Abstract
There is a lack of systematised information on respiratory sounds of healthy people. This impairs health professionals from differentiating respiratory sounds of healthy people from people with respiratory diseases, which may affect patients' diagnosis and treatment. Therefore, this systematic review aimed to characterise respiratory sounds of healthy people. The Web of knowledge, MEDLINE, EMBASE and SCOPUS databases were searched and studies using computerised analyses to detect/characterise respiratory sounds in healthy people were included. Data were extracted using a structured table-format. Sixteen cross-sectional studies assessing respiratory sounds in 964 subjects (aged 1 day-70 yrs) were included: 13 investigated normal respiratory sounds (frequency, intensity and amplitude) and 3 adventitious respiratory sounds (crackles and wheezes). The highest sound frequencies were observed at the trachea (inspiration: 447-1323 Hz; expiration: 206-540 Hz). Women (444-999 Hz) and infants (250-400 Hz) presented the highest frequencies at maximum power. Inspiratory sounds were more intense at the left posterior lower lobe (5.7-76.6 dB) and expiratory sounds at the trachea (45.4-85.1 dB). Nevertheless, studies establishing direct comparisons between inspiratory and expiratory sounds showed that inspiratory sounds presented the highest intensities (p < 0.001). Amplitude was higher at the left upper anterior chest (1.7 ± 0.8 V) and lower at the right posterior lower lobe (1.2 ± 0.7 V). Crackles were the adventitious respiratory sound most frequently reported. Respiratory sounds show different acoustic properties depending on subjects' characteristics, subjects' position, respiratory flow and place of recording. Further research with robust study designs, different populations and following the guidelines for computerised respiratory sound analysis are urgently needed to build evidence-base.
Highlights
The full-text of 29 potentially relevant articles was assessed and 27 articles were excluded due to the following reasons: i) did not assess computerised respiratory sounds (n Z 6); ii) did not included healthy people (n Z 9); iii) studies were conducted in animals (n Z 1); iv) were written in German (n Z 1); v) aimed to validate algorithms (n Z 5); vi) did not present quantitative data on respiratory sounds (n Z 1); and vii) analysed artificial respiratory sounds (n Z 4)
- Records were made from the chest wall over the right posterior lower lobe (RPLL) and from the trachea
Frequency at maximum power (Fmax) was studied in inspiratory and expiratory sounds at trachea, right upper anterior chest (RUAC), RPLL and left posterior lower lobe (LPLL)
Summary
The search for relevant articles within the reference list of the included and excluded papers by full-text analysis retrieved 14 additional studies. A total of 16 studies were included in this review (Fig. 1). Studies included in this review ranged from 1983 to 2008 and used cross-sectional methodologies. Respiratory sounds in healthy people healthy subjects (68% male) participated in the studies, 169 were smokers and 258 non-smokers. To analyse the sound data, studies applied different filters (50e2240 Hz), sample rates (4000e12,000 Hz) and Figure 1 PRISMA flow diagram of the included studies
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