Fig 1.
Flow chart of the proposed respiratory sound recording and CAS analysis approach.
BD, bronchodilator; CAS, continuous adventitious sounds; Q1-Q4, flow quartiles; RS, respiratory sounds; ΔCASGlob, change in the number of CAS after bronchodilation.
Fig 2.
Respiratory sounds and flows recorded during the performance of a progressive maneuver at baseline.
Segmented respiratory phases are highlighted in black (inspiration) and dark grey (expiration). Q1-Q4 labels indicate the flow quartile assigned to each respiratory phase.
Fig 3.
Segmentation of acoustic components from the Hilbert spectrum.
For each subfigure: flow and respiratory sound signals of a respiratory cycle (top), the Hilbert spectrum of the respiratory sound signal (middle), and the acoustic components segmented using our acoustic component segmentation method [34] (bottom). In the Hilbert spectrums, CAS areas are plotted in green, and normal areas are plotted in red. A) Two inspiratory CAS components occurring at different times (multiple monophonic CAS). B) A single expiratory CAS component. C) D) Inspiratory CAS components overlapping in time (polyphonic CAS). Subfigures B, C, and D also show some low-pitched non-CAS components that correspond to normal respiratory sounds but are similar to CAS components, and therefore are segmented by our acoustic component segmentation method.
Fig 4.
Background noises from the clinical environment.
Four examples of respiratory cycles containing background noises, including talking (A), footsteps (B), banging (C), and furniture dragging (D), from the clinical environment. These sounds appear in the Hilbert spectrum as high-pitched (above 200 Hz) acoustic components with a certain degree of temporal and frequency continuity, similar to CAS components.
Fig 5.
Features of the classification dataset.
In all subfigures, each circle represents an acoustic component of the classification dataset. Subfigures A and B show the duration (D), mean frequency (FMean), and intensity (I) of CAS and non-CAS components, respectively. Subfigures C and D show the standard deviation frequency (σF), mean point-by-point σF (), and type of analysis area of CAS and non-CAS components, respectively.
Table 1.
Anthropometric and spirometry data of the study subjects.
Table 2.
Performance of the acoustic component classifier.
Fig 6.
Number of CAS of the three groups of subjects.
Box plot distributions of the number of CAS at baseline (#CASGlobPre-BD) and after bronchodilator administration (#CASGlobPost-BD) for the flow quartiles (Q1-Q4) and the total flow range of controls (A), BDR- patients (B), and BDR+ patients (C). Circles within boxes = medians, boxes = interquartile ranges. Comparisons between #CASGlobPre-BD and #CASGlobPost-BD in the total flow range of BDR- and BDR+ groups were made using Wilcoxon rank sum tests. Significant differences (p<0.05) are indicated with an asterisk.
Fig 7.
Individual change in the number of CAS after bronchodilator administration.
A) Number of CAS at baseline (#CASGlobPre-BD) and change in the number of CAS (ΔCASGlob) of each study subject. The dashed line is the line of equality (ΔCASGlob = #CASGlobPre-BD). That is, points on the line corresponded to subjects whose CAS completely disappeared after bronchodilation. Points under the line corresponded to subjects whose number of CAS was partially reduced after bronchodilation. Points above the line corresponded to subjects whose number of CAS increased after bronchodilation. B) ΔFEV1 and nΔCASGlob of BDR- patients whose #CASGlobPre-BD was >5% (white points to the right of the red dashed line in A). Points in A and B corresponding to the same subject have been labelled with the same Roman numeral. As in A, the dashed line in B represents ΔCASGlob = #CASGlobPre-BD, which means nΔCASGlob = 100% (see Eq 6). Pink area: 0%<nΔCASGlob<33%, purple area: 33%<nΔCASGlob<66%, blue area: 66%<nΔCASGlob.
Fig 8.
Population change in the number of CAS after bronchodilator administration.
Boxplot distribution of the population change in the number of CAS. Circles within boxes = medians, boxes = interquartile ranges, whiskers = 1.5*interquartile ranges. Pink area = low response (L1), purple area = medium response (L2), blue area = high response (L3).
Fig 9.
Change in the number of CAS (nΔCASGlob) (A). Pink area = low response (L1), purple area = medium response (L2), blue area = high response (L3). Boxplot distributions of the mean frequency (FMean) (B), duration (D) (C), and intensity (I) (D) of CAS at baseline (GlobPre-BD) from BDR+ patients (79 CAS components from 5 patients), BDR- patients with a high response (147 CAS components from 6 patients), and BDR- patients with a medium response (59 CAS components from 4 patients). CAS features after bronchodilator administration (GlobPost-BD) are also shown for the BDR- L2 group, since these patients still had an appreciable number of CAS after bronchodilator (27 CAS components from 4 patients). Circles within boxes = medians, boxes = interquartile ranges, whiskers = 1.5*interquartile ranges. Significant differences (p<0.05) are indicated with an asterisk.