Respiratory symptoms in Tasmanian adolescents: a follow up of the 1961 birth cohort

The Dose-Response Association between Nitrogen Dioxide Exposure and Serum Interleukin-6 Concentrations

Systemic inflammation is an integral part of chronic obstructive pulmonary disease (COPD), and air pollution is associated with cardiorespiratory mortality, yet the interrelationships are not fully defined. We examined associations between nitrogen dioxide (NO₂) exposure (as a marker of traffic-related air pollution) and pro-inflammatory cytokines, and investigated effect modification and mediation by post-bronchodilator airflow obstruction (post-BD-AO) and cardiovascular risk. Data from middle-aged participants in the Tasmanian Longitudinal Health Study (TAHS, n = 1389) were analyzed by multivariable logistic regression, using serum interleukin (IL)-6, IL-8 and tumor necrosis factor-α (TNF-α) as the outcome. Mean annual NO₂ exposure was estimated at residential addresses using a validated satellite-based land-use regression model. Post-BD-AO was defined by post-BD forced expiratory ratio (FEV₁/FVC) < lower limit of normal, and cardiovascular risk by a history of either cerebrovascular or ischaemic heart disease. We found a positive association with increasing serum IL-6 concentration (geometric mean 1.20 (95% CI: 1.1 to 1.3, p = 0.001) per quartile increase in NO₂). This was predominantly a direct relationship, with little evidence for either effect modification or mediation via post-BD-AO, or for the small subgroup who reported cardiovascular events. However, there was some evidence consistent with serum IL-6 being on the causal pathway between NO₂ and cardiovascular risk. These findings raise the possibility that the interplay between air pollution and systemic inflammation may differ between post-BD airflow obstruction and cardiovascular diseases.

Preterm birth and low birth weight continue to increase the risk of asthma from age 7 to 43

BACKGROUND

Perinatal events can influence the development of asthma in childhood but current evidence is contradictory concerning the effects on life-time asthma risk.

OBJECTIVE

To assess the relationship between birth characteristics and asthma from childhood to adulthood.

METHODOLOGY

All available birth records for the Tasmanian Longitudinal Health Study (TAHS) cohort, born in 1961 were obtained from the Tasmanian State Archives and Tasmanian hospitals. Low birth weight (LBW) was defined as less than 2500 grams. Preterm birth was defined as delivery before 37 weeks' gestation. Small for gestational age (SGA) was defined as a birth weight below the 10^th percentile for a given gestational age. Multivariate logistic and cox regression were used to examine associations between birth characteristics and lifetime risk of current and incident asthma, adjusting for confounders.

RESULTS

The prevalence of LBW was 5.2%, SGA was 13.8% and preterm was 3.3%. LBW (OR = 1.65, 95%CI 1.12,2.44) and preterm birth (OR = 1.81, 95%CI 0.99, 3.31) were both associated with an increased risk of current asthma between the ages of 7 to 43 years. There was no association between SGA and current asthma risk. However, SGA was associated with incident asthma (HR = 1.32, 95%CI 1.00, 1.74), and there was an interaction with sex (p value = 0.08), with males having a greater risk of incident asthma (HR = 1.70, 95%CI 1.16-2.49) than females (HR = 1.04, 95%CI 0.70-1.54).

CONCLUSIONS

Preterm birth and LBW were associated with an increased risk of current asthma into middle-age. These findings are the first to demonstrate the continuing impact of these characteristics on asthma risk into middle-age.

Current asthma contributes as much as smoking to chronic bronchitis in middle age: a prospective population-based study

BACKGROUND AND OBJECTIVE

Personal smoking is widely regarded to be the primary cause of chronic bronchitis (CB) in adults, but with limited knowledge of contributions by other factors, including current asthma. We aimed to estimate the independent and relative contributions to adult CB from other potential influences spanning childhood to middle age.

METHODS

The population-based Tasmanian Longitudinal Health Study cohort, people born in 1961, completed respiratory questionnaires and spirometry in 1968 (n=8,583). Thirty-seven years later, in 2004, two-thirds responded to a detailed postal survey (n=5,729), from which the presence of CB was established in middle age. A subsample (n=1,389) underwent postbronchodilator spirometry between 2006 and 2008 for the assessment of chronic airflow limitation, from which nonobstructive and obstructive CB were defined. Multivariable and multinomial logistic regression models were used to estimate relevant associations.

RESULTS

The prevalence of CB in middle age was 6.1% (95% confidence interval [CI]: 5.5, 6.8). Current asthma and/or wheezy breathing in middle age was independently associated with adult CB (odds ratio [OR]: 6.2 [95% CI: 4.6, 8.4]), and this estimate was significantly higher than for current smokers of at least 20 pack-years (OR: 3.0 [95% CI: 2.1, 4.3]). Current asthma and smoking in middle age were similarly associated with obstructive CB, in contrast to the association between allergy and nonobstructive CB. Childhood predictors included allergic history (OR: 1.3 [95% CI: 1.1, 1.7]), current asthma (OR: 1.8 [95% CI: 1.3, 2.7]), "episodic" childhood asthma (OR: 2.3 [95% CI: 1.4, 3.9]), and parental bronchitis symptoms (OR: 2.5 [95% CI: 1.6, 4.1]).

CONCLUSION

The strong independent association between current asthma and CB in middle age suggests that this condition may be even more influential than personal smoking in a general population. The independent associations of childhood allergy and asthma, though not childhood bronchitis, as clinical predictors of adult CB raise the possibility of some of this burden having originated in childhood.

Clinical and functional differences between early-onset and late-onset adult asthma: a population-based Tasmanian Longitudinal Health Study

BACKGROUND

Differences between early-onset and late-onset adult asthma have not been comprehensively described using prospective data.

AIMS

To characterise the differences between early-onset and late-onset asthma in a longitudinal cohort study.

METHODS

The Tasmanian Longitudinal Health Study (TAHS) is a population-based cohort. Respiratory histories and spirometry were first performed in 1968 when participants were aged 7 (n=8583). The cohort was traced and resurveyed from 2002 to 2005 (n=5729 responses) and a sample, enriched for asthma and bronchitis participated in a clinical study when aged 44 (n=1389).

RESULTS

Of the entire TAHS cohort, 7.7% (95% CI 6.6% to 9.0%) had early-onset and 7.8% (95% CI 6.4% to 9.4%) late-onset asthma. Atopy and family history were more common in early-onset asthma while female gender, current smoking and low socioeconomic status were more common in late-onset asthma. The impact on lung function of early-onset asthma was significantly greater than for late-onset asthma (mean difference prebronchodilator (BD) FEV₁/FVC -2.8% predicted (-5.3 to -0.3); post-BD FEV₁FVC -2.6% predicted (-5.0 to -0.1)). However, asthma severity and asthma score did not significantly differ between groups. An interaction between asthma and smoking was identified and found to be associated with greater fixed airflow obstruction in adults with late-onset asthma. This interaction was not evident in adults with early-onset disease.

CONCLUSIONS

Early-onset and late-onset adult asthma are equally prevalent in the middle-aged population. Major phenotypic differences occur with asthma age-of-onset; while both share similar clinical manifestations, the impact on adult lung function of early-onset asthma is greater than for late-onset asthma.

Mother's smoking and complex lung function of offspring in middle age: A cohort study from childhood

BACKGROUND AND OBJECTIVE

Existing evidence that supports maternal smoking to be a potential risk factor for chronic obstructive pulmonary disease (COPD) for adult offspring has barely been mentioned in major guideline documents, suggesting a need for more robust and consistent data. We aimed to examine whether such early life exposure can predispose to COPD in middle age, possibly through its interaction with personal smoking.

METHODS

The fifth-decade follow-up of the Tasmanian Longitudinal Health Study cohort, which was first studied in 1968 (n = 8583), included a 2004 postal survey (n = 5729 responses) and subsequent laboratory attendance (n = 1389) for comprehensive lung function testing between 2006 and 2008. Multivariable linear and logistic regression models included sampling weights.

RESULTS

Post-bronchodilator airflow obstruction (less than fifth percentile) was detected for 9.3% (n = 123) of middle-aged offspring. Its association with heavy maternal smoking (>20 cigarettes/day) during childhood was 2.7-fold higher than for those without exposure (95% confidence interval [1.3, 5.7] P = 0.009). Maternal smoking per se approximately doubled the adverse effect of personal smoking on gas transfer factor (z-score -0.46 [-0.6 to -0.3] vs -0.25 [-0.4 to -0.1], P[interaction] = 0.048) and was paradoxically associated with reduced residual volumes for non-smokers.

CONCLUSIONS

Heavy maternal smoking during childhood appears to predispose to spirometrically defined COPD. The interplay between maternal and personal smoking on gas transfer factor suggests that early life exposure increases an individual's susceptibility to adult smoking exposure. These findings provide further evidence to suggest that maternal smoking might be a risk factor for COPD and reinforce the public health message advocating smoking abstinence.

Hormonal contraception increases risk of asthma among obese but decreases it among nonobese subjects: a prospective, population-based cohort study

Epidemiological data on asthma suggest a sex difference that varies with age. Hormonal effects have been suggested as a possible explanation for these differences but there is a scarcity of evidence on these relationships. Our objective was to examine the relationship between reproductive factors and asthma risk among females and to examine whether body mass index (BMI) modifies this relationship.

Female participants in the 2004 fifth decade follow-up postal survey of the Tasmanian Longitudinal Health Study formed the study population. Reproductive history and data on hormonal contraceptive (HC) use were collected on 2764 females. Multiple logistic regression was used to assess the association between the reproductive factors and current asthma.

The mean age of participants was 43 years and the prevalence of middle-aged current asthma was 12.8%. Females with very early menarche (≤10 years) had higher odds of middle-aged current asthma (OR 1.91, 95% CI 1.14–3.2). Pregnancy history (number of births and age at first pregnancy) were not associated with current asthma risk at 44 years. Ever having used HCs, years of use and age started using HCs were not individually associated with current asthma risk. However, body mass index significantly modified the relationship between HC use and asthma. We found increasing years of pill use was associated with a significantly increased risk of current asthma in overweight/obese women but a reduced risk in normal weight women (interaction p=0.015).

Hormonal effects from use of HCs and early menarche may contribute to the sex differential in asthma risk. Our findings suggest that in obese women with a history of long-term HC use may be at an increased risk of chronic respiratory disease, and regular monitoring for asthma and asthma symptoms may be recommended.

Overweight or obese women are at increased risk of asthma if they use hormonal contraceptives for extended periodshttp://ow.ly/SwY8p

Childhood infections and the risk of asthma: a longitudinal study over 37 years

BACKGROUND

Few studies have examined common childhood infections and adult asthma. We examined associations between childhood infectious diseases, childhood pneumonia, and current, persisting, and incident asthma to middle age.

METHODS

We analyzed data from the Tasmanian Longitudinal Health Study (TAHS). A history of pneumonia was ascertained from their parents when the TAHS participants were 7 years old. Measles, rubella, mumps, chickenpox, diphtheria, and pertussis were identified from school medical records. Associations with current, persisting, or incident asthma were examined using regression techniques.

RESULTS

Greater infectious diseases load was negatively associated with persisting asthma at all ages. Individually, pertussis (adjusted OR [aOR], 0.53; 95% CI, 0.28-1.00) was negatively associated with asthma persisting to age 13 years, chickenpox (aOR, 0.58; 95% CI, 0.38-0.88) was negatively associated with asthma persisting to age 32 years, and rubella was negatively associated with asthma persisting to ages 32 (aOR, 0.61; 95% CI, 0.31-0.96) and 44 years (aOR 0.53; 95% CI, 0.35-0.82). Pertussis was associated with preadolescent incident asthma (adjusted hazard ratio [aHR], 1.80; 95% CI, 1.10-2.96), whereas measles was associated with adolescent incident asthma (aHR, 1.66; 1.06-2.56). Childhood pneumonia was associated with current asthma at ages 7 (aOR, 3.12; 95% CI, 2.61-3.75) and 13 years (aOR, 1.32; 95% CI, 1.00-1.75), an association stronger in those without than those with eczema (aOR, 3.46; 95% CI, 2.83-4.24 vs aOR, 2.08; 95% CI, 1.38-3.12).

CONCLUSIONS

Overall, childhood infectious diseases protected against asthma persisting in later life, but pertussis and measles were associated with new-onset asthma after childhood. Measles and pertussis immunization might lead to a reduction in incident asthma in later life.

The interplay between the effects of lifetime asthma, smoking, and atopy on fixed airflow obstruction in middle age

RATIONALE

The contribution by asthma to the development of fixed airflow obstruction (AO) and the nature of its effect combined with active smoking and atopy remain unclear.

OBJECTIVES

To investigate the prevalence and relative influence of lifetime asthma, active smoking, and atopy on fixed AO in middle age.

METHODS

The population-based Tasmanian Longitudinal Health Study cohort born in 1961 (n = 8,583) and studied with prebronchodilator spirometry in 1968 was retraced (n = 7,312) and resurveyed (n = 5,729 responses) from 2002 to 2005. A sample enriched for asthma and chronic bronchitis underwent a further questionnaire, pre- and post-bronchodilator spirometry (n = 1,389), skin prick testing, lung volumes, and diffusing capacity measurements. Prevalence estimates were reweighted for sampling fractions. Multiple linear and logistic regression were used to assess the relevant associations.

MEASUREMENTS AND MAIN RESULTS

Main effects and interactions between lifetime asthma, active smoking, and atopy as they relate to fixed AO were measured. The prevalence of fixed AO was 6.0% (95% confidence interval [CI], 4.5-7.5%). Its association with early-onset current clinical asthma was equivalent to a 33 pack-year history of smoking (odds ratio, 3.7; 95% CI, 1.5-9.3; P = 0.005), compared with a 24 pack-year history for late-onset current clinical asthma (odds ratio, 2.6; 95% CI, 1.03-6.5; P = 0.042). An interaction (multiplicative effect) was present between asthma and active smoking as it relates to the ratio of post-bronchodilator FEV(1)/FVC, but only among those with atopic sensitization.

CONCLUSIONS

Active smoking and current clinical asthma both contribute substantially to fixed AO in middle age, especially among those with atopy. The interaction between these factors provides another compelling reason for atopic individuals with current asthma who smoke to quit.

Childhood immunization and atopic disease into middle-age--a prospective cohort study

The association between childhood immunizations and risk of atopic diseases is unclear. No study has examined possible associations between childhood immunizations and such diseases in middle age. The Tasmanian Longitudinal Health Study (TAHS) is a population based cohort study of respiratory disease. The TAHS participants were followed from 7 to 44 yrs of age. Immunizations during childhood were examined for any association with asthma and atopic disease at age 44 yrs. Multivariable regression models were used to estimate relative risks while adjusting for confounders. Cox regression was used to estimate the association between childhood immunizations and asthma developing after the age of 7 yrs. We found no association between any childhood immunization (Diphtheria, Tetanus, Pertussis, Polio, Smallpox) and asthma (ORs ranged from 0.87 to 1.17 p > 0.05), eczema (ORs ranged from 0.99 to 1.07 p > 0.05), food allergy (ORs ranged from 0.97 to 1.11 p > 0.05), or hay fever (ORs ranged from 1.02 to 1.05 p > 0.05) at age 44. Nor did we find any association between childhood immunizations and an increased risk of incident asthma after the age of 7 yrs (Diphtheria HR = 1.06, 95% CI 0.82, 1.36; Tetanus HR = 1.13, 95% CI 0.88, 1.44; Pertussis HR = 1.03, 95% CI 0.81, 1.30; Polio HR = 1.15, 95% CI 0.86, 1.54; Smallpox HR = 1.21, 95% CI 0.99, 1.48; DTP HR = 1.05, 95% CI 0.85, 1.30). Our analysis does not support any association between common childhood immunizations and risk of asthma and atopic disease in middle-age. Our findings should provide reassurance that in terms of life time risk of asthma and atopic disease, childhood immunization is safe.

Poor lung function and tonsillectomy in childhood are associated with mortality from age 18 to 44

BACKGROUND

The aim of this analysis was to examine associations between lung health in childhood and mortality between ages 18 and 44 years in the Tasmanian Longitudinal Health Study (TAHS).

METHODS

The 1961 Tasmanian birth cohort who attended school in 1968 (n=8583) were linked to the Australian National Death Index (NDI) to identify deaths. Additional deaths were notified by families through a 37 year follow-up postal questionnaire. Information on lung health at age 7 years and on potential confounders was obtained from the original 1968 TAHS survey and school medical records. Cox proportional hazards modelling was used to assess determinants of mortality.

RESULTS

A total of 264 (3%) deaths were identified. The principal causes of death were external injury (56.1%, n=97) and cancer (17.9%, n=31). Males were more likely than females to have died (p=<0.1). Only two (1.1%) participants had died from respiratory conditions. Having an FEV(1)<80% predicted at 7 years of age was associated with a 2-fold increased incidence of death. Tonsillectomy before age 7 years was associated with a 1.5-fold increase in mortality (p=0.05); being male with a 3.6-fold increase in mortality (p=0.0001); and repeated chest illnesses at age 7 years causing >30 days confinement in the last year, was associated with a 2.2-fold increase in mortality (p=0.03).

CONCLUSIONS

Childhood lung health appears to be associated with increased mortality in adulthood, perhaps by affecting the ability to survive trauma, major illnesses and other physical stresses.

Breast-feeding and atopic disease: a cohort study from childhood to middle age

BACKGROUND

The literature regarding the association between breast-feeding and atopic diseases has been contradictory.

OBJECTIVE

We have assessed the relationship between breast-feeding and atopic disorders in a cohort followed into middle age.

METHODS

The Tasmanian Asthma Study is a population-based prospective cohort study that has followed participants from the age of 7 to 44 years. Exclusive breast-feeding in the first 3 months of life was examined as a risk factor for atopic diseases by using multiple logistic regression and generalized estimating equation analyses.

RESULTS

At age 7 years, exclusively breast-fed children with a maternal history of atopy had a marginally lesser risk of current asthma than those not exclusively breast-fed (odds ratio [OR], 0.8; 95% CI, 0.6-1.0). However, after age 7 years, the risk reversed, and exclusively breast-fed children had an increased risk of current asthma at 14 (OR, 1.46; 95% CI, 1.02-2.07), 32 (OR, 1.84; 95% CI, 1.06-3.3), and 44 (OR, 1.57; 95% CI, 1.15-2.14) years. Exclusively breast-fed children also had a reduced risk of food allergy at age 7 years but an increased risk of food allergy (OR, 1.26; 95% CI, 1.1-1.5) and allergic rhinitis (OR, 1.2; 95% CI, 1.0-1.3) at 44 years.

CONCLUSION

Exclusively breast-fed babies with a maternal history of atopy were less likely to develop asthma before the age of 7 years, but more likely to develop asthma after the age of 7 years.

CLINICAL IMPLICATIONS

The current recommendation to breast-feed high-risk infants for protection against early wheezing illness can be confirmed. However, the recommendation should be reconsidered for protection against allergic asthma and atopy in the longer term.

Is childhood immunisation associated with atopic disease from age 7 to 32 years?

BACKGROUND

There is ongoing conjecture over whether childhood immunisation leads to an increased risk of developing atopic diseases.

OBJECTIVE

To examine associations between childhood immunisation and the risk of atopic disease.

METHOD

Immunisation histories of 8443 Tasmanian children born in 1961 obtained from school medical records were linked to the Tasmanian Asthma Study. Associations between immunisation status and atopic diseases were examined while adjusting for possible confounders using multiple logistic regression.

RESULTS

Diphtheria immunisation was weakly associated with an increased risk of asthma by age 7 years (odds ratio (OR) 1.3, 95% confidence interval (CI) 1.1 to 1.7), but there was no evidence of any association for four other vaccinations studied. An increased risk of eczema by age 7 years was associated with immunisation against diphtheria (OR 1.5, 95% CI 1.1 to 2.1), tetanus (OR 1.5, 95% CI, 1.1 to 2.0), pertussis (OR 1.5, 95% CI 1.1 to 1.9) and polio (OR 1.4, 95% CI 1.0 to 1.9) but not small pox. Similar but slightly weaker patterns of association were observed between the risk of food allergies and immunisation against diphtheria (OR 1.5, 95% CI 1.0 to 2.1), pertussis (OR 1.4, 95% CI 1.1 to 1.9), polio (OR 1.4, 95% CI 1.00 to 2.1) and tetanus (OR 1.30 95% CI 0.99 to 1.70), but not with small pox. There was no evidence of associations between immunisation history and hay fever, or incidence of later-onset atopic outcomes.

CONCLUSIONS

The few effects seen in this study are small and age-dependent, and nearly all our findings support numerous previous studies of no effect of vaccines on asthma. Based on these findings, the fear of their child developing atopic disease should not deter parents from immunising their children, especially when weighed against the benefits.

Phosphodiesterase 3 inhibition and cough in elderly asthmatics

Aims

Cough is a common symptom of bronchial asthma, a chronic inflammatory airway disease. Recently, the therapeutic effects of selective phosphodiesterase (PDE) inhibitors have been focused on bronchial asthma. This study was designed to investigate the clinical effect of PDE 3 inhibition on cough reflex sensitivity in elderly patients with bronchial asthma.

Methods

Effects of cilostazol, a PDE 3 inhibitor, on cough response to inhaled capsaicin were examined in 11 patients over 70 years with stable asthma in a randomized, placebo-controlled cross over study. Capsaicin cough threshold, defined as the lowest concentration of capsaicin eliciting five or more coughs, was measured as an index of airway cough reflex sensitivity.

Results

The cough threshold was significantly (p < 0.05) increased after two-week treatment with cilostazol (100 mg twice a day orally) compared with placebo [48.8 (GSEM 1.4) vs. 29.2 (GSEM 1.3) μM].

Conclusion

These findings indicate that PDE 3 inhibition may be a novel therapeutic option for elderly patients with asthma, especially for their cough symptoms.

Effect of carbocysteine on cough reflex to capsaicin in asthmatic patients

AIMS

Cough, one of the main symptoms of bronchial asthma, is a chronic airway inflammatory disease with functionally damaged bronchial epithelium. Recently, we established an animal model with cough hypersensitivity after antigen challenge and clearly showed the protective effect of carbocysteine in this model. This study was designed to investigate the clinical effect of carbocysteine for cough sensitivity in patients with bronchial asthma.

METHODS

The effects of the two orally active mucoregulatory drugs, carbocysteine and ambroxol hydrochloride, on cough response to inhaled capsaicin were examined in 14 patients with stable asthma. Capsaicin cough threshold, defined as the lowest concentration of capsaicin eliciting five or more coughs, was measured as an index of airway cough sensitivity.

RESULTS

Geometric mean values of the cough threshold at run-in (baseline) and after 4 weeks' treatment of placebo, 1500 mg day-1 of carbocysteine and 45 mg day-1 of ambroxol hydrochloride were 12.8 micro M (95% confidence interval [CI] 5.5, 29.6), 11.0 micro M (95% CI 4.4, 27.5), 21.0 micro M (95% CI 8.8, 50.2) and 11.6 micro M (95% CI 5.8, 23.3), respectively. The cough threshold for carbocysteine was significantly greater than those of ambroxol hydrochloride (P = 0.047) and placebo (P = 0.047), respectively.

CONCLUSIONS

These findings indicate that carbocysteine administration may be a novel therapeutic option for asthmatic patients, especially with cough variant asthma.

The pathophysiology of asthma

Asthma is a chronic disorder of the airways that is characterized by reversible airflow obstruction and airway inflammation, persistent airway hyperreactivity, and airway remodeling. The etiology of asthma is complex and multifactorial. Recent advances have demonstrated the importance of genetics in the development of asthma, particularly atopic asthma. Environmental stimuli, particularly early childhood infections, have also been associated with the development of asthma. Most current data seem to suggest that these factors drive the development of a Th-2 lymphocyte-predominant immune response, which has been associated with atopy and IgE-mediated inflammation. The concept of reversible airflow obstruction has also recently been challenged. It is now clear that chronic airway changes occur, which may contribute to progressive airflow obstruction. We discuss the important influence of genetic and environmental factors on the emergence of the asthmatic phenotype. The significance of Th-1 and Th-2 lymphocyte-mediated immunity are discussed, and the inflammatory processes leading to chronic airway inflammation are detailed.

Characteristics and diagnostic significance of spontaneous wheezing in children with asthma: results of continuous in vivo sound recording

The characteristics and diagnostics of wheezing during induced airway obstruction are well documented. The present study addressed (a) the characteristics of spontaneous wheezing with respect to a possible distinction between wheezes during in vivo versus induced airway obstruction, and (b) the relationship between in vivo wheezing and fluctuations in peak expiratory flow (PEF). Tracheal sounds were continuously recorded from 50 children and adolescents with asthma and 10 without asthma in the home environment. Wheezes underwent a qualitative analysis, including their concomitant sound frequencies. Presence of wheezing was scored by two examiners independently and was related to PEF. Spontaneous wheeze varied from solitary rhonchi to prolonged rhythms of loud stridor, and resembled the "induced" wheezes recorded previously. Power spectra showed that the spectral contents (frequency distribution) were comparable, although the in vivo patterns were more prolonged in duration. The diagnostic sensitivity and specificity of wheezing for a reduction in PEF of >20% were 88% and 92%, respectively. It was concluded that in vivo wheeze resembled induced wheeze and was a diagnostically reliable symptom with respect to asthma exacerbations.

Cough as the ambiguous indicator of airway obstruction in asthma

This study tested the hypothesis that cough frequency during induced airway obstruction in children and adolescents with asthma relates significantly to other symptoms. The second hypothesis was that cough during remission may often be a conditioned or voluntary response. In experiment 1, tracheal sounds were recorded from 30 participants with asthma during a histamine challenge test. In experiment 2, tracheal sounds were recorded from 30 participants with and 30 without asthma during a standardized physical exercise task. Cough and respiratory wheeze were assessed from the sound records by two examiners independently. The results showed that cough during airway obstruction did not relate to other variables. Only the second hypothesis was supported. In both experiments the frequency of cough was independent of lung function (forced expiratory volume in 1 sec [FEV1]), wheezing, dyspnea, and severity of asthma. The percentage of participants with asthma who coughed in experiment 1 increased from 21% (baseline) to 71% after histamine inhalation. During experiment 2, the cough percentage increased from 52% to 69% in asthmatics, and from zero to 57% in controls. It was concluded that cough in asthma is not diagnostically useful for assessment of airway obstruction. Excessive baseline cough among asthmatics could be the result of acquired responses to anticipated exercise-induced symptoms.

Diagnostics of spontaneous cough in childhood asthma: results of continuous tracheal sound recording in the homes of children

Spontaneous cough is a symptom with diffuse diagnostic significance for childhood asthma. Information on the interrelations between presence/frequency of cough and other symptoms of asthma are not available to the physician. Tracheal sounds were continuously recorded in the homes of 60 children with and 30 without asthma, at 72 and 24 h, respectively. Presence and frequency of cough and presence of wheeze were scored by trained examiners. Wheeze was used to indicate airway obstruction during hours when peak expiratory flow (PEF) values were not available. PEF and self-reported dyspnea were assessed every 4 h. Results showed that asthmatics coughed significantly more often than control subjects during exacerbations, but not during remission. The highest diagnostic sensitivity percentages of cough were 72% for wheeze and 69% for a reduction in PEF > 20%. However, the diagnostic specificity was poor, 41% for wheeze and 34% for a reduction in PEF > 20%. Cough and dyspnea were independent. Three children did not cough during exacerbations. Persistent, isolated cough was observed in two children. It was concluded that spontaneous cough is modestly predictive of asthmatic exacerbations, but not of a diagnosis of asthma or severity of asthma.

Characteristics and diagnostic significance of wheezes during exercise-induced airway obstruction in children with asthma

The diagnostic significance of wheezes for childhood asthma has not been studied systematically (to our knowledge), even though alternative diagnostic methods are limited, especially with children too young for lung function testing. To fill this gap, tracheal sounds were continuously recorded of 70 school-aged children with and 30 without asthma during standardized physical exercise. Wheezes were digitally analyzed and compared with sound patterns previously recorded after histamine inhalation. Exercise-induced wheezes proved to be indistinguishable from sound patterns associated with histamine. The diagnostic sensitivity and specificity of any wheeze for a fall in FEV1 greater than 20% after exercise were, respectively, 86% and 99%. The sensitivity and specificity of any wheeze for a diagnosis of asthma were, respectively, 19% and 100%. Wheezes were often audible for a short time only, making traditional (stethoscopic) detection unlikely and thereby restricting clinical diagnostic significance. This suggests that the development of automated detection techniques may be warranted.

Incidence and prognosis of asthma and wheezing illness from early childhood to age 33 in a national British cohort

OBJECTIVE

To describe the incidence and prognosis of wheezing illness from birth to age 33 and the relation of incidence to perinatal, medical, social, environmental, and lifestyle factors.

DESIGN

Prospective longitudinal study.

SETTING

England, Scotland and Wales.

SUBJECTS

18,559 people born on 3-9 March 1958. 5801 (31%) contributed information at ages 7, 11, 16, 23, and 33 years. Attrition bias was evaluated using information on 14, 571 (79%) subjects.

MAIN OUTCOME MEASURE

History of asthma, wheezy bronchitis, or wheezing obtained from interview with subjects' parents at ages 7, 11, and 16 and reported at interview by subjects at ages 23 and 33.

RESULTS

The cumulative incidence of wheezing illness was 18% by age 7, 24% by age 16, and 43% by age 33. Incidence during childhood was strongly and independently associated with pneumonia, hay fever, and eczema. There were weaker independent associations with male sex, third trimester antepartum haemorrhage, whooping cough, recurrent abdominal pain, and migraine. Incidence from age 17 to 33 was associated strongly with active cigarette smoking and a history of hay fever. There were weaker independent associations with female sex, maternal albuminuria during pregnancy, and histories of eczema and migraine. Maternal smoking during pregnancy was weakly and inconsistently related to childhood wheezing but was a stronger and significant independent predictor of incidence after age 16. Among 880 subjects who developed asthma or wheezy bronchitis from birth to age 7, 50% had attacks in the previous year at age 7; 18% at 11, 10% at 16, 10% at 23, and 27% at 33. Relapse at 33 after prolonged remission of childhood wheezing was more common among current smokers and atopic subjects.

CONCLUSION

Atopy and active cigarette smoking are major influences on the incidence and recurrence of wheezing during adulthood.

Factors in childhood as predictors of asthma in adult life

OBJECTIVE

To determine which factors measured in childhood predict asthma in adult life.

DESIGN

Prospective study over 25 years of a birth cohort initially studied at the age of 7.

SETTING

Tasmania, Australia.

SUBJECTS

1494 men and women surveyed in 1991-3 when aged 29 to 32 (75% of a random stratified sample from the 1968 Tasmanian asthma survey of children born in 1961 and at school in Tasmania).

MAIN OUTCOME MEASURES

Self reported asthma or wheezy breathing in the previous 12 months (current asthma).

RESULTS

Of the subjects with asthma or wheezy breathing by the age of 7, as reported by their parents 25.6% (190/741) reported current asthma as an adult compared with 10.8% (81/753) of subjects without parent reported childhood asthma (P < 0.001). Factors measured at the age of 7 that independently predicted current asthma as an adult were being female (odds ratio 1.57; 95% confidence interval 1.19 to 2.08); having a history of eczema (1.45; 1.04 to 2.03); having a low mild forced expiratory flow rate (interquartile odds ratio 1.40; 1.15 to 1.71); having a mother or father with a history of asthma (1.74 (1.23 to 2.47) and 1.68 (1.18 to 2.38) respectively); and having childhood asthma (1.59; 1.10 to 2.29) and, if so, having the first attack after the age of 2 (1.66; 1.17 to 2.36) or having had more than 10 attacks (1.70; 1.17 to 2.48).

CONCLUSION

Children with asthma reported by their parents in 1968 were more likely than not to be free of symptoms as adults. The subjects who had more severe asthma (especially if it developed after the age of 2 and was associated with reduced expiratory flow), were female, or had parents who had asthma were at an increased risk of having asthma as an adult. These findings have implications for the treatment and prognosis of childhood asthma, targeting preventive and educational strategies and understanding the onset of asthma in adult life.

The associations between childhood asthma and atopy, and parental asthma, hay fever and smoking

The aim of this analysis was to examine the degree to which a life time prevalence of asthma in a 7-year-old child is statistically associated with atopic conditions of the child, and with parental asthma, hay fever and smoking. In 1968, 8585 children who were born in 1961 and who were attending school in Tasmania were surveyed. This comprised 99% of the eligible population. The prevalence of a history of asthma in the 7-year-olds was 16.2% (males 19.0%, females 13.2%). Multiple logistic regression analysis showed that a history of asthma in a 7-year-old was associated with the child being male (odds ratio [OR] 1.56; 99% confidence interval 1.30-1.86), having a history of hay fever (3.86; 3.12-4.78), eczema (2.04; 1.63-2.55), hives (1.34; 1.09-1.65) or allergy to foods or medicines (1.70; 1.26-2.30), the child's mother or father having a history of asthma (2.63; 2.08-3.31 or 2.52; 1.99-3.19, respectively), and the mother being a smoker (1.26; 1.05-1.51). Parental hay fever and paternal smoking were not independently associated with childhood asthma. The strength of association between childhood asthma and parental asthma was independent of the sex of either the parent or the child, and of atopic conditions in the child. In the 133 children for whom both parents were asthmatic, 65 (49%) had a history of asthma.(ABSTRACT TRUNCATED AT 250 WORDS)

The epidemiology of genetic epidemiology

Familial aggregation for disease is important; strong familial risk factors must exist even if the increased risk to a relative of an affected individual is modest. It is in practice difficult, however, to conduct studies in genetic epidemiology which conform to strict epidemiological principles. For twin studies there are two major questions: Are twins 'no different' from the population on which inference is to be made? Are study twins 'no different' to twins in the population? The importance of each question of bias depends on the scientific question, the trait(s) studied, and sampling issues. The strength of the twin design is its ability to refute the null hypothesis that genetic factors do not explain variation in a trait. Following the Popperian paradigm, alternate hypotheses should be considered in depth (both theoretically and empirically), with a design and sample size sufficient to exclude not just naive explanations. More sophisticated statistical techniques are now being applied, so the philosophy, assumptions, and limitations of statistical modelling must be appreciated. The concept of 'heritability' has, in the past, been misunderstood and misused. New advances in DNA technology promise to revolutionise epidemiological thinking, and so case-control-pedigree designs may well become standard tools. The strengths and limitations of studies based on related individuals as the sampling unit are discussed.

Asthma from birth to age 23: incidence and relation to prior and concurrent atopic disease

BACKGROUND

Few studies present prospective data on the incidence of asthma. Its associations with sex and with prior and concurrent hay fever and eczema were examined in a nationally representative sample followed from birth to 23 years of age (British 1958 birth cohort).

METHODS

Reports of asthma or wheezy bronchitis, hay fever and eczema were obtained by interview of parents of children at ages 7, 11, and 16 years, and of cohort members at age 23 years. Linked data from all four interviews were available on 7225 subjects (43% of the original birth cohort).

RESULTS

The cumulative incidence of asthma or wheezy bronchitis was 18.2%, 21.8%, 24.5%, and 28.6% by the ages of 7, 11, 16, and 23 years respectively. Over the four incidence periods examined (0 to 7 years, 8 to 11 years, 12 to 16 years, 17 to 23 years) the average annual incidence of new cases was 2.6%, 1.1%, 0.71%, and 0.76% respectively. The male:female incidence ratio rose from 1.23 in the 0 to 7 year period to 1.48 at 12 to 16 years but had reversed to 0.59 at 17 to 23 years. A prior report of hay fever or eczema each increased the subsequent incidence of asthma or wheezy bronchitis by a factor of 1.7 to 2.0 independently of sex. This effect of prior atopic illness, however, was largely explained by the strong independent association of incidence of asthma and wheezy bronchitis with atopic disease at the end of each incidence period (odds ratios 2.0 to 2.5 per atopic condition, p < 0.01).

CONCLUSIONS

Gender differences in the incidence of asthma or wheezy bronchitis vary with age and are not explained by atopy. The incidence of asthma or wheezy bronchitis can be predicted from a clinical history of hay fever or eczema but is more strongly associated with the presence of atopic disease at the time of onset.

Has the prevalence of asthma increased in children? Evidence from the national study of health and growth 1973-86

OBJECTIVES

To estimate changes in the prevalence of reported symptoms of respiratory disease and reported diagnoses of asthma and bronchitis in primary school children in England between 1973 and 1986.

DESIGN

Mixed longitudinal survey.

SETTING

Representative sample of English primary schools in 22 areas.

PARTICIPANTS

15,000 Boys and 14,156 girls each studied at least once between 1973 and 1986.

DATA COLLECTED

Whether, according to the parent or guardian, the child had wheezed, wheezed on most days or nights, or had attacks of bronchitis or asthma in the past year.

RESULTS

Within age groups trends in successive annual cohorts showed an increasing prevalence of asthma for each annual birth cohort (boys, 6.9%, p less than 0.001; girls, 12.8%, p less than 0.001) and of wheeze on most days or nights (boys, 4.3% per cohort, p less than 0.001; girls, 6.1% per cohort, p less than 0.001) and a falling prevalence of bronchitis (boys, -4.7% per cohort, p less than 0.001; girls, -5.8% per cohort, p less than 0.001). There was a smaller increase in the prevalence of wheeze whether or not it occurred on most days or nights, and this increase was significant only among the girls (boys, 1.0% per cohort, p greater than 0.05; girls, 1.7% per cohort, p less than 0.05). Although the rate of increase of "asthma" was greater than the rate of decrease in "bronchitis," the baseline prevalence of asthma was much lower than that of bronchitis, and the total proportion of children with either diagnosis declined slightly over the whole period. The main change was an increase in the proportion of children whose parents stated that they had persistent wheeze and yet did not have a report of either "asthma" or "bronchitis."

CONCLUSIONS

These results suggest that there has been a true increase in morbidity that is not simply due to changes in diagnostic fashion. The increase is large enough to explain much if not all of the increase in admission to hospital and mortality, and it underlines the importance of an understanding of the aetiology of asthma in tackling the causes of the recent increase.

The natural history of asthma in childhood

The incidence and prognosis of childhood asthma and wheezing illness (AW) was studied using data obtained at ages 7, 11, and 16 from a national cohort of 8806 children born in 1958. By the age of 16, 24.7% were reported to have experienced at least one episode of AW. In 18.3% AW had started before the age of 8, but only 4.2% continued to have symptoms in later childhood. A further 3.6% began to have AW between the ages of 8 and 11, and 2.8% began between the ages of 12 and 16. Of those with AW at age 7, 28.3% had symptoms at 11 and 16.5% at 16; these proportions were about doubled if AW at 7 had been severe. The associations between natural history and a large number of perinatal, social, environmental, and medical factors were examined. Those which predicted the onset of AW after the age of 7 were: male sex of child; mother aged 15-19 at child's birth; history of pneumonia, whooping cough, throat or ear infections or tonsillectomy; eczema, allergic rhinitis; and periodic vomiting or abdominal pain.