Acoustic transmission of the respiratory system using speech stimulation

Abstract

Two methods for the analysis of the acoustic transmission of the respiratory system are presented. Continuous speech utterance is used as acoustic stimulation. The transmitted acoustic signal is recorded from various sites over the chest wall. The AR method analyzes the power spectral density function of the transmitted sound, which heavily depends on the microphone assembly and the utterance. The method was applied to a screening problem and was tested on a small database that consisted of 19 normal and five abnormal patients. Using the first five AR coefficients and the prediction error of an AR(10) model, as discriminating features, the system screened all abnormals. An ARMA method is suggested, which eliminates the dependence on microphone and utterance. In this method, the generalized least squares identification algorithm is used to estimate the ARMA transfer function of the respiratory system. The normal transfer function demonstrates a peak at the range of 130-250 Hz and sharp decrease in gain for higher frequencies. A pulmonary fibrotic patient demonstrated a peak at the same frequency range, a much higher gain in the high frequency range with an additional peak at about 700 Hz.

Sound transmission in the lung as a function of lung volume

“…The sound speed we calculated of 37 m/s is consistent with speeds that have been reported by others (1,7,9,10,14). Rice (9) found values of sound speed in excised horse lungs to be between 25 and 70 m/s, and Kraman (6) found values in human lungs between 23 and 33 m/s.…”

“…Using a "coded" input signal, we were able to measure the transit times of sound through the lung with precision. The frequencies of the input sound we used (130-150 Hz) are in the range of frequencies shown by others to exhibit optimal transfer of acoustic energy through the lung (1,8). Many previous studies have inserted sound over a range of frequencies.…”

Improved Detection of Lung Fluid With Standardized Acoustic Stimulation of the Chest

“…The dominant frequency of parenchymal pathology ranges from 200 to 2000 Hz. Previous work investigating sound transmission in the chest cavity demonstrated significant attenuation at frequencies above 1000 Hz, suggesting an area of interest for analysis below this cutoff [25] , [27] , [28] . These frequency considerations led to the choice of stimulation frequencies between 50 to 1000 Hz.…”

Tabla: A Proof-of-Concept Auscultatory Percussion Device for Low-Cost Pneumonia Detection

“…In addition to breath sounds, speech can also be analyzed to detect pneumonia. In one study, subjects hummed a low vowel sound, which was recorded via an electronic stethoscope and analyzed to detect the presence of pneumonia [ 15 ]. Because it relies on a continuous hum, this approach would likely be very difficult to use when working with infants or non-vocal patients.…”