Removal of cardiac beat artifact in esophageal pressure measurement via a modified adaptive noise cancellation scheme.

Information on volume-pressure relationships of human lungs is usually based on indirect determination of intrapleural pressure (P(ip)) obtained from the esophagus. Unfortunately, cardiac beat artifact frequently corrupts measurement of esophageal pressure (P(es)). In this study, we presented a modified adaptive noise cancellation (MANC) scheme for removing the cardiac beat artifact in the P(es) signal. The proposed methodology used an airflow signal as the reference signal with least-mean-square method as the adaptive algorithm. The results of six experiments on two Brown-Norway rats showed a significant reduction of the apparent cardiac pulsation with minimal distortion of the P(es) signal. The MANC filter also showed evidence of peak suppression at integer multiples of heart rate in the fast Fourier transform of the P(es) signal while leaving the remaining spectrum largely unperturbed. A t-test method and the ratio of standard deviation to mean (std/mean) statistics of airway resistance (R(aw)) values were used to evaluate the performance of the MANC filter. In all six experiments, a reduction of std/mean of R(aw) by 12.5%-68% was obtained, indicating the effectiveness of the proposed scheme.