Lung sound analysis helps localize airway inflammation in patients with bronchial asthma

Figures & data

Figure 1 (A) Seven lung sound recording positions; (B) lung sound analysis sonograms.

Notes: The upper panel represents an airflow curve. The portions below and above the horizontal central line represent the inhalation and exhalation air flows, respectively. The vertical axis represents frequency (in hertz), and the horizontal axis represents time (in seconds). The colors indicate different sound pressure levels (in decibels [dB_SPL]).
Abbreviation: Ch, channel.

Table 1 Patient characteristics

Characteristics	Healthy volunteers (n=20)	Asthmatic subjects (n=22)
Age, years	49.4±7.4	39.5±14.0*
BMI, kg/m^2	23.8±3.7	21.5±2.6
Male/female, n	20/0	7/15**
Asthma duration, years	–	5.1±10.4
Atopic/nonatopic, n	–	17/5
Smoking status: non/ex/current, n	–	15/5/0
Smoking amount, pack-years	–	3.1±7.3
IgE, IU/mL	–	698±793
FeNO level, ppb	–	90±83
<38 ppb, n	–	7
38–69 ppb, n	–	5
≥70 ppb, n	–	10
PC20, μg/mL	–	1504±2116
logPC20	–	2.78±0.63
FEV1.0/FVC%, %	–	78.3±8.7
FEV1.0%pred, %	–	94.8±13.6
V50%pred, %	–	72.9±26.8
V25%pred, %	–	55.4±26.5

Notes: The values are presented as number or mean ± standard deviation;

** p<0.001,

* p<0.01. “Atopic” is defined as a patient having ≥1 allergen or an IgE-RAST score ≥2.

Abbreviations: BMI, body mass index; FeNO, fractional exhaled nitric oxide concentration; FEV_1.0, forced expiratory volume in 1 second; FVC, forced vital capacity; IgE, immunoglobulin E; PC₂₀, a provocative concentration of acetylcholine causing a 20% decrease in FEV₁; %pred, % predicted; RAST, radioallergosorbent testing; V₅₀, V_25.

Figure 2 E/I values in each frequency band in asthmatic subjects and healthy volunteers.

Notes: The vertical axis represents E/I values, and the horizontal axis denotes frequency bands (in hertz). The medians of E/I in individual frequency bands are plotted separately for patients with V₅₀%pred <80%, asthmatic subjects with V₅₀%pred ≥80%, and healthy volunteers.
Abbreviations: E/I, expiration-to-inspiration sound pressure ratio; %pred, %predicted; Ch, channel.

Table 2 Comparison of E/I values in each frequency band between asthmatic subjects and healthy volunteers

Frequency band (Hz)	Recording location		Healthy volunteers (n=20)	Asthmatic subjects
				%V50≥80% (n=10)	%V50<80% (n=12)
			Med (25%, 75%)	Med (25%, 75%)	Med (25%, 75%)
20–50	Ch 1: anterior chest	Right	0.76 (0.67, 0.83)	0.88 (0.86, 0.91)*	0.99 (0.89, 1.06)**
	Ch 2	Left	0.79 (0.68, 0.82)	0.96 (0.82, 1.01)*	1.00 (0.91, 1.08)**
	Ch 3: posterior upper	Right	0.85 (0.73, 0.92)	0.87 (0.80, 0.91)	0.87 (0.79, 1.01)
	Ch 4	Left	0.79 (0.70, 0.90)	0.89 (0.82, 0.98)	0.93 (0.81, 1.10)***
	Ch 5: posterior lower	Right	0.85 (0.74, 1.00)	0.89 (0.82, 1.00)	0.98 (0.93, 1.04)***
	Ch 6	Left	0.85 (0.75, 0.94)	0.91 (0.87, 1.01)	1.08 (0.94, 1.18)*
	Ch 7: trachea	–	0.72 (0.69, 0.82)	0.81 (0.67, 0.99)	0.83 (0.73, 0.91)
50–100	Ch 1: anterior chest	Right	0.61 (0.54, 0.68)	0.76 (0.66, 0.90)***	0.87 (0.79, 1.03)**
	Ch 2	Left	0.62 (0.54, 0.65)	0.71 (0.61, 0.85)***	0.91 (0.83, 0.94)**
	Ch 3: posterior upper	Right	0.75 (0.55, 0.81)	0.81 (0.74, 0.92)	0.95 (0.72, 1.06)***
	Ch 4	Left	0.69 (0.62, 0.85)	0.76 (0.67, 0.93)	0.95 (0.83, 1.06)*
	Ch 5: posterior lower	Right	0.66 (0.56, 0.86)	0.79 (0.66, 0.99)	0.96 (0.88, 1.07)**
	Ch 6	Left	0.66 (0.55, 0.80)	0.73 (0.67, 1.01)	0.99 (0.85, 1.17)**
	Ch 7: trachea	–	0.64 (0.49, 0.76)	0.77 (0.61, 0.88)	0.86 (0.77, 0.89)*
100–200	Ch 1: anterior chest	Right	0.45 (0.35, 0.56)	0.63 (0.52, 0.70)***	0.77 (0.70, 0.87)**,#
	Ch 2	Left	0.42 (0.37, 0.46)	0.39 (0.37, 0.60)	0.68 (0.63, 0.74)**,#
	Ch 3: posterior upper	Right	0.54 (0.44, 0.65)	0.65 (0.57, 0.94)	0.85 (0.63, 0.98)***
	Ch 4	Left	0.52 (0.39, 0.59)	0.45 (0.39, 0.70)	0.75 (0.62, 0.89)**,#
	Ch 5: posterior lower	Right	0.47 (0.40, 0.68)	0.60 (0.45, 0.70)	0.75 (0.63, 0.93)*
	Ch 6	Left	0.45 (0.36, 0.56)	0.47 (0.40, 0.59)	0.73 (0.67, 0.87)**,##
	Ch 7: trachea	–	0.61 (0.48, 0.73)	0.81 (0.69, 1.04)	0.93 (0.67, 1.16)***
200–400	Ch 1: anterior chest	Right	0.45 (0.32, 0.53)	0.57 (0.43, 0.60)	0.70 (0.63, 0.85)**,##
	Ch 2	Left	0.37 (0.33, 0.46)	0.40 (0.28, 0.59)	0.66 (0.57, 0.76)**,#
	Ch 3: posterior upper	Right	0.38 (0.35, 0.50)	0.53 (0.39, 0.68)	0.66 (0.57, 0.78)**
	Ch 4	Left	0.43 (0.30, 0.54)	0.38 (0.27, 0.48)	0.67 (0.51, 0.79)**,#
	Ch 5: posterior lower	Right	0.31 (0.23, 0.43)	0.37 (0.32, 0.52)	0.59 (0.47, 0.68)**
	Ch 6	Left	0.37 (0.26, 0.46)	0.36 (0.32, 0.56)	0.69 (0.49, 0.72)**,#
	Ch 7: trachea	–	0.83 (0.63, 0.94)	0.98 (0.68, 1.30)	1.03 (0.78, 1.27)
400–800	Ch 1: anterior chest	Right	0.61 (0.45, 0.76)	0.63 (0.50, 0.78)	0.69 (0.67, 0.83)
	Ch 2	Left	0.52 (0.39, 0.67)	0.71 (0.38, 0.82)	0.59 (0.50, 0.94)
	Ch 3: posterior upper	Right	0.58 (0.42, 0.79)	0.58 (0.51, 0.73)	0.71 (0.58, 0.79)
	Ch 4	Left	0.53 (0.39, 0.75)	0.55 (0.38, 0.59)	0.66 (0.57, 0.75)
	Ch 5: posterior lower	Right	0.52 (0.31, 0.69)	0.54 (0.31, 0.68)	0.68 (0.46, 0.86)
	Ch 6	Left	0.55 (0.41, 0.70)	0.55 (0.41, 0.79)	0.69 (0.53, 0.78)
	Ch 7: trachea	–	0.98 (0.77, 1.17)	1.20 (0.77, 1.61)	1.17 (0.88, 1.64)

Notes: p-values vs healthy volunteers:

*** p<0.001,

** p<0.01,

* p<0.05; p-values vs %V₅₀≥80% asthmatic subjects:

# p<0.05,

## p<0.01. Ch 1, right anterior chest; Ch 2, left anterior chest; Ch 3, right posterior upper; Ch 4, left posterior upper; Ch 5, right posterior lower; Ch 6, left posterior lower; Ch 7, trachea.

Abbreviations: Ch, channel; Med, median; E/I, expiration-to-inspiration sound pressure ratio.

Table 3 Correlation of E/I, E_SPL, and I_SPL values with spirometry, PC₂₀, and FeNO data in each frequency band (n=22)

Recording location	Parameters	Expiration/inspiration (E/I)						Expiration sound pressure level (ESPL)						Inspiration sound pressure level (ISPL)
		100−200 Hz		200−400 Hz		400−800 Hz		100−200 Hz		200−400 Hz		400−800 Hz		100−200 Hz		200−400 Hz		400−800 Hz
		r	p-Value	r	p-Value	r	p-Value	r	p-Value	r	p-Value	r	p-Value	r	p-Value	r	p-Value	r	p-Value
Ch 1	FEV1.0/FVC	−0.49	0.025	−0.50	0.021	−0.30	0.19	0.01	0.97	0.11	0.63	0.04	0.88	0.17	0.45	0.14	0.55	0.11	0.65
	FEV1.0%pred	−0.47	0.032	−0.39	0.08	−0.09	0.70	0.19	0.41	0.08	0.73	−0.11	0.64	0.22	0.33	0.09	0.69	−0.01	0.96
	V50%pred	−0.54	0.011	−0.63	0.002	−0.26	0.26	0.14	0.55	0.14	0.54	0.01	0.98	0.23	0.31	0.17	0.47	0.09	0.69
	V25%pred	−0.41	0.06	−0.46	0.034	−0.20	0.38	0.11	0.64	0.07	0.78	−0.01	0.98	0.11	0.64	0.05	0.82	0.04	0.86
	logPC20	−0.53	0.021	−0.37	0.11	−0.02	0.95	−0.06	0.81	0.07	0.77	0.08	0.75	0.22	0.36	0.25	0.30	0.15	0.54
	FeNO	0.41	0.06	0.42	0.06	0.07	0.76	0.09	0.69	−0.04	0.87	−0.26	0.25	−0.15	0.51	−0.21	0.36	−0.23	0.31
Ch 2	FEV1.0/FVC	−0.38	0.09	−0.55	0.010	−0.15	0.51	−0.09	0.70	−0.02	0.92	−0.08	0.72	0.27	0.24	0.28	0.21	0.09	0.71
	FEV1.0%pred	−0.12	0.59	−0.46	0.035	−0.02	0.93	0.32	0.16	0.11	0.63	−0.07	0.75	0.31	0.17	0.19	0.41	−0.01	0.97
	V50%pred	−0.47	0.03	−0.71	0.0003	−0.18	0.43	0.09	0.69	0.07	0.76	−0.04	0.87	0.39	0.08	0.37	0.10	0.18	0.45
	V25%pred	−0.32	0.16	−0.55	0.010	−0.10	0.68	0.10	0.65	0.11	0.64	0.01	0.97	0.23	0.32	0.24	0.29	0.19	0.40
	logPC20	−0.23	0.35	−0.56	0.013	−0.33	0.17	−0.03	0.90	−0.02	0.93	−0.16	0.51	0.31	0.19	0.34	0.15	0.20	0.41
	FeNO	0.34	0.14	0.46	0.036	0.08	0.73	0.24	0.29	0.12	0.60	0.06	0.80	−0.19	0.40	−0.27	0.24	−0.16	0.47
Ch 3	FEV1.0/FVC	−0.24	0.29	−0.42	0.054	−0.35	0.11	−0.06	0.79	−0.11	0.63	−0.17	0.46	0.12	0.59	0.10	0.67	−0.10	0.67
	FEV1.0%pred	0.16	0.49	−0.02	0.94	0.02	0.95	0.24	0.29	−0.05	0.84	−0.06	0.80	0.01	0.95	−0.11	0.64	−0.16	0.48
	V50%pred	−0.05	0.84	−0.26	0.24	−0.17	0.44	0.14	0.54	−0.02	0.93	−0.07	0.75	0.11	0.62	0.07	0.77	−0.09	0.68
	V25%pred	−0.15	0.51	−0.30	0.17	−0.27	0.22	0.18	0.41	0.05	0.81	0.02	0.93	0.17	0.46	0.11	0.63	0.03	0.91
	logPC20	−0.31	0.19	−0.24	0.31	−0.11	0.65	0.00	1.00	0.12	0.61	0.25	0.29	0.28	0.23	0.25	0.30	0.26	0.27
	FeNO	0.28	0.21	0.21	0.36	0.13	0.57	0.27	0.22	0.05	0.82	−0.02	0.92	−0.06	0.78	−0.15	0.52	−0.05	0.81
Ch 4	FEV1.0/FVC	−0.43	0.046	−0.50	0.018	−0.39	0.077	0.09	0.70	0.00	0.98	−0.12	0.59	0.44	0.042	0.25	0.26	0.03	0.89
	FEV1.0%pred	−0.16	0.46	−0.23	0.30	−0.23	0.31	0.26	0.24	−0.08	0.71	−0.16	0.49	0.20	0.38	−0.05	0.81	−0.06	0.80
	V50%pred	−0.37	0.10	−0.50	0.017	−0.41	0.062	0.24	0.28	0.08	0.74	0.01	0.96	0.42	0.05	0.22	0.32	0.15	0.52
	V25%pred	−0.36	0.10	−0.47	0.026	−0.45	0.038	0.27	0.23	0.16	0.48	−0.02	0.91	0.40	0.07	0.24	0.29	0.09	0.70
	logPC20	−0.14	0.56	−0.32	0.17	−0.32	0.17	0.07	0.77	0.30	0.20	0.25	0.29	0.36	0.11	0.49	0.030	0.39	0.087
	FeNO	0.50	0.018	0.49	0.020	0.37	0.094	0.10	0.65	−0.25	0.26	−0.33	0.13	−0.47	0.029	−0.59	0.004	−0.48	0.023
Ch 5	FEV1.0/FVC	−0.51	0.014	−0.63	0.002	−0.48	0.03	−0.11	0.62	−0.13	0.56	−0.20	0.37	0.24	0.28	0.23	0.29	−0.01	0.95
	FEV1.0%pred	−0.06	0.79	−0.18	0.42	−0.29	0.18	0.25	0.25	0.23	0.29	0.01	0.96	0.19	0.39	0.20	0.37	0.17	0.44
	V50%pred	−0.32	0.15	−0.52	0.014	−0.41	0.06	0.18	0.42	0.16	0.48	−0.01	0.96	0.44	0.041	0.39	0.07	0.17	0.44
	V25%pred	−0.31	0.15	−0.55	0.008	−0.55	0.01	0.14	0.53	0.06	0.78	−0.16	0.46	0.34	0.12	0.32	0.15	0.14	0.52
	logPC20	−0.49	0.030	−0.27	0.25	−0.34	0.15	0.05	0.82	0.09	0.71	0.17	0.48	0.38	0.10	0.34	0.14	0.25	0.28
	FeNO	0.54	0.010	0.23	0.30	0.06	0.80	0.27	0.22	0.16	0.47	−0.10	0.67	−0.07	0.76	−0.05	0.81	−0.01	0.95
Ch 6	FEV1.0/FVC	−0.62	0.002	−0.58	0.005	−0.36	0.10	−0.14	0.53	−0.06	0.80	−0.07	0.75	0.25	0.26	0.19	0.39	0.06	0.78
	FEV1.0%pred	−0.27	0.23	−0.33	0.13	−0.27	0.23	0.19	0.38	0.20	0.38	0.00	1.00	0.25	0.27	0.24	0.29	0.15	0.51
	V50%pred	−0.57	0.006	−0.57	0.006	−0.30	0.17	0.02	0.92	0.06	0.80	0.00	0.99	0.33	0.13	0.25	0.27	0.11	0.61
	V25%pred	−0.52	0.013	−0.56	0.007	−0.44	0.04	0.09	0.69	0.07	0.75	−0.07	0.77	0.22	0.32	0.14	0.53	0.09	0.71
	logPC20	−0.30	0.20	−0.45	0.049	−0.27	0.26	0.08	0.74	0.11	0.64	0.17	0.48	0.33	0.16	0.37	0.11	0.26	0.27
	FeNO	0.49	0.021	0.46	0.032	0.05	0.83	0.30	0.17	0.13	0.56	−0.10	0.65	−0.13	0.56	−0.15	0.51	−0.06	0.77
Ch 7	FEV1.0/FVC	0.01	0.97	−0.04	0.87	−0.18	0.42	−0.29	0.19	−0.19	0.41	−0.28	0.21	−0.19	0.40	−0.15	0.49	−0.17	0.46
	FEV1.0%pred	−0.19	0.41	−0.12	0.60	0.09	0.68	0.32	0.15	0.25	0.26	0.14	0.55	0.43	0.047	0.37	0.094	0.33	0.13
	V50%pred	0.01	0.98	−0.01	0.96	−0.03	0.88	0.04	0.85	0.10	0.67	−0.02	0.92	0.15	0.52	0.17	0.45	0.15	0.51
	V25%pred	0.00	0.99	−0.06	0.80	−0.12	0.59	−0.12	0.61	−0.12	0.60	−0.25	0.27	−0.04	0.85	−0.03	0.90	−0.07	0.76
	logPC20	−0.20	0.40	−0.21	0.37	−0.16	0.51	−0.04	0.87	−0.04	0.86	0.08	0.75	0.06	0.80	0.05	0.82	0.10	0.68
	FeNO	0.17	0.46	0.18	0.43	0.28	0.21	0.36	0.10	0.18	0.43	0.13	0.56	0.22	0.32	0.20	0.37	0.16	0.49

Notes: Ch 1, right anterior chest; Ch 2, left anterior chest; Ch 3, right posterior upper; Ch 4, left posterior upper; Ch 5, right posterior lower; Ch 6, left posterior lower; Ch 7, trachea.

Abbreviations: %pred, %predicted; E/I, expiration-to-inspiration sound pressure ratio; E_SPL, expiration sound pressure level; I_SPL, inspiration sound pressure level; PC₂₀, provocative concentration of acetylcholine causing a 20% decrease in FEV_1.0; FeNO, fractional exhaled nitric oxide concentration; FEV_1.0, forced expiratory volume in 1 second; FVC, forced vital capacity.

Table 4 Differences in E/I MF among recording points in asthmatic subjects

ROC		Anterior chest		Posterior upper		Posterior lower
		Right	Left	Right	Left	Right	Left
AUC		0.82	0.77	0.81	0.67	0.76	0.75	–
(Sensitivity, specificity)		(0.81, 0.70)	(0.73, 0.75)	(0.82, 0.80)	(0.59, 0.65)	(0.64, 0.75)	(0.68, 0.70)	–
Cutoff		0.51	0.50	0.50	0.50	0.40	0.47	–
FeNO	Subject number							V50%pred <80%
<38 ppb	1	0.57	0.30	0.94	0.27	0.60	0.37	–
	2	0.73	0.71	0.79	0.84	0.60	0.58	Yes
	3	0.58	0.58	0.51	0.42	0.38	0.54	–
	4	0.43	0.20	0.35	0.27	0.22	0.29	–
	5	0.41	0.43	0.54	0.44	0.50	0.61	–
	6	0.61	0.51	0.58	0.55	0.39	0.44	Yes
	7	0.50	0.31	0.32	0.32	0.25	0.35	–
38–69 ppb	8	0.71	0.94	0.66	0.71	0.95	0.69	Yes
	9	0.44	0.23	0.48	0.22	0.35	0.25	–
	10	0.63	0.37	0.40	0.45	0.34	0.35	–
	11	0.67	0.59	0.56	0.51	0.67	0.69	Yes
	12	0.63	ND	0.59	0.34	0.34	0.33	–
≥70 ppb	13	ND	0.61	1.05	0.86	0.87	0.69	Yes
	14	0.62	0.56	0.66	0.44	0.46	0.47	Yes
	15	1.26	0.89	0.93	0.75	0.55	0.55	Yes
	16	0.70	0.78	0.50	0.50	0.37	0.33	Yes
	17	0.72	0.66	0.62	0.53	0.59	0.72	Yes
	18	0.89	0.68	0.70	0.81	0.70	0.78	Yes
	19	0.53	0.46	0.51	0.64	0.58	0.69	Yes
	20	0.91	0.66	0.77	0.71	0.49	0.69	Yes
	21	0.68	0.66	0.78	0.85	0.69	0.84	Yes
	22	0.58	0.55	0.59	0.59	0.40	0.48	–

Note: Bold values are greater than the cutoff value.

Abbreviations: %pred, %predicted; ROC, receiver operating characteristic; AUC, area under the curve; E/I, expiration-to-inspiration sound pressure ratio; MF, mid frequency; FeNO, fractional exhaled nitric oxide concentration; ND, not done.