Ploysongsang Y, Iyer V K, Ramamoorthy P A
Department of Internal Medicine, College of Engineering, Univeristy of Cincinnati, Ohio.
Am Rev Respir Dis. 1989 Apr;139(4):951-6. doi: 10.1164/ajrccm/139.4.951.
Lung sounds were recorded from five normal male subjects during tidal breathing. Simultaneous electrocardiograms were recorded and used as index signals to generate simulated heart sounds for digital subtraction from recorded lung sounds to obtain purer lung sounds. Five random breaths from each subject were analyzed. Sound signals were band-pass filtered 25 to 1,000 Hz (antialiasing), digitized at 3,000 Hz, and then subjected to (1) direct fast Fourier transform (FFT) without filtering (NF); (2) digital high-pass filtering at 75 Hz and subsequent FFT (75 HzF); (3) adaptive filtering and subsequent FFT (AF). The FFT algorithms of all lung sounds were characterized by mean, median, and mode frequencies. The mean, median, and mode of NF were lower than those of 75 HzF (64.98 +/- 4.04 versus 150.42 +/- 17.49, mean +/- SE, p less than 0.003; 44.57 +/- 2.06 versus 111.81.5.78, p less than 0.0003; 36.81 +/- 1.77 versus 86.16 +/- 3.13, p less than 0.0001) and those of AF (64.98 +/- 4.04 versus 96.87 +/- 11.58, p less than 0.01; 44.57 +/- 2.06 versus 68.23 +/- 10.44, p less than 0.05; 36.81 +/- 1.78 versus 52.24 +/- 8.97, p less than 0.06). The mean, median, and mode of AF were lower than those of 75 HzF (96.87 +/- 11.58 versus 150.42 +/- 17.49, p less than 0.02; 68.23 +/- 10.44 versus 111.81 +/- 5.77, p less than 0.007; 52.24 +/- 8.97 versus 86.16 +/- 3.73, p less than 0.01). The results indicated that by filtering out low frequency heart sounds, the frequency spectrum of lung sounds was moved upward.(ABSTRACT TRUNCATED AT 250 WORDS)
在平静呼吸期间，从五名正常男性受试者记录了肺部声音。同时记录心电图，并将其用作索引信号来生成模拟心音，以便从记录的肺部声音中进行数字减法运算，从而获得更纯净的肺部声音。分析了每个受试者的五次随机呼吸。声音信号经过25至1000赫兹的带通滤波（抗混叠），以3000赫兹进行数字化，然后进行：（1）未滤波的直接快速傅里叶变换（FFT）（NF）；（2）75赫兹的数字高通滤波及随后的FFT（75HzF）；（3）自适应滤波及随后的FFT（AF）。所有肺部声音的FFT算法均以平均、中值和众数频率为特征。NF的平均、中值和众数低于75HzF（分别为64.98±4.04对150.42±17.49，平均±标准误，p<0.003；44.57±2.06对111.81±5.78，p<0.0003；36.81±1.77对86.16±3.13，p<0.0001）以及AF（分别为）64.98±4.04对96.87±11.58，p<0.01；44.57±2.06对68.23±10.44，p<0.05；36.81±1.78对52.24±8.97，p<0.06）。AF的平均、中值和众数低于75HzF（分别为96.87±11.58对150.42±17.49，p<0.02；68.23±10.44对111.81±5.77，p<0.007；52.24±8.97对86.16±3.73，p<0.01）。结果表明，通过滤除低频心音，肺部声音的频谱向上移动。（摘要截短于250字）
