New Technique to Analyze the Breath Sound Spectrum in Children with Asthma.

OBJECTIVE: Breath sound parameters have been reported as useful biomarkers for evaluating the airway condition. METHODS: The reliability of breath sound analysis using an improved method was investigated. Eighty-three asthmatic children were included in the present study. After adjusting the 0 level based on the background noises of the breath sound spectrum, the total area under the curve of the dBm (AT), the roll-off from 600-1200 Hz (Slope), the ratio of the third and fourth area to the AT (A3/AT and B4/AT), and the ratio of power and frequency at 50% and 75% of the highest frequency (RPF75 and RPF50), were evaluated before and after ß2 agonist inhalation. Spirography and the forced oscillation technique were also used to evaluate all subjects. RESULTS: Using the new method, A3/AT, B4/AT, RPF75 and RPF50, were significantly increased after ß2 agonist inhalation. The increase in A3/AT and B4/AT were significantly correlated with the increase in FEV1 and FEE25-75, and the increase in RPF75 was reversibly correlated with that in R5-R20. CONCLUSIONS: The spectrum curve indices using the adjusted 0 level can indicate bronchial dilation with ß2 agonist inhalation. These parameters may be useful for the assessment of bronchial reversibility in asthmatic children.

[EFFECT OF INSPIRATORY FLOW ON BREATH SOUND ANALYSIS IN CHILDREN WITH ASTHMA].

BACKGROUND: In order to determine the optimal breathing method for childhood lung sound analyses, it is important to study the effect of airflow on the parameters of lung sounds. METHODS: Sixty-one well-controlled children with atopic asthma (median; 12 years) participated. After confirming that there was no wheezing or respiratory symptoms, the lung sound spectrums of the inspiratory flow before and after inhalation of a ß2 stimulant were analyzed. At the same time, their lung function was measured by a spirogram and the forced oscillation technique. RESULTS: Before ß2 agonist inhalation, the area under the entire curve (AT) and 99% frequency (F99) in the lung sound of inspiratory flow around 2.0L/s due to slightly strong breathing were significantly higher than the lung sound of inspiratory flow around 1.0L/s due to rest breathing. However, no marked differences were observed in the lung sound parameters based on the lung sound spectrum. The improvement in the lung sound parameters after ß2 agonist inhalation was clearer at an inspiratory flow around 1.0L/s than that around 2.0L/s. CONCLUSION: The present study showed that changes after ß2 agonist inhalation and the correlation with the lung function parameters were clear during resting breathing. This method may be used for the long-term montoring of children with asthma.

Differences in Virus Detection and Cytokine Profiles between First Wheeze and Childhood Asthma.

OBJECTIVE: To distinguish between first wheeze and asthma in early childhood, we investigated respiratory viruses and cytokine/chemokine profiles among patients with first wheeze and established asthma. METHODS: We enrolled children with acute exacerbations of wheezing (17 first wheeze and 32 asthma) and 11 controls (no wheezing) aged between 10 months and 6 years. Nasal aspirates were obtained, and virus detection was performed with antigenic assay kits and/or RT-PCR. Serum 27 cytokines/chemokines were assayed by a multi-cytokine detection system. RESULTS: Rhinovirus and respiratory syncytial (RS) virus were dominant in acute exacerbations of asthma. However, many types of viruses were isolated in first wheeze. Serum IL-8 and IL-12 values were significantly higher in first wheeze than in acute asthma or the controls. IL-5 and IP-10 levels in acute asthma and first wheeze cases were higher than in the controls. Both of them were significantly higher in cases of acute asthma than in convalescence stage of asthma cases. Only IP-10 was significantly higher in first wheeze than in convalescence stage of first wheeze cases. CONCLUSIONS: Different profiles in virus detection and production of IL-8 and IL-12 might distinguish between first wheeze and childhood asthma.

A Lung Sound Analysis in Infants with Risk Factors for Asthma During Acute Respiratory Infection.

Background: The parameters of lung sounds have been suggested as biomarkers of airway changes. Using a commercially available lung sound analyzer, we investigated the characteristics of the lung sounds in infants with acute respiratory infection (ARI). Methods: Infants with ARI who were 6 to 18 months of age were included in this study. The lung sound parameters, the ratio of the third area and fourth areas to the total area under the curve of the sound spectrum (A3/AT and B4/AT), and the ratio of power and frequency at 75% and 50% of the highest frequency of the power spectrum (RPF75 and RPF50) were evaluated. With an original Japanese questionnaire based on American Thoracic Society-Division of Lung Disease, the risk factors of asthma development in infants were examined. Results: One hundred ten infants with ARI and 248 infants in good health for comparison were included. All infants were completely analyzed, and then divided into 2 age groups for a stratification analysis (6-12 and 13-18 months). In the overall analysis, among infants with a history of wheezing, recurrent wheezing, allergy, and atopic dermatitis, the values of RPF50 of infants with ARI were significantly lower compared with those without ARI. In the 6- to 12-month-old group, the RPF50 values of atopy-positive infants with ARI were lower compared with those without ARI (P = 0.003). Conclusions: The lung sounds of the infants with asthma-developing risk factors were more affected by ARI than those of infants without risk factors. Analyzing the changes in the lung sounds induced by ARI may be useful for evaluating the characteristics of the airways in infants.

The Suppressive Role of Streptococcus pneumoniae Colonization in Acute Exacerbations of Childhood Bronchial Asthma.

INTRODUCTION: Little is known about the association between bacterial infections and exacerbations of bronchial asthma. OBJECTIVE: To elucidate the effect of bacterial infections on bronchial asthma, we examined pharyngeal bacterial colonization, duration of wheezing, and serum levels of cytokines and chemokines during acute exacerbations of asthma in children. METHODS: Potential bacterial pathogens were investigated in pharyngeal samples and viruses obtained from nasal secretions of 111 children who were outpatients and/or in patients with acute exacerbations of asthma (mean/median age: 2.8/2.6, respectively). We also measured serum levels of 27 different cytokines/chemokines. RESULTS: Pharyngeal bacterial cultures were positive in 110 of 111 children. The 3 major bacterial pathogens were Streptococcus pneumoniae (29.7%), Moraxella catarrhalis (11.7%), and Haemophilus influenzae (10.8%). M. catarrhalis was detected more frequently in patients with pneumonia. Furthermore, patients with S. pneumoniae colonization had significantly shorter wheezing episodes than those without it. In contrast, the duration of wheezing did not differ significantly among cases with other bacteria such as M. catarrhalis and H. influenzae. Furthermore, the length of wheezing episode in patients with S. pneumoniae colonization showed significant inverse correlation with peripheral white blood cell count, neutrophil count, and C-reactive protein, while there was no significant correlation between duration of wheezing and these 3 parameters among patients with M. catarrhalis or H. influenza. Among the 27 cytokines/chemokines, only serum tumor necrosis factor (TNF)-α was significantly lower in patients with S. pneumoniae colonization than in those without it. CONCLUSIONS: These results suggested that pharyngeal S. pneumoniae colonization plays a suppressive role on the pathophysiology during acute exacerbations of asthma.

The Evaluation of Changes in the Breath Sound Spectrum with Bronchoconstriction and Bronchodilatation in Asthmatic Children.

OBJECTIVE: Focusing on the relative-middle sound area of the breath sound spectrum, the relationship between airway changes and breath sounds in asthmatic children was investigated. METHODS: In Study 1, 77 children (6-16 years old) were included. The breath sound parameters, the ratio of the second area to the third area of the power spectrum (A2/A3) and the ratio of the third area to the fourth area (B3/B4) were evaluated 3 times, before and just after methacholine inhalation and after ß2 agonist inhalation. Other breath sound parameters, the frequency limiting 99% of the power spectrum (F99), the rolloff from 600-1200 Hz (Slope) and the ratio of the third and fourth area to the total area under the curve (A3/AT and B4/AT), and the ratio of power and frequency at 50% and 75% of the highest frequency of the power spectrum (RPF75 and RPF50), were also evaluated. In Study 2, 91 children (6-16 years old) were included, with evaluations performed twice: before and after ß2 a gonist inhalation. Spirography a nd forced o scillation technique were also performed. RESULTS: In Study 1, A2/A3 and B3/B4 were significantly increased after methacholine inhalation and decreased after ß2 agonist inhalation (p < 0.001, P < 0.001, respectively). In Study 2, A2/A3 and B3/B4 were significantly decreased after ß2 agonist inhalation. These changes in A3/AT and B4/AT were the inverse of those in other spectrum curve indices. CONCLUSIONS: A2/A3 and B3/B4, indicate the breath sound changes after bronchoconstriction and bronchodilatation. These parameters may be useful for assessing bronchial reversibility in asthmatic children.

Objective evaluation of wheezing in normal infants.

BACKGROUND: To evaluate the frequency of wheezing in infants, the presence of wheezing was examined in normal infants using a breath sound analyzer, METHODS: A total of 443 infants (age range, 3-24 months) were included in the present study. The existence of audible wheezing and faint wheezing/inaudible wheezing-like noises (FW) was confirmed on chest auscultation and a sound spectrogram. The breath sound parameters of the sound spectrum, frequency limiting 99% of power spectrum (F99 ), roll-off from 600 to 1,200 Hz (slope) and spectrum curve indices, total area under the curve of dB data (A3 /AT and B4 /AT ), and ratio of power and frequency at 50% and 75% of the highest frequency of the power spectrum (RPF50 and RPF75 ) were calculated. Using an original Japanese questionnaire, we examined the characteristics of the airway condition of all infants. RESULTS: Finally, a total of 398 infants were analyzed in the present study, and 283 were in good health while 115 had acute respiratory infection (ARI) in the last 7 days. No infants had audible wheezing on auscultation. Three infants without ARI (1.1%) and 10 infants with ARI (8.7%) had FW. In the evaluation of breath sound parameters, there were no marked differences between the infants with and without FW. CONCLUSIONS: Using a breath sound analyzer, wheezing and FW were recognized in only a few infants in good health. Infants recognized to have audible wheezing in daily practice may be at risk of developing recurrent wheezing/asthma.

Objective measurement of nocturnal cough in infants with acute bronchiolitis.

OBJECTIVES: The objective measurement of the cough severity and the assessment of the pattern of nocturnal coughing could be useful in the treatment of respiratory diseases in children. STUDY DESIGN: In children with respiratory syncytial virus (RSV)-induced acute bronchiolitis, coughs were recorded using our original system with a microphone and accelerometer, and analyzed using our customized software program. The number of coughs in every 30-minute interval was measured in patients with acute bronchiolitis (n = 20), and their results were compared with those of infants with asthma exacerbation (n = 16). RESULTS: The cough count in children with acute bronchiolitis (median: 108.0/night) was almost as high as that in children with asthma exacerbation (median: 119/night). However, the time-dependent pattern of overnight cough was different in infants with acute bronchiolitis and those with asthma exacerbation. In the infants with asthma exacerbation, cough frequency significantly increased while falling asleep and waking up as compared to midnight (p < 0.001 and p < 0.001, respectively). However, these differences were not found in infants with acute bronchiolitis. CONCLUSIONS: Our data demonstrated that the number of coughing events due to acute bronchiolitis was similar to that of acute asthma exacerbation, although the acute bronchiolitis did not show a characteristic overnight cough pattern.

A breath sound analysis in children with cough variant asthma.

BACKGROUND: Cough variant asthma (CVA) is characterized by a chronic cough and bronchial hyperresponsiveness without confirmation of wheezing. Using a breath sound analyzer, we evaluate the characteristics of breath sound in children with CVA. METHODS: Nine children with CVA (median age, 7.0 years) participated. The existence of breath sounds was confirmed by sound spectrogram. Breath sound parameters, the frequency limiting 50% and 99% of the power spectrum (F50 and F99), the roll-off from 600 to 1200 Hz (Slope) and spectrum curve indices, the ratio of the third and fourth area to the total area of the power spectrum (P3/PT and P4/PT) and the ratio of power and frequency at 50% and 75% of the highest frequency of the power spectrum (RPF75 and RPF50) were calculated before and after ß2 agonist inhalation. A spirogram and/or forced oscillation technique were performed in all subjects. RESULTS: On a sound spectrogram, wheezing was confirmed in seven of nine patients. All wheezing on the image was polyphonic, and they almost disappeared after ß2 agonist inhalation. An analysis of the breath sound spectrum showed that PT, P3/PT, P4/PT, RPF50 and RPF75 were significantly increased after ß2 agonist inhalation. CONCLUSIONS: Children with CVA showed a high rate of inaudible wheezing that disappeared after ß2 agonist inhalation. Changes in the spectrum curve indices also indicated the bronchial reversibility. These results may suggest the characteristics of CVA in children.

Characteristics of breath sound in infants with risk factors for asthma development.

BACKGROUND: Breath sound parameters have been suggested as biomarkers of the airway narrowing in children. Using a commercially available breath sound analyzer, the characteristics of the airway condition were investigated in infants with the risk factors for asthma development. METHODS: A total of 443 infants (mean age, 9.9 months; range, 3-24 months) were included in the present study. The breath sound parameters of the frequency limiting 99% of the power spectrum (F99), the roll-off from 600 to 1200 Hz (Slope) and spectrum curve indices, the total area under the curve of the dBm data (A3/AT) and the ratio of power and frequency at 50% and 75% of the highest frequency of the power spectrum (RPF75 and RPF50), were evaluated. Using an ATS-DLD based original Japanese questionnaire, we examined the characteristics of airway condition of infants. RESULTS: Finally, 283 infants in good health were included in the present study. The RPF75, RPF50, Slope and F99 in infants with positive results of allergy and atopic dermatitis were significantly increased more than those in the infants with negative result. CONCLUSIONS: Our data highlight the characteristics of breath sounds in infants with risk factors for asthma. The breath sound analysis may be useful for assessing the airways of infants for asthma development.

Clinical Application of High-pitched Breath Sound in Children with Asthma.

OBJECTIVE: Breath sound parameters have been suggested to be a new biomarker of airway conditions in asthmatic patients. We investigated new breath sound parameters to determine their utility for evaluating asthmatic children. METHODS: Fifty-seven children (mean age, 9.0 years, 6-16 years) were included in the present study. The new breath sound parameters, the area under the curve (AUC)>1,000 Hz (A1000 [dBm·Hz]) and the ratio of the A1000 to the total AUC at 100 Hz to the highest frequency of the dBm power spectrum (AT) (A1000/AT [%]) were measured before and after ß2 agonist inhalation. Spirography and the forced oscillation technique were also used to evaluate all subjects. RESULTS: The value of A1000 was negatively correlated with the FEV1 (p=0.028). The increase in the ΔFEV1 was correlated with the decrease in the ΔA1000 (p=0.001) and the ΔA1000/AT (p=0.036). CONCLUSIONS: The A1000 indicates the airway condition, and the ΔA1000 and the ΔA1000/AT well describe the dilatation of the airways. These parameters are useful for the assessment of bronchial reversibility in asthmatic children.

Changes in the breath sound spectrum with bronchodilation in children with asthma.

BACKGROUND: Breath sound parameters have been suggested to be new biomarkers of airway function in patients with asthma. METHODS: We investigated the effect of bronchodilation on breath sound parameters in sixty-four children (mean age, 8.9 years; range, 6-16 years) using a breath sound analyzer. The breath sound parameters included frequency limiting 50% and 99% of the power spectrum (F50 and F99), roll-off from 600-1200 Hz (slope), and spectrum curve indices such as the ratios of the third and fourth power area to the total area of the power spectrum (P3/PT and P4/PT), total area under the curve (A3/AT and B4/AT), and the ratio of power and frequency at 50% and 75% of the highest frequency of the power spectrum (RPF75 and RPF50). Lung function was assessed using spirometry and the forced oscillation technique (FOT). All variables were assessed before and after inhalation of a ß2-agonist. RESULTS: The spectrum curve indices, A3/AT, B4/AT, RPF75, and RPF50, showed statistically significant increase following ß2-agonist inhalation. The increase in RPF50 was correlated with the decrease in the difference between resistance at 5 Hz and 20 Hz, R5-R20, measured by FOT. In the multiple regression analysis adjusted for the effect of ΔRPF75, the changes in A3/AT and B4/AT were positively correlated with that in the forced expiratory volume in one second. CONCLUSIONS: The spectrum curve indices indicated bronchodilation, and may be useful for the assessment of bronchial reversibility in children with asthma.

Changes in the breath sound spectrum during methacholine inhalation in children with asthma.

BACKGROUND AND OBJECTIVE: An effort-independent breath sound analysis is expected to be a safe and simple method for clinical assessment of changes in airway function. The effects of bronchoconstriction and bronchodilation on novel breath sound parameters in asthmatic children were investigated. METHODS: The study population included 49 children with atopic asthma (male = 33; mean age: 10.2 years). We evaluated breath sound parameters of the highest frequency of the power spectrum (HFp), frequency limiting 50% and 99% of the power spectrum (F50 and F99 ) and roll-off from 600 Hz to the HFp (Slope). We also assessed new parameters obtained using the ratios of sound spectrum parameters (spectrum curve indices), such as the ratio of the third and fourth power area to the total power area (P3 /PT and P4 /PT ), the ratio of the third and fourth areas to the total area under the curve (A3 /AT and B4 /AT ) and the ratio of power and frequency at 75% of HFp and 50% of HFp (RPF75 and RPF50 ). This was measured before and after methacholine inhalation challenge and after ß2 agonist inhalation. RESULTS: The parameters, F50 and F99 , showed no changes after methacholine inhalation. Conversely, the A3 /AT (12.5-10.0%, P < 0.001), B4 /AT (7.6-5.5%, P < 0.001), RPF75 (6.7-4.0 dBm/Hz, P < 0.001) and RPF50 (5.8-4.3 dBm/Hz, P < 0.001) were significantly decreased. These values returned to the original level after ß2 agonist inhalation. CONCLUSION: Spectrum curve indices indicate bronchoconstriction and bronchodilation. These parameters may play a role in the assessment of airway narrowing in asthmatic children.

An objective evaluation of nocturnal cough count and cough pattern in children with psychogenic cough.

Two patients with a chronic, barking cough were diagnosed with psychogenic cough. Using an original cough counter we studied the nocturnal cough count and pattern. While the number of coughs when awake was extremely high for both patients, the number of coughs was remarkably reduced during sleep, similar to an exacerbation of asthma. Moreover, the properties of the coughs when awake were clearly different from those of coughs during sleep. In conclusion, an objective examination using a cough counter was useful for the diagnosis, treatment and management of psychogenic cough.

A clinical method for detecting bronchial reversibility using a breath sound spectrum analysis in infants.

BACKGROUND: Using a breath sound analyzer, we investigated clinical parameters for detecting bronchial reversibility in infants. METHODS: A total of 59 infants (4-39 months, mean age 7.8 months) were included. In Study 1, the intra- and inter-observer variability was measured in 23 of 59 infants. Breath sound parameters, the frequency at 99% of the maximum frequency (F99), frequency at 25%, 50%, and 75% of the power spectrum (Q25, Q50, and Q75), and highest frequency of inspiratory breath sounds (HFI), and parameters obtained using the ratio of parameters, i.e. spectrum curve indices, the ratio of the third and fourth area to total area (A3/AT and B4/AT, respectively) and ratio of power and frequency at F75 and F50 (RPF75 and RPF50), were calculated. In Study 2, the relationship between parameters of breath sounds and age and stature were studied. In Study 3, breath sounds were studied before and after ß2 agonist inhalation. RESULTS: In Study 1, the data showed statistical intra- and inter-observer reliability in A3/AT (p=0.042 and 0.034, respectively) and RPF50 (p=0.001 and 0.001, respectively). In Study 2, there were no significant relationships between age, height, weight, and BMI. In Study 3, A3/AT and RPF50 significantly changed after ß2 agonist inhalation (p=0.001 and p<0.001, respectively). CONCLUSIONS: Breath sound analysis can be performed in infants, as in older children, and the spectrum curve indices are not significantly affected by age-related factors. These sound parameters may play a role in the assessment of bronchial reversibility in infants.

IP-10 Is Elevated in Virus-Induced Acute Exacerbations in Childhood Asthma.

OBJECTIVE: Viral infections and sensitization to aeroallergens are major factors in the exacerbation of asthma and its development during early childhood. However, the cytokine profiles and eosinophil activation status linked to the association between viral infections and sensitization to aeroallergens are incompletely understood. Here we investigated respiratory viruses, serum eosinophil cationic protein (ECP), and various cytokines/chemokines in acute exacerbation of childhood asthma. METHODS: We analyzed peripheral eosinophil counts, serum ECP, and 27 cytokines/chemokines in 76 virus-induced acute asthma cases with or without aeroallergen sensitization. Asthma due to sensitization was defined by a positive reaction to at least one aeroallergen in serum specific IgE antibody tests. Virus detection was performed using antigen detection kits and/or RT-PCR, followed by direct DNA sequencing analysis. Serum cytokines/chemokines were measured using a multi-cytokine detection system. RESULTS: Peripheral eosinophil counts and serum ECP and IL-5 levels were significantly elevated in sensitized cases compared with nonsensitized cases. Conversely, IP-10 values were significantly higher in nonsensitized cases. An inverse correlation between IP-10 and IL-5 production was identified in virus-induced acute exacerbations of asthma but not in controls. CONCLUSIONS: Cytokine profiles and eosinophil activation status might be different between sensitized and nonsensitized cases of virus-induced acute exacerbations of asthma.

Objective measurement of frequency and pattern of nocturnal cough in children with asthma exacerbation.

BACKGROUND: Although a number of patients with asthma report experiencing persistent cough during sleep, it has not yet been objectively investigated. OBJECTIVE: To classify cough severity and evaluate a characteristic pattern of cough frequency in children with asthma using an objective cough monitoring system. METHODS: An objective cough monitoring system that specialized in children was used to measure cough frequency and nocturnal cough patterns. Coughs were recorded with microphone and accelerometer and analyzed using a customized software program. The number of nocturnal coughs and the pattern of cough frequency in 30-minute intervals were measured along with the severity of each asthma exacerbation, and the results were compared with children without asthma. RESULTS: The total overnight cough count of 34 children with asthma was higher than that of 15 children without asthma (P < .001). The total overnight cough count in children with severe asthma exacerbation was higher than that in children with moderate asthma exacerbation (P < .05). The cough counts were significantly increased at the time of falling asleep and waking. This pattern was not observed in children without asthma. The total cough counts and cough patterns in children with asthma were not affected by sex, age, cause of asthma exacerbation, or therapy. CONCLUSION: Our data indicate huge cough counts and characteristic nocturnal cough patterns in children with asthma. Objective and precise cough monitoring is useful for the management of childhood asthma.

A novel method for detecting airway narrowing using breath sound spectrum analysis in children.

BACKGROUND: Using a breath sound analyzer, we investigated new clinical parameters that are rarely affected by airflow in young children. METHODS: A total of 65 children with asthma participated in this study (mean age 9.6 years). In Study 1, the intra- and inter-observer variability was measured. Common breath sound parameters, frequency at 99%, 75%, and 50% of the maximum frequency (F99, F75, and F50) and the highest frequency of inspiratory breath sounds were calculated. In addition, new parameters obtained using the ratio of sound spectra parameters, i.e., the spectrum curve indexes including the ratio of the third and fourth area to the total area and the ratio of power and frequency at F75 and F50, were calculated. In Study 2, 51 children underwent breath sound analyses. In Study 3, breath sounds were studied before and after methacholine inhalation. RESULTS: In Study 1, the data showed good inter- and intra-observer reliability. In Study 2, there were significant relationships between the airflow rate, age, height, and spirometric and common breath sound parameters. However, there were no significant relationships between the airflow rate and the spectrum curve indexes. Moreover, the spectrum curve indexes showed no relationships with age, height, or spirometric parameters. In Study 3, all parameters significantly changed after methacholine inhalation. CONCLUSIONS: Some spectrum curve indexes are not significantly affected by the airflow rate at the mouth, although they successfully indicate airway narrowing. These parameters may play a role in the assessment of bronchoconstriction in children.

A new method for objectively evaluating childhood nocturnal cough.

OBJECTIVE: Cough is so common that the best method for evaluating nocturnal cough in children is required. METHODS: We developed a cough monitoring system by evaluating 50 child volunteers, and validated the cough monitor in 20 samples from 10 children with cough overnight. Coughs were recorded using a video camera and digital sound recording. At the same time, our system with microphone and accelerometer was used. The number of coughs in each eight hour video-audio recording was counted manually by three trained observers, and all cough data were printed out and the defined cough events, using both these printed-out data and video-audio recordings, were then calculated by three observers. RESULTS: The cough monitoring system demonstrated excellent agreement between the number of coughs counted by volunteers, and those counted by cough monitoring system (sensitivity 98.8%, specificity 97.8%). Also, there was significant agreement in the counts of coughs between the video-audio method and our system (P < 0.0001), and between the defined cough events and our system (P < 0.0001). CONCLUSIONS: Our method demonstrated well agreement with the video-audio recording method in children, and is considered to be highly useful for the objective monitoring of overnight cough in children with respiratory diseases.