Auditory brain-stem responses (ABRs) in sleep respiratory disorders.

Neurophysiological repercussions of sleep respiratory disorders (SRDs) are still unclear. It has been shown that SRDs induce disturbance on auditory event-related potentials with a delayed latency of the cognitive P300 potentials. Since the Auditory Brainstem Responses (ABRs) explore the auditory brainstem structures and are independent on cognition, we evaluated the neurological impact of SDRs on central nervous system by ABRs in these patients. Four groups of patients were studied: snorers (S, 17 subjects), sleep apnoea syndrome (SAS, 48 subjects), apnoeic patients with respiratory insufficiency (SAI, 17 patients) and patients with respiratory insufficiency alone (RI, 12 subjects). A standard polysomnographic study was done in each patient with further quantitative analysis of sleep, respiratory events, and oxygen arterial saturation. ABRs were recorded before the study night and interpeak latencies (IPLs) between waves I, III and V were measured. Results were expressed as the mean of each group for all the different parameters. ABR IPL latencies (IPLI-III, IPLIII-V, IPLI-V) of the four groups were within the normal range. However, comparing groups between themselves, there were significant differences (ANOVA) between groups. Longer IPLIII-V and IPLI-V (which explored the central conduction time) were observed in group SAI compared to group SAS. No evidence on the origin of this elongation was found; the level of hypoxia, in particular, was not related to IPL values. These results show that SAS alone do not affect lower brainstem auditory function, in contrast to the association of SAS and RI.