Effect of supraglottic mechanoreceptors on spatial mapping of respiratory related evoked responses using wavelet and Laplacian methods

Respiratory related evoked potentials (RREPs) were recorded from eight normal subjects in response to brief pressure pulses of -10 cm H2O with a duration of 200 ms to identify the contribution of supralaryngeal mechanoreceptors to the evoked responses by constraining application of the stimulus to the larynx and sublarvngeal regions through insertion of a larvngeal mask airway (LMA). Wavelet decomposition of RREP responses from 30 electrodes on the right side of the scalp was performed for eight frequency scales in time. The RREPs at each wavelet scale were enhanced by eliminating the wavelet coefficients due to artifacts and noise. After denoising, the third (125-150 Hz), fourth (62.5-125 Hz), fifth (31.25-62.5 Hz) and sixth (13.62-31.25 Hz) wavelet scales were used fnr estimation of the Laplacian. In addition, the global field power was calculated to quantify the wavelet-filtered RREP activity and to extract features for statistical analysis, Our results show that estimates of the global field power at the fourth and fifth wavelet scales are more significantly decreased after the insertion of the LMA than was true for scales 3 and 6. Further, after the LMA was inserted, the Laplacian showed reduced activity in the posterior-lateral region in four subjects and reductions in other places in the rest. (C) 2000 Biomedical Engineering Society. [S0090-6964(00)00811-0].