"The most promising technology for primary care use is likely to be a portable device such as the Wheezometer, which could be used by patients or carers to assess the severity of wheezing at home."
Clinical Question(s): In community-based settings, does automated lung sound analysis identify the presence of wheeze compared to routine practice? In community-based settings, does automated lung sound analysis accurately diagnose new-onset asthma and/or identify changes in asthma severity compared to routine practice? In community-based settings, can automated lung sound analysis be used for home monitoring of asthma severity compared to routine practice? In community-based settings, does automated lung sound analysis have an added clinical value when compared to auscultation by a GP? Device(s): Pulmotrack (Karmelsonix, Haifa, Israel) Wheezometer (Karmelsonix, Haifa, Israel) VRI (Deep Breeze, Or-Akiva, Israel) LSA-2000 (Kenzmedico, Japan) Multichannel STG (Stethographics, Boston, USA) Advantages over Current Practice:
The current British Guidelines on the Management of Asthma (1) note that there is no gold standard for the diagnosis of asthma, although most definitions include the presence of symptoms such as wheeze, breathlessness, cough and chest tightness, and variable airway obstruction. A diagnosis of asthma is more likely if there is widespread wheeze on auscultation, and the history of wheeze is an important component in the diagnosis (1). Automated lung sound analysis could provide quantification of the amount and severity of wheeze present, both in the clinic, and via home monitoring.
Definitive diagnosis in children may be assisted by an assessment of response to therapeutic agents, or lung function testing. This may include spirometry or administering substances likely to cause airway hyper-responsiveness (1). In young children, lung function testing may be difficult or impractical, and alternative methods using quantification of wheeze may be preferable.
Monitoring of asthma control is important to optimise treatment, and identify exacerbations early, and can involve symptom questionnaires, peak flow meters or other forms of lung function testing, or monitoring the use of regular and rescue medications. However, compliance with home monitoring of asthma is currently poor, particularly using peak flow meters. Home and clinic monitoring of the presence and severity of wheeze may assist with monitoring changes in severity, and provide more objective answers to symptom questionnaires, which frequently ask about the presence of wheeze or nocturnal asthma. (1).
Details of Technology:
Automated lung sound analysis technology requires the attachment of specialist microphone sensors to the chest wall and/or trachea to monitor lung sounds. The number of sensors and the method of attachment vary between the different technologies, as shown in Table 1. The different technologies also carry out a variety of analyses on the recorded data. The VRI and STG technologies both provide visualisation of the data, and the STG technology also provides counts of detected crackles, wheezes and rhonchi. Pulmotrack provides respiratory rate and inspiratory:expiratory time ratio, although it is likely that these are derived from the additional respiration belt. Both the Pulmotrack and Wheezometer devices calculate %Wz (wheeze rate), the proportion of time that wheezing is present. Pulmotrack also reports separate %Wz values for the inspiratory and expiratory portions of the respiratory cycle. Wheeze rate differs from current clinical assessments of lung sounds, which tend to focus on how widespread sounds are, their type (e.g. wheeze, crackles), and whether they occur in the inspiratory or expiratory portion of the respiratory cycle.
Pulmotrack 2 sensors attached over trachea and right apex (other locations possible) with adhesive pads Respiration belt around lower ribcage Lung sounds %Wz (inspiratory, expiratory and total)
Respiratory rate
Inspiratory:expiratory time ratio
Cough detection
Wheezometer 1 sensor positioned manually over trachea None Lung sounds Total %Wz
VRI 40 sensors (34 for children) in 2 arrays vacuum coupled to posterior chest wall None Vibration energy Grayscale image of lung vibration energy at various points in respiratory cycle
LSA-2000 1 to 4 sensors attached to chest wall with adhesive pads None Lung sounds Not specified
Multichannel STG 14 sensors embedded in foam pad positioned against posterior chest wall + tracheal and heart sensors None Lung sounds Visualisation of waveforms
Counting and visualisation of crackles, wheezes and rhonchi
Two devices are included in the research overview, but were not considered in this report. The ELENS-DSA device appears to have been discontinued, and the Meditron electronic stethoscope does not appear to include any analysis ability; it is designed for recording lung sounds only. However, the addition of an associated software analysis system may allow electronic stethoscopes to be used for clinical lung sound analysis in the future.
Patient Group and Use:
?Identification of nocturnal asthma in adults and children with an existing diagnosis of asthma ?Assessing symptom severity in acute asthma exacerbations ?Quantifying level of asthma control and response to trial of therapeutic medication ?Assessment of response to bronchial provocation testing in young children where the diagnosis of asthma is uncertain Importance:
In 2004, Asthma UK estimated that there were 5.2 million people with asthma in the UK, of whom 1.1 million were children (2). Asthma UK currently estimates that 5.4 million people in the UK are currently receiving treatment, of whom 1.1 million are children (3). Mortality from asthma is low (1,131 people died from asthma in 2009) (3), but 30-80% of these deaths may be preventable if optimal treatment was available (4,5).
Asthma patients utilise a large number of GP appointments (over 4.1million per year), and may also require hospital admission (over 69,000 admissions in 2002), costing the NHS an estimated ?889 million (estimate for 2001), in addition to the burden of lost work and school days (2). Improving the control of asthma may reduce the need for acute consultations, in addition to decreasing morbidity and mortality.
Previous Research:
There is a large body of research on automated analysis of lung sounds for a variety of clinical conditions. However, much of this relates to recordings made using research devices, which are not available for routine clinical use. The studies summarised below were identified as using commercially available equipment specifically designed for capture and analysis of lung sounds, and which are appropriate for use in clinical situations. In addition, five clinical trials using the Pulmotrack and Wheezometer devices were identified from a search of current trial registries (6-10).
Accuracy compared to existing technology
Two studies using devices not included in the list of devices above investigated agreement between %Wz measurement and clinician classification of wheeze. These devices were not included as they have either been discontinued (11), or do not currently include an analysis capability (12). One study showed that a cut-off of 3% produced sensitivity and specificity values of around 70% when compared to wheeze detection by a clinician listening to the same audio recordings (11), while the other reported very good agreement at a cut-off of 10%, with a positive predictive value of 100%, and a negative predictive value of 91% when compared to clinical auscultation during bronchial provocation testing (12).
Detection of wheeze using the Pulmotrack device has been shown to be at least as accurate as manual auscultation in intensive and emergency care settings (13,14), with one study showing that the Pulmotrack device had a sensitivity of 75%, and specificity of 76% for detection of wheeze when compared to auditory review of the recorded sound files by a panel of experienced clinical specialists in paediatric respiratory or intensive care (13). A %Wz measurement of 3% has been shown to correspond to the upper limit of normality in children (15), although the cut-off for detection of wheeze is typically set at 5% (16,17). The Pulmotrack cough counter was shown to have a sensitivity of 96% and a specificity of 94% when compared to expert listeners (18). Measurement of %Wz was shown to have significant correlation with physician classification of wheeze severity (r=0.83), with 77% agreement between a four-point score of wheeze s (19). Two studies reported inconsistent correlation with FEV1 measures and symptom scoring children with asthma (16,17). However, these two studies had relatively small sample sizes of 9 and 15 subjects, and so would have been underpowered to detect significant relationships.
The Wheezometer device is a simplified version of the Pulmotrack technology, and measures of %Wz using this device have been reported to correlate with clinical assessments of wheeze, spirometry, and symptom scores (20). However, there is limited information available on the degree of correlation, or how relevant it might be to clinical practice.
The VRI device operates in a different manner to the other devices considered in this report, and produces an output in the form of a grayscale image, which must be interpreted by a trained assessor. This requirement, combined with the large number of sensors required, may make this device impractical for primary care use. Studies of simulated data have shown inter-rater reliability of 94% (21), and qualitative assessments of the VRI images indicate that different disease processes may lead to identifiable changes in the output (22,23). Use of the device by trained assessors to differentiate between ?normal? (healthy) and ?abnormal? (pneumonia or pleural effusion) results showed a sensitivity of 82.5%, rising to 90% if additional clinical information was provided (24). Use by a trained assessor also produced 77% accuracy in differentiating patients with COPD and asthma based on images taken before and after bronchodilator therapy (25). Automated detection of wheeze using the device showed 83% agreement with expert opinion (26).
One study reported use of the LSA-2000 to identify interstitial pneumonia in adults. Although a number of automated measures showed significant differences between patients and healthy controls, these were consistently outperformed by identification of crackles using manual auscultation, which resulted in higher areas under the ROC curve (27).
One case-control study assessed an ?acoustic pneumonia score?, using the frequency of rhonchi and crackles detected using the Multichannel STG. A score of greater than six was shown to have a sensitivity of 78% and a specificity of 88% for radiographic evidence of pneumonia in hospitalised patients (28). However, the size and complexity of this device means that it is unlikely to be more practical or cost-effective than radiography.
Impact compared to existing technology
Use of overnight Pulmotrack measurement of a ?nocturnal wheeze index? in asthmatic children showed that it could be used to assess response to treatment with montelukast, and correlated with both FEV1 and bronchial provocation test results (29). Use of the Wheezometer device in the community has been reported to show a non-linear relationship between %Wz and both FEV1 and symptom scores, potentially allowing this technology to provide patients with an objective measure of wheeze severity (20).
Guidelines and Recommendations
The current British Guidelines on the Management of Asthma (1) recognise the lack of a gold standard for the diagnosis of asthma. In children, it is recommended that diagnosis focuses on the clinical history and examination, as well as consideration of alternative diagnoses. Where diagnosis is uncertain, testing the response to therapeutic agents, and lung function testing such as spirometry or bronchial provocation testing are recommended. In adults, spirometry is recommended as an initial test to assess the presence and severity of airflow restriction, in addition to the clinical history and examination, followed by a trial of therapeutic agents (1).
Peak flow measurement, spirometry, and symptom reporting are all recognised as methods by which the response to treatment may be assessed (1). In primary care, it is recommended that asthma is monitored using symptom and exacerbation questionnaires, and lung function testing by spirometry or peak flow measurement (1). It is recommended that asthma patients, particularly those with severe asthma, should have a written action plan and their own peak flow meter to enable them to appropriately adjust medication doses, and seek medical help in the event of an exacerbation (1). Peak flow measurement is also recommended for diagnosis of the onset, severity, and resolution of acute asthma in primary and secondary care settings, and for the diagnosis of occupational asthma in adults (1).
Cost-effectiveness and economic impact:
There is some evidence that lung sound analysis is comparable to manual auscultation by clinicians in detecting wheeze. As stethoscopes are cheap, any benefit of automated wheeze detection is likely to be limited to situations where a trained clinician is not available, such as confirming patient-reported wheezing episodes. However, with the possible exception of the Wheezometer device, which has limited evidence for its use, the existing technology is not suited to these settings, as the equipment is typically large and complex, and is likely to be too expensive for cost-effective use.
Research Questions:
The evidence for the use of lung sound analysis in the diagnosis of asthma is limited, although it may be of assistance in gauging response to treatment or as an alternative to spirometry in bronchial provocation testing, particularly where this is difficult to perform (e.g. young children). Clinical trials to assess the practicality and accuracy of acoustic measures as an alternative to existing diagnostic techniques are required for both paediatric and adult patient groups before this technology could be routinely adopted.
There is currently very little evidence to support the use of automated lung sound analysis in primary care or community settings. Further trials are required to assess the accuracy of automated home monitoring of wheeze, and to identify whether home monitoring of wheeze can be used to improve self-management, or provide early warning of deterioration. In such settings, it may not be appropriate or cost-effective to use some of the more complex multi-sensor devices such as the Multichannel STG or VRI, and so research should concentrate on the more practical devices.
A major difficulty in assessing the accuracy of devices for diagnosis and monitoring of asthma is the lack of a gold standard method. A comparison of the performance of both the device and clinicians, compared to spirometry or bronchial provocation testing may be an acceptable compromise for the assessment of diagnostic accuracy, whereas the ability to predict the need for rescue therapy may be a useful marker for accuracy in monitoring asthma.
Suggested next step:
The most promising technology for primary care use is likely to be a portable device such as the Wheezometer, which could be used by patients or carers to assess the severity of wheezing at home. The ability of this type of device to assist in self-management of asthma should be investigated. The technology should be compared with current home-monitoring techniques such as symptom scoring and peak flow measurement. As these are cheap and easy to administer, the acoustic monitoring would have to demonstrate significant improvements to be economically viable.
Expected outcomes:
Home monitoring of wheeze severity may be a useful adjunct to an asthma action plan, particularly for patients with limited communication ability such as young children or those with learning difficulties, where symptom scoring and peak flow measurement may be impractical. For use in this environment, the device should allow for storage of a number of readings. This is currently possible with the Wheezometer, which can store up to 10 readings, although this may not be sufficient for regular monitoring (e.g. when titrating a new treatment or to identify exacerbations), when multiple reading are likely to be required each day for a period of time.
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