas mixtures for up to 45 min while recording ABP and monitoring CO2 and O2 in the respired gases, arterial blood gas levels, pH, arterial blood pressure, body temperature and EEG. The extremes of pH were 6.68 and 7.46. The EEG was depressed or became isoelectric during hypercapnia. In general, the wave form, amplitude and latencies of the ABP waves were not much affected by these conditions. Loss of ABP was observed only when the animal was ventilated with about 5% O2 and this was secondary to and following cardiac failure and depressed arterial blood pressure, presumably leading to brain ischaemia. Thus, even though the cortex (EEG) is depressed, the brain stem seems to be resistant to these alterations in the blood gases in spite of the relatively higher rates of metabolism reported for the brain stem auditory structures.
D000328:Adult; D000818:Animals; D001921:Brain / Q000378:metabolism; D001933:Brain Stem / Q000503:physiopathology*; D002415:Cats; D002560:Cerebrovascular Circulation; D005072:Evoked Potentials, Auditory; D005947:Glucose / Q000378:metabolism; D006801:Humans; D006935:Hypercapnia / Q000175:diagnosis / Q000503:physiopathology*; D000860:Hypoxia / Q000175:diagnosis / Q000503:physiopathology*; D000159:Vestibulocochlear Nerve / Q000502:physiology
D005947:Glucose