Problems and possibilities in understanding the natural history of asthma

In early life, asthma symptoms can occur intermittently or may not be severe enough to limit normal activities, which makes it difficult for the clinician to make reliable predictions and administer therapy with some precision. In the case of pediatric asthma, the identification of children who will experience the development of a clinically important illness that will impair their quality of life can be a complex process. The usual methods for describing this information include the prognostic statistics of sensitivity, specificity, likelihood ratio, and positive predictive value. The sensitivity, specificity, and likelihood ratio of various early markers of asthma have been calculated from several cohort studies.

Lung function growth and its relation to airway hyperresponsiveness and recent wheeze. Results from a longitudinal population study

To evaluate the association between growth in height and growth in lung function, and to identify the potential temporal relationships between airway hyperresponsiveness (AHR), respiratory symptoms, and lung function growth during adolescence and young adulthood, we analyzed data collected from the Belmont cohort. Among the 718 schoolchildren initially studied at 1982 (aged 8-10 yr), 557 were studied between two times and six times at 2-yr intervals until 1992. Baseline lung function, AHR by histamine inhalation test, and recent wheeze by questionnaires, were measured at each visit. We found that between 17 and 19 yr of age, when growth in height had stopped, growth in FEV(1) was approximately 200 ml/yr in boys and 100 ml/yr in girls. Peak growth velocity of height occurred at age 13 both in boys and in girls, whereas peak growth velocity of FEV(1) occurred at the same age only in girls and 1 yr later in boys. Having AHR and recent wheeze at the previous study time were both associated with lower subsequent growth in FEV(1), but not with subsequent growth in FVC. We conclude that lung function continues to grow after the cessation of height growth and that growth in FEV(1) is reduced in subjects with AHR and/or recent wheeze.

The effect of parental smoking on presence of wheez or airway hyper-responsiveness in New South Wales school children

BACKGROUND AND AIMS

To assess accurately the effect of parental smoking on the respiratory health of New South Wales (NSW) school children, we obtained a large data set by pooling data from seven cross-sectional studies conducted in NSW between 1991 and 1993.

METHODS

A random sample of 6394 children age eight to 11 years was studied. Respiratory symptoms, family history of asthma and parental smoking history were measured by questionnaire, atopy by skin prick test and airway hyper-responsiveness (AHR) by histamine inhalation test.

RESULTS

In total, 58.3% of children had at least one parent who smoked; 38.5% were exposed to maternal smoking. After adjusting for potential confounders, such as atopy, parental history of asthma and bronchitis in the first two years, children who were exposed to maternal smoking had a significantly increased risk of recent wheeze but not of AHR (odds ratios 1.33; 95% CI: 1.2-1.5 and 1.00; 95% CI: 0.9-1.2).

CONCLUSIONS

The positive association with wheeze and the lack of an association with AHR suggests that exposure to parental smoking leads to wheezing, but does not increase airway responsiveness.

Comparison of three definitions of asthma: a longitudinal perspective

In epidemiological studies, defining "current asthma" as the presence of both wheeze in the last year and airway hyperresponsiveness (AHR) identifies children with more severe abnormality compared with children with either measure alone. The predictive value of this definition of asthma and other commonly used definitions have not been compared. In 1982, we enrolled a random sample of 718 schoolchildren aged 8-10 years, and in 1992, we restudied a representative sample of 407. On both occasions, we measured wheeze, medication use, morbidity, AHR, and atopy. We compared three asthma definitions-"current asthma," recent wheeze, and doctor-diagnosed asthma. Approximately 70% of subjects classified by each definition remained consistently classified in 1992. However, the current asthma definition distinguished a group with more severe illness after 10 years than did the other asthma definitions. The current asthma definition not only differentiates children with more severe asthma, but also differentiates those with a more severe prognosis.

Serum IgE levels, atopy, and asthma in young adults: results from a longitudinal cohort study

To explore the natural history of asthma and its relation to allergic responses, we examined the relation between total serum IgE in early adulthood and a history of respiratory symptoms, airway hyperresponsiveness (AHR), and atopy during childhood. We studied 180 subjects aged 18-20 years who had been studied since the age of 8-10 years. We measured wheeze in the previous year by questionnaire, AHR by histamine inhalation test, atopy by skin prick tests, and serum IgE levels by immunoassay. Subjects with AHR in early adulthood had higher IgE levels (mean 257.0 IU/ml) than subjects with past AHR (mean 93.3 IU/ml) or with lifelong normal responsiveness (mean 67.6 IU/ml) (P < 0.001). Subjects who had symptoms had higher IgE levels (mean 125.9 IU/ml) than those who were lifelong asymptomatic (mean 63.1 IU/ml) (P < 0.001). Recent wheeze, AHR, and allergic sensitization all had a positive relation to serum IgE, but IgE was not more predictive of AHR than skin prick tests. The finding that young adults who are sensitized to common allergens are highly likely to have AHR even in the absence of symptoms is further evidence of the fundamental role of IgE-mediated responses in the natural history of AHR throughout childhood and into adulthood.

House dust mite allergens. A major risk factor for childhood asthma in Australia

If house dust mite allergen (Der p I) is an important cause of asthma, there should be a direct relationship between level of exposure to this allergen and asthma severity. To examine this, we studied six large random samples of children in different regions of New South Wales, Australia. We measured recent wheeze by questionnaire, airway hyperresponsiveness (AHR) by histamine inhalation test and sensitization to house dust mites by skin prick tests. Current asthma was defined as the presence of recent wheeze and AHR. We measured Der p I levels in the beds of approximately 80 children in each region. In regions where Der p I levels were high, more children were sensitized to house dust mites, and these children had significantly more AHR and recent wheeze. After adjusting for sensitization to other allergens, we found that the risk of house dust mite-sensitized children having current asthma doubled with every doubling of Der p I level. There was a modest correlation between AHR and Der p I exposure in individuals (r = 0.23, p < 0.03). These data suggest that house dust mite allergens are an important cause of childhood asthma and that reducing exposure to these allergens could have a large public health benefit in terms of asthma prevention.

Mite allergen (Der p 1) concentration in houses and its relation to the presence and severity of asthma in a population of Sydney schoolchildren

House dust mite (HDM) allergen exposure and its relation to HDM allergy and asthma was assessed in a case-control study conducted over three seasons in 74 Sydney schoolchildren, 33 of whom were allergic to HDM and 12 of whom had current asthma. In each season histamine inhalation tests and skin prick tests were performed, symptom questionnaires were administered, and dust samples were collected. The mean concentrations of HDM allergen (in micrograms of Der p 1 per gram of fine dust) were: bed, 38.9 (95% confidence interval [CI], 31.8 to 47.5); bedroom floor, 22.4 (95% CI, 18.3 to 27.5); and lounge room floor, 13.7 (95% CI, 10.7 to 17.6). The mean of the highest allergen concentration in each house was 51.0 (95% CI, 43.2 to 60.1). All but two subjects had at least one site in all seasons with an HDM allergen concentration greater than 10 micrograms/gm, the proposed threshold for asthma symptoms. Subjects with allergy to HDM, symptoms of asthma, or airway hyperresponsiveness did not have higher HDM allergen concentrations in their house. In this study we were unable to test hypotheses concerning proposed thresholds for risk of sensitization and for risk of asthma symptoms because virtually all subjects were exposed to HDM allergen levels above the proposed thresholds.

Prevalence and severity of childhood asthma and allergic sensitisation in seven climatic regions of New South Wales

OBJECTIVE

To compare the prevalence and severity of asthma and of allergic sensitisation in children in different regions. We hypothesised that regions with different standardised hospital admission rates would have different prevalences of childhood asthma and that diverse climates would result in a range of sensitisations to different allergens.

DESIGN AND SETTING

We studied large random population samples of children in seven regions in New South Wales (NSW) in 1991-1993. Hospitalisation rates were obtained from NSW Department of Health data.

PARTICIPANTS

6394 children aged 8-11 years.

OUTCOME MEASURES

History of respiratory symptoms by self-administered questionnaire; airway hyperresponsiveness by histamine inhalation test; and sensitisation to allergens by skin-prick tests.

RESULTS

Children in all regions had a high prevalence of recent wheeze (22%-27%), of diagnosed asthma (24%-38%) and of use of asthma medications (22%-30%), but no region was consistently higher or lower for all measurements. The prevalence of current asthma in children living in three coastal regions (where sensitisation to house-dust mites was high) and in the far west (where sensitisation to alternaria was high) was 12%-13%, which was significantly higher than the prevalence of 7%-10% in children living in three inland regions (where sensitisation to these allergens was lower) (P < 0.01).

CONCLUSIONS

We found significant variations in the prevalence and severity of childhood asthma in NSW. The prevalence of hospitalisations, diagnosed asthma, recent symptoms and medication use may relate to different regional diagnostic patterns, whereas current asthma prevalence may relate to different levels of allergic sensitisation.

The cost of childhood asthma to Australian families

There have been no estimates of the actual cost of asthma care to Australian families. Previous estimates have been of the total cost to the community and have relied upon data collected by government departments and agencies. It was the aim of this investigation to estimate the cost of childhood asthma from the parents perspective in Australian families. A total of 238 asthmatic children aged 8-12 years were identified through prevalence studies of asthma in Sydney and Belmont, N.S.W. Children were selected if they had wheezed in the previous 12 months, had used asthma medicines or had airway hyperresponsiveness when tested. The study sample had a wide range of asthma severity. Data were collected retrospectively and prospectively. Parents completed a questionnaire which asked about health insurance and special asthma equipment costs in the previous 12 months. Every 2 weeks for a total of 3 months between February and June parents completed further questionnaires which assessed costs incurred because of their child's asthma, together with time spent obtaining treatment. Items included doctor consultations and tests, alternative practitioner consultations and tests, medications and alternative therapies purchased, hospital and ambulance use, and the cost of childcare as a consequence of asthma. We collected two or more months of prospective data from a total of 193 children. The mean annual cost of asthma to the family was A$212.48 per asthmatic child and 13.4 hr were spent obtaining treatment. For the group of children who had not visited a doctor in the previous year, the mean annual cost was A$85.60 and 13.1 hr were spent obtaining treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of two epidemiological protocols for measuring airway responsiveness and allergic sensitivity in adults

In recent years, airway responsiveness has commonly been measured in epidemiological studies using one of two methods. In one method, histamine is administered via a handheld DeVilbiss nebulizer and in the other, methacholine is administered via a dosimeter. Allergic sensitivity has commonly been measured by either the allergen droplet method or by Phazet. We wanted to assess the comparability of airway responsiveness and of allergic sensitivity measured by both methods. A total of 48 volunteers, including normal and asthmatic subjects, participated in the study. Subjects first underwent one of the two tests of airway responsiveness and allergic sensitivity, and then returned within 10 days to undergo tests using the second protocol. Commencement protocol was allocated in random order. There was good agreement between both methods for assessing airway responsiveness and for assessing allergic sensitivity. The difference for dose response ratio (DRR) between histamine and methacholine was a 1.19 (95% (CI) 0.78, 1.82) fold changes, which was not statistically significant. Agreement between allergic sensitivity methods was perfect for Alternaria tenuis, good for rye-grass (kappa = 0.71) and moderate for cat and Dermatophagoides pteronyssinus (kappa approximately 0.5). It is possible to compare data from epidemiological studies which use these methods.

An exercise challenge protocol for epidemiological studies of asthma in children: comparison with histamine challenge

We investigated whether an exercise challenge protocol is suitable for measuring bronchial responsiveness in epidemiological studies of asthma in children, and determined its comparability with histamine challenge. The exercise challenge was 6 minutes of outdoor, free-range running at 85-90% of maximum heart rate, measured by heart rate monitor. Nose clips were worn. Distance run was measured to estimate oxygen consumption. Water content of the inspired air was < 10 mg H2O.l-1. Histamine challenge was by the rapid method. We used questionnaires to measure respiratory symptoms and skin prick tests to measure atopy. A total of 96 children aged 8-11 years were studied. Bronchial hyperresponsiveness (BHR) to exercise challenge was defined as a fall in forced expiratory volume in one second (FEV1) of 13% of greater. Eleven children had a positive response to exercise challenge and 11 to histamine challenge but 12 responded to one challenge and not to the other. The correlation coefficient between the two tests was 0.65 (p = 0.0001). Exercise challenge thus proved to be a practical epidemiological tool for objective measurements of bronchial responsiveness in children. In this sample, some children responded to one challenge and not to the other which suggests that the two challenges identify different abnormalities of the airways.

Evaluation of a community-based asthma management program in a population sample of schoolchildren

OBJECTIVE

To assess the effect of a community-based management program, incorporating both education and treatment directed at children, parents, doctors, pharmacists, community nurses and school teachers.

DESIGN

The effect of this intervention in a population sample of 65 children with a wide range of morbidity due to asthma was compared with a control group of 55 children living in a different area. Both groups were re-evaluated concurrently after three and six months.

MAIN OUTCOME MEASURES

Forced expiratory volume in one second (FEV1); bronchial responsiveness to histamine measured as the provoking dose causing a 20% fall in FEV1 (PD20FEV1) and as dose-response ratio (DRR); Airflometer variability; symptom frequency; and knowledge of asthma. Morbidity was measured by parents using a self-administered questionnaire and included days absent from school and unscheduled doctor or emergency room visits.

RESULTS

At three months, the intervention group had a significant improvement in knowledge of asthma compared with both their baseline and the control group's change in knowledge. Also, FEV1 improved in this group and symptoms which limit activity decreased significantly. However, the largest improvements were recorded at the six-month follow up. In the intervention group, bronchial responsiveness and night cough were reduced significantly and FEV1 was improved, compared with both baseline measurements and the control group. Knowledge of asthma also improved significantly from baseline, and unscheduled doctor or emergency room visits were reduced.

CONCLUSION

These improvements in this group of children, many of whom had mild asthma, verify that community-based management programs can be effective in treating childhood asthma.

Predictive nature of bronchial responsiveness and respiratory symptoms in a one year cohort study of Sydney schoolchildren

We wanted to examine the predictive nature, over one year, of bronchial hyperresponsiveness (BHR) and recent wheeze (in the previous 12 months), which are the measurements frequently used to classify asthma for epidemiology. A prospective cohort study of 236 children, aged 8-11 yrs, was undertaken, with an initial baseline study, followed by four studies at three monthly intervals over one year. At each study, we measured bronchial responsiveness to histamine by the rapid method, respiratory symptoms by parent questionnaire, and atopy by skin prick tests to common allergens. Airflometer readings, which are closely related to FEV1, were self-recorded. Baseline data were used to classify children into the four categories of "current asthma" (BHR and wheeze), "wheeze only", "BHR only", or "normal". During the year following baseline study, the group initially classified as "wheeze only" had normal Airflometer variability, and 59% had wheeze, and 33% had BHR, which tended to be mild. In the group initially classified as "BHR only", 52% had wheeze with a peak in winter, and 62% had BHR during the following year. This group had more severe bronchial responsiveness and Airflometer variability than the normal and wheeze only groups. The group initially classified as current asthma had a more severe condition, with continued BHR (100%), and wheeze (93%), increased Airflometer variability and more atopy. Thus, the natural history of bronchial responsiveness, respiratory symptoms and allergic history in this group was different from the other three groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Predictive nature of bronchial responsiveness and respiratory symptoms in a one year cohort study of Sydney schoolchildren

We wanted to examine the predictive nature, over one year, of bronchial hyperresponsiveness (BHR) and recent wheeze (in the previous 12 months), which are the measurements frequently used to classify asthma for epidemiology. A prospective cohort study of 236 children, aged 8-11 yrs, was undertaken, with an initial baseline study, followed by four studies at three monthly intervals over one year. At each study, we measured bronchial responsiveness to histamine by the rapid method, respiratory symptoms by parent questionnaire, and atopy by skin prick tests to common allergens. Airflometer readings, which are closely related to FEV1, were self-recorded. Baseline data were used to classify children into the four categories of "current asthma" (BHR and wheeze), "wheeze only", "BHR only", or "normal". During the year following baseline study, the group initially classified as "wheeze only" had normal Airflometer variability, and 59% had wheeze, and 33% had BHR, which tended to be mild. In the group initially classified as "BHR only", 52% had wheeze with a peak in winter, and 62% had BHR during the following year. This group had more severe bronchial responsiveness and Airflometer variability than the normal and wheeze only groups. The group initially classified as current asthma had a more severe condition, with continued BHR (100%), and wheeze (93%), increased Airflometer variability and more atopy. Thus, the natural history of bronchial responsiveness, respiratory symptoms and allergic history in this group was different from the other three groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Toward a definition of asthma for epidemiology

Because there is no "gold standard" for defining asthma for epidemiology, we have defined current asthma as bronchial hyperresponsiveness (BHR) plus recent wheeze (in the 12 months prior to study). To describe the characteristics of groups categorized by these measurements, we studied two samples of children aged 7 to 12 yr: 210 from a population sample and 142 self-identified asthmatics. Bronchial responsiveness to histamine was measured by the rapid method, respiratory symptom history, and asthma medication use by self-administered questionnaire to parents and atopy by skin prick tests to 14 allergens. Children recorded daily Airflometer readings and symptom scores for 2 wk. Children with current asthma had more severe bronchial responsiveness, greater Airflometer variability, more symptoms, more atopy (particularly to house dust mites), and used more asthma medication than children with BHR or recent wheeze alone. Children with BHR, but not with recent wheeze, were intermediate between the current asthma and normal groups in terms of bronchial responsiveness, Airflometer variability, and atopy. Children with recent wheeze and normal responsiveness differed from the normal group only in symptoms and medication use. Our definition of current asthma discriminates a group of children that is clearly different in terms of both clinical features and physiologic measures. As such, it is the most useful definition to date for measuring the prevalence of clinically important asthma in populations.

Reliability of a respiratory history questionnaire and effect of mode of administration on classification of asthma in children

Because there is no consensus definition of asthma for epidemiology, we have examined the reliability of a questionnaire and the effect of its mode of administration on classification of asthma in children. A symptom history questionnaire was parent self-administered and then readministered within three months by a nurse. The questions of diagnosed asthma, cumulative wheeze, and recent wheeze (wheeze in the previous 12 months) were more repeatable than questions of night cough, but 7 percent of children changed diagnosed asthma category, 13 percent changed cumulative wheeze category, and 9 percent changed recent wheeze category at second questionnaire. Because the numbers who changed from symptom positive to negative roughly equalled the changes from negative to positive, prevalence estimates were not affected. Methods of measuring asthma with greater precision are urgently needed. Because of reporting bias, epidemiologic information collected by current questionnaires should be treated with some caution.

Repeatability of histamine bronchial challenge and comparability with methacholine bronchial challenge in a population of Australian schoolchildren

To measure the repeatability of the bronchial challenge test and the comparability of histamine and methacholine as provoking agents, we studied a population sample of children and conducted histamine bronchial challenge tests on each of 3 consecutive days followed by a methacholine bronchial challenge on the fourth day. Bronchial responsiveness was measured using the rapid inhalation method. A total of 393 children had satisfactory bronchial challenge data for all 4 days. The measurements derived from the dose-response curve were the PD20 FEV1, which was measured as the provoking dose causing a 20% fall in FEV1, and the dose-response slope (DRS), which was measured as the percentage fall in FEV1 at final dose/total dose administered. Children who had a PD20 FEV1 were categorized as having bronchial hyperresponsiveness (BHR). The percentage of children with BHR each day was between 7 and 11. One-third of the children with BHR reacted only to histamine or methacholine. The within-subject range for histamine PD20 FEV1 values compared with methacholine suggested that histamine and methacholine are not directly comparable bronchial challenge agents. The dose-response slope values, which could be obtained for all children, had slightly better repeatability than PD20 FEV1 values. Because DRS values obtain data for the entire sample, have good repeatability, and are equally repeatable in children with normal responsiveness or bronchial hyperresponsiveness, they should prove more useful than PD20 FEV1 values for measuring bronchial responsiveness in populations.