Volume-dependent variations of regional lung sound, amplitude, and phase

Computerized respiratory sounds: a comparison between patients with stable and exacerbated COPD

INTRODUCTION

Diagnosis of acute exacerbations of chronic obstructive pulmonary disease (AECOPD) is often challenging as it relies on patients' clinical presentation. Computerized respiratory sounds (CRS), namely crackles and wheezes, may have the potential to contribute for the objective diagnosis/monitoring of an AECOPD.

OBJECTIVES

This study explored if CRS differ during stable and exacerbation periods in patients with COPD.

METHODS

13 patients with stable COPD and 14 with AECOPD were enrolled. CRS were recorded simultaneously at trachea, anterior, lateral and posterior chest locations using seven stethoscopes. Airflow (0.4-0.6l/s) was recorded with a pneumotachograph. Breathing phases were detected using airflow signals; crackles and wheezes with validated algorithms.

RESULTS

At trachea, anterior and lateral chest, no significant differences were found between the two groups in the number of inspiratory/expiratory crackles or inspiratory wheeze occupation rate. At posterior chest, the number of crackles (median 2.97-3.17 vs. 0.83-1.2, P < 0.001) and wheeze occupation rate (median 3.28%-3.8% vs. 1.12%-1.77%, P = 0.014-0.016) during both inspiration and expiration were significantly higher in patients with AECOPD than in stable patients. During expiration, wheeze occupation rate was also significantly higher in patients with AECOPD at trachea (median 3.12% vs. 0.79%, P < 0.001) and anterior chest (median 3.55% vs. 1.28%, P < 0.001).

CONCLUSION

Crackles and wheezes are more frequent in patients with AECOPD than in stable patients, particularly at posterior chest. These findings suggest that these CRS can contribute to the objective diagnosis/monitoring of AECOPD, which is especially valuable considering that they can be obtained by integrating computerized techniques with pulmonary auscultation, a noninvasive method that is a component of patients' physical examination.

Quantile Acoustic Vectors vs. MFCC Applied to Speaker Verification

In this paper we describe speaker and command recognition related experiments, through quantile vectors and Gaussian Mixture Modelling (GMM). Over the past several years GMM and MFCC have become two of the dominant approaches for modelling speaker and speech recognition applications. However, memory and computational costs are important drawbacks, because autonomous systems suffer processing and power consumption constraints; thus, having a good trade-off between accuracy and computational requirements is mandatory. We decided to explore another approach (quantile vectors in several tasks) and a comparison with MFCC was made. Quantile acoustic vectors are proposed for speaker verification and command recognition tasks and the results showed very good recognition efficiency. This method offered a good trade-off between computation times, characteristics vector complexity and overall achieved efficiency.

A method of estimating inspiratory flow rate and volume from an inhaler using acoustic measurements

Inhalers are devices employed to deliver medication to the airways in the treatment of respiratory diseases such as asthma and chronic obstructive pulmonary disease. A dry powder inhaler (DPI) is a breath actuated inhaler that delivers medication in dry powder form. When used correctly, DPIs improve patients' clinical outcomes. However, some patients are unable to reach the peak inspiratory flow rate (PIFR) necessary to fully extract the medication. Presently clinicians have no reliable method of objectively measuring PIFR in inhalers. In this study, we propose a novel method of estimating PIFR and also the inspiratory capacity (IC) of patients' inhalations from a commonly used DPI, using acoustic measurements. With a recording device, the acoustic signal of 15 healthy subjects using a DPI over a range of varying PIFR and IC values was obtained. Temporal and spectral signal analysis revealed that the inhalation signal contains sufficient information that can be employed to estimate PIFR and IC. It was found that the average power (Pave) in the frequency band 300-600 Hz had the strongest correlation with PIFR (R(2) = 0.9079), while the power in the same frequency band was also highly correlated with IC (R(2) = 0.9245). This study has several clinical implications as it demonstrates the feasibility of using acoustics to objectively monitor inhaler use.

Modified classification of normal lung sounds applying Quantile vectors

In this paper a novel Lung Sound Automatic Verification (LSAV) system and front-end Quantile based acoustic models to classify Lung Sounds (LS) are proposed. The utilization of Quantiles allowed an easier and objective assessment with smaller computational demand. Moreover, less-complex Gaussian Mixture Models (GMM) were computed than those previously reported. The LSAV system allowed us to reach practically negligible error in healthy (normal) LS verification. LASV system efficiency and the optimal GMM's were evaluated by using Equal Error Rate (EER) and Bayesian Information Criterion (BIC) techniques respectively. These approaches could provide a tool for broader medical evaluation which does not rely, as it is often the case, on a qualitative and subjective description of LS.

Early detection of deteriorating ventilation by monitoring bilateral chest wall dynamics in the rabbit

PURPOSE

Mechanical complications during assisted ventilation can evolve due to worsening lung disease or problems in airway management. These complications affect lung compliance or airway resistance, which in turn affect the chest wall dynamics. The objective of this study was to explore the utility of continuous monitoring of the symmetry and dynamics of chest wall motion in the early detection of complications during mechanical ventilation.

METHODS

The local tidal displacement (TDi) values of each side of the chest and epigastrium were measured by three miniature motion sensors in 18 rabbits. The TDi responses to changes in peak inspiratory pressure (n = 7), induction of one-lung intubation (n = 7), and slowly progressing pneumothorax (PTX) (n = 6) were monitored in parallel with conventional respiratory (SpO(2), EtCO(2), pressure and flow) and hemodynamic (HR and BP) indices. PTX was induced by injecting air into the pleural space at a rate of 1 mL/min.

RESULTS

A strong correlation (R(2) = 0.99) with a slope close to unity (0.94) was observed between percent change in tidal volume and in TDi. One-lung ventilation was identified by conspicuous asymmetry development between left and right TDis. These indices provided significantly early detection of uneven ventilation during slowly developing PTX (within 12.9 ± 6.6 min of onset, p = 0.02) almost 1 h before the SpO(2) dropped (77.3 ± 27.4 min, p = 0.02). Decreases in TDi of the affected side paralleled the progression of PTX.

CONCLUSIONS

Monitoring the local TDi is a sensitive method for detecting changes in tidal volume and enables early detection of developing asymmetric ventilation.

A new method for continuous monitoring of chest wall movement to characterize hypoxemic episodes during HFOV

INTRODUCTION

Monitoring ventilated infants is difficult during high-frequency oscillatory ventilation (HFOV). This study tested the possible causes of hypoxemic episodes using a new method for monitoring chest wall movement during HFOV in newborn infants.

METHODS

Three miniature motion sensors were attached to both sides of the chest and to the epigastrium to measure the local tidal displacement (TDi) at each site. A >20% change in TDi was defined as deviation from baseline.

RESULTS

Eight premature infants (postmenstrual age 30.6 ± 2.6 weeks) were monitored during 10 sessions (32.6 h) that included 21 hypoxemic events. Three types of such events were recognized: decrease in TDi that preceded hypoxemia (n = 11), simultaneous decrease in TDi and SpO2 (n = 6), and decrease in SpO(2) without changes in TDi (n = 4). In the first group, decreases in TDi were detected 22.4 ± 18.7 min before hypoxemia, and were due to airway obstruction by secretions or decline in lung compliance. The second group resulted from apnea or severe abdominal contractions. In the third group, hypoxia appeared following a decrease in FiO2.

CONCLUSIONS

Monitoring TDi may enable early recognition of deteriorating ventilation during HFOV that eventually leads to hypoxemia. In about half of cases, hypoxemia is not due to slowly deteriorating ventilation.

Changes in regional distribution of lung sounds as a function of positive end-expiratory pressure

Introduction

Automated mapping of lung sound distribution is a novel area of interest currently investigated in mechanically ventilated, critically ill patients. The objective of the present study was to assess changes in thoracic sound distribution resulting from changes in positive end-expiratory pressure (PEEP). Repeatability of automated lung sound measurements was also evaluated.

Methods

Regional lung sound distribution was assessed in 35 mechanically ventilated patients in the intensive care unit (ICU). A total of 201 vibration response imaging (VRI) measurements were collected at different levels of PEEP between 0 and 15 cmH₂O. Findings were correlated with tidal volume, oxygen saturation, airway resistance, and dynamic compliance. Eighty-two duplicated readings were performed to evaluate the repeatability of the measurement.

Results

A significant shift in sound distribution from the apical to the diaphragmatic lung areas was recorded when increasing PEEP (paired t-tests, P < 0.05). In patients with unilateral lung pathology, this shift was significant in the diseased lung, but not as pronounced in the other lung. No significant difference in lung sound distribution was encountered based on level of ventilator support needed. Decreased lung sound distribution in the base was correlated with lower dynamic compliance. No significant difference was encountered between repeated measurements.

Conclusions

Lung sounds shift towards the diaphragmatic lung areas when PEEP increases. Lung sound measurements are highly repeatable in mechanically ventilated patients with various lung pathologies. Further studies are needed in order to fully appreciate the contribution of PEEP increase to diaphragmatic sound redistribution.

Analysis of respiratory sounds: state of the art

OBJECTIVE

This paper describes state of the art, scientific publications and ongoing research related to the methods of analysis of respiratory sounds.

METHODS AND MATERIAL

Review of the current medical and technological literature using Pubmed and personal experience.

RESULTS

The study includes a description of the various techniques that are being used to collect auscultation sounds, a physical description of known pathologic sounds for which automatic detection tools were developed. Modern tools are based on artificial intelligence and on technics such as artificial neural networks, fuzzy systems, and genetic algorithms…

CONCLUSION

The next step will consist in finding new markers so as to increase the efficiency of decision aid algorithms and tools.

Acoustic thoracic images for transmitted glottal sounds

Sound transmission has been of interest for many years in an attempt to study the structure of the lung and different researches have shown that artificial sounds produce a lateralization of sound information at the thoracic surface. Most of these studies have use non-simultaneous recording and input sounds introduced at the mouth or other thoracic points. In this paper, we present acoustic thoracic images, for transmitted glottal sounds, formed by a multichannel system with an array of 5x5 microphones. The study was done using 4 healthy subjects and 4 subjects having diffuse interstitial pneumonia. In both groups of subjects, it was found that the thorax behaves as a lowpass filter depending on the physical properties of its components, and that the transmitted acoustic thoracic imaging (TATHI) could reflect such properties. In most of the healthy subjects right to left asymmetries and heterogeneous apical to basal distribution were found. In patients the lateral dominance was lost and an intensity increment in the frequency band of 300 to 600 Hz was revealed. We conclude that TATHI permits to observe easily the spatial extension of the disease through sound transmission.

Velocity and attenuation of sound in the isolated fetal lung as it is expanded with air

We measured the velocity and attenuation of audible sound in the isolated lung of the near-term fetal sheep to test the hypothesis that the acoustic properties of the lung provide a measure of the volume of gas it contains. We introduced pseudorandom noise (bandwidth 70 Hz–7 kHz) to one side of the lung and recorded the noise transmitted to the surface immediately opposite, starting with the lung containing only fetal lung liquid and making measurements after stepwise inflation with air until a leak developed. The velocity of sound in the lung fell rapidly from 187 ± 28.2 to 87 ± 3.7 m/s as lung density fell from 0.93 ± 0.01 to 0.75 ± 0.01 g/ml (lung density = lung weight/gas volume plus lung tissue volume). For technical reasons, no estimate of velocity could be made before the first air injection. Thereafter, as lung density fell to 0.35 ± 0.01 g/ml, there was a further decline in velocity to 69.6 ± 4.6 m/s. High-frequency sound was attenuated as lung density decreased from 1.0 to 0.5 g/ml, with little change thereafter down to a density of 0.35 ± 0.01 g/ml. We conclude that both the velocity of audible sound through the lung and the degree to which high-frequency sound is attenuated in the lung provide information on the degree of inflation of the isolated fetal lung, particularly at high lung densities. If studies of sound transmission through the lung in the intact organism were to confirm these findings, the acoustic properties of the lung could provide a means for monitoring lung aeration during mechanical ventilation of newborn infants.