Age-related changes in bronchial hyperreactivity to methacholine in asthmatic children

Cross-sectional study of cholinergic urticaria subtypes and bronchial hyperresponsiveness

Cholinergic urticaria (CholU) is classified into several subtypes: (1) conventional sweat allergy-type CholU (conventional SAT-CholU), (2) CholU with palpebral angioedema (CholU-PA), 3) CholU with acquired anhidrosis and/or hypohidrosis (CholU-Anhd); 1) and 2) include SAT based on pathogenesis. There have been no studies on differences in the prevalence of bronchial asthma among the subtypes. We analyzed bronchial responsiveness using the methacholine dose indicator D_min, respiratory symptoms, and exhaled nitric oxide (FeNO). Median log10 D_min (interquartile range) of patients with conventional SAT-CholU (n = 11), CholU-PA (n = 11), and CholU-Anhd (n = 11) was 0.381 (- 0.829, 1.079), 0.717 (0.249, 0.787), and 1.318 (0.121, 1.699), respectively (p = 0.516). Respiratory symptoms were less frequently observed in CholU-Anhd than in conventional SAT-CholU or CholU-PA. FeNO of patients with conventional SAT-CholU, CholU-PA, and CholU-Anhd was 23 (18.5, 65.0), 39 (32.0, 59.5), and 25 (19.0, 33.0) ppb, respectively (p = 0.237). Nine% of conventional SAT-CholU patients and more than half of CholU-PA patients required treatment for asthma. Log D_min tended to be lower in patients with SAT-CholU than in those with CholU-Anhd. CholU-PA might be associated with asthma.

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/P_T and P₄/P_T) 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 β₂ 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 β₂ agonist inhalation. An analysis of the breath sound spectrum showed that P_T, P₃/P_T, P₄/P_T, RPF₅₀ and RPF₇₅ were significantly increased after β₂ agonist inhalation.

CONCLUSIONS

Children with CVA showed a high rate of inaudible wheezing that disappeared after β₂ agonist inhalation. Changes in the spectrum curve indices also indicated the bronchial reversibility. These results may suggest the characteristics of CVA in children.

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/A_T and B₄/A_T, 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 β₂ agonist inhalation.

RESULTS

In Study 1, the data showed statistical intra- and inter-observer reliability in A₃/A_T (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/A_T and RPF₅₀ significantly changed after β₂ 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.

Concerns with beta2-agonists in pediatric asthma - a clinical perspective

Beta2-adrenoreceptor agonists (β2-agonists) are extensively used in the treatment of childhood asthma. However, there have been concerns regarding their adverse effects and safety. In 2005, the FDA commissioned a "Black Box Warning" communicating the potential for an increased risk for serious asthma exacerbations or asthma related deaths, with the regular use of LABAs. In a meta-analysis of controlled clinical trials, the incidence of severe adverse events appeared to be highest in the 4-11 year age group. Several mechanisms have been proposed regarding the risk of regular use of β2-agonists, such as masking patients' perception of worsening asthma, desensitization and downregulation of the β2-adrenoreceptor, pro-inflammatory effects of β2-agonists, pharmacogenetic effects of β2-adrenoreceptor polymorphisms and age related differences in pathophysiology of asthma. In this paper, we review β2-receptor pharmacology, discuss the concerns regarding treatment with β2-agonists in childhood asthma, and provide suggestions for clinical pediatric practice in the light of current literature.

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.

Response to Nonallergenic Irritants in Children With Allergic and Nonallergic Rhinitis

Purpose

Nonallergenic irritants can aggravate the symptoms of rhinitis. We investigated the clinical responses of children with allergic rhinitis (AR) and nonallergic rhinitis (NAR) to nonallergenic irritants, and identified factors associated with these responses.

Methods

Children with chronic rhinitis (n=208) were classified as having AR or NAR based on the presence of aeroallergen-specific IgE. Healthy controls (n=24) were recruited for comparison. The Allergic Rhinitis and its Impact on Asthma (ARIA) guidelines were used to classify patients, and their irritant score (0-21 points) and current symptom score (5-35 points) were measured. Subjects with irritant scores ≥3 and <3 were classified as having irritant and nonirritant rhinitis, respectively.

Results

The mean age of enrolled subjects was 6.8 years (range: 1.8-16.0 years). The AR and NAR groups had similar irritant scores (P=0.394) and proportions of subjects with irritant scores ≥3 (P=0.105). Irritant score correlated positively with symptom score (P=0.005), and the proportion of subjects with irritant scores ≥3 was greater in children with moderate-severe rhinitis than in those with mild rhinitis (P=0.046). Multiple logistic regression analysis indicated that the presence of atopic eczema increased the risk for sensitivity to a nonallergenic irritant (aOR=2.928, 95% CI 1.567-5.473, P=0.001).

Conclusions

Response to a nonallergenic irritant was useful for gauging the severity of rhinitis, but not for differentiating AR from NAR. AR and NAR patients with atopic eczema may increase nasal sensitivity to nonallergenic irritants.

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.

Relationship between bronchial hyperresponsiveness and lung function in children age 5 and 6 with and without asthma

BACKGROUND AND OBJECTIVE

It is unknown whether wheezy children have bronchial hyperresponsiveness (BHR) or which lung function parameters are correlated with BHR in children. We evaluated the relationship between BHR parameters and the lung functions by minimizing the effects of age and height in asthmatic, non-asthmatic wheezers and healthy children.

METHODS

The subjects comprised of 154 children aged 5 and 6 years (78 males, 76 females), who were divided into three groups: asthmatics, non-asthmatic wheezers and healthy controls. Spirometry and a methacholine inhalation challenge by the oscillation method were performed.

RESULTS

The age of the study cohort was 5.9 ± 0.2 years (mean ± standard deviation), and the height was 114.4 ± 5.3 cm. No significant differences in height, weight, body mass index or lung function were observed in the three groups. The minimal dose of methacholine to start bronchoconstriction, a parameter of bronchial sensitivity, was lower in asthmatics and non-asthmatic wheezers than that in controls. The speed of bronchoconstriction in response to methacholine, a parameter of bronchial reactivity, was strongly correlated with baseline respiratory resistance (Rrs cont) in all three groups.

CONCLUSIONS

Our data suggest that it not possible to distinguish preschool children with asthma from non-asthmatic wheezers based on their bronchial sensitivity and that the baseline Rrs has a strong effect on the bronchial reactivity 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.

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.

Relationship between bronchial hyperreactivity and asthma remission during adolescence

BACKGROUND

Many children with asthma outgrow this disease after the onset of puberty. However, the precise mechanism of outgrowing asthma in children is still unclear.

OBJECTIVE

To evaluate the characteristics of respiratory physiology during adolescence.

METHODS

The results of the lung function test and methacholine inhalation challenge were prospectively evaluated in adolescent patients with asthma with and without symptoms. One hundred sixty children with asthma participated. Twenty-eight children had symptom-free adolescent asthma (i.e., remission asthma) (boy to girl ratio, 16:12; mean age, 14.6 years), 25 had intermittent adolescent asthma (boy to girl ratio, 16:9; mean age, 14.9 years), and 47 had symptomatic adolescent asthma (boy to girl ratio, 27:20; mean age, 12.7 years). For comparison purposes, 60 younger children with symptomatic asthma participated. The parameters of bronchial hyperresponsiveness, baseline respiratory resistance, threshold of methacholine (Dmin) (bronchial sensitivity), and speed of bronchial constriction (Sm) (bronchial reactivity) were measured by methacholine inhalation challenge using the continuous oscillation method.

RESULTS

There was no significant difference in lung function results, such as forced vital capacity and forced expiratory volume in 1 second, between the intermittent asthma and the remission asthma groups. Also, there was no significant difference in baseline respiratory resistance and Dmin between the 2 groups. However, the value of Sm of the remission asthma group was significantly lower than that of the intermittent asthma group (P = .02) and the symptomatic asthma group (P = .02).

CONCLUSIONS

These data show that the adolescents with asthma remission showed a significant decrease of Sm, whereas Dmin was not changed. These results suggest one of the mechanisms by which asthma is outgrown in children and explain the common clinical aspects of adolescent asthma, such as symptom-free but bronchial hyperresponsive asthma.

Effect of bronchoconstriction on exhaled nitric oxide levels in healthy and asthmatic children

BACKGROUND

Exhaled nitric oxide (eNO) has recently been proposed to be a noninvasive marker of airway inflammation in asthma.

OBJECTIVE

To evaluate the effect of bronchoconstriction by means of methacholine inhalation challenge on levels of eNO in children.

METHODS

Spirometry, impulse oscillometry, and eNO measurements were performed before and after methacholine inhalation challenge (bronchoconstriction phase) and after beta2-agonist inhalation (bronchodilation phase) in 92 children (62 children with asthma, 13 wheezy children, and 17 healthy children).

RESULTS

A significant decrease occurred in the eNO level after methacholine inhalation challenge (P < .01). This decrease did not correlate with the percentage decrease in forced expiratory volume in 1 second or with the change in large airway resistance (R20), but it did correlate with the percentage decline in maximal expiratory flow at 50% vital capacity and with the change in small airway resistance (R5-R20). The eNO decrease lasted for 15 minutes after beta2-agonist inhalation in the group with a high percentage decrease in R5-R20 (>200%). On the other hand, in the group with a low percentage decrease in R5-R20 (< or =200%), eNO recovered to the previous level immediately after beta2-agonist inhalation.

CONCLUSIONS

The eNO level significantly decreases after methacholine inhalation challenge. This decrease primarily depends on bronchoconstriction of the small airways.

Airway hyper-responsiveness in young adults with asthma that remitted either during or before adolescence

BACKGROUND AND OBJECTIVE

More than 50% of patients with childhood asthma enter clinical remission by puberty, although 40-50% of these people will probably develop asthma symptoms during early adulthood. The mechanism of relapsing asthma in early adulthood remains unclear. This study determined the characteristics of young adults whose asthma remitted either during or before adolescence.

METHODS

A comparative study was performed on 24 students whose childhood asthma had gone into clinical remission by puberty (remission group), 25 atopic students with no history of asthma (atopy group) and 19 non-atopic students without allergic diseases (control group). Examinations included spirometry, levels of serum-specific IgE-antibodies, airway responsiveness to methacholine, exhaled nitric oxide (eNO) and evidence of airway inflammation in induced sputum.

RESULTS

Airway responsiveness (P < 0.01), eosinophil counts in sputum (P < 0.05) and the prevalence of sensitization to Dermatophagoides forinae (P < 0.01) were significantly higher, and FEF(25-75%) and FEF(75%) (P < 0.01) were significantly lower in the remission group than in the atopy and control groups. Furthermore, 50% and 33% of the remission group had airway hyper-responsiveness (AHR) and sputum eosinophilia, respectively. The eNO levels in the remission (P < 0.01) and atopy (P < 0.05) groups were significantly higher than in controls. Remission group members with AHR had a significantly longer period of childhood asthma, a shorter period of remission and greater airway eosinophilic inflammation than those without AHR (P < 0.05).

CONCLUSION

One half of young adults with childhood asthma that remitted either during or before adolescence continued to have evidence of AHR and airway eosinophilic inflammation, and might be at risk of future relapse.

Effect of age on relationship between exhaled nitric oxide and airway hyperresponsiveness in asthmatic children

BACKGROUND

Numerous studies have examined the relationship between the fractional concentration of exhaled nitric oxide (Feno) and airway hyperresponsiveness (AHR). Our objective was to determine the effects of age on the relationship between Feno and AHR in asthmatic children.

METHODS

AHR was examined in 267 asthmatic patients (age range, 5 to 20 years). A challenge test was performed using acetylcholine chloride (Ach). We determined the provocative concentration of Ach producing a 20% decrease in FEV(1) from baseline (PC(20)). Feno was examined using the recommended online method before the Ach challenge test.

RESULTS

In children < 12 years of age (range, 5 to 11 years), decreasing AHR (PC(20)) was significantly related to higher Feno (r = -0.43; beta = -0.28; p < 0.001). In adolescents >or= 12 years of age (range, 12 to 20 years), decreasing PC(20) was associated with peripheral airway obstruction (FEV(1): r = 0.32; beta = 5.5; p = 0.002; forced expiratory flow at 50% of the FVC: r = 0.24; beta=8.4; p = 0.006; and forced expiratory flow at 25% of FVC: r = 0.28; beta=11.4; p = 0.002). AHR and Feno were weakly related (r = -0.18; beta = -0.14; p = 0.02).

CONCLUSIONS

In children with asthma, AHR is associated with airway inflammation. AHR in children with asthma may consist of variable components mainly reflecting airway inflammation. In contrast, in adolescents with asthma, AHR is associated with airway structural changes and weakly with airway inflammation. AHR in adolescents with asthma may consist of chronic components mainly reflecting airway remodeling.

Factors affecting bronchial hyperreactivity in asthmatic children

Bronchial hyperresponsiveness (BHR), the exaggerated airway narrowing in response to nonspesific stimuli, is a common characteristic of asthma. One hundred thirty-five children who were diagnosed asthma in the outpatient clinic of Gazi University Hospital, Pediatric Allergy and Asthma Department between January 2007 and January 2008 were retrospectively analysed from the asthma database of the division. BHR was not found to be different according to sex. Younger the age of the patient, more severe was BHR (p = 0.096, r = 0.164). Younger the age at onset of the symptoms, the more severe was the BHR (p < 0.001, r = 0.307). Patients who had an asthmatic first degree relative and who were exposed to passive smoking at home, had more severe BHR (p = 0.006 and p = 0.032, respectively). There were more hospitalizations among the asthmatic children with moderate-severe BHR (p = 0.027) however no correlation was found between chronic asthma severity and the degree of BHR). In this study we found that age, age at onset of symptoms, having a parent with asthma, exposure to tobacco smoke and baseline lung function are related to BHR measured at referral. Serum levels of Ig E or skin prick test positivity were not found to have any effect on BHR severity. Considering BHR severity, we could not reveal any relation between atopic and nonatopic children. However among atopic subjects, the ones with indoor allergen sensitization had more severe BHR.

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.

Evaluation of bronchial hyperresponsiveness by monitoring of transcutaneous oxygen tension and arterial oxygen saturation during methacholine challenge in asthmatic children

BACKGROUND

Bronchial hyperresponsiveness (BHR) is a key feature of asthma, but the measurement of BHR is hampered by the fact that most tests of airway caliber are difficult to conduct at a young age. Methacholine-induced bronchoconstriction is associated with significant hypoxemia, which can be assessed noninvasively by transcutaneous oxygen pressure (tcPO2) and pulse oximetry. Evaluating BHR by monitoring tcPO2 instead of respiratory resistance (Rrs) has been used over a wide age range in childhood.

OBJECTIVE

To investigate whether there is a consistent relationship between changes in arterial oxygen saturation (SaO2) and respiratory resistance (Rrs) similar to the relationship between tcPO2 and Rrs during methacholine challenge in young children and to assess the usefulness of SaO2 as a parameter for the indirect measurement of BHR.

METHOD

We performed methacholine inhalation challenge by monitoring SaO2, tcPO2 and Rrs in 37 asthmatic children 5 to 7 years of age. Consecutive doses of methacholine were doubled until a 10% decrease in tcPO2 from the baseline was reached. We recorded the cumulative dose of methacholine (Dmin) at the inflection point of tcPO2 (Dmin-tcPO2), SaO2 (Dmin-SaO2), and Rrs(Dmin-Rrs).

RESULTS

The mean value of Dmin-Rrs was 4.27 +/- 2.02 units, the mean value of Dmin-tcPO2 was 4.48 +/- 2.01 units, and the mean value of Dmin-SaO2 was 4.57 +/- 0.20 units. Inhalation of increasing doses of methacholine raised Rrs curvilinearly and depressed tcPO2 and SaO2. There were no significant differences between any of the parameters. There were significant relationships between Dmin-tcPO2 and Dmin-Rrs (r = 0.914, p < 0.001) and between Dmin-SaO2 and Dmin-Rrs (r = 0.905, p < 0.001) and a relationship between Dmin-tcPO2 and Dmin-SaO2 (r = 0.949, p < 0.001).

CONCLUSION

We concluded that measurement of SaO2 and/or tcPO2 during methacholine inhalation challenge may be used to assess bronchial hyperresponsiveness. This study showed that both SaO2 and tcPO2 monitoring are safe, useful, and tolerable for use in children who are too young to cooperate with lung function tests.

Characteristics of asthma resistant to moderate dose inhaled corticosteroid treatment on bronchial hyperresponsiveness

OBJECT

This study was performed to determine the clinical characteristics of asthmatics with bronchial hyperresponsiveness (BHR) that could not be normalized by 6 months of treatment with a moderate dose of an inhaled corticosteroid (ICS).

METHODS

Thirty-four symptomatic patients with mild to moderate asthma, who had never received any ICS, were treated with 200 mug of inhaled fluticasone propionate twice a day for 6 months. Spirometry, BHR to methacholine, exhaled nitric oxide (NO) and eosinophils in induced sputum were examined before and 2 and 6 months after beginning treatment.

RESULTS

FEV1 was increased and bronchial responsiveness, exhaled NO and sputum eosinophilia were significantly decreased 2 and 6 months after starting ICS treatment. Bronchial responsiveness was further decreased at 6 months together with a further increase in FEV1. In 13 patients, BHR was not normalized despite the 6 months of treatment. This group showed a higher prevalence of males, those with a smoking history and airflow limitation, a higher eosinophil count in the sputum following 6 months of treatment and a longer history of asthma. Multiple, stepwise, linear regression analysis showed that sputum eosinophilia and lower FEV1/FVC following 6 months of treatment and a longer history of asthma were significant independent determinants for BHR after 6 months of ICS treatment.

CONCLUSIONS

These findings suggest that the resistance to a moderate dose of ICS for BHR in asthmatics may be significantly associated with remained airflow limitation, eosinophilic airway inflammation resistive to moderate dose of ICS, and delayed introduction of ICS therapy.

Bronchial sensitivity and bronchial reactivity in children with cough variant asthma

BACKGROUND

Cough variant asthma (CVA) is diagnosed in some children with chronic cough who do not have wheezing. However, the precise mechanism of CVA in children is unclear.

OBJECTIVE

To evaluate the physiologic differences in the airways of children with classic asthma and CVA, the methacholine dose-response curves of respiratory resistance (Rrs) were studied.

PATIENTS AND METHODS

CVA was diagnosed in 31 children with chronic cough (age range, 5 to 14 years; 19 boys and 12 girls; mean age, 8.5 years) on the basis of methacholine inhalation challenge using an oscillation method. For comparison, the study included 86 age-matched children with classic asthma (age range, 5 to 15 years; 42 boys and 44 girls; mean age, 9.5 years), 25 age-matched children with cough (age range, 5 to 15 years; 17 boys and 8 girls; mean age, 8.8 years), and 23 age-matched control subjects (8 boys and 15 girls; mean age, 9.2 years). Consecutive doses of methacholine were doubled until a 200% increase in Rrs from baseline was reached. The cumulative dose of methacholine at the inflection point of Rrs was considered to represent the bronchial sensitivity to inhaled methacholine (minimum dose of methacholine [Dmin]). The slope of the methacholine dose-response curve (SRrs), which was considered to represent bronchial reactivity, was measured from the increasing Rrs curve.

RESULTS

The values of Dmin in classic asthma patients and in CVA patients were significantly lower than those for cough patients and control subjects. There was no significant difference in the values of Dmin between the classic asthma and CVA patients. The value of SRrs in CVA patients was significantly lower than that in classic asthma patients, cough patients, and control subjects (p < 0.05, p < 0.01, and p < 0.01, respectively). There was no significant difference in the value of SRrs between classic asthma patients, cough patients, and control subjects.

CONCLUSIONS

These data show that bronchial reactivity in the children with CVA was significantly lower than that in the children with classic asthma, and this specificity has an effect on prolonged cough without wheezing in children with CVA.

Childhood cough variant asthma and its relationship to classic asthma

BACKGROUND

In pediatrics, some patients with chronic cough who have no evidence of a causative disease are diagnosed as having cough variant asthma (CVA). The precise prognosis of infants and children with CVA, however, is still unclear.

OBJECTIVE

To evaluate the relationship between CVA and classic asthma in childhood.

METHODS

To diagnose CVA, we performed a methacholine inhalation challenge with use of a transcutaneous oxygen pressure (tcPO2) monitoring system in 100 children with chronic cough, and 75 children (45 boys and 30 girls; mean age, 5.7 years) were diagnosed as having CVA. These patients underwent follow-up monitoring for more than 3 years to ascertain whether classic asthma developed. For comparison, 53 age-matched children with classic asthma (30 boys and 23 girls; mean age, 5.6 years) and 30 age-matched control subjects (12 boys and 18 girls; mean age, 5.5 years) also participated in this study. Consecutive doses of methacholine were doubled until a 10% decrease in tcPO2 from the baseline was reached. The cumulative dose of methacholine at the inflection point of tcPO2 (Dmin-PO2) was considered to represent the sensitivity of tcPO2 to inhaled methacholine.

RESULTS

After 3 years or more of follow-up assessments, 52 of the 75 patients answered our questionnaire. Of the responding patients, 28 had been diagnosed as having classic asthma. A significant difference was noted in the age at onset of CVA between the children in whom classic asthma developed (the asthma-developed group) and those in whom classic asthma did not develop (the asthma-free group). No statistically significant differences in Dmin-PO2 between the asthma-developed group and the asthma-free group or between the girls and the boys, however, were foun

CONCLUSIONS

This study showed that 75% of children with chronic cough had CVA, that classic asthma developed in 54% of the children with CVA, and that it is not the severity of bronchial hyperresponsiveness in CVA but the age at onset of CVA that is a risk factor for the development of classic asthma in childhood CVA.

Sputum eosinophilia and bronchial responsiveness in patients with chronic non-productive cough responsive to anti-asthma therapy

OBJECTIVE

We aimed to examine airway inflammation and bronchial responsiveness in patients with chronic non-productive cough responsive to anti-asthma therapy.

METHODOLOGY

Bronchial responsiveness to methacholine as well as the number of inflammatory cells and concentration of eosinophil cationic protein (ECP) in induced sputum were measured in 42 patients with chronic non-productive cough of unknown origin. Their response to bronchodilator, antiallergic and inhaled or oral glucocorticoid therapy was subsequently assessed.

RESULTS

Complete remission of coughing was attained with anti-asthma therapies in 34 patients (responder group), while eight patients did not respond (non-responder group). Twenty patients in the responder group and three in the non-responder group showed bronchial hyperresponsiveness (BHR). The number of eosinophils and ECP levels in the sputum from responders with BHR were significantly increased when compared with those from non-responders and healthy subjects. These sputum measures were also significantly increased in responders without BHR when compared with healthy subjects. However, there were no significant differences in these inflammatory markers between the responders with and without BHR. The neutrophil numbers in the sputum from non-responders and responders both with and without BHR were also significantly higher than in control subjects, but there were no significant differences.

CONCLUSIONS

These findings suggest that patients with chronic non-productive cough responsive to anti-asthma therapy characteristically have eosinophilic airway inflammation, which may play an important role in the development of chronic cough. Furthermore, the evaluation of not only bronchial responsiveness but also airway inflammation by examination of induced sputum may be useful for diagnosis and deciding on therapeutic strategies.

Low-attenuation areas of the lungs on high-resolution computed tomography in asthma

To investigate the low-attenuation areas of the lungs (LAA) in asthma, we compared the mean lung density (MLD) and the LAA in 22 asthmatics (12 ex-smokers and 10 nonsmokers) and 13 patients with chronic obstructive pulmonary disease (COPD) by high-resolution computed tomography. The MLD and the relative area of the lung with attenuation values lower than -950 Hounsfield Units at full inspiration (inspiratory RA950) were significantly different in nonsmoking asthmatics compared to patients with COPD and asthmatics with a smoking history. The MLD and the RA950 correlated significantly with the FEV1 in all groups and with the DL(CO) in patients with COPD and asthmatics with a smoking history but not in nonsmoking asthmatics. We concluded that the LAA in asthmatics with a smoking history indicates the presence of emphysema, but in nonsmoking asthmatics it reflects hyperinflation and nonemphysematous expiratory airflow limitation rather than emphysematous lesions.

Age-dependent relationship between bronchial hyperresponsiveness to methacholine and total serum IgE level in asthmatic children

BACKGROUND

A relationship between nonspecific bronchial hyperresponsiveness and allergic airway inflammation has been reported in children and in adults with asthma, but the relationship in infants with asthma is still unclear.

OBJECTIVE

To evaluate the relationship between bronchial hyperresponsiveness and total serum IgE level throughout childhood. Bronchial reactivity to methacholine from the age of 1 to 16 years was studied by methacholine inhalation challenge using transcutaneous oxygen pressure (tcPO2) monitoring.

METHODS

Two hundred one asthmatic children (boys:girls = 132:69; 7.3+/-4.0 years of age, mean +/- SD) were enrolled in this study. The tcPO2 was measured using a tcPO2 monitor. Serial doses of methacholine were doubled until a 10% decrease in tcPO2 from the baseline was reached. The cumulative dose of methacholine at the inflection point of tcPO2 was considered to represent the bronchial reactivity to methacholine.

RESULTS

There was no relationship between the cumulative dose of methacholine at the inflection point of tcPO2 and total serum IgE level in the group of children aged 1 to 4 years (P = 0.212), but significant correlations were found in the groups aged 5 to 10 years and 11 to 16 years (P = 0.044 and P = 0.014, respectively).

CONCLUSIONS

We conclude that there is an age-dependent relationship between bronchial reactivity to methacholine and the total serum IgE level and that inhaled allergens, which were more common allergens in older children, may have some effects on the degree of bronchial reactivity to methacholine in children with asthma.

Relationship between bronchial hyperresponsiveness and development of asthma in wheezy infants

STUDY OBJECTIVES

To evaluate the relationship between bronchial hyperresponsiveness (BHR) in infants with wheezing and the subsequent development of asthma.

INTERVENTION

Bronchial reactivity to inhaled methacholine (BRm) during the infantile period was studied using the transcutaneous partial pressure of oxygen (tcPO(2)) method. Children were followed long-term for the development of asthma.

PATIENTS

Fourteen children with bronchiolitis (mean age, 0.7 years) and 48 with wheezy bronchitis (mean age, 2.3 years) were enrolled. For comparison, 40 children with asthma (mean age, 4.6 years) and 27 healthy control subjects without chronic respiratory disease (mean age, 2.7 years) were studied.

MEASUREMENTS

Consecutive doses of methacholine were doubled until a 10% decrease in tcPO(2) from baseline was reached. The cumulative dose of methacholine (Dmin) at the inflection point of tcPO(2) (Dmin-PO(2)) was recorded.

RESULTS

During > 10 years of follow-up, seven patients with bronchiolitis developed asthma and all patients in the higher BRm set developed asthma, compared with none in the lower BRm set. In the wheezy bronchitis group, Dmin-PO(2) values in the 32 patients who developed asthma were lower than those in patients who had not developed asthma (p < 0.001).

CONCLUSIONS

We concluded that there is a tendency for infants with a clinical diagnosis of bronchiolitis or wheezy bronchitis and who show BHR in the infantile period to develop asthma. The presence of increased BHR after infantile respiratory diseases associated with wheezing may be a prelude to the development of childhood asthma.

Development of bronchial hyperresponsiveness during childhood

Bronchial hyperresponsiveness (BHR) produces the characteristic pathological abnormalities seen in asthma and clearly plays a central role in the pathophysiology of asthma. The presence of BHR has been demonstrated in infants with asthma, as has the possibility of BHR persisting through the childhood period. The level of BHR may not only reflect the state of the airways, as a marker of airway dysfunction, but may also predict the persistent prognosis of the disease. Thus, measurement of BHR may provide important information about the symptoms and lung function in children with asthma. In view of multiple pathophysiological mechanisms, BHR does not seem to have a single cause. Many potential confounding variables, such as age, gender and genetic status, and some environmental factors, such as allergens, infections, and pollutants, could be responsible for the establishment of childhood BHR. There may be differences between the mechanisms that induce transient BHR and the mechanisms that induce persistent BHR. Also, there may be differences between the causes that induce BHR in the infantile period and the causes that maintain persistent BHR during childhood asthma. There is also disagreement as to the most suitable method to measure BHR in children, especially in infants. The assessment of BHR in young children has not been uniformly successful, and measurements of BHR changes over the childhood period (are associated with a number of problems. To resolve these problems, there may be two ways to study childhood BHR. One is to use age-matched specific techniques to clarify the precise BHR in each age group; the other is to use simple techniques that can be performed over the childhood period on a large number of subjects. In studies of infantile respirator, dysfunction the ultimate goal is to establish a simple, noninvasive method by which measurements of respiratory function may be obtained in infants. Further investigations and acceptable methods will be needed to clarify, the mechanisms involved in the establishment of asthma throughout the childhood period.

Bronchial hyperresponsiveness before and after the diagnosis of bronchial asthma in children

OBJECTIVE

To assess at what age bronchial hyperresponsiveness (BHR) is acquired in children with asthma.

BACKGROUND

A relationship between BHR and infantile wheezing diseases has been reported. Infants with a genetic predisposition to atopy are more likely to wheeze with respiratory viral infection or bronchiolitis, and it is suspected that the continued BHR after the first attack of asthma may be induced or triggered by some viral infections. Also, recent studies have reported the existence of atopic and BHR-related genes. However, whether BHR is congenital or acquired after asthma attacks, and when BHR in children with asthma is established or acquired remain unclear.

METHODS

We performed methacholine inhalation challenge using a transcutaneous oxygen pressure (tcPO(2)) monitoring system in 205 children without asthma from 6 months to 6 years of age. During follow-up, 18 of these participants were diagnosed with asthma (group N-A). This group and 15 age-matched children without asthma (group N-N) were tested twice using methacholine inhalation challenge. For comparison, 39 age-matched atopic-type asthmatic children (group A-A) were also given the inhalation challenge twice. Methacholine inhalation challenge using a tcPO(2) monitoring system was performed while the participants were asleep in the supine position. Sequential doses of inhaled methacholine delivered by oxygen mask were doubled until a 10% decrease in tcPO(2) from the baseline was reached. The cumulative dose of methacholine at the inflection point of tcPO(2) (minimal dose of methacholine [Dmin]-PO(2)) was considered to represent BHR.

RESULTS

In groups N-N and A-A, there was no difference in Dmin-PO(2) between the first and second challenge. However, the Dmin-PO(2) in group N-A significantly decreased from the first challenge to the second challenge. There was no significant difference between the Dmin-PO(2) in group N-N and the first Dmin-PO(2) in group N-A; or between the Dmin-PO(2) in group A-A and the second Dmin-PO(2) in group N-A.

CONCLUSIONS

These data suggest that BHR in many infants with asthma is acquired after several asthma attacks.bronchial hyperresponsiveness, childhood asthma, methacholine inhalation challenge, transcutaneous oxygen pressure.

Racial differences in physiologic parameters related to asthma among middle-class children

BACKGROUND

Asthma morbidity and mortality are higher in the United States for African-American (AA) children when compared to European-American (EA) children.

STUDY OBJECTIVES

To explore racial differences in physiologic factors associated with pediatric asthma severity.

DESIGN

Cross-sectional.

METHODS

We analyzed data from two groups of children in suburban Detroit, one of which contains non-urban, middle-class AA children, a group not usually included in childhood asthma studies. All children were 6 to 8 years of age. Clinical evaluations included medical history, physical examination, skin testing, spirometry, and methacholine challenge.

RESULTS

The study population (n = 569) was 14% African American, 51% of the participants were male, and the mean age was 6.8 +/- 0.4 years. Socioeconomic status (parental education) was similar overall by race, although some strata-specific differences were observed. The prevalence of physician-diagnosed asthma was 10% for both AA and EA groups. AA children were more reactive to methacholine than EA children (42% vs 22%, respectively; p = 0.001), and had significantly higher total IgE than EA children (geometric mean, 60. 6 vs 27.5 IU/mL; p = 0.001). Serum IgE was related to methacholine reactivity in EA children (p = 0.001), but not AA children (p = 0. 73). These differences remained after adjustment for gender, age, parental education, parental smoking, and maternal smoking during pregnancy.

CONCLUSIONS

Our data support previous reports of racial differences in lung volume, airway responsiveness, and serum IgE concentrations. We found a racial difference in the relationship between total serum IgE and airway responsiveness that is unreported elsewhere. Overall, our results suggest that AA children may be predisposed to asthma.

Bronchial reactivity to inhaled methacholine in infants with asthma and age-matched controls

To evaluate bronchial hyperresponsiveness (BHR) in infants with asthma and the influence of aging on BHR during the infantile period, bronchial reactivity to inhaled methacholine (BRm) in infants was monitored using the transcutaneous oxygen pressure (tcPO2) method. One hundred thirty-seven infants with asthma (from 1 to 5 years, mean 3.4 years) and 97 age-matched children without chronic respiratory diseases (from 6 months to 5 years, mean 2.1 years) were enrolled in this study. Consecutive doses of methacholine were doubled until a 10% decrease in tcPO2 from the baseline was reached. The cumulative dose of methacholine at the inflection point of tcPO2 (Dmin-PO2) was considered to represent the reactivity of tcPO2 to inhaled methacholine. Dmin-PO2 values in the asthma groups were lower than those in the control groups in each year-group from 1 to 5. There was no statistical difference in Dmin-PO2 among the 1-4-year-old asthma groups, but Dmin-PO2 in the 5-year-old asthma group was significantly lower than Dmin-PO2 in the 1-4-year-old asthma groups. The same age-related change in Dmin-PO2 was also seen in the control groups. There was no difference in age-related Dmin-PO2 change between the female group and the male group. We concluded that BRm in asthmatic children increases during the infantile period, and that the age-related changes in BRm, observed in both asthmatic and control infants, may have an effect on the clinical symptoms of asthma during childhood.

Difference in airway reactivity in children with atopic vs nonatopic asthma

STUDY OBJECTIVE

To examine the difference in the mechanisms of bronchial hyperresponsiveness (BHR) in nonatopic asthma and in atopic asthma, we studied bronchial reactivity against nonspecific stimuli in children with atopic asthma and nonatopic asthma.

DESIGN AND PARTICIPANTS

Fourteen children with nonatopic asthma, 24 children with atopic asthma, and 20 age-matched controls participated in this study.

MEASUREMENTS

Inhalation challenge was performed by administering progressively doubling doses of methacholine with a continuous inhalation provocation method. The speed of bronchoconstriction to methacholine (Sm) and the speed of reversal of bronchoconstriction to methacholine after inhalation of a beta2-agonist (r-Sm), which was considered to represent the effect of the beta2-agonist, were calculated from the dose-response curve.

RESULTS

The value of Sm was higher in the nonatopic asthma group than in the atopic asthma group and the control group. The value of r-Sm was also higher in the nonatopic asthma group than in the atopic asthma group, but did not differ from that in the control group.

CONCLUSION

These results indicate that bronchial reactivity against methacholine and the beta2-agonist was greater in nonatopic asthma than in atopic asthma, and that the mechanism of BHR in children with nonatopic asthma may differ from that in children with atopic asthma.

Diurnal variation of peak expiratory flow in children with cough variant asthma

Cough variant asthma (CVA) is thought to be a variant form of asthma in which cough is the sole clinical manifestation of airways hyperresponsiveness, a characteristic feature of asthma. Another characteristic feature of asthma includes an increased diurnal variation of peak expiratory flow (PEF) compared to normal subjects. To examine whether diurnal variation of PEF might also increase in children with CVA, we have examined the degree of diurnal variation of PEF in these children (n = 7) by measuring peak flow serially for a week, and compared it with those in mild to moderate asthma (n = 17) and in control children without cough (n = 8). In control children without cough, the average value of the mean diurnal variation of PEF was 10.4 +/- 0.8%. In both groups of children with asthma and with CVA, there was a significant increase in the value (20.5 +/- 1.3% and 23.6 +/- 3.6%, respectively) compared to that in control children (p < 0.01 in both groups), although there was no significant difference between these 2 groups. These results show that mild, but significant airway obstruction is occurring in children with CVA, although clinical wheezing is not recognized. Serial measurements of diurnal variation of PEF may be helpful for the diagnosis of CVA in children.

Transcutaneous oxygen tension measurements during methacholine challenge of prematurity in infants with chronic lung disease

Chronic lung disease (CLD) of prematurity may be caused by a number of insults during mechanical ventilation, including barotrauma and hyperoxia. To evaluate bronchial hyperresponsiveness (BHR) in infants with CLD of prematurity, we measured changes in transcutaneous oxygen tensions (tcPO2) during methacholine inhalation challenge. Twelve infants with CLD and 22 age-matched children without respiratory diseases were enrolled in this study (ages--5 to 36 months; mean age--16.2 months). Serial doses of methacholine were doubled until a 10% decrease in tcPO2 from baseline was reached. The cumulative dose of methacholine inhaled by the time tcPO2 had been reached (Dmin-PO2) was considered to represent the dose at which reactivity to methacholine (RO2meth) had occurred. In the CLD group, Dmin-PO2 (3.50 +/- 0.1 log x milli-units) was significantly lower than in the preterm control infant group (4.31 +/- 0.2 log x milli-units) and the term infant group (4.21 +/- 0.1 log x milli-units) (P = 0.004, P < 0.001). Dmin-PO2 in the preterm control infant group was not significantly different than in the term infant group (P > 0.5). These results suggest that infants who require additional therapeutic oxygen and mechanical ventilation during the early months of life are at risk of developing early-onset, long-lasting respiratory disease that is related to an acquired BHR.

Serum eosinophil cationic protein as a marker of eosinophilic inflammation in asthma

BACKGROUND

The serum level of eosinophil cationic protein (ECP) has been used as a clinical marker in asthma, on the assumption that it reflects ongoing eosinophilic inflammation of the airways. However, only a few studies have investigated this issue, using bronchial secretions but not tissue specimens.

OBJECTIVE

To evaluate cross-sectionally the correlation between serum ECP level or blood eosinophil count, and the degree of eosinophilia in bronchoalveolar lavage fluid (BALF) and bronchial biopsy tissue, and disease activity, in asthmatic patients.

METHODS

Thirty-three adults with symptomatic asthma and six healthy controls were studied. The blood eosinophil count, ECP levels in serum and BALF, percentage of eosinophils in BALF, number of eosinophils in bronchial tissue, pulmonary function, and methacholine bronchial responsiveness of these subjects were clarified. An asthma severity score and inhaled beta2-agonist requirement (puffs/day) were also assessed for the asthmatic patients.

RESULTS

The asthmatic patients, compared with the controls, had more obstructive (as tested by %FEV1, FEV1/FVC, and FEF25-75%) and more responsive airways, and showed a significant increase in the number of eosinophils in the blood, BALF, and tissue, and in the serum ECP levels. The ECP levels in BALF were below the detection limit for most of the subjects in both groups examined. In the asthmatic patients, serum ECP level demonstrated correlations with the number or percentage of eosinophils in BALF and tissue, whereas the blood eosinophil count correlated only with the percentage of eosinophils in BALF. Serum ECP level correlated with all indices of disease activity examined; %FEV1, FEV1/FVC, FEF25-75% bronchial responsiveness, severity score and beta2-agonist usage, whereas the blood eosinophil count correlated only with %FEV1 and bronchial responsiveness.

CONCLUSION

The data suggest that serum ECP level reflects the intensity of eosinophilic airway inflammation, as well as the disease activity, and may be useful as an inflammatory marker in asthma.

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

To evaluate the effects of age, height and prechallenge respiratory system resistance (Rrs) on bronchial responsiveness to methacholine inhalation (BRm) as measured by the oscillation technique in children with mild asthma, we studied BRm in 92 atopic children aged from 8 to 13 years (mean +/- SD, 10.5 +/- 1.7 years). Inhalation challenge was performed by administering progressively doubling doses of methacholine, until a twofold increase in Rrs from baseline had been reached. The minimum cumulative dose of methacholine (Dmin) at which Rrs deviated from baseline was identified by the point of deflection of the continuously recorded Rrs tracing. The Dmin represented the amount of methacholine which elicited BRm. By using single-regression analysis, height was negatively correlated with Rrs (p < 0.001). Height was positively and Rrs was negatively correlated with age (p < 0.001 and p < 0.001, respectively). Furthermore, height and age were correlated with Dmin (p < 0.001 and p < 0.001, respectively), but prechallenge Rrs was not correlated with Dmin (p > 0.1). To minimize the effect of height and prechallenge Rrs on BRm, the relationships between Dmin and age was studied in a subgroup with a narrow range of heights (135-155 cm, n = 32), and a narrow range of prechallenge Rrs (5.0-6.9 cmH2 O/L/s, n = 42); there remained a statistically significant correlation between Dmin and age in the groups with comparable heights (p = 0.026) and Rrs (p = 0.003). These data suggest that the BHR in childhood asthma may be affected by height and age when measured by the oscillation technique. Considering the many advantages of the oscillation method, this technique may be very suitable for measuring BHR in childhood asthma.