Prevalence and clinical associations of wheezes and crackles in the general population: the Tromsø study.

BACKGROUND: Wheezes and crackles are well-known signs of lung diseases, but can also be heard in apparently healthy adults. However, their prevalence in a general population has been sparsely described. The objective of this study was to determine the prevalence of wheezes and crackles in a large general adult population and explore associations with self-reported disease, smoking status and lung function. METHODS: We recorded lung sounds in 4033 individuals 40 years or older and collected information on self-reported disease. Pulse oximetry and spirometry were carried out. We estimated age-standardized prevalence of wheezes and crackles and associations between wheezes and crackles and variables of interest were analyzed with univariable and multivariable logistic regressions. RESULTS: Twenty-eight percent of individuals had wheezes or crackles. The age-standardized prevalence of wheezes was 18.6% in women and 15.3% in men, and of crackles, 10.8 and 9.4%, respectively. Wheezes were mostly found during expiration and crackles during inspiration. Significant predictors of expiratory wheezes in multivariable analyses were age (10 years increase - OR 1.18, 95%CI 1.09-1.30), female gender (1.45, 1.2-1.8), self-reported asthma (1.36, 1.00-1.83), and current smoking (1.70, 1.28-2.23). The most important predictors of inspiratory crackles were age (1.76, 1.57-1.99), current smoking, (1.94, 1.40-2.69), mMRC ≥2 (1.79, 1.18-2.65), SpO2 (0.88, 0.81-0.96), and FEV1 Z-score (0.86, 0.77-0.95). CONCLUSIONS: Nearly over a quarter of adults present adventitious lung sounds on auscultation. Age was the most important predictor of adventitious sounds, particularly crackles. The adventitious sounds were also associated with self-reported disease, current smoking and measures of lung function. The presence of findings in two or more auscultation sites was associated with a higher risk of decreased lung function than solitary findings.

Breath stacking in children with neuromuscular disorders.

Respiratory muscle weakness in neuromuscular disorders (NMD) can lead to shallow breathing and respiratory insufficiency over time. Children with NMD often cannot perform maneuvers to recruit lung volume. In adults, breath stacking with a mask and one-way valve can achieve significantly increased lung volumes. To evaluate involuntary breath stacking (IBS) in NMD, we studied 23 children of whom 15 were cognitively aware and able to communicate verbally. For IBS, a one-way valve and pneumotachograph were attached to a face mask. Tidal volumes (Vt) and minute ventilation (VE ) were calculated from airflow over 30 sec before and after 15 sec of expiratory valve closure. Six cooperative male subjects with Duchenne muscular dystrophy (DMD) participated in a subsequent comparison of IBS with voluntary breath stacking (VBS) and supported breath stacking (SBS). The average Vt in those studied with IBS was 277 ml (range 29-598 ml). The average increase in volume by stacking was 599 ml (range -140 to 2,916 ml) above Vt . The average number of stacked breaths was 4.5 (range 0-17). VE increased on average by 18% after stacking (P < 0.05, paired t-test). Oxygen saturation did not change after stacking. Four of the 23 children did not breath stack. Compared to IBS, VBS achieved similar volumes in the six subjects with DMD but SBS was more successful in those with greatest muscle weakness. IBS may achieve breath volumes of approximately three times Vt and may be particularly useful in non-cooperative subjects with milder degrees of respiratory muscle weakness.

Classification of lung sounds during bronchial provocation using waveform fractal dimensions.

Lung sounds (LS) of children after bronchoconstriction should differ from baseline LS in terms of amplitude and pattern characteristics. To test these hypotheses, time-domain and fractal based analyses have been applied to LS acquired from eight children ages 9-15 y pre- and post-methacholine challenge (MCh). Change in forced expiratory volume in 1 s after MCh ranged from -4% to -37%, with change proportional to severity of bronchoconstriction. Sounds were recorded over the posterior right lower lung lobe while subjects breathed normally for 60 s with flow measurement, and during 10 s of breath hold (BH). From root-mean-square (RMS) of LS and BH signals, signal-to-noise ratio (SNR) was determined. Two fractal dimension (FD) algorithms were applied, based on signal variance and morphology. Feature vectors for 1-nearest-neighbor classification contained FD and RMS values within flow plateau ranges. Results for LS within 75-600 Hz indicate that the combination of RMS-SNR and morphology-based FD values offers better classification of bronchoconstriction with LS, relative to using RMS-SNR with variance-based FDs and RMS-SNR alone. True positive classification was 90.3%, 63.5% and 58.3% respectively, and false positive classification was 23.4%, 24.9% and 26.1% respectively. Both RMS-SNR and FD values provide useful insight into LS changes post-bronchoconstriction.

Acoustic imaging of the human chest.

STUDY OBJECTIVES: A novel method for acoustic imaging of the human respiratory system is proposed and evaluated. DESIGN: The proposed imaging system uses simultaneous multisensor recordings of thoracic sounds from the chest wall, and digital, computer-based postprocessing. Computer simulations and recordings from a life-size gelatin model of the human thorax are used to evaluate the system in vitro. Spatial representations of thoracic sounds from 8-microphone and 16-microphone recordings from five subjects (four healthy male adults and one child with lung consolidation) are used to evaluate the system in vivo. RESULTS: Results of the in vitro studies show that sound sources can be imaged to within 2 cm, and that the proposed algorithm is reasonably robust with respect to changes in the assumed sound speed within the imaged volume. The images from recordings from the healthy volunteers show distinct patterns for inspiratory breath sounds, expiratory breath sounds, and heart sounds that are consistent with the assumed origin of the respective sounds. Specifically, the images support the concept that inspiratory sounds are produced predominantly in the periphery of the lung while expiratory sounds are generated more centrally. Acoustic images from the subject with lung consolidation differ substantially from the images of the healthy subjects, and localize the abnormality. CONCLUSIONS: Acoustic imaging offers new perspectives to explore the acoustic properties of the respiratory system and thereby reveal structural and functional properties for diagnostic purposes.

Auditory detection of simulated crackles in breath sounds.

BACKGROUND: Computerized analysis of breath sounds has relied on human auditory perception as the reference standard for identifying crackles. In this study, we tested the human audibility of crackles by superimposing artificial clicks on recorded breath sounds and having physicians listen to the recordings to see if they could identify the crackles. OBJECTIVES: To establish the audibility of simulated crackles introduced in breath sounds of different intensity, to study the effects of crackle characteristics on their audibility, and to investigate crackle detection within and between observers. METHODS: Fine, medium, and coarse crackles with large and small amplitude were synthesized by computer software. Waveform parameters were based on published characteristics of lung sound crackles. The amplitude for small crackles was defined as just above the threshold of audibility for simulated crackles inserted in sound recorded during breath hold. Simulated crackles were then superimposed on breath sounds recorded at 0 L/s (breath hold), 1 L/s, and 2 L/s airflow. Five physicians listened during playback on two separate occasions to determine if crackles could be heard and to calculate the interobserver and intraobserver variations. RESULTS: Failed detection of crackles was significantly more common in the following conditions: (1) background breath sounds had higher intensity (2 L/s airflow) compared to lower intensity (1 L/s), (2) crackle type was coarse or medium compared to fine, and (3) crackle amplitude was small compared to large. Both intraobserver and interobserver agreements were high (kappa > 0.6). RELEVANCE: The validation of automated techniques for crackle detection in lung sound analysis should not rely on auscultation as the only reference. Detection of crackles is facilitated when patients take slow, deep breaths that generate little breath sounds.

An acoustic model of the respiratory tract.

With the emerging use of tracheal sound analysis to detect and monitor respiratory tract changes such as those found in asthma and obstructive sleep apnea, there is a need to link the attributes of these easily measured sounds first to the underlying anatomy, and then to specific pathophysiology. To begin this process, we have developed a model of the acoustic properties of the entire respiratory tract (supraglottal plus subglottal airways) over the frequency range of tracheal sound measurements, 100 to 3000 Hz. The respiratory tract is represented by a transmission line acoustical analogy with varying cross sectional area, yielding walls, and dichotomous branching in the subglottal component. The model predicts the location in frequency of the natural acoustic resonances of components or the entire tract. Individually, the supra and subglottal portions of the model predict well the distinct locations of the spectral peaks (formants) from speech sounds such as /a/ as measured at the mouth and the trachea, respectively, in healthy subjects. When combining the supraglottic and subglottic portions to form a complete tract model, the predicted peak locations compare favorably with those of tracheal sounds measured during normal breathing. This modeling effort provides the first insights into the complex relationships between the spectral peaks of tracheal sounds and the underlying anatomy of the respiratory tract.

Computerised acoustical respiratory phase detection without airflow measurement.

A simple, non-invasive acoustical method is developed to detect respiratory phases in relationship to swallows without the direct measurement of airflow. In 21 healthy subjects (4-51 years) breath sounds are recorded at the trachea and at five different recording locations at the chest wall, with simultaneous recording of airflow by a pneumotachograph. The chest signal with the greatest inspiratory-expiratory power difference ('best location') is either in the mid-clavicular line in the second interspace on the left or third interspace on the right. Using the 'best location' on the chest wall and the tracheal signal, a phase detection algorithm is developed and achieves 100% accuracy in the estimation of respiratory phases without using the measured airflow signal. Thus, acoustically monitoring breaths and swallows holds promise as a non-invasive and reliable assessment tool in the study of swallowing dysfunction.

Effect of a Soft Boston Orthosis on pulmonary mechanics in severe cerebral palsy.

Spinal braces such as the Soft Boston Orthosis (SBO) help stabilize scoliosis and improve sitting, positioning, and head control in individuals with cerebral palsy. However, their impact on pulmonary mechanics in this population has not been studied. We examined the effect of a Soft Boston Orthosis on the pulmonary mechanics and gas exchange in 12 children and young adults (5-23 years of age) with severe cerebral palsy. Pulmonary resistance, compliance, tidal volume, minute ventilation, work of breathing, oxygen saturation, and end-tidal CO2 tension were measured with the subjects seated both with and without the orthosis and in the supine position without the orthosis. There were no significant differences in the measured parameters when comparing subjects with and without their orthoses in the sitting or in the supine position. As would be expected in individuals with severe cerebral palsy, pulmonary resistance was increased (7.33 cm H2O/L/s) and compliance was decreased (0.12 L/cm H2O) compared to reported normal values. Work of breathing was greatest in the sitting position without the orthosis (1.2 dynes/cm), suggesting that the improved positioning achieved with the orthosis may decrease the work of breathing. We conclude that the application of a Soft Boston Orthosis does not impact negatively on pulmonary mechanics and gas exchange in young people with severe cerebral palsy.

Effect of ambient respiratory noise on the measurement of lung sounds.

The effect of ambient sounds, generated during breathing, that may reach a sensor at the chest surface by transmission from mouth and nose through air in the room, rather than through the airways, lungs and chest wall, is studied. Five healthy male non-smokers, aged from 11 to 51 years, are seated in a sound-proof acoustic chamber. Ambient respiratory noise levels are modified by directing expiratory flow outside the recording chamber. Low-density gas (HeO2 = 80% helium, 20% oxygen) is used to modify airway resonances. Spectral analysis is applied to ambient noise and to respiratory sounds measured on the chest and neck. Flow-gated average sound spectra are compared statistically. A prominent spectral peak around 960 Hz appears in ambient noise and over the chest and neck during expiration in all subjects. Ambient noise reduction decreases the amplitude of this peak by 20 +/- 4 dB in the room and by 6 +/- 3.6 dB over the chest. Another prominent spectral peak, around 700 Hz in adults and 880 Hz in children, shows insignificant change, i.e. a maximum reduction of 3 dB, during modifications of ambient respiratory noise. HeO2 causes an upward shift in tracheal resonances that is also seen in the anterior chest recordings. Ambient respiratory noise explains some, but not all, peaks in the spectra of expiratory lung sounds. Resonance peaks in the spectra of expiratory tracheal sounds are also apparent in the spectra of expiratory lung sounds at the anterior chest.

Nebulized budesonide and oral dexamethasone for treatment of croup: a randomized controlled trial.

CONTEXT: The effectiveness of glucocorticoids for patients with croup is well established but it remains uncertain which glucocorticoid regimen is most effective. OBJECTIVE: To determine the effectiveness of 3 glucocorticoid regimens in patients with croup. DESIGN: Randomized controlled trial with parallel design. SETTING: Emergency departments of 2 Canadian pediatric tertiary care hospitals. PARTICIPANTS: Children with a clinical syndrome consistent with croup, aged 3 months to 5 years, with a croup score of 2 or greater following at least 15 minutes of mist therapy. INTERVENTIONS: Oral dexamethasone, 0.6 mg/kg, and nebulized placebo; oral placebo and nebulized budesonide, 2 mg; or oral dexamethasone, 0.6 mg/kg, and nebulized budesonide, 2 mg. MAIN OUTCOME MEASURES: Westley croup score (primary outcome), hospital admission rates, time spent in the emergency department, return visits to the emergency department, or ongoing symptoms at 1 week. RESULTS: The mean change in the croup score from baseline to the final study assessment was -2.3 (95% confidence interval [CI], -2.6 to -2.0) in the budesonide group (n = 65), -2.4 (95% CI, -2.6 to -2.2) in the dexamethasone group (n = 69), and -2.4 (95% CI, -2.7 to -2.1) in the budesonide and dexamethasone group (n = 64, P = .70). CONCLUSIONS: Based on the similar outcomes in the 3 groups, oral dexamethasone is the preferred intervention because of its ease of administration, lower cost, and more widespread availability.

Effects of breathing pathways on tracheal sound spectral features.

The spectra of sounds recorded over the trachea of adults typically reveal peaks near 700 and 1500 Hz. We assessed the anatomical determinants of these peaks and the conditions contributing to their presence. We studied five adult subjects with normal lung function, measuring sounds at the suprasternal notch and on the right cheek. The subjects breathed at target airflows of 15 and at 30 ml sec(-1) kg(-1) both through the mouth with nose clips and then through the mouth and nose using a cushioned face mask. The mouth breathing maneuvers were performed with three lengths (3.6, 21.1 and 38.6 cm) of 2.6 cm diameter tubing between the mouth and the pneumotachograph. The nose breathing maneuver was performed with the longest tube (between the mask and pneumotachograph). The signals occurring at the target flows +/- 20% were used to create averaged, spectral estimates. We found that all subjects had two predominant spectral peaks; a approximately 700 Hz peak loudest over the cheek and a approximately 1500 Hz peak loudest over the trachea. The frequency of both peaks negatively correlated with body height (and presumably, airway length). There was no systematic effect of breathing phase, flow rate or length of the tube connecting the mouth to the pneumotachograph on the spectral peaks. Breathing into the mask and breathing through the nose did markedly alter the spectra. We conclude that the higher tracheal sound peak reflects resonance within the major airways and is relatively independent of extrathoracic influences during mouth breathing through a tube.

Asymmetry of respiratory sounds and thoracic transmission.

Breath sounds heard with a stethoscope over homologous sites of both lungs in healthy subjects are presumed to have similar characteristics. Passively transmitted sounds introduced at the mouth, however, are known to lateralise, with right-over-left dominance in power at the anterior upper chest. Both spontaneous breath sounds and passively transmitted sounds are studied in four healthy adults, using contact sensors at homologous sites on the anterior upper and posterior lower chest. At standardised air flow, breath sound intensity shows a right-over-left dominance at the anterior upper chest, similar to passively transmitted sounds. At the posterior lung base, breath sounds are louder on the left, with a trend to similar lateralisation in transmitted sounds. It is likely that the observed asymmetries are related to the effects of cardiovascular structures and airway geometry on sound generation and transmission.

Chest surface mapping of lung sounds during methacholine challenge.

Wheeze as an indicator of airway obstruction during bronchoprovocation lacks sensitivity. We therefore studied whether induced airway narrowing is revealed by changes in normal (vesicular) lung sounds. Fifteen subjects with asthma and nine healthy controls, aged 8-16 years, performed a standardized methacholine challenge. Respiratory sounds were recorded with eight contact sensors, placed posteriorly over the right and left superior and basal lower lobes, and anteriorly over both upper lobes, the right middle lobe, and the trachea. Average spectra of normal inspiratory and expiratory sounds, excluding wheeze, were characterized in 12 asthmatics and 9 controls at flows of 1 +/- 0.2 L/sec. Airway narrowing was accompanied by significant changes in lung sounds, but not in tracheal sounds. Lung sounds showed a decrease in power at low frequencies during inspiration and an increase in power at high frequencies during expiration. These changes already occurred at a decrease in forced expiratory volume in 1 sec of less than 10% from baseline and were fully reversed after inhalation of salbutamol. Thus, lung sounds were sensitive to changes in airway caliber, but were not specific indicators of bronchial hyperresponsiveness.

Posture-dependent change of tracheal sounds at standardized flows in patients with obstructive sleep apnea.

BACKGROUND: The ability of awake subjects with obstructive sleep apnea (OSA) to dilate their pharynx during inspiration may be defective. Airflow through a relatively more narrow pharyngeal passage should lead to increased flow turbulence and hence to louder respiratory sounds. We therefore studied the increase of tracheal sound intensity (TSI) in the supine position as an indicator of abnormal pharyngeal dynamics in patients with documented OSA. SUBJECTS AND METHODS: Sound was recorded with a contact sensor at the suprasternal notch in 7 patients with OSA (age, 52 +/- 8 years; body mass index, 29.0 +/- 3; apnea-hypopnea index, 58 +/- 17; means +/- SD), and in 8 control subjects, including obese subjects and snorers (age, 39 +/- 8 years; body mass index, 28.6 +/- 4). Subjects breathed through a pneumotachograph and aimed at target flows of 1.5 to 2 L/s, first sitting, then supine. Flow and sound signals were digitized at a 10-KHz rate. Fourier analysis was applied to sounds within the target flow range and average power spectra were obtained. Spectral power was calculated for frequency bands 0.2 to 1, 1 to 2, and 2 to 3 KHz. RESULTS: In the supine position, OSA patients had a significantly greater increase of inspiratory TSI than control subjects: 7.5 +/- 1.2 dB vs 1.7 +/- 3.4 dB (p < 0.001); 6.6 +/- 1.7 dB vs 1.3 +/- 3.9 dB (p < 0.005); and 12.2 +/- 3.2 dB vs 5.6 +/- 3.1 dB (p < 0.001) at low, medium, and high frequencies, respectively. Expiratory TSI also increased in supine subjects, but the change was significantly greater in OSA subjects only at high frequencies. These findings confirm our earlier observations that did not include obese subjects or snorers among control subjects. SUMMARY: Measuring posture effects on tracheal sounds is noninvasive and requires little time and effort. The greater increase of inspiratory TSI in supine OSA patients compared to subjects without OSA suggests a potential value for daytime acoustic screening.

Lung sound spectra at standardized air flow in normal infants, children, and adults.

To investigate the effect of age and body size on normal lung sounds, we studied 10 newborn infants within 3 d after birth, nine children between 6 to 8 yr, and 10 adults between 25 and 37 yr of age. Lung sounds were recorded with a contact transducer over the posterior right lower lobe, and air flow was measured at the mouth. Computer analysis provided average power spectra of lung sounds at flows of 15 ml/s/kg. In children and adults measurements were also made at flows of 30 ml/s/kg. Lung sounds were referenced to background noise, measured at zero air flow. The spectra in infants contained less power below 300 Hz compared with children and adults, resulting in significantly higher quartile and spectral edge frequencies. Resonances of the thoracic cavity may explain some of the differences among the study groups. Sound attenuation above 300 Hz was similar at all ages. At increased air flows, lung sounds in children and adults were above background noise at frequencies as high as 2,000 Hz. High-frequency expiratory lung sounds of low intensity were present in all children and in eight of 10 adults at increased flows. Normal lung sounds of low intensity are present above traditionally accepted frequency limits and warrant further investigation.

Effect of gas density on respiratory sounds.

The generation of normal lung sounds by turbulent air flow has been questioned because gas density appears to have only a minor effect. We studied whether gas density has a greater influence on lung sounds at higher frequencies than traditionally measured. Six healthy adult men breathed air followed by a mixture of 80% helium and 20% oxygen (He-O2) at a target flow of 1.5 L/s. Flow and sounds at the trachea and posterior right lower lobe were simultaneously acquired by computer. Fourier analysis was applied to sounds at target flow +/- 0.2 L/s. Average power spectra were computed for each recording site, respiratory phase, and respired gas. He-O2 reduced the power of inspiratory lung sounds below 300 Hz by only 1.7 +/- 1.5 dB whereas power between 300 and 600 Hz was reduced by 4.6 +/- 1.4 dB (p<0.05). Tracheal sound power was reduced less consistently but all subjects showed an upward frequency shift in power maxima on He-O2, similar to formant shifts observed in helium speech. Our findings suggest that flow turbulence is the major determinant of lung sounds at higher frequencies. Current instruments for auscultation and recording of respiratory sounds may have to be modified to optimize their response in this higher frequency range.

Measurement of respiratory acoustic signals. Effect of microphone air cavity width, shape, and venting.

STUDY OBJECTIVE: We have previously investigated the effects of microphone type and coupler air chamber depth on lung sound characteristics. We now report the results of experiments exploring the effects of air chamber width, shape, and venting on lung sounds. DESIGN: We used a single electret microphone with a variety of plastic couplers. The couplers were identical except for the diameter and shape of the air chamber. We used cylindrical chambers of 5, 10, and 15 mm in diameter at the skin and conical chambers of 8, 10, and 15 mm in diameter. We compared the inspiratory lung sound spectra obtained using each of the couplers. We also examined the tendency of various needle vents to transmit ambient noise into the microphone chamber. SETTING: Anechoic chamber. MEASUREMENTS AND RESULTS: The shape and diameter had little important effect on the lung sound spectrum below 500 Hz. From approximately 500 to 1,500 Hz, the 5-mm diameter couplers showed slightly less sensitivity than the 10- and 15-mm diameter couplers. All conical couplers provided approximately 5 to 10 decibel more sensitivity than the cylindrical couplers. All vents allowed some ambient noise to enter the chamber but the amount was trivial using the narrowest, longest vent. CONCLUSIONS: These data suggest that the optimal electret microphone coupler chamber for lung sound acquisition should be conical in shape, between 10 and 15 mm in diameter at the skin, and either not vented or vented with a tube no wider than 23-g or shorter than 20 mm.

Pulmonary blastomycosis in children: findings on chest radiographs.

OBJECTIVE: The purpose of this study was to identify characteristic radiographic findings in children with pulmonary blastomycosis. SUBJECTS AND METHODS: We reviewed the charts and radiographs of 18 children with culture-proven acute pulmonary blastomycosis. The 10 boys and eight girls were from 1 to 16 years old. Sixteen were Native Canadian Indians, and two were white. All available chest radiographs, including those obtained in follow-up after treatment was terminated, were reviewed by a pediatric radiologist. Consolidation was classified by location and extent, and other abnormalities were noted. RESULTS: Initial chest radiographs showed consolidation in 16 patients. Seven patients had single lobe involvement, most commonly of the left lower lobe. Nine patients had multiple lobe involvement. The left lower lobe was most commonly involved in these cases, but the middle lobe was most severely affected. The upper lobes were involved only in children with multiple lobe disease and were only mildly affected. Cavitation developed in two patients, followed by bronchogenic spread of the disease. Pleural effusions were seen in three patients; two also had rib lesions. Hilar adenopathy developed in two children. Five patients had radiographs available, which had been obtained more than a year after onset, and three of these were abnormal. CONCLUSION: The most common radiologic finding in children with pulmonary blastomycosis is pulmonary consolidation in one or several lobes, which may undergo cavitation. Lymphadenopathy and pleural effusions are uncommon. Chronic abnormalities may develop.