The investigation of K-complex and vertex sharp wave activity in response to mid-inspiratory occlusions and complete obstructions to breathing during NREM sleep

Study Objectives: To determine whether the cortical response to mid-inspiratory occlusions can be used as a model of the cortical response to obstructive events during sleep; and to determine whether the vertex sharp wave (VSW) and K-complex are exclusive contributors to the N350 and N550 components respectively of the stage 2 sleep event-related potential. Design: Two types of respiratory stimuli were used to elicit evoked potential responses during stage 2 NREM sleep. These were mid-inspiratory occlusions and complete breath obstructions. Trials were grouped according to the type of phasic response elicited; isolated K-complex (KC), VSW associated with a K-complex (VSW/KC), isolated VSW, and no evoked response (other). Evoked responses were averaged separately within these categories. Setting: Data were collected in the University of Melbourne Sleep Laboratory. Participants: Six young healthy male adults, Interventions: N/A Measurements and Results: Data were recorded from 29 scalp sites referenced to linked ears. Mask pressure (Pm) and airflow were also recorded. Intra-thoracic pressure, as indicated by Pm, reached a more negative level following complete obstructions than brief occlusions. However, both types of respiratory stimuli elicited the two late latency components. Although latency varied across the two respiratory conditions in a manner consistent with the intra-thoracic pressure rise time differences, the elicitation characteristics and topographic distribution of these components did not vary across the two types of stimuli. In addition, an N350 was only present in the average for those categories that included VSWs, while an N550 was only present in those categories that contained K-complexes. Conclusions: Mid-inspiratory occlusions can be used as a model of obstructive events. VSWs contribute exclusively to the N350 component. while K-complexes contribute exclusively to the N550 component.