An adaptive filter to reduce cardiogenic oscillations on esophageal pressure signals

Measurements of pressure swings in the esophagus (Pes) can be used to estimate variables of clinical importance, e.g., intrinsic positive end-expiratory pressure (PEEPi). Unfortunately, cardiogenic oscillations frequently corrupt Pes and complicate further analysis. Due to significant band overlap with the respiratory component of Pes, cardiogenic oscillations cannot be suppressed adequately using standard filtering techniques. In this article, we present an adaptive filter that employs the electrocardiogram to identify and suppress the cardiogenic oscillations. This filter was tested using simulated data, where the variance accounted for relative to the simulated respiratory pressure swings increased from as low as 55% for the unfiltered Pes signal to over 95% when the adaptive filter was used. In patient data, the adaptive filter reduced the apparent cardiogenic oscillations without noticeably distorting the sharp deflections in Pes due to respiration. Furthermore, the filter suppressed peaks in the Fourier transform of Pes at integer multiples of the heart rate, while the remaining frequencies remained largely unchanged. During stable breathing, the standard deviation of PEEPi was reduced by between 44% and 71% in these four patients when the filter was used. We conclude that our filter removes a significant fraction of the cardiogenic oscillations that corrupt records of Pes.