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Recordings of biological signals such as vibrocardiography often contain contaminating noise. Noise sources may include respiratory, gastrointestinal, and muscles movement, or environmental noise. Depending on individual physiology and sensor location, the vibrocardiographic (VCG) signals may be obscured by these noises in the time-frequency plane, which may interfere with automated characterization of VCG. In this study, polynomial chirplet transform (PCT) and smoothed pseudo Wigner-Ville distribution (SPWVD) were used to estimate the instantaneous frequency (IF) of two simulated VCG signals. One simulated signal contained a time-varying IF while the other had a fixed IF. The error in estimating IF was then calculated for signal-to-noise ratios (SNR) from -10 to 10 dB. Analysis was repeated 100 times at each level of noise using randomized sets of white noise. Error analysis showed that the range of errors in estimating IF was wider when SNR decreased. Results also showed that PCT tended to outperform SPWVD at high SNR. For example, PCT was more accurate at SNR > 3 dB for a simulated VCG signal with constant frequency components, at SNR>-10 dB for a simulated VCG signal with time-varying frequency, and at SNR > 0 for an actual VCG.

Contact transducers are a key element in experiments involving body sounds. The characteristics of these devices are often not known with accuracy. There are no standardized calibration setups or procedures for testing these sensors. This study investigated the characteristics of a new computer-controlled sound source phantom for testing sensors. Results suggested that sensors with different sizes require special phantom requirements. The effectiveness of certain approaches on increasing the spatial and spectral uniformity of the phantom surface signal was studied. Non-uniformities >20 dB were removable, which can be particularly helpful in comparing the characteristics of different size sensors more accurately.

Introduction Many strategies and technologies have been developed to minimize readmissions and manage HF. These strategies are often either labor intensive, invasive and/or expensive. New methodologies for accurate, rapid and low-cost ambulatory metrics of HF status are needed, of which seismocardiography (SCG) may be particularly useful. SCG uses accelerometer sensors to detect both audible, and sub-audible (i.e., below the frequencies detectable by the human ear) vibration signals. Although described decades ago, new sensor and digital processing capabilities are expanding the possible utility of this approach. Objective To investigate the use of SCG for HF monitoring. Methods Twenty patients (ages 51 to 75, 30 % female) admitted for HF were studied with a contact SCG sensor on the left lower sternal border of the chest wall at the 4thintercostal space for 1 min at two points in time with an interval of 2 to 48 hrs between assessments. The collected data contained 34 SCG waveform pairs: 17 pairs for patients with a NYHA class change from IV to III and 17 pairs for patients who stayed in class III. Results SCG signal waveform time-amplitude features were analyzed and the waveform variation quantified between the recording pairs. Results showed that the waveform variation was significantly different for those w/ and w/o NYHA class change (p Conclusions SCG changes may be a useful, safe and inexpensive modality for outpatient HF monitoring, enabling more timely intervention. These preliminary findings are supportive of an ability to differentiate HF functional status change. Further prospective studies are warranted.

Mechanical models of soft tissue are useful for studying vibro-acoustic phenomena. They may be used for validating mathematical models and for testing new equipment and techniques. The objective of this study was to measure density and visco-elastic properties of synthetic materials that can be used to build such models. Samples of nine different materials were tested under dynamic (0.5 Hz) compressive loading conditions. The modulus of elasticity of the materials was varied, whenever possible, by adding a softener during manufacturing. The modulus was measured over a nine month period to quantify the effect of ageing and softener loss on material properties. Results showed that a wide range of the compression elasticity modulus (10 to 1400 kPa) and phase (3.5 degrees -16.7 degrees ) between stress and strain were possible. Some materials tended to exude softener over time, resulting in a weight loss and elastic properties change. While the weight loss under normal conditions was minimal in all materials (

Many pulmonary injuries and pathologies may lead to structural and functional changes in the lungs resulting in measurable sound transmission changes on the chest surface. Additionally, noninvasive imaging of externally driven mechanical wave motion in the chest (e.g., using magnetic resonance elastography) can provide information about lung structural property changes and, hence, may be of diagnostic value. In the present study, a comprehensive computational simulation (in silico) model was developed to simulate sound wave propagation in the airways, lung, and chest wall under normal and pneumothorax conditions. Experiments were carried out to validate the model. Here, sound waves with frequency content from 50 to 700 Hz were introduced into airways of five porcine subjects via an endotracheal tube, and transmitted waves were measured by scanning laser Doppler vibrometry at the chest wall surface. The computational model predictions of decreased sound transmission with pneumothorax were consistent with experimental measurements. The in silico model can also be used to visualize wave propagation inside and on the chest wall surface for other pulmonary pathologies, which may help in developing and interpreting diagnostic procedures that utilize sound and vibration.

Numerical modeling of sound propagation in the airways requires accurate knowledge of the airway geometry. These models are often validated using human and animal experiments. While many studies documented the geometric details of the human airways, information about the geometry of pig airways is scarcer. In addition, the morphology of animal airways can be significantly different from that of humans. The objective of this study is to measure the airway diameter, length and bifurcation angles in domestic pigs using computed tomography. After imaging the lungs of 3 pigs, segmentation software tools were used to extract the geometry of the airway lumen. The airway dimensions were then measured from the resulting 3 D models for the first 10 airway generations. Results showed that the size and morphology of the airways of different animals were similar. The measured airway dimensions were compared with those of the human airways. While the trachea diameter was found to be comparable to the adult human, the diameter, length and branching angles of other airways were noticeably different from that of humans. For example, pigs consistently had an early airway branching from the trachea that feeds the superior (top) right lung lobe proximal to the carina. This branch is absent in the human airways. These results suggested that the human geometry may not be a good approximation of the pig airways and may contribute to increasing the errors when the human airway geometric values are used in computational models of the pig chest.

Pneumothorax (PTX) is an abnormal accumulation of air between the lung and the chest wall. It is a relatively common and potentially life-threatening condition encountered in patients who are critically ill or have experienced trauma. Auscultatory signs of PTX include decreased breath sounds during the physical examination. The objective of this exploratory study was to investigate the changes in sound transmission in the thorax due to PTX in humans. Nineteen human subjects who underwent video-assisted thoracic surgery, during which lung collapse is a normal part of the surgery, participated in the study. After subjects were intubated and mechanically ventilated, sounds were introduced into their airways via an endotracheal tube. Sounds were then measured over the chest surface before and after lung collapse. PTX caused small changes in acoustic transmission for frequencies below 400 Hz. A larger decrease in sound transmission was observed from 400 to 600 Hz, possibly due to the stronger acoustic transmission blocking of the pleural air. At frequencies above 1 kHz, the sound waves became weaker and so did their changes with PTX. The study elucidated some of the possible mechanisms of sound propagation changes with PTX. Sound transmission measurement was able to distinguish between baseline and PTX states in this small patient group. Future studies are needed to evaluate this technique in a wider population.

Endotracheal tube (ETT) malpositioning into a mainstem bronchus or the esophagus may result in significant hypoxemia. Current methods to determine correct ETT position include auscultation, radiography, and bronchoscopy, although the current acceptable standard procedure for proper endotracheal (versus esophageal) intubation is detection of end-tidal carbon dioxide (ETco(2)) by capnography, capnometry, or colorimetric ETco(2) devices. Unfortunately, capnography may be unavailable or unreliable in nonhospital/emergency settings or in low cardiac output states, and it does not detect endobronchial intubation. The purpose of this study was to quantify and assess breath sound characteristics using electronic stethoscopes placed over each hemithorax and epigastrium to determine their ability to detect ETT malposition. We recorded breath sounds in 19 healthy, non-obese adults before general surgical procedures. After intubation of the trachea, the ETT was bronchoscopically positioned 3 cm above the carina, after which 3 breaths of 500 mL were given and breath sounds were recorded. A second ETT was placed in the esophagus and the same series of breaths and recordings were performed. Finally, the tracheal ETT was advanced into the right mainstem bronchus and breath sounds were recorded. Using computerized analysis, breath sounds were digitized and filtered to remove selected frequencies, and acoustic signals and energy ratios were obtained for all 3 positions. Total energy ratios using band-pass filtering of the acoustic signals accurately identified all esophageal and endobronchial intubation (P < 0.001). These preliminary results suggest that this technique, when incorporated into a 3-component, electronic stethoscope-type device, may be an accurate, portable mechanism to reliably detect ETT malposition in adults when ETco(2) may be unavailable or unreliable.

Pneumothorax is a common clinical condition that can be life threatening. The current standard of diagnosis includes radiographic procedures that can be costly and may not always be readily available or reliable. The objective of this study was to investigate the hypothesis that pneumothorax causes detectable pathognomonic changes in pulmonary acoustic transmission. An animal model was developed whereby 15 mongrel dogs were anaesthetised, intubated and mechanically ventilated. A thoracoscopic trocar was placed into the pleural space for the introduction of air and confirmation of a approximately 30% pneumothorax by direct visualisation. Broadband acoustic signals were introduced into the endotracheal tube, while transmitted waves were measured at the chest surface. Pneumothorax was found consistently to lower the pulmonary acoustic transmission in the 200-1200 Hz frequency band, whereas smaller transmission changes occurred at lower frequencies (p0.0001, sign test). The ratio of acoustic energy between low-(220 Hz) and high-(550-770 Hz) frequency bands was significantly different in the control and pneumothorax states (p0.0001, sign test). This implies that pneumothoraces can be reliably detected using pulmonary acoustic transmission measurements in the current animal model. Further studies are needed to investigate the feasibility of using this technique in humans.

Air accumulations within living organisms are sometimes pathologic. An example is free air within the abdomen from perforation of the intestines (a condition called pneumoperitoneum). The objectives of the described research were to define the acoustic signatures of abdominal air cavities at low frequencies and to investigate the feasibility of using these signatures for pneumoperitoneum diagnosis. The central hypothesis was that low-frequency vibro-acoustic property changes are detectable using broad-band acoustic excitation applied at the abdominal surface. Band-limited white noise (0-3200 Hz) was introduced at the abdominal surface of sedated dogs and response was measured by a surface vibro-acoustic sensor. The transfer function and coherence were estimated from these measurements. The presence of pneumoperitoneum caused increased resonances and anti-resonances (p0.01). Measures of the latter parameters were proposed and evaluated to quantitatively measure their magnitude. Resonant spectral peaks of more than 3 dB were consistent with pneumoperitoneum (p0.01), and both resonance and anti-resonance increased with condition severity (p0.03). The data also suggest a possible reduction in the resonant and anti-resonant frequencies with decreasing air cavity volumes (p = 0.14) as supported by theoretical predictions. Finally, anti-resonance was also found to be associated with a drop in coherence. These findings suggest that the proposed technique may be useful in the diagnosis of pneumoperitoneum.

Alterations in the structure and function of the pulmonary system that occur in disease or injury often give rise to measurable changes in lung sound production and transmission. A better understanding of sound transmission and how it is altered by injury and disease might improve interpretation of lung sound measurements, including new lung imaging modalities that are based on an array measurement of the acoustic field on the torso surface via contact sensors or are based on a 3-dimensional measurement of the acoustic field throughout the lungs and torso using magnetic resonance elastography. It is beneficial to develop a computational acoustic model that would accurately simulate generation, transmission and noninvasive measurement of sound and vibration within the pulmonary system and torso caused by both internal and external sources. In the present study, sound transmission in the airway tree and coupling to and transmission through the surrounding lung parenchymal tissue were investigated on a mechanical lung phantom with a built-in bifurcating airway tree through airway insonification. Sound transmission in the airway tree was studied by applying the Horsfield self-consistent model of asymmetric dichotomy for the bronchial tree. The acoustics of the bifurcating airway segments and lung phantom surface motion were measured by microphones and scanning laser Doppler vibrometty respectively. Finite element simulations of sound transmission in the lung phantom were performed. Good agreement was achieved between experiments and finite element simulations. This study validates the computational approach for sound transmission and provides insights for simulations on real lungs.Copyright © 2013 by ASME

Noninvasive measurement of mechanical wave motion (sound and vibration) in the lungs may be of diagnostic value, as it can provide information about the mechanical properties of the lungs, which in turn are affected by disease and injury. In this study, two previously derived theoretical models of the vibroacoustic behavior of the lung parenchyma are compared: (1) a Biot theory of poroviscoelasticity and (2) an effective medium theory for compression wave behavior (also known as a “bubble swarm” model). A fractional derivative formulation of shear viscoelasticity is integrated into both models. A measurable “fast” compression wave speed predicted by the Biot theory formulation has a significant frequency dependence that is not predicted by the effective medium theory. Biot theory also predicts a slow compression wave. The experimentally measured fast compression wave speed and attenuation in a pig lung ex vivo model agreed well with the Biot theory. To obtain the parameters for the Biot theory prediction, the following experiments were undertaken: quasistatic mechanical indentation measurements were performed to estimate the lung static shear modulus; surface wave measurements were performed to estimate lung tissue shear viscoelasticity; and flow permeability was measured on dried lung specimens. This study suggests that the Biot theory may provide a more robust and accurate model than the effective medium theory for wave propagation in the lungs over a wider frequency range.

Detailed quantitative measurements of three‐dimensional subharmonic waves have been obtained with a scanning laser anemometer in the near‐wake region of a circular cylinder. A spatial decomposition technique has been used to separate the secondary three‐dimensional flow from the primary Strouhal vortex flow. The appearance of subharmonic frequencies in the spectrum of the secondary instability field at Reynolds numbers of 300 and above provides experimental evidence consistent with the scenario of a period‐doubling route to turbulence. The basic flow structure of the secondary field responsible for producing the subharmonics is shown to be pairs of counter‐rotating streamwise vortices, which alternate the direction of rotation every Strouhal period.

Extension of the percussion technique is implemented by applying vibro-acoustic excitation to the torso surface and using an array of measurement locations on the torso of three healthy human subjects via noncontacting scanning laser Doppler vibrometry. A 3-dimensional finite element model for simulating the vibro-acoustic response of the human upper torso is also developed. The soft tissue, ribcage, sternum and major internal organs were detailed to create an accurate geometric model. Experimental measurements partially validate the FE simulation model.

Noninvasive measurement of mechanical wave motion (sound and vibration) in the lungs may be of diagnostic value, as it can provide information about the mechanical properties of the lungs, which in turn are affected by disease and injury. In this study, two theoretical models of the vibro-acoustic behavior of the lung parenchyma are compared: (1) a Biot theory of poroviscoelasticity and (2) a simplified “bubble swarm” model for compression wave behavior. A “slow” compression wave speed predicted by the Biot theory formulation agrees well with the bubbly swarm theory in both analytical calculations and computational simulation. Biot theory also predicts a fast compression wave and a shear wave. The relative contributions of all three wave types are assessed. The effect of the air volume fraction is also investigated. Preliminary experimental measurements of the slow compression wave speed in the lung parenchyma are carried out and agree with theoretical predictions.

Documenting the characteristics of contact body-sound sensors is important since they are an integral part of vibroacoustic experiments. To facilitate sensor testing, a repeatable sound source is desirable. The purpose of this study was to construct a sound source phantom for testing sensors with different sizes. To facilitate accurate comparison of the characteristics of these sensors a uniform acoustic signal at the phantom surface is required. The acoustic output at the phantom surface was documented using a laser Doppler vibrometer. A rigid plate was embedded within the phantom to help achieve a uniform acoustic signal at the surface. Measurements showed that the surface acoustic output has high spatial uniformity (about ±1dB over a 6 cm diameter). The developed phantom is compact (≫ 250 ml), easy to construct, requires no special storage, and has mechanical properties similar to soft tissue.

An acoustic boundary element model is used to simulate sound propagation in the lung parenchyma and surrounding chest wall. It is validated theoretically and numerically and then compared with experimental studies on lung-chest phantom models that simulate the lung pathology of pneumothorax. Studies quantify the effect of the simulated lung pathology on the resulting acoustic field measured at the phantom chest surface. This work is relevant to the development of advanced auscultatory techniques for lung, vascular, and cardiac sounds within the torso that utilize multiple noninvasive sensors to create acoustic images of the sound generation and transmission to identify certain pathologies.

An acoustic boundary element (BE) model is used to simulate sound propagation in the lung parenchyma. It is computationally validated and then compared with experimental studies on lung phantom models. Parametric studies quantify the effect of different model parameters on the resulting acoustic field within the lung phantoms. The BE model is then coupled with a source localization algorithm to predict the position of an acoustic source within the phantom. Experimental studies validate the BE-based source localization algorithm and show that the same algorithm does not perform as well if the BE simulation is replaced with a free field assumption that neglects reflections and standing wave patterns created within the finite-size lung phantom. The BE model and source localization procedure are then applied to actual lung geometry taken from the National Library of Medicine’s Visible Human Project. These numerical studies are in agreement with the studies on simpler geometry in that use of a BE model in place of the free field assumption alters the predicted acoustic field and source localization results. This work is relevant to the development of advanced auscultatory techniques that utilize multiple noninvasive sensors to construct acoustic images of sound generation and transmission to identify pathologies.

A mechanical phantom model was built to simulate percussive techniques for diagnosing pneumothorax (PTX) and hydrothorax (HTX) (collapsed lung with air or water in the pleural space, respectively). The model was built with materials that have similar acoustic properties to that of human parenchyma, soft tissue and ribs. A bladder was embedded into the parenchyma-mimicking foam to simulate PTX or HTX. Experimental frequency response measurements were taken on the mechanical phantom model for the simulated pathologies and the healthy case with percussive excitation and noninvasive response measurements at the soft tissue surface. To aid in understanding experimental measurements, a finite element model of the experimental setup was constructed in ANSYS and used to simulate these same cases. Normal velocity amplitudes over the soft tissue surface measured from the experimental setup and calculated via the finite element model were analyzed in the frequency domain to identify any patterns or signatures that could be exploited for diagnosis. Experiment and numerical studies agree in identifying the key features of the PTX condition versus the healthy case, but differ somewhat on how HTX can be distinguished from PTX and the healthy case. Reasons for this discrepancy are discussed. With some improvements, these computational and experimental phantom models may aid in the development of improved noninvasive acoustic techniques for identifying these and other life-threatening conditions.Copyright © 2007 by ASME

An acoustic boundary element (BE) model for porous compliant material like the lung parenchyma is developed and validated theoretically and experimentally. This BE model is coupled with a source localization algorithm to predict the position of an acoustic source within a lung phantom. The BE model is also coupled with a finite element (FE) model to simulate the surrounding shell-like chest wall. Experimental studies validate the BE-based source localization algorithm and show that the same algorithm fails if the BE simulation is replaced with a free field assumption that neglects reflections and standing wave patterns created within the finite-size lung phantom. This research is relevant to the development of advanced auscultatory techniques for lung, vascular and cardiac sounds within the torso that utilize multiple noninvasive sensors to create acoustic images of the sound generation and transmission to identify certain pathologies.Copyright © 2006 by ASME

A system was constructed to test the performance of transducers for the detection of body surface vibrations. A phantom was manufactured of a gel that approximates properties of soft tissue and the different sensors were used to measure the vibrations at the model surface. One speaker was buried in the phantom to introduce a simulated signal, and another introduced simulated ambient room noise. The frequency-dependent sensor sensitivity to the input signal and ambient noise was investigated for six different sensor types. The laser Doppler sensor provided non-contact measurement with no surface loading, and was chosen as the reference sensor. The sensitivity of all sensors to ambient noise was satisfactory with the all-coupled sensor being most sensitive. The electronic stethoscope had the advantages of high sensitivity to the desired signal, low sensitivity to ambient noise and low cost.

The primary objective of the study was to investigate the effects of pneumothorax (PTX) on breath sounds and to evaluate their use for PTX diagnosis. The underlying hypothesis is that there are diagnostic breath sound changes with PTX. An animal model was created in which breath sounds of eight mongrel dogs were acquired and analysed for both normal and PTX states. The results suggested that pneumothorax was associated with a reduction in sound amplitude, a preferential decrease in high-frequency acoustic components and a reduction in sound amplitude variation during the respiration cycle (p

This study is aimed at enhancing bowel sound (or gastrointestinal acoustic phenomena-[GAP]) analysis in an anesthetized rat model. The measured signal at the rat's abdominal wall primarily contains infrequent GAP activities against a strong background of ongoing heart sounds (HS). The bandwidth of GAP events overlaps with that of HS rendering use of fixed band-pass filters inadequate. Therefore, an adaptive filter (AF) is necessary. Because no reference signal is readily available, the reference signal is generated by exploiting the low variability in HS properties. Effects of the adaptation parameter and filter order on SNR and GAP distortion due to filtering are discussed. The GAP waveform distortions were minimum for a filter dimension of 1 to 5 points and an adaptation parameter of 5 to 20% of the value at the onset of filter instability. Typical overall SNR enhancement by HS removal with the current system was 25 to 30 dB for a wide range of adaptation parameters and filter dimensions. It is concluded that an AF system can be implemented to study GAP activity in anesthetized rats.

Pneumoperitoneum refers to free air within the abdominal cavity that typically signifies serious abdominal pathology such as a perforated gut. The principal hypothesis of the study was that abdominal structure alterations due to pneumoperitoneum cause diagnostic changes in the sounds induced by abdominal percussion. The current pilot study investigated these changes in a mongrel dog model. Abdominal percussion was performed at baseline and after creation of pneumoperitoneum states. The resulting acoustic events were acquired, digitised and analysed. The event attack and decay rates and dominant frequencies during decay decreased with pneumoperitoneum (p = 0.084, 0.014 and 0.004, respectively; Wilcoxon signed-rank test). Simple theoretical models were constructed and predicted the observed decrease in resonant frequencies with increasing air pocket size. The results suggested that the normal and the 1,000 ml pneumoperitoneum states can be separated using thresholds of the attack and decay rates and resonant frequency (specificity = 80%, 100% and 100%, and sensitivity = 100%, 100% and 100%, respectively). Separating the control and the 500 ml pneumoperitoneum cases may be also possible (specificity = 80%, 100%, 100% and sensitivity = 50%, 70% and 90%, respectively), but separating the two levels of pneumoperitoneum was not feasible using the current approach. Therefore analysis of abdominal percussion sounds may prove useful for pneumoperitoneum detection, but not for distinguishing different levels of that condition.

A theoretical and experimental study was undertaken to examine the feasibility of using audible-frequency vibro-acoustic waves for diagnosis of pneumothorax, a collapsed lung. The hypothesis was that the acoustic response of the chest to external excitation would change with this condition. In experimental canine studies, external acoustic energy was introduced into the trachea via an endotracheal tube. For the control (nonpneumothorax) state, it is hypothesized that sound waves primarily travel through the airways, couple to the lung parenchyma, and then are transmitted directly to the chest wall. In contradistinction, when a pneumothorax is present the intervening air presents an added barrier to efficient acoustic energy transfer. Theoretical models of sound transmission through the pulmonary system and chest region to the chest wall surface are developed to more clearly understand the mechanisms of intensity loss when a pneumothorax is present, relative to a baseline case. These models predict significant decreases in acoustic transmission strength when a pneumothorax is present, in qualitative agreement with experimental measurements. Development of the models, their extension via finite element analysis, and comparisons with experimental canine studies are reviewed.

This study is aimed at detecting gastrointestinal sounds (GIS) and correlating their characteristics with gastrointestinal (GI) conditions. The central hypotheses are that GIS generation depends on the motility patterns and the mechanical properties of the gut, and that changes in those result in measurable differences in GIS. An animal model which included both healthy rats and those with small bowel obstruction (SBO) was developed. The acoustic bursts, of GIS were detected by amplitude thresholding the signal envelope. Three methods of envelope estimation were proposed and evaluated. Envelope estimation using a Hilbert transform was found to produce the best results in the current application. The duration and dominant frequency of each detected GIS event was estimated and clear differences between healthy and diseased rats were discovered. In the control state, GIS events were found to consistently be of relatively short duration (3–65ms). Although the majority of events in the SBO state had similar short duration, infrequent longer events were also detected and appeared to be pathognomonic. Long duration events (>100 ms) occurred in each of seven obstructed, but in none of 14 non-obstructed, cases (p

An analytical solution is developed for the problem of surface wave generation on a linear viscoelastic half-space by a finite rigid circular disk located on the surface and oscillating normal to it. The solution is an incremental advancement of theoretical work reported in articles focused on seismology. Since the application of interest here is medical diagnostics, the solution is verified experimentally using a viscoelastic phantom with material properties comparable to biological soft tissue. Findings suggest that prior estimates in the literature of the shear viscosity in human soft tissue may not be accurate in the low audible frequency range. Measurement of wave motion on the skin surface caused by internal biological functions or external stimuli has been studied by a few researchers for rapid, nonintrusive diagnosis of a variety of specific medical ailments. It is hoped that the developments reported here will advance these techniques and also provide insight into related diagnostic methods, such as sonoelastic imaging and other methodologies that utilize disease-related variations in tissue shear elasticity or variations in density due to gaseous inclusions.

Acoustic wave propagation in the pulmonary system and torso is simulated by coupling a numerical acoustic boundary element model that predicts sound propagation throughout the solid tissues with a proven comprehensive analytical model for sound wave propagation in the airways of the bronchial tree that is valid up to at least 2 kHz. This approach enables modeling various pathologies that result in structural changes in the lung and/or changes in breath sound source and strength. The model may be also used to predict the resulting acoustic changes measured by acoustic sensors, e.g., stethoscopes, accelerometers, or other skin‐contact sensors. Experimental studies in a novel lung phantom model are used to partially validate the computational model. This study focuses on low audible frequencies, i.e., less than 2 kHz. This range encompasses naturally generated respiratory sounds that have been shown to have diagnostic value, as well as externally‐introduced vibro‐acoustic stimuli used for diagnosis. [Work supported by NIH EB 003286‐01.]

Diagnostic techniques are provided to enable the detection of a respiratory condition with a patient's body. The diagnostic techniques compare the acoustic generation and transmission characteristics of the patient's chest and lungs to reference acoustic characteristics and/or predetermined threshold values to determine if an abnormal respiratory condition is present within the patient. The diagnostic techniques process sound waves or vibrations that have interacted with a respiratory condition within a patient and which impinge on the chest wall of the patient. The sound waves or vibrations may be initiated by a speaker (20) that emits sounds waves into the mouth and trachea of the patient (12) or may be indigenous sounds. Alternatively, the sounds waves or vibrations may be initiated using percussive inputs to the chest wall of the patient (12). In processing (38) the sound waves, the diagnostic techniques calculate energy ratios using energy values within high and low frequency bands, signal time delays, and/or dominant frequencies and compare the calculated values to predetermined reference thresholds to generate outputs indicative of the respiratory condition within the patient.

Small bowel obstruction (SBO) is a common surgical emergency which may be mimicked by ileus or other nonsurgical conditions. The aims of this work is to delineate gastrointestinal sound (GIS) correlates in a rat model. Seven rats were studied in paired SBO and control states. Computerized analysis of GIS was performed under continuous IV sedation. After adaptive filtering, every GIS event was isolated and analyzed for duration and dominant frequency. It was found that long duration sounds (greater than 100 ms) occurred in each of the obstructed, but in none of the nonobstructed cases (p=0.02). The overall mean event duration and dominant frequency in SBO compared to control states was both significantly longer and lower (22.42.6 vs 7.0±2.6 ms, p=0.001 for duration; and 296±34 vs 427±33, p=0.001 for frequency). Besides these mean differences, there was also a clear evolution with time in GIS characteristics, with lengthening of the duration (+0.56 ms/min, p=0.001) and lowering of the dominant frequency (−3.3 Hz/min, p=0.01). It is concluded that GIS analysis may prove useful in the noninvasive, rapid, and accurate diagnosis of SBO.