Relationship between correlation dimension and indices of linear analysis in both respiratory movement and electroencephalogram

Objective: We investigate the relationships between signals from the electr oencephalogram (EEG) and those from respiratory movement using the correlat ion dimension (D-2) Methods: Respiratory movement and EEG were recorded for 7.5 h from 7 clinic ally healthy men. D-2 was calculated by applying an algorithm slightly modi fied from that proposed by Grassberger and Procaccia (Phys Rev Lett 50 (198 3) 346). Non-linearity in respiratory movement and EEG was tested by compar ing D-2 for the original data with that for surrogate data. Results: A statistically significant positive correlation between D-2 of th e EEG and D-2 Of the respiratory movement was observed for the original dat a. but not for the surrogate data. Conclusions: A reduced D-2 of the EEG may be associated with an increased r egularity of breathing in deep sleep (stage TV). Likewise, the increased D- 2 of respiratory movement during rapid eye movement may be associated with increased complexity of the signals. Whether there is a direct coordination between brain and lungs or whether brainstem systems, including that of th e cholinergic system, affect both respiration and cortex requires further i nvestigation. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.