Information on volume-pressure relationships of human lungs is usually based on indirect determination of intrapleural pressure (Pip) obtained from the esophagus. Esophageal pressure (Pes) measurements are important in medical research and useful in clinical diagnosis. Unfortunately, the measurement results contaminate heavily by cardiac artifact and complicate further analyses. In clinical measurement of Pes, the conventional strategy to minimize cardiac beat artifact is to adjust the position of esophageal balloon or the posture of the body. Adaptive finite impulse response (AFIR) filter and modified adaptive noise cancellation (MANC) method are adopted to filter cardiac beat interference in this research. Six experiments on two Brown-Norway rats are used to verify filters’ performance and these filtered results are later compared.
In MANC methodology, an airflow signal is used as the reference signal with least mean square (LMS) method as the adaptive algorithm. The proposed MANC filter has successfully demonstrated the ability to significantly reduce the apparent cardiac pulsation without noticeably distorting the sharp deflections in the measured Pes signal. Furthermore, the MANC filter also shows evidence of suppressing peaks at integer multiples of heart rate in the Fast Fourier Transform (FFT) of the Pes signal while leaving the remaining spectrum largely unperturbed. A t-test method and the ratio of standard deviations to means (std/mean) statistics of airway resistance (Raw) values were used to evaluate the performance of MANC filter. In all six experiments, with the MANC filter, reductions of std/mean of Raw by 12.5% to 68% were obtained.
In the frequency domain, frequency variations and spectral overlap between the Pes components and cardiac beat signal components impact on the performance of filter. In this paper, the spectrum and waveform of measured Pes signal obtained after carefully adjusting the esophageal balloon are the best situation in clinical medicine and is used as the standard reference. From our experimental results on power strength, the 4th or higher harmonics did not have any significant effect on the filter performance. However, the 2nd harmonics of these signals had a significant effect on the filtering result. Thus, in the design of AFIR filters, attention is needed to minimize these effects. In frequency analysis, these harmonics or overlapping frequencies do not affect MANC. MANC is the better method for eliminating cardiac beat artifact in Pes measurement. The dynamic compliance (Cdyn) was also used to evaluate the performance of MANC and AFIR. The standard deviation of Cdyn is less than 0.15 using MANC, compared with the standard deviations as high as 0.57 for AFIR.
Experimental results indicating the effectiveness of MANC scheme as a filtering method to remove the cardiac beat artifacts in Pes measurement and we can conclude that MANC has better performance than AFIR. Furthermore, the LMS algorithm is simple to implement the online signal-processing device by DSP chips. (in 2001)
這是本人之博士論文題目，研究重點如下：
肋膜壓(Pip)在肺生理是相當重要的生理參數，通常它是利用間接量測的方法由食道量測食道壓(Pes)來取代肋膜壓的量測。
但是在食道壓量測信號中，有嚴重的心跳信號的干擾，這干擾會影響到之後許多的肺生理參數的計算與分析。在臨床上，通常是以調整食道球（esophageal balloon）的位置與受測者的姿勢來降低心跳信號的干擾。
在這個研究中，適應性有限脈衝反應（Adaptive finite impulse response； AFIR）濾波器與修正型適應性雜訊消除法（modified adaptive noise cancellation； MANC）方法被使用來濾除心跳干擾。
我們使用兩隻棕色挪威鼠（Brown-Norway rats）設計了六個實驗來驗證濾波器的效能並在之後比較兩種濾波方法的優劣。
此研究已發表論文如下：
鄭怡平,Research of adaptive filtering method for removal of cardiac beat artifact in measured esophageal pressure signal. (食道壓量測信號之心跳雜訊濾除方法之研究)，國立台灣大學電機工程學研究所博士論文，January, 2001.
Y.P. Cheng, H.D. Wu, G.J. Jan, and C.Y. Wang, “Adaptive method for removing cardiac beat artifact in esophageal pressure measurement”, Annals of Biomedical Enginerring, March , Vol. 29, p. 1-8, 2001. （SCI，2006 Impact Factor 2.276 ）
Yi-Ping Cheng, Huey-Dong Wu, Cheng-Yi Wang and Gwo-Jen Jan, “Removal cardiac beat artifact in esophageal pressure measurement”, Medical & Biomedical Engineering & Computing, Vol. 37, Nov. p.776-783, 1999. （SCI，2006 Impact Factor 1.018）
Y.P.Cheng, H.D.Wu, G.J.Jan, “Comparing two adaptive methods for removing cardiac beat artifact in esophageal pressure measurement: MANC and AFIR”, Proceeding of the 20th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBS'98) , Hong Kong, China, pp. 1640-1642, 1998.
Yi-Ping Cheng, Gwo-Jen Jan, Hwei-Dung Wu, Cheng-Yi Wang, "Digital Filter Method for Cancellation of Heart Beat Artifact in Esophageal Pressure Measurement ", 全球華人醫學工程會議暨1996醫學工程科技研討會, Taipei, Taiwan, 五月29～30日, 1996.
