Subjective assessment vs computer analysis of wheezing in asthma

"To wheeze or not to wheeze": That is not the question

BACKGROUND

The diagnosis of asthma in young children is difficult and based on clinical assessment of symptoms and results of physical examination. Respiratory wheeze has traditionally been used to define asthma in young children.

OBJECTIVE

We sought to compare the qualitative diagnosis of wheeze with a quantitative global assessment of significant troublesome lung symptoms during the first 3 years of life as a predictor of asthma by age 7 years.

METHODS

Children born to asthmatic mothers (n= 411) were followed prospectively to age 7 years. Parents were instructed to visit the research clinic during the first 3 years of life each time the child had significant troublesome lung symptoms for 3 days. At the clinic, a research physician performed a physical examination, including auscultation for wheeze and excluding differential diagnoses. We tested whether wheeze was independently associated with asthma at age 7 years after adjusting for the total number of episodes.

RESULTS

Three hundred thirteen children had full follow-up by age 7 years. In a multivariable analysis the total number of acute clinic visits for asthma symptom was significantly associated with later asthma (P< .0001), whereas the presence of wheeze at these visits was not (P= .5). The total number of acute clinic visits for significant troublesome lung symptoms was also significantly associated with later asthma in children who had never presented with any wheeze (P= .03).

CONCLUSION

A quantitative global assessment of significant troublesome lung symptoms in the first 3 years of life is a better predictor of asthma than assessment of wheeze. Doctor-diagnosed wheeze is not a prerequisite for the diagnosis of asthma, and relying on the symptom of wheeze will likely be an important cause of undertreatment.

Asymmetry in lung sound intensities detected by respiratory acoustic thoracic imaging (RATHI) and clinical pulmonary auscultation

RATHI was introduced as an attempt to further improve the association between anatomical zones and specific breathing activity, both spatially and temporally. This work compares RATHI with clinical pulmonary auscultation (PA) to assess the concordance between both procedures to detect asymmetries in lung sound (LS) intensities. Twelve healthy young males participated in the study and were auscultated by two experts. RATHI consisted in the acquisition of acoustical signals with an array of 5x5 sensors, while experts auscultated and described the intensity of LS heard using the same stethoscope on each sensor's position within the array. Comparisons were established looking for intensity asymmetries between apical vs. basal pulmonary regions and right vs. left hemithorax. By RATHI, most of the subjects showed asymmetries between apical and basal regions higher than 20%, whereas between left and right hemithorax asymmetries higher than 20% occurred only half of the time. RATHI and PA agreed 83 to 100% when apical to base acoustical information was compared, but when left to right asymmetries were considered these figures were about 40 to 50%. We concluded that RATHI has advantages as it gave more detailed and measurable information on LS than clinicians, who could not detect intensity asymmetries mainly below 20%.

Evaluation of obstructive lung disease with vibration response imaging

As optimal treatment and prognosis differ between asthma and COPD, a new diagnostic approach to differentiating between the two disorders would be clinically desirable. We evaluated the utility of vibration response imaging in differentiating between asthma and COPD. Sixty-six subjects with asthma or COPD were recorded, before and after the administration of a short-acting bronchodilator, using a computerized lung sound analysis device. Gray-scale images of breath sound distribution in the lungs, quantitative data in breath sound graphs (timing, amplitude) and automatic crackle and wheeze detection programs were used to differentiate between asthma and COPD subjects. Imaging data were compared with the clinical diagnosis, made by the standard methods (medical history, physical examination, and spirometric indices). Blinded evaluation of images demonstrated a significantly higher rate of improvement in image dynamics, shape and overall improvement following bronchodilator in subjects with asthma compared with those with COPD. Quantitative data showed distinct patterns in timing and amplitude for these two pathologies. Combined analyses based on qualitative image evaluation and quantitative data demonstrated an overall 85% accuracy (84% for asthma, 86% for COPD) in differentiating between asthma and COPD. Combined qualitative and quantitative evaluations of lung sounds are quite sensitive in distinguishing between lung sound recordings of COPD and asthma individuals. Lung sound features of synchronization in timing and intensity provide objective data that may further differentiate these two airway disorders.

Validation of automatic wheeze detection in patients with obstructed airways and in healthy subjects

Computerized lung-sound analysis is a sensitive and quantitative method to identify wheezing by its typical pattern on spectral analysis. We evaluated the accuracy of the VRI, a multi-sensor, computer-based device with an automated technique of wheeze detection. The method was validated in 100 sound files from seven subjects with asthma or chronic obstructive pulmonary disease and seven healthy subjects by comparison of auscultation findings, examination of audio files, and computer detection of wheezes. Three blinded physicians identified 40 sound files with wheezes and 60 sound files without wheezes. Sensitivity and specificity were 83% and 85%, respectively. Negative predictive value and positive predictive value were 89% and 79%, respectively. Overall inter-rater agreement was 84%. False positive cases were found to contain sounds that simulate wheezes, such as background noises with high frequencies or strong noises from the throat that could be heard and identified without a stethoscope. The present findings demonstrate that the wheeze detection algorithm has good accuracy, sensitivity, specificity, negative predictive value and positive predictive value for wheeze detection in regional analyses with a single sensor and multiple sensors. Results are similar to those reported in the literature. The device is user-friendly, requires minimal patient effort, and, distinct from other devices, it provides a dynamic image of breath sound distribution with wheeze detection output in less than 1 minute.

Automatic wheeze detection based on auditory modelling

Automatic wheeze detection has several potential benefits compared with reliance on human auscultation: it is experience independent, an automated historical record can easily be kept, and it allows quantification of wheeze severity. Previous attempts to detect wheezes automatically have had partial success but have not been reliable enough to become widely accepted as a useful tool. In this paper an improved algorithm for automatic wheeze detection based on auditory modelling is developed, called the frequency- and duration-dependent threshold algorithm. The mean frequency and duration of each wheeze component are obtained automatically. The detected wheezes are marked on a spectrogram. In the new algorithm, the concept of a frequency- and duration-dependent threshold for wheeze detection is introduced. Another departure from previous work is that the threshold is based not on global power but on power corresponding to a particular frequency range. The algorithm has been tested on 36 subjects, 11 of whom exhibited characteristics of wheeze. The results show a marked improvement in the accuracy of wheeze detection when compared with previous algorithms.

Wheeze detection: recordings vs. assessment of physician and parent

BACKGROUND

Parental and professional agreement as to the presence of wheezing in infants and preschool children has been shown to be poor. Agreement on the absence or presence of physical signs on chest examination in these populations is far from perfect, even among experienced physicians.

OBJECTIVES

We sought to compare the assessment of a parent, nurse, and physician with the "gold standard" of acoustic analysis for the presence of wheezing in infants and preschool children attending a hospital clinic.

SETTING AND SUBJECTS

Urban district general hospital in North London, England. Wheezy children under 6 years old attending a "walk-in" emergency pediatric ambulatory care unit.

RESULTS

Comparisions were completed on 31 children (age range 4-62 months). The severity of wheeze was independently evaluated by a parent, nurse, and experienced pediatrician, and these were compared with breath sounds recorded and analyzed by acoustic techniques for the presence and severity of wheezing. In only 10 of 31 (32%) children did the parent and the physician agree on the wheeze severity score. In 13 infants, the parent scored higher than the doctor and in 8 the parent scored lower. In 16 (52%) of the children, there was complete agreement as to the severity of wheezing by the nurse and the physician. In 24 of the 31 children (77%), the acoustic wheeze score agreed with the physician wheeze score; in 6 children the acoustic score was lower and in 1 it was higher.

CONCLUSIONS

The physician was able reliably to judge the severity of wheeze measured objectively, whereas nurses and parents were not. This study has important implications for the interpretation of parental questionnaire studies of asthma prevalence and severity.

Validity and reliability of acoustic analysis of respiratory sounds in infants

OBJECTIVE

To investigate the validity and reliability of computerised acoustic analysis in the detection of abnormal respiratory noises in infants.

METHODS

Blinded, prospective comparison of acoustic analysis with stethoscope examination. Validity and reliability of acoustic analysis were assessed by calculating the degree of observer agreement using the kappa statistic with 95% confidence intervals (CI).

RESULTS

102 infants under 18 months were recruited. Convergent validity for agreement between stethoscope examination and acoustic analysis was poor for wheeze (kappa = 0.07 (95% CI, -0.13 to 0.26)) and rattles (kappa = 0.11 (-0.05 to 0.27)) and fair for crackles (kappa = 0.36 (0.18 to 0.54)). Both the stethoscope and acoustic analysis distinguished well between sounds (discriminant validity). Agreement between observers for the presence of wheeze was poor for both stethoscope examination and acoustic analysis. Agreement for rattles was moderate for the stethoscope but poor for acoustic analysis. Agreement for crackles was moderate using both techniques. Within-observer reliability for all sounds using acoustic analysis was moderate to good.

CONCLUSIONS

The stethoscope is unreliable for assessing respiratory sounds in infants. This has important implications for its use as a diagnostic tool for lung disorders in infants, and confirms that it cannot be used as a gold standard. Because of the unreliability of the stethoscope, the validity of acoustic analysis could not be demonstrated, although it could discriminate between sounds well and showed good within-observer reliability. For acoustic analysis, targeted training and the development of computerised pattern recognition systems may improve reliability so that it can be used in clinical practice.

Reported versus confirmed wheeze and lung function in early life

AIMS

To investigate the relation between parentally reported wheeze (unconfirmed), physician confirmed wheeze, and subsequent lung function.

METHODS

Children at risk of allergic disease (one parent atopic) were recruited antenatally and followed prospectively from birth. During the first three years of life parents were asked to contact the study team if their child was wheezy. The presence of wheeze was confirmed or not by the primary care or study physician. Respiratory questionnaire and specific airway resistance measurement (sR(aw), body plethysmograph) were completed at age 3 years.

RESULTS

A total of 454 children were followed from birth to 3 years of age. One hundred and eighty six (40.9%) of the parents reported their child wheezing in the first three years of life, and in 130 (28.6%) the wheeze was confirmed. A total of 428 children attended the three year clinic review, of whom 274 (64%) successfully carried out lung function tests. There was no significant difference in sR(aw) (kPa.s; geometric mean, 95% CI) between children who had never wheezed (n = 152; 1.03, 1.00 to 1.06) and those with a parentally reported but unconfirmed wheeze (n = 36; 1.02, 0.96 to 1.07, p = 1.00). sR(aw) was significantly higher in children with a physician confirmed wheeze (n = 86; 1.17, 1.11 to 1.22, p < 0.001) compared to those with no history of wheeze or with unconfirmed wheeze.

CONCLUSIONS

Children with physician confirmed wheeze have significantly poorer lung function compared to those with parentally reported but unconfirmed and those who have never wheezed. A proportion of parents may have little understanding of what medical professionals mean by the term "wheeze".

[Dependence of nocturnal bronchial obstruction on sleep position]

Patients with bronchial obstructions often have problems to stay asleep at night. The interaction between sleep position and bronchial obstructions has not been investigated until now. A total of 20 patients was included in this study. All patients were recorded one night in our sleep laboratory with a parallel recording of lung sounds using a commercial Pulmotrack 1010 system. The bronchial obstructions were lower in lateral position than in supine position for both tracheal and chest sounds (p = 0,083 and p = 0,036; n.s.). This effect seemed to be especially high in patients with many obstruction episodes. From our results we can conclude that there is a small dependence of bronchial obstructions from sleep position. Further investigations are needed to verify this result.

Auscultation revisited: the waveform and spectral characteristics of breath sounds during general anesthesia

Although auscultation is commonly used as a continuous monitoring tool during anesthesia, the breath sounds of anesthetized patients have never been systematically studied. In this investigation we used digital audio technology to record and analyze the breath sounds of 14 healthy adult patients receiving general anesthesia with positive pressure ventilation. Sounds recorded from inside the esophagus were compared to those recorded from the surface of the chest, and corresponding airflow was measured with a pneumotachograph. The sound samples associated with inspiratory and expiratory phases were analyzed in the time domain (RMS amplitude) and frequency domain (peak frequency, spectral edge, and power ratios). There was a positive linear correlation (R2 > 0.9) between inspiratory flow and sound amplitude in the precordial and esophageal samples of all patients. The RMS amplitude of the inspiratory and expiratory sounds was approximately 13 times greater when recorded from inside the esophagus than from the surface of the chest in all patients at all flows (p < 0.001). The peak frequency (Hz) was significantly higher in the esophageal recordings than the precordial samples (298 +/- 9 vs 181 +/- 10, P < 0.0001), as was the 97% spectral edge (Hz) (740 +/- 7 vs 348 +/- 16, P < 0.0001). In the adult population esophageal stethoscopes yield higher frequencies and greater amplitude than precordial stethoscopes. Quantification of lung sounds may provide for improved monitoring and diagnostic capability during anesthesia and surgery.

Evaluation of nocturnal bronchoconstriction by all night tracheal sound monitoring

BACKGROUND

A study was undertaken to evaluate the reliability of a digital tracheal sound analyser (ELENS-DSA) in predicting nocturnal changes in airways resistance in asthmatic patients. This device allows continuous measurement of the proportion of the time occupied by wheezing (Wh%).

METHODS

Nocturnal polygraphic studies with simultaneous continuous monitoring of tracheal sounds and airways resistance were performed in seven patients with nocturnal asthma. In order to evaluate the possible bias in wheezing estimation, each tracheal sound recording was passed through the automatic analyser and simultaneously monitored with earphones by an experienced observer.

RESULTS

The device detected audible wheezing with an optimal sensitivity and specificity of 70%. Snoring was a minor cause of the relatively poor characteristics of the system. A close correlation (p < 0.001) between Wh% and airways resistance was observed only in those patients with the highest increase in resistance; when the results of all the subjects were pooled the correlation observed was poor. The predictive value of Wh% in detecting changes in airways resistance during 10 minute intervals was lower than 70%. The positive and negative predictive values of Wh% were raised to 79% and 83%, respectively, for 30 minute intervals.

CONCLUSIONS

The ELENS-DSA system is a relatively crude means of detecting wheezing and assessing bronchoconstriction quantitatively. However, it is able to detect accurately nocturnal bronchoconstriction for 30 minute intervals. This finding, along with the fact that the monitoring is non-invasive, suggests that it may be a promising tool, especially for patients during sleep.

Classification of lung sounds in patients with asthma, emphysema, fibrosing alveolitis and healthy lungs by using self-organizing maps

The performance of the self-organizing map (SOM), an artificial neural network, was evaluated in the classification of lung sounds. Patients with asthma (n = 8), emphysema (n = 8) and fibrosing alveolitis (n = 8), and patients with healthy lungs (n = 8) were selected for the study. Fast Fourier transform (FFT) spectra from midinspiratory breath sounds recorded at the right lower lobe area were used to construct feature vectors in the learning and classification process of SOM. The sound segments did not contain wheezing sounds. The lung sounds of 25/32 (78%) patients were classified correctly, with an overall kappa (kappa) value of 0.71. The agreement between the clinical and proposed diagnoses based on classification of lung sounds was good among patients with emphysema (kappa = 0.92) and those with healthy lungs (kappa = 0.83), but only moderate among patients with asthma (kappa = 0.52) and fibrosing alveolitis (kappa = 0.54). This is due to the limitations in distinguishing breath sounds of asthmatics without wheezing sounds from those with crackles in fibrosing alveolitis by the spectral pattern alone. The results indicate that SOM based on FFT spectra is potentially useful in the classification of lung sounds, e.g. in health screening or in differential diagnosis of pulmonary disorders. To enhance the performance of SOM, other features of lung sounds should be combined with FFT spectra.

Frequency spectra of normal breath sounds in childhood

Clinicians who auscultate the chest of normal children note that the frequency content of their breath sounds appears to vary with age. Because these changes have not been systematically documented before, we recorded and analyzed inspiratory breath sounds in 35 children (0 to 13 years) and five adults (34 to 43 years). Our objective was to determine if the frequency content of normal breath sounds differed with age. Using a Fast Fourier Transform program, we calculated an average amplitude frequency spectrum from the inspiratory portion of the breath sounds of each subject (n = 10 breaths), and we compared the shape of the AFS and the values of selected frequency parameters. We found that the shape of the AFS of the youngest children differed most from the AFS of adults. Three of four selected frequency parameters (F25, F50, F95) differed significantly between children and adults (p less than 0.05), and one parameter (F75) did not (p = 0.11). The F25, F50, and F75 parameters of children (but not F95) were correlated (p less than 0.001) with increasing height and age. These results suggest that differences in the frequency content of the normal breath sounds of children and adults contribute to the differences that clinicians detect during clinical auscultation.

Continuous adventitious lung sounds

Recent research has increased the still limited understanding about the generation of continuous adventitious lung sounds. These sounds all have a definite pitch, such as in stridor and wheezing. With the use of waveform analysis, one can examine more closely the relationship between what is heard and the pathophysiology causing the sound. Clinical examples are given to show the utility and limitations of current lung sounds analysis techniques.

Digital respirosonography. New images of lung sounds

We used tape recordings from normal subjects and from patients with lung disease to generate spectrographic images of respiratory sounds on a personal computer. These digital respirosonograms presented timing and frequency content of lung sounds, with the sound intensities displayed on a color scale. Respiratory sounds during inspiration and expiration could be recognized by their association with concurrent respiration curves. Contributions of low-frequency cardiac sounds were visually identified by their relationship to simultaneously recorded ECGs. Typical characteristics of normal and adventitious lung sounds were documented and displayed both in the time and the frequency domain. Digital respirosonography provides an easy way to assess lung sound amplitudes, frequencies and timing over several breaths.

Nomenclature used by health care professionals to describe breath sounds in asthma

We studied the spontaneous, uninstructed description by 40 health care professionals of breath sounds in asthmatic patients, and their use of lung sound terminology following current recommendations. Tape play-back auscultation of recorded tracheal and lung sounds was performed by ten observers in each group of residents, nurses, staff physicians and physiotherapists. They repeated the test after two weeks to three months. Individual descriptions were compared to computer-aided characterization of the breath sound recordings. We found significant differences in the preferred terms for description of adventitious lung sounds between the groups of health care professionals. There was considerable intraobserver variability, with less agreement when suggestions for a more complex characterization were followed. Our observations indicate the importance of teaching a standardized nomenclature for lung sounds to health care professionals, using only terms which are clearly informative of pulmonary disease.