Abnormal respiratory-related evoked potentials in untreated awake patients with severe obstructive sleep apnoea syndrome

Obstructive sleep apnoeas generate an intense afferent traffic leading to arousal and apnoea termination. Yet a decrease in the sensitivity of the afferents has been described in patients with obstructive sleep apnoea, and could be a determinant of disease severity. How mechanical changes within the respiratory system are processed in the brain can be studied through the analysis of airway occlusion-related respiratory-related evoked potentials. Respiratory-related evoked potentials have been found altered during sleep in mild and moderate obstructive sleep apnoea syndrome, with contradictory results during wake. We hypothesized that respiratory-related evoked potentials' alterations during wake, if indeed a feature of the obstructive sleep apnoea syndrome, should be present in untreated severe patients. Ten untreated patients with severe obstructive sleep apnoea syndrome and eight matched controls were studied. Respiratory-related evoked potentials were recorded in Cz-C3 and Cz-C4, and described in terms of the amplitudes and latencies of their components P1, N1, P2 and N2. Components amplitudes were similar in both groups. There was no significant difference in P1 latencies. This was also the case for N1 in Cz-C3. In contrast, N1 latencies in Cz-C4 were significantly longer in patients with obstructive sleep apnoea syndrome [median 98 ms (interquartile range 16.00) versus 79.5 ms (5.98), P = 0.015]. P2 and N2 were also significantly delayed, on both sides. The cortical processing of airway occlusion-related afferents seems abnormal in untreated patients with severe obstructive sleep apnoea syndrome. This could be either a severity marker and/or an aggravating factor.