Effect of age, height, and prechallenge respiratory resistance on bronchial hyperresponsiveness in childhood asthma using the forced oscillation technique

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 /P_T and P₄ /P_T ), the ratio of the third and fourth areas to the total area under the curve (A₃ /A_T and B₄ /A_T ) 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 β₂ agonist inhalation.

RESULTS

The parameters, F₅₀ and F₉₉ , showed no changes after methacholine inhalation. Conversely, the A₃ /A_T (12.5-10.0%, P < 0.001), B₄ /A_T (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 β₂ 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.

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.

Forced oscillation technique and childhood asthma

Most infants and preschool children are not able to voluntarily perform the physiological maneuvers required to complete the pulmonary function tests that are used in adults and older children. Recently, commercial devices using forced oscillation technique (FOT) suitable for young children have become available. In devices with FOT, an oscillation pressure wave is generated by a loud speaker, is applied to the respiratory system, usually at the mouth, and the resulting pressure-flow relationship is analyzed in terms of impedance (Zrs). Zrs encompasses both resistance (Rrs) and reactance (Xrs). Rrs is calculated from pressure and flow signals, and is a measure of central and peripheral airway caliber. Xrs is derived from the pressure in the phase with volume and is related to compliance (Crs) and inertance (Irs). These parameters individually indicate the condition of the small and large airways in each patient and indirectly suggest the presence of airway inflammation. It is agreed that the clinical diagnostic capacity of FOT is comparable to that of spirometry. One of the advantages of FOT is that minimal cooperation of the patient is needed and no respiratory maneuvers are required. The use of FOT should be considered in patients in whom spirometry or other pulmonary function tests cannot be performed or in cases where the results of other tests appear to be unreliable. In addition, this approach is effective in assessing bronchial hyperresponsiveness. Considering these qualities, FOT is a useful method to study pulmonary function in preschool children with asthma.

Relationship between exhaled nitric oxide and small airway lung function in normal and asthmatic children

BACKGROUND

In children, exhaled nitric oxide (eNO) is usually confounded by factors such as age and height. We evaluated the relationship between eNO and lung function by minimizing the effects of aging and height.

METHODS

In Study 1, the subjects comprised 738 elementary school children and junior high school children (aged 6 to 15 years, 366 males and 372 females). They were divided into two groups according to age (6-10 years and 11-15 years). A height range was determined by a histogram of height in each group. In Study 2, lung function, respiratory resistance and eNO level were measured in age- and height-limited groups.

RESULTS

In Study 1, total of 148 younger children ranging in height from 120 to 130 cm and 180 older children ranging in height from 148 to 158 cm participated in Study 2. The level of eNO among asthmatic children was higher than that of normal children in both the younger and the older groups. The decrease in forced expiratory volume in 1 second (FEV(1)) and other parameters of central airway resistance did not correlate with the eNO level. However, the small airway parameters of MMEF and V(25)/HT in older asthmatic children, and V(25)/HT and R(5)-R(20) in younger asthmatic children inversely correlated with eNO.

CONCLUSIONS

Our data suggest that eNO level inversely correlates with small airway narrowing, and airway inflammation has a significant effect on small airway lung function in asthmatic school children.

Consistently high levels of exhaled nitric oxide in children with asthma

BACKGROUND

Exhaled nitric oxide (eNO) levels in children are unstable because they are regulated by many potent factors. The purpose of the current study was to evaluate the reliability of eNO levels between a long interval and other lung functions in normal and asthmatic children.

METHODS

Eighty-three elementary school children (aged 11-12 years; male : female, 39 : 44) participated in this study. Lung function, airway resistance and eNO levels were measured twice: the first measurement was in autumn 2007, and the second was one year later.

RESULTS

There were 62 non-asthmatic control children (male : female, 31 : 31) and 21 asthmatic children (male : female, 8 : 13). In both the first and the second examination, the levels of eNO in children with asthma were higher than those in children without asthma. The parameters of lung function and the respiratory resistance in children without asthma showed a good correlation between the results of the first and second examinations. The eNO level in non-asthmatic children showed a good correlation between the two. On the other hand, the peripheral airway parameters of lung function and the respiratory resistance in children with asthma were not correlated between the first and the second examinations. The eNO level in these patients was well correlated between the two examinations.

CONCLUSIONS

These data suggest that the eNO level showed good reproducibility in children with and without asthma. The eNO level is therefore considered to be a useful marker for reproducibly evaluating a subject's airway condition.

Respiratory impedance and response to salbutamol in asthmatic Vietnamese children

There is a high incidence of pediatric asthma in Vietnam, but little lung function data are available. The aim of the study was to compare respiratory resistance (Rrs), reactance (Xrs), and responses to salbutamol between asthmatic and healthy primary school children in Hanoi. Because respiratory mechanics vary along the breathing cycle, measurements were assessed separately in inspiration (Rrsi, Xrsi) and expiration (Rrse, Xrse).Inpatients with doctor-diagnosed asthma were measured 2-3 days following admission using the forced oscillation technique (FOT) at a single frequency (8 Hz). Z-scores and responses to salbutamol were compared between 102 asthmatics and 98 controls, and accuracy of group classification by FOT parameters was assessed by Youden index, an indicator to the proportion of subjects correctly classified in each group.In asthmatics versus controls, Rrsi-but not Rrse-was significantly larger and both Xrsi and Xrse were significantly more negative (P < 0.01). Both Rrs and Xrs responses to salbutamol were significantly larger in asthmatics than controls (P < 0.001). Youden indexes indicated response to salbutamol generally had better diagnostic values than Z-scores and was best discriminative first with Rrsi, then with Xrse.It is concluded that different FOT characteristics may be described in asthmatic and healthy Vietnamese children. The diagnostic value of each parameter depends upon the breathing cycle. Most useful in practice probably is the response to salbutamol measured by Rrsi.

Effect of age on bronchial reactivity in children with asthma

In contrast to an abundance of data concerning age-related changes of bronchial sensitivity, the relationship between age and rapidity of bronchoconstriction (bronchial reactivity) remains unclear. We studied age and bronchial reactivity in children with asthma. Enrolled in this study were 511 asthmatic subjects and 115 age-matched control subjects 1 to 16 years of age. Bronchial reactivity was represented by the slope of the methacholine transcutaneous oxygen pressure dose-response curve (SPO(2)) in younger children and the slope of the respiratory resistance dose-response curve (SRrs) in older children. Overall, SPO(2) and SRrs were higher in asthmatic than control subjects. SPO(2) increased significantly from 1 to 6 years in asthmatic subjects, reaching a plateau after age 7. This age-related change in SPO(2) also was seen in controls. SRrs in asthmatic subjects decreased after age 13, while SRrs in controls showed no significant change between age 7 and 16. Age-related change in bronchial reactivity occurs during childhood, possibly reflecting early changes in airway smooth muscle maturity and later changes in airway wall rigidity.

Effect of aging on the relationship between asthma severity and bronchial hyperresponsiveness in children with asthma

An association between asthma and bronchial hyperresponsiveness (BHR) has been demonstrated. It is possible that the relationship between asthma severity and BHR in children with asthma is different in infants and in adolescents. The aim of this study is therefore to evaluate the effect of aging on the relationship between the severity of asthma and BHR in children with asthma. We measured BHR in 386 subjects ranging from 2 to 20 years of age. The subjects consisted of 323 children with asthma (boys:girls = 193:130, mean age 9.7 years) and 63 age-matched controls (boys:girls = 25:38, mean age 8.2 years). BHR was measured using the methacholine inhalation challenge by measuring the transcutaneous oxygen pressure (tcPO2) in children less than 6 years of age (Dmin-PO2) and by measuring the respiratory resistance (Rrs) in children 6 years of age and older (Dmin-Rrs). Throughout the whole age range, both the Dmin-PO2 and Dmin-Rrs in each asthma severity group were higher than those in the controls. In the asthmatics aged 2-5 years, the Dmin-PO2 levels in the mild asthma group were higher than those in the moderate and severe asthma groups (p < 0.001, p < 0.001, respectively), and the Dmin-PO2 levels in the moderate asthma group were also higher than those in the severe asthma group. This tendency was also found in the age ranges of 6-9 years and 10-13 years. In the asthmatics aged 14-20 years, the Dmin-Rrs levels were not significantly different among the three groups. Taken together, these data show that aging has an effect on the relationship between the severity of asthma and BHR during childhood and that BHR may not be the sole determinant for the severity of asthma in adolescence.

Bronchial challenge with carbachol in 3-6-year-old children: body plethysmography assessments

Several studies of airway responsiveness in young children (3-6 years old) have been reported, but few have attempted measurements of airway resistance by body plethysmography. Therefore, we decided to study nonspecific bronchial responsiveness following cumulative doses of inhaled carbachol in 44 children with clinical asthma (CA group), 44 children with chronic cough (CC group), 38 children with wheezy bronchitis in the first 2 years of life (WB group), and 40 controls. Specific airway resistance (sRaw) was measured in a body plethysmograph, and specific airway conductance (sGaw=1/sRaw) was calculated. Two parameters were used to assess individual bronchial responses: 1) PD100 (the dose of carbachol which induced a 100% increase in sRaw), and 2) bronchial reactivity (BR), i.e., the slope of the log-dose sGaw response to carbachol. Significant differences were observed in PD100 and BR between the control group and the three groups of young patients (P < 0.001). Moreover, PD100 of the CA group was significantly lower than in the CC group (83.1 +/- 7.8 microg vs. 108.0 +/- 10.2 microg, respectively, P < 0.05), but was similar to the WB group PD100 (94.4 +/- 8.5 microg). BR in the CA group was significantly higher than in both the CC and WB groups (0.127 +/- 0.009 cm H2O-L.sec(-1) x log microg(-1) vs. 0.073 +/- 0.006 cm H2O(-1) x sec(-1) x log microg(-1) and 0.082 +/- 0.006 cm H2O(-1) x sec(-1) x log microg(-1), respectively, P < 0.001). Repeatability and coefficients of variation were always acceptable. Continuous SaO2 monitoring in some children of the CA group demonstrated the safety of the method, which is proposed as a technique in future studies.

Recombinant Aspergillus fumigatus allergens: from the nucleotide sequences to clinical applications

Members of the genus Aspergillus are opportunistic pathogens for cold- and warm-blooded animals. They are associated with an impressive spectrum of diseases in humans, ranging from benign colonization of the lung to life-threatening diseases such as invasive aspergillosis or allergic bronchopulmonary aspergillosis (ABPA). Aspergillus fumigatus is the etiological agent identified in most of the Aspergillus-related human diseases and is therefore of particular clinical relevance. A major problem in the diagnosis of A. fumigatus-related complications arises from the lack of standardized fungal extracts. The allergenicity of commercial A. fumigatus extracts depends on many factors including the strain used, growth conditions, harvesting and extraction procedures hampering the development of diagnostic reagents suitable for the discrimination between A. fumigatus-related diseases. Molecular DNA/RNA technologies and biotechnological procedures allow cloning, characterization and production of large amounts of single, highly pure allergens. The development of phage surface display technologies for cloning cDNAs has speeded up the isolation of candidate cDNAs encoding allergens. Screening of an A. fumigatus cDNA library displayed on the surface of phage M13 allowed characterization and production of a panel of allergens identified as proteins with known biological function or as allergens without sequence homology to known proteins. They belong to two functional categories: secreted and cytoplasmic proteins. Secreted allergens are recognized by serum IgE of A. fumigatus-sensitized individuals with or without ABPA, whereas nonsecreted allergens are exclusively recognized by serum IgE of ABPA patients. The dissection of IgE-mediated immune responses to single A. fumigatus allergens allows a discrimination between ABPA and A. fumigatus sensitization with high specificity and sensitivity demonstrating the power of recombinant allergens for the differential diagnosis of A. fumigatus-related pulmonary complications.