The interrelationship among bronchial hyperresponsiveness, the diagnosis of asthma, and asthma symptoms

Bronchial responsiveness is not always increased after allergen challenge

Increased bronchial responsiveness has been reported at various time points following allergen challenge (AC), and may be related to the magnitude of the late response (LAR). We have studied 20 mild asthmatics, who were known to develop a late asthmatic response to inhalation of house dust mite extract (fall of > 15% from post-diluent baseline FEV1 from 2 to 7h after AC). The provocation concentration of methacholine causing a 20% fall in FEV1 (PC20 FEV1) was measured before and 24 h after challenge with house dust mite extract (HDM). The mean (SEM) change in log(PC20) was 0.08 (0.09) mg ml-1, and was not significant (P = 0.38; paired t-test). The change in PC20 for each subject was not significantly correlated with the size of LAR (r = -0.33; P > 0.05), but was significantly correlated with the absolute change from baseline FEV1 at 24 h (r = 0.67; P < 0.01). Our subjects had a high baseline responsiveness, when compared with previous studies. We suggest they may have been approaching a maximally responsive state prior to study, and allergen challenge may have had little effect in further increasing responsiveness. Exposure to allergen in late responders is not necessarily followed by an increase in non-specific bronchial responsiveness.

Prognostic value of methacholine challenge in patients with respiratory symptoms

BACKGROUND

The objective was to study the current clinical status of 78 adults with respiratory symptoms, who were referred 3 to 10 years ago for diagnostic methacholine challenge. We tested the hypothesis that methacholine hyperresponsiveness would be associated on follow-up with increased symptoms of chest tightness, dyspnea, wheezing, cough, and more frequent use of selected treatment modalities.

METHODS

Current symptoms were evaluated by means of interview questionnaire, and methacholine challenge was repeated during follow-up examination. Comparisons were made between patients who were and those who were not hyperresponsive to methacholine at initial and follow-up challenges by using specific symptoms and calculated symptom and treatment scores.

RESULTS

We found that subjects who had positive methacholine challenge results on initial challenge (n = 37) were significantly more likely than those with negative results (n = 41) to have nonexertional chest tightness, wheezing, and dyspnea, but not cough. A high proportion of both groups had current symptoms. Two thirds of the patients continued to have positive (n = 25) or negative (n = 27) methacholine challenge results, and one third had a change in status (n = 26). Significant correlations were also found between follow-up methacholine responsiveness and concurrent symptoms, again with the exception of cough.

CONCLUSIONS

Methacholine challenge warrants cautious interpretation in the individual patient as an aid to diagnosis and prognosis in the evaluation of respiratory symptoms, especially cough.

Health insurance status and ambulatory care for children

BACKGROUND

Many children in the United States lack health insurance. We tested the hypothesis that these children are less likely than children with insurance to visit a physician when they have specific conditions for which care is considered to be indicated.

METHODS

We examined the association between whether children were covered by health insurance and whether they received medical attention from a physician for pharyngitis, acute earache, recurrent ear infections, or asthma. Data were obtained on the subsample of 7578 children and adolescents 1 through 17 years of age who were included in the 1987 National Medical Expenditures Survey, a national probability sample of the civilian, noninstitutionalized population.

RESULTS

Uninsured children were more likely than children with health insurance to receive no care from a physician for all four conditions (unadjusted odds ratios, 2.38 for pharyngitis; 2.04 for acute earache; 2.84 for recurrent ear infections; and 1.87 for asthma). Multiple logistic-regression analysis was subsequently used to control for age, sex, family size, race or ethnic group, region of the country, place of residence (rural vs. urban), and household income. After adjustment for these factors, uninsured children remained significantly more likely than insured children to go without a visit to a physician for pharyngitis (adjusted odds ratio, 1.72; 95 percent confidence interval, 1.11 to 2.68), acute earache (1.85; 95 percent confidence interval, 1.15 to 2.99), recurrent ear infections (2.12; 95 percent confidence interval, 1.28 to 3.51), and asthma (1.72; 95 percent confidence interval, 1.05 to 2.83).

CONCLUSIONS

As compared with children with health insurance, children who lack health insurance are less likely to receive medical care from a physician when it seems reasonably indicated and are therefore at risk for substantial avoidable morbidity.

Bronchial responsiveness in children living in areas with different air pollution levels

This study evaluated the prevalence of increased bronchial responsiveness (BR) in children living in two areas with different air pollution levels. A total of 1,215 methacholine challenge tests were performed among a random sample of primary schoolchildren in an industrial town polluted by oil-fired thermoelectric power plants and in a rural area chosen as a control. The two groups showed similar lung function data (forced vital capacity [FVC] and forced expiratory volume in 1 s [FEV1.0]) and prevalence of positive prick tests to common aeroallergens. All children responding with a 20% drop in FEV1.0 to a methacholine concentration < or = 64 mg/ml, "all responders" (PC20FEV1.0 < or = 64 mg/ml), and the subgroup of "strong responders" (PC20FEV1.0 < or = 4 mg/ml) were compared separately with "nonresponders" (PC20FEV1.0 > 64 mg/ml), calculating odds ratios (ORs). There were more "all responders" (57.2% versus 41.4%) and "strong responders" (20.0% versus 14.8%) among subjects living in the industrial area; the excess remained when several potential confounders were taken into account ("all responders": OR = 2.0, 95% confidence interval [95% CI] = 1.5-2.6; "strong responders": OR = 1.9, 95% CI = 1.3-2.8), and it was even more pronounced among girls. When the effect of clinical predictors of increased airways responsiveness (history of asthma, allergic rhinitis, baseline airways caliber, skin reactivity, recent respiratory infection) was considered through multiple logistic regression, the odds ratios associated with living in the industrial area were still significantly increased in girls. The cross-sectional approach and the lack of individual exposure data limit the interpretation of the findings.(ABSTRACT TRUNCATED AT 250 WORDS)

Normal range of methacholine responsiveness in relation to prechallenge pulmonary function. The Normative Aging Study

Methacholine airway responsiveness has been observed to be related to prechallenge level of pulmonary function; however, normal ranges of responsiveness for specific levels of lung function have not been reported. We examined methacholine airway responsiveness in relation to level of prechallenge pulmonary function in a sample of 547 middle-aged and elderly men who denied any history of respiratory illness or symptoms and who had normal levels of prechallenge FEV1 and FEV1/FVC ratio. The cumulative dose of methacholine provoking a 20 percent decline in FEV1 (PD20FEV1) was positively correlated with prechallenge FEV1 percent predicted (Spearman correlation r = 0.35, p < 0.0001). The fifth percentile of PD20FEV1, chosen as an estimate of the lower limit of the normal range, varied with the level of prechallenge FEV1. When applied to a larger sample of 838 men with normal pulmonary function, the use of FEV1-specific cut-off values to separate "normal" from "abnormal" PD20FEV1 did not improve the sensitivity or specificity of methacholine challenge as a test for questionnaire-reported asthma or wheezing. These data provide lower limits of normal PD20FEV1 which are specific for a subject's prechallenge FEV1; however, these FEV1-specific lower limits of normal PD20FEV1 provided no greater sensitivity and specificity for detecting asthma and wheezing than did a single lower limit of normal PD20FEV1 for all subjects.

Eucapnic voluntary hyperventilation as a bronchoprovocation technique. Comparison with methacholine inhalation in asthmatics

Methacholine inhalation challenge (MIC) is probably the most widely used and best standardized test for nonspecific bronchoprovocation challenge (BPC). There has been increasing interest in developing "physical" stimuli such as eucapnic voluntary hyperventilation (EVH) with dry gas to assess airway hyperreactivity (AHR), because of inherent problems with using a pharmacologic agent in epidemiologic surveys. To our knowledge, no studies exist that compare MIC with EVH in known asthmatics. We conducted a prospective, randomized, crossover trial with a group of subjects (n = 16) who met the American Thoracic Society definition of asthma with these objectives: (1) to compare the sensitivity of EVH with MIC; (2) to compare the quantitative response of one test with the response to the other challenge; and (3) to correlate the response of both tests with symptoms, serum IgE levels, and serum eosinophil counts. We found that (1) EVH was positive in 75 percent of cases and MIC was positive in 81 percent of cases; one subject reacted to EVH but not to MIC and vice-versa. (2) The quantitative response to one test correlated with the response to the other test (r = -0.60, p = 0.01). (3) There was a correlation between severity of asthma symptoms and the response to EVH (r = 0.62; p = 0.01), but not to MIC. (4) Response to MIC (log PD20), but not EVH, correlated with serum IgE level (r = -0.53, p = 0.04). We suggest that EVH may be used for the initial assessment of AHR in the evaluation of asthma. Eucapnic voluntary hyperventilation is a sensitive measure of AHR and it correlates well with symptoms. Furthermore, though these points were not addressed in our study, it is more physiologic than MIC, and it is easy and less expensive to perform.

Airway response to a bronchodilator in healthy parents of infants with bronchiolitis

In order to assess the role of genetic factors and environmental influences in bronchial responsiveness, we studied the airway response to an inhaled bronchodilator in 66 nonasthmatic parents (age, 30.9 +/- 5.9 years) of infants with bronchiolitis (group 1). It was a placebo-controlled double-blind study. A control group (group 2) of healthy parents of infants who did not have bronchiolitis also were investigated with the test of bronchodilator response. All subjects showed normal expiratory airflow and lung volumes (forced vital capacity [FVC], forced expiratory volume in 1 s [FEV1], and mean forced expiratory flow during the middle half of FVC [FEF25-75%] > 80 percent of predicted) at baseline forced expiratory maneuver. In 16 (24.2 percent) subjects of group 1, there was significant increase in at least one parameter after salbutamol administration, but not after placebo inhalation, with respect to baseline levels. Furthermore, no significant changes in FVC, FEV1, or FEF25-75% values were found in group 2. In conclusion, this study confirms that parents of infants with bronchiolitis have an enhanced airway responsiveness, greater than control parents. Further studies are needed to assess whether one may infer the outcome of infants with bronchiolitis from this characteristic in their parents.

Physiologic measures: pulmonary function tests. Asthma outcome

When the effectiveness of asthma interventions are evaluated in the research setting, the physiologic manifestation of asthma-variable airways obstruction-is always objectively measured by some of the following pulmonary function tests: (1) Baseline spirometry gives a highly accurate "snapshot" of asthma severity and the degree of airways obstruction. The FEV1, derived from spirometry, is the most reproducible pulmonary function parameter and is linearly related to the severity of airways obstruction. There are no contraindications for the test, spirometers are widely available at reasonable cost, and methods and result interpretation are comprehensively standardized. (2) The post-bronchodilator FEV1 measures the best lung function that can be achieved by bronchodilator therapy on the day of the visit and therefore is a more stable measure in asthmatics than comparing visit-to-visit baseline FEV1. Although a positive acute response to bronchodilator helps to confirm the diagnosis of asthma, the degree of bronchodilator reversibility from visit-to-visit (change in reversibility) is not a useful index of asthma outcome. (3) Airway responsiveness (bronchial challenge) measures the degree to which an individual withstands nonspecific stimuli that trigger asthmatic attacks. The methacholine challenge test is safe and requires less than an hour, but it requires more technical skill than baseline spirometry and is contraindicated in some situations. (4) Ambulatory monitoring, using peak flow meters or hand-held spirometers, provides multiple measurements of the degree of obstruction for days to weeks in the patient's natural setting. PEF meters are very inexpensive and almost all asthmatics can use them, but PEF results are less reliable than the FEV1. The often asymptomatic obstruction of an asthmatic has both short-term (within a day and day-to-day) and longer-term variations that are triggered by naturally occurring stimuli. These changes are measured by PEF lability but not by spirometry during clinic visits. (5) Other pulmonary function tests, such as absolute lung volumes and airways resistance, may provide confirmatory data, but the instruments are large, expensive, and technically demanding. The results of all the above pulmonary function tests are significantly correlated with each other and with symptom scores and medication use in large groups of patients with widely varying degrees of asthma severity. Since a "gold standard" with which to measure asthma severity does not currently exist, all of these tests contribute an additional amount of unique information when measuring asthma outcome in a clinical trial.

Bronchial responsiveness in children and adolescents: a comparison between previously asthmatic, currently asthmatic, and normal subjects

The aim of this study was to examine the degree of bronchial responsiveness in previously asthmatic subjects. Of 253 patients, born within 1964-1974, followed in the pediatric department at the University hospital in Copenhagen, 224 subjects (89%) were successfully contacted by telephone; of these 195 complained of persistent asthma and 29 (13%) had had no asthmatic symptoms for at least 2 years. On the basis of the degree of respiratory symptoms, 58 individuals were examined at the outpatient clinic. Of these, (1) 19 were previously asthmatics, (2) 20 had current mild asthma, and (3) 19 had current severe asthma. Furthermore, 19 healthy individuals, age-matched with the preceding asthmatic subjects, were selected as controls. In all subjects, skin prick tests, lung function tests, and bronchial challenge tests with inhaled histamine and bronchodilator were performed. Furthermore, the subjects measured their peak expiratory flow (PEF) twice daily during a period of 4 weeks. Of the 39 current asthmatic subjects, 82% had a PC20 < or = 8 mg/ml, whereas all previously asthmatic subjects and the controls had a PC20 > 8 mg/ml. The degree of bronchial responsiveness as indicated by the dose-response slope (DRS), the percentage change in forced expiratory volume in 1 sec (FEV1) per inhaled mumol of histamine, was found to be significantly higher in previously asthmatic patients (median logDRS 0.1 delta %FEV1/mumol) than in controls (median logDRS-0.4 delta %FEV1/mumol) (p < 0.001). Furthermore previously asthmatic subjects had significantly increased change in FEV1 after inhalation of bronchodilator and peak expiratory flow variability compared to controls. These findings suggest that apparently asymptomatic previously asthmatic subjects have increased airway variability.

Allergic bronchospasm and airway hyperreactivity in the guinea pig

In passively sensitized guinea pigs, show infusion of an amount of ovalbumin insufficient to evoke airway obstruction induces hyperreactivity of the airways. A wide range of changed responsivity was observed for different test spasmogens, with leukotriene C4 > histamine > prostaglandin F2 alpha > bradykinin > leukotriene E4 > serotonin > acetylcholine. Injection of ovalbumin as a bolus produced pronounced airway obstruction without hyperreactivity. Airway obstruction due to vascular engorgement (dextran infusion) or edema (histamine infusion) did not result in hyperreactivity. Infusion of PAF induced pronounced airway obstruction together with hyperreactivity, but with a rank order of histamine > leukotriene C4 > serotonin > bradykinin > leukotriene E4 > acetylcholine. It can be concluded that allergic airway hyperreactivity in the guinea pig is spasmogen-selective and largely independent of airway obstruction. These observations question the presumption of non-selective hyperreactivity in allergic asthma and cast doubt upon the proposal that airway hyperreactivity is secondary to airway obstruction.

Childhood asthma: diagnosis and treatment

This discussion of asthma management should be regarded as providing guidelines, not dogma. The underlying principles of asthma management include recognition of the variability of the disease and the importance of the underlying inflammatory condition. Clinical assessment is not enough and objective monitoring with PEFR or spirometry provides important data. The treatment protocols require individualization. It is important that the patient and family are team members working together with the medical staff toward a goal of good asthma management. In the discussion of the management of asthma, much emphasis was placed on spirometry and home measurement of PEFR. Office use of spirometry is now the norm for asthma management. Providing asthmatic patients with peak flow meters and instructions in their use is part of the routine care of asthma. Instruction of the patient and family in the proper use of medications is paramount. The MDI devices need to be prescribed with careful instructions regarding their use. When the patient comes in for follow-up, part of the examination should include the patient's demonstration of how he uses this device. Discussion of the proper and safe use of bronchodilators is important. Overuse of inhaled bronchodilators may be a reflection of increasing asthma or, at the very least, evidence that the patient does not understand appropriate treatment of asthma. If a patient is dependent on regular use of an inhaled beta agent, it is likely that he would benefit from therapy directed at the underlying inflammation of asthma. The patient and the family should understand the purpose of each medication, the side effects, and the risks and benefits of their use. In particular, if steroid medications are necessary, the reasons for their use should be explained. Carefully matching the severity of the asthma with the therapeutic protocols provides an organized approach to asthma treatment. Avoiding triggers of asthma and controlling the environmental exposure to potential triggers leads to lower medication requirements and less lability. Offering the family written instructions to cope with changes in the child's condition, based on assessment of clinical and PEFR observations, allows them more autonomy and comfort in the day-to-day care of the asthmatic child.

An alternative method for comparing and describing methacholine response curves

Tests of nonspecific airway hyperresponsiveness are frequently used in the study of asthma both in the clinical settings and in epidemiologic studies. However, standard methods for characterizing individual tests and comparing results between subgroups have not been established. The most frequently used method of characterizing response curves is to report the dose that results in a 20% fall in FEV1 from the initial or baseline FEV1 value (PD20FEV1). Other investigators have suggested using the response slopes. In this study we demonstrate an alternative method of analysis that uses all of each subject's response data, makes comparisons between subgroups, and can include explanatory covariables. This approach is demonstrated using methacholine challenge data obtained in New Zealand children at 9 and 11 yr of age. The results showed significant differences between the mean dose-response curves of wheezers and nonwheezers, that responsiveness increased with the frequency of reported wheeze, and that initial pulmonary function and serum IgE are significantly related to responsiveness. These factors were not always significant using more traditional methods of analysis, indicating an increased sensitivity with this method of analysis.

Diagnostic value of the bronchial provocation test with methacholine in asthma. A Bayesian analysis approach

The Bayesian analysis was used in this study to investigate the diagnostic value of the bronchial provocation test with methacholine in patients with asthma. The best cutoff value of accumulated concentration of methacholine administered that caused a 20 percent fall in FEV1 post-saline (PC20) in our sample, determined with a receiver operator characteristic curve, was 15 mg/ml. The interval security of the test was established by a pretest probability between 0.16 and 0.87 and the best test results were obtained when pretest probability was 0.48. The positive final diagnostic gain of the test was maximal at this pretest probability. We conclude that the application of Bayes' theorem, considering the pretest probability of asthma and the sensitivity and specificity of the individual PC20 obtained, increases the accuracy of the bronchial provocation test with methacholine in the diagnosis of asthma.

Evaluation of cold air challenge data in a population sample using a model of bronchial hyperreactivity and disposition to bronchial obstruction

To explore the role of bronchial hyperreactivity and obstruction after cold air challenge, data from a cross-sectional study of more than 7,000 10-year-old children were used. Current knowledge of hyperreactivity is primarily based on pharmacological provocation tests with variable prechallenge flow rates and their decrease relative to baseline. Using forced expiratory volume (FEV) in 1 sec values before and after cold air challenge, however, it is possible to define a subsample of children with predominant hyperreactivity and a subsample with predominant obstruction after challenge. The prevalence of respiratory symptoms and the diagnoses in the two subsamples were compared. The analysis showed that children with bronchial obstruction have nearly the same frequency of respiratory symptoms as those with bronchial hyperreactivity. A combined model of bronchial obstruction and hyperreactivity was, therefore, more predictive of symptoms than a model of hyperreactivity alone.

Relationship between viral antibodies and bronchial hyperresponsiveness in 495 unselected children and adolescents

The purpose of this study was to investigate whether recent and previous subclinical viral respiratory infection can explain the presence of increased bronchial responsiveness to histamine. We studied a randomly selected population of 495 children and adolescents, aged 7-16 years, from Copenhagen. If the subjects had had symptoms of respiratory infection recently, the examination was postponed for at least 6 weeks. Bronchial hyperresponsiveness (BHR) to inhaled histamine was found in 79 (16%) of the subjects, of whom 28 had asthma. Forty-eight subjects (10%) had increased levels of serum IgM antibodies against either parainfluenza, influenza, adenovirus, or respiratory syncytial virus (RSV), reflecting a recently acquired infection. No association between BHR and antibodies against respiratory viruses was found, as 7 (8.9%) of the 79 subjects with BHR and 41 (9.9%) of the 416 subjects without BHR had viral antibodies. Furthermore, no association between degree of bronchial responsiveness and viral antibodies was found. Moreover, 251 individuals (51%) had signs of earlier RSV infection, i.e. IgG antibodies against RSV. No relationship was found between age of the subjects and the presence of antibodies against either respiratory viruses in general or IgG-RSV. No relationship was found between the presence of antibodies against RSV and BHR; furthermore, evidence of earlier RSV infection was unrelated to the level of lung function and degree of bronchial responsiveness. We conclude that increased bronchial responsiveness in asymptomatic, unselected schoolchildren and adolescents is not likely to be caused by recent or previous viral respiratory infections.

Mast cell activation enhances airway responsiveness to methacholine in the mouse

Mast cell-deficient mutant mice and their normal littermates were used to determine whether activation of mast cells by anti-IgE enhances airway responsiveness to bronchoactive agonists in vivo. Pulmonary conductance was used as an index of airway response as the mice were challenged with increasing intravenous doses of methacholine (Mch) or 5-hydroxytryptamine (5-HT). Mast cell activation with anti-IgE enhanced pulmonary responsiveness to Mch in both types of normal mice (P < 0.0001 by analysis of variance) but not in either genotype of mast cell-deficient mouse. Additionally, anti-IgE pretreatment of genetically mast cell-deficient W/Wv mice whose mast cell deficiency had been repaired by infusion of freshly obtained bone marrow cells or bone marrow-derived cultured mast cells from congenic normal mice led to significant (P < 0.0001) enhancement of Mch responsiveness. 5-HT responsiveness was not significantly influenced by anti-IgE pretreatment in any of the mice studied. The data support the hypothesis that IgE-mediated activation of mast cells enhances pulmonary responsiveness to cholinergic stimulation.

Exercise-induced airflow obstruction in a healthy military population

Clinical asthma is estimated to occur in 4 to 7 percent of the US population, but respiratory symptoms are much more common. The correlation between asthma, tests of bronchial hyperresponsiveness, and symptoms is imprecise and difficult to ascertain. The prevalence of exercise-induced airflow obstruction is not well known in healthy adults. We studied 100 consecutive US Air Force members to determine the prevalence of respiratory symptoms and the incidence of airflow obstruction after standardized free-run exercise. Subjects who developed airflow obstruction with exercise underwent methacholine challenge. We found that 31 percent of our population had respiratory complaints, but only 6 percent had significant airflow obstruction after exercise. Three of six subjects with abnormal results on exercise spirometry had bronchial hyperresponsiveness in response to methacholine. In summary, objective evidence of exercise-induced airflow obstruction was uncommon in our healthy subjects, although nonspecific respiratory complaints were frequent. In our study, methacholine challenge was positive in only half the subjects with abnormal spirometric data after exercise. We conclude that the diagnosis of exercise-induced asthma in healthy individuals is difficult because of the uncertain relationship between symptoms and objective testing and between modes of objective testing. Additionally, the role of free-run exercise testing needs further investigation in adults being screened for asthma.

Wheezing and airflow obstruction during methacholine challenge in children with cystic fibrosis and in normal children

To study wheeze as an indicator of bronchial responses during standardized methacholine challenge (MCH), we used computerized analysis of respiratory sounds in children with cystic fibrosis (CF) and in healthy control subjects. We recorded tracheal and lung sounds from 10 young CF = yCF patients, mean age 5.7 yr (range 4 to 7 yr), 13 older CF = oCF, age 10.5 yr (8 to 18 yr), 7 young normal subjects = yNO, age 5.3 yr (4 to 7 yr), and 11 older normal subjects = oNO, age 11 yr (8 to 16 yr). Spirometry was obtained after each doubling concentration of methacholine until the concentration provoking a > or = 20% fall in FEV1 (PC20) or the end point (8 mg/ml) was reached. Sound and calibrated flow signals were recorded on tape and later analyzed by respirosonography. The concentration of methacholine associated with wheeze (PCw) was noted. Wheezing was quantified by its duration during inspiration (Tw/TI) and expiration (TW/TE). We found a positive response to MCH in 11 of 13 oCF (PC20 0.75 mg/ml, range 0.08 to 3.0) and in 3 of 11 oNO (PC20 4.2 mg/ml, range 2.5 to 6.5). Wheezing occurred in 6 oCF (PC20 < 8 mg/ml). In 7 yCF PC20 or PCW developed (1.51 mg/ml, range 0.125 to 4.0) versus 4 yNO (4.0 mg/ml, range 2.0 to 8.0). In 10 oCF subjects who performed MCH on three occasions within a 2-wk period, both positive and negative wheeze responses were reproducible. Patients who wheezed had a lower FRC compared with patients who did not (109 versus 147% of predicted, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

An interview study to estimate prevalence of asthma and chronic bronchitis. The obstructive lung disease in northern Sweden study

A questionnaire of respiratory symptoms and diseases completed by 6610 adults in 3 age cohorts (35-36 y; 50-51 y and 65-66 y) in northern Sweden was followed-up by interview and lung function testing of 1243 subjects with asthmatic or bronchitic symptoms and 263 subjects assessed from the postal questionnaire as being healthy. We report the results of this follow-up study. According to the criteria used, 292 subjects (5.1% of the original study sample) were diagnosed as having asthma. Out of the 1243 subjects 334 (5.9% of the original study population) were diagnosed as having chronic bronchitis. However, examination of the 263 subjects who were healthy according to the postal questionnaire showed that elderly smokers, in particular, under-reported bronchitic symptoms; taking this into account, the prevalence of chronic bronchitis is estimated to be of the order of 9%. Diagnostic difficulties were noted in 70 subjects (corresponding to 1.2% of the original study sample) in whom asthma or chronic bronchitis were strongly suspected. Further investigation of these subjects was considered necessary. In this cross-sectional study, FEV1 < 80% of predicted values was found in 36% of subjects diagnosed as having asthma and in 31% of those with chronic bronchitis. Among subjects with attacks of breathlessness and wheezing, diagnostic criteria often used for asthma in questionnaire studies, 70% were diagnosed as having asthma. Of those with chronic productive cough, 62% were diagnosed as having chronic bronchitis. We consider that trained nurses provide reliable data that may be used in epidemiological surveys of obstructive lung diseases.

Relation between response to exercise and diurnal variability of peak expiratory flow in primary school children

BACKGROUND

Variability in peak expiratory flow (PEF) has been proposed as a simple method of screening for asthma in epidemiological studies. This study was designed to assess whether the bronchial response to exercise and the diurnal variation in PEF identified the same subjects.

METHODS

Bronchial response to a free running exercise test was assessed in a cohort of 918 seven year old children and was compared with variability of PEF as assessed by twice daily recordings for a one week period. Mini Wright peak flow meters were used throughout the study.

RESULTS

Baseline PEFs of both tests were highly correlated but there was no significant correlation between a response to exercise and variability of PEF. Of 33 children with a physician's diagnosis of asthma, 18 had at least one abnormal test, but only five children were abnormal in both tests, showing that the tests did not identify the same subjects.

CONCLUSION

Increased variability of PEF, as well as a response to exercise, was associated with respiratory symptoms, but only a response to exercise was closely associated with atopy (defined as a positive skin test to any of seven aero-allergens).

Methacholine reactivity and asthma. Report from the Northern Sweden Obstructive Lung Disease Project

Methacholine tests were used in an epidemiologic study of the prevalence of asthma and chronic bronchitis in northern Sweden. Of 6610 subjects in three age groups from eight representative geographic areas in the northernmost province of Sweden, 5698 (86%) completed a postal questionnaire on respiratory symptoms, and 1506 underwent a structured interview and a lung function test. A total of 292 (5%) were diagnosed as having asthma. A subsample of 284 subjects (of 320 invited) classified at the interview as having asthma (n = 98) or as having respiratory symptoms that might be due to asthma but not fulfilling the interview criteria for the diagnosis of asthma (n = 186) underwent a methacholine test. Subjects who, before the interview study, already had a well-defined asthma diagnosis were not invited to the methacholine testing. Of those 98 subjects classified as having asthma, 61% reacted to methacholine doses < or = 4 mg/ml and 79% to doses < or = 8 mg/ml, while the corresponding figures in the symptomatic but nonasthma group were 20% and 34%, respectively. The results show that a carefully performed structured interview accurately diagnoses asthma in epidemiologic studies. The methacholine tests provide important diagnostic information primarily in subjects in whom the medical history is equivocal.

Acoustic vs. spirometric assessment of bronchial responsiveness to methacholine in children

To study wheezing as an indicator of bronchial responsiveness during methacholine challenge (MC) in children, we used computer analysis of respiratory sounds and compared wheeze measurements to routine spirometry. MC was performed in 30 symptomatic subjects (sympt), age 11 +/- 3.1 years (mean +/- SD), with suspected asthma and in 12 controls (contr), age 10 +/- 3.4 years. Respiratory rate (RR), spirometry, arterial oxygen saturation (SaO2), and cough were registered until the concentration provoking a > or = 20% fall in forced expiratory flow in 1 second (FEV1;PC20), or the end point (8 mg/mL) was reached. For 1 min after each inhalation, sounds over the trachea and posterior right lower lobe were recorded together with calibrated airflow. Computer analysis of respiratory sounds was used for objective wheeze quantification. Wheezing was measured as its duration relative to inspiration (Tw/Ti) and expiration (Tw/Te). Seventeen of the sympt group developed wheezing (sympt/W) with > or = 5% Tw/Ti or > or = 5% Tw/Te. Thirteen of the sympt did not wheeze (sympt/no W). Three contr developed wheeze (contr/W) while 9 did not (contr/no W). In sympt/W, RR increased from 20 +/- 6.2 per min at baseline to 25 +/- 9.2 (P < 0.05) at the MC concentration provoking wheeze (PCw), and SaO2 decreased from 97.4 +/- 1.2% to 95.3 +/- 2.4 (P < 0.05). In contr/W, RR did not change, but SaO2 decreased from 97.3 +/- 1.5% to 95.7% +/- 1.2% (P < 0.05). Wheezing occurred at both recording sites and was as common during inspiration as during expiration.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway inflammation, bronchial reactivity and asthma

Asthma is a common disease of children the basis of which is a state of chronic immunological inflammation which causes bronchial hyperreactivity and renders the patient liable to develop widespread airways obstruction in response to a variety of stimuli. In many instances it is likely that the immunological inflammation results from ongoing antigenic stimuli with the release of chemical mediators responsible for short term bronchospasm and cytokines responsible for the ongoing inflammatory process. Other insults can apparently result in very similar immunological events in asthmatics, particularly viral infections and a similar process can be initiated in children without asthma, including those with chronic bacterial infections of the lungs. There are differences in the bronchial hyperreactivity of asthma and other diseases which suggest that in the asthmatic the mast cell is either different structurally or functionally and this renders the patient susceptible to exercise induced asthma in addition to the bronchial hyperreactivity to chemical mediators common to a number of diseases with hyperreactivity. There is good evidence of direct genetic control of atopy and the large majority of children with asthma are atopic but there is no direct genetic link between atopy and asthma and twin studies strongly suggest the existence of a 'permissive' asthma gene which will allow the disease to develop if there is an appropriate external trigger. The only drugs which have been shown to significantly reduce bronchial reactivity are the corticosteroids with a lesser effect noted for sodium cromoglycate and nedocromil. Inhaled corticosteroids can reverse the immunologic inflammatory process and reduce bronchial reactivity, sometimes to normal levels, but on stopping treatment the patient reverts back to the asthmatic state. At the present time it appears that controlled longterm inhaled corticosteroid therapy is the most rational treatment for significant perennial childhood asthma.

Prevalence of childhood asthma: facts, tendencies and interpretations

Questionnaire surveys are an appropriate instrument to assess epidemiologic data on respiratory ill health, to analyse influences of environmental factors on respiratory morbidity and to evaluate treatment strategies. To investigate the prevalence rates of asthma and symptoms suggestive of asthma we performed population surveys in Swiss school children. Special attention is drawn to particular aspects such as atypical symptoms, underdiagnosis and undertreatment of asthma.

Relationship between pulmonary test variables and asthma and wheezing: a validation of self-report of asthma

We investigated the relationship between the pulmonary test variable measurements and self-reported asthma and wheezing from a cross-sectional study conducted in Saskatchewan. Based on the responses to the questionnaire, the subjects were classified into asthmatic, wheezing, and asymptomatic groups. For both male and female subjects the mean values of forced expiratory volume in 1 s (FEV1), forced expiratory flow during the middle half of the forced vital capacity (FEF25-75), and FEV1/FVC ratio were lowest in asthmatics, followed by wheezing and asymptomatic groups, respectively. This trend was also observed in forced vital capacity (FVC) for men but not for women. After adjusting for current smoking status, the trend in the means across the three groups was statistically significant in men for FEV1 (p = 0.03), FEF25-75 (p = 0.002), and FEV1/FVC ratio (p = 0.002) and in women for FEF25-75 (p < 0.001) and FEV1/FVC ratio (p < 0.001). The differences in the adjusted means of FVC, FEV1, FEF25-75, and FEV1/FVC ratio between asymptomatic subjects and the other two groups were significant in both male and female subjects. Significant differences were also observed between asthmatics and wheezing groups in the adjusted means of FEF25-75 and FEV1/FVC ratio in male and female subjects. We conclude that the self-report of asthma has a high level of validity against the criterion of concurrently measured pulmonary test variables.

Bronchial responsiveness and lung function in infants with lower respiratory tract illness over the first six months of life

The aim of this study was to determine whether increased bronchial responsiveness to histamine is associated with lower respiratory tract illness (one or more episodes of wheeze or cough, or both) in infancy. Fifty four normal newborn infants who had at least one atopic parent were recruited. At a median age of 6.5 months, 45 infants, 23 with a history of lower respiratory tract illness, and 22 without, underwent pulmonary function testing during a symptom free period. The maximum flow at functional residual capacity (VmaxFRC) was calculated from partial forced expiratory flow volume curves using the squeeze technique. Bronchial responsiveness to increasing doses of histamine was assessed by determining the provoking concentration which caused a 30% decrease in VmaxFRC (PC30). The length adjusted VmaxFRC was lower for symptomatic infants before the challenge (median 125 ml/s; 95% confidence intervals (CI) 85 to 164 ml/s) compared with control infants (median 215 ml/s; 95% CI 159 to 298 ml/s). There was no significant difference in PC30 between symptomatic infants (median 10.3 g/l; 95% CI 2.8 to 23.8 g/l) and control infants (median 16.5 g/l; 95% CI 2.4 to 27.9 g/l). Bronchial responsiveness to histamine can be shown in most infants early in life and is independent of lower respiratory tract symptoms including wheezing.

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.

Viruses as precipitants of asthma symptoms. II. Physiology and mechanisms

The upper and lower airways have complimentary roles in the ultimate object of supplying the body with oxygen whilst removing waste products of metabolism. Pathology in one area may trigger a response in another, the physiology of which, in the case of virus-induced asthma exacerbations remains poorly characterized. Viral infection of the upper airways by common cold viruses frequently triggers a response in the lower airways leading to prolonged morbidity, especially in subjects with significant pre-existing airway disease. The induction or amplification of BHR may be an important mechanism whereby asthmatic symptoms are produced although the cellular and tissue events or reflex mechanisms activated by viral illnesses and underlying BHR changes are poorly defined and may be dependent on the type and the severity of infection. Children and asthmatics tend to develop frequent colds setting in motion a sequence of events culminating in airway obstruction and symptoms of wheezing, coughing and chest tightness. This may reflect independent inflammatory changes caused by a simply additive effect of viral damage to the mucosa superimposed upon pre-existing allergic inflammation (Fig. 1). Few if any symptoms will develop in normal subjects with a mild cold whereas significant symptoms may ensue if the cold is severe and induces marked lower airway swelling, secretions and smooth muscle contraction; pathology to which children who have small calibre airways may be particularly susceptible. In asthmatics even a mild cold frequently induces exacerbation of symptoms, while serious life-threatening asthma attacks may occur associated with a severe cold. Some studies have suggested that this effect is not only additive but also synergistic and brought about by release of the mediators already present in increased quantities, the induction of IgE synthesis, or by the potentiation of neural and epithelial damage. The combined effect of both asthma and viruses may thus be amplified and result in a sustained and refractory period of airway obstruction, severe symptoms and unstable asthma. As most hospital admissions for asthma occur over the winter months and soon after the start of the school terms [115], spread of viruses through the community to susceptible individuals may be the single most important cause of sustained exacerbations of asthma. Definition of the pathological and physiological mechanisms involved will lead to better understanding and may thus provide a basis for prevention and the development of effective forms of treatment for virus-induced asthma.

Bronchial responsiveness to exercise in a random sample of 494 children and adolescents from Copenhagen

To investigate the bronchial response to exercise, we studied a random sample of 494 children and adolescents, aged 7-16 years, from Copenhagen. Exercise challenge consisted of steady running on a 10% sloping treadmill for 6 min in a climate chamber. Furthermore, in 464 subjects a histamine challenge test was also performed. Of the 494 subjects studied, 81 (16%) had at least 10% and 30 (6%) at least 15% reduction in FEV1 within 15 min after exercise. Twenty-nine (6%) subjects had bronchial hyperresponsiveness to both histamine and exercise, 48 (10%) subjects had bronchial hyperresponsiveness to exercise, but histamine responsiveness within the normal range, whereas 340 (73%) subjects had neither bronchial hyperresponsiveness to exercise nor inhaled histamine. With regard to the presence of asthma defined as substantial exercise induced bronchoconstriction (delta-FEV1 greater than or equal to 10%), exercise testing may not be appropriate for identifying clinical asthma in a random sample, because the highest predictive value of a positive test was 25%. On the other hand, a history of clinical asthma was frequently associated with increased bronchial responsiveness to exercise (77%). In conclusion, 16% of a random sample of children and adolescents had abnormal bronchial responsiveness to exercise (delta FEV1 greater than or equal to 10%), 6% of the subjects had a delta FEV1 greater than or equal to 15%. Furthermore, because of a low predictive value of a positive test, the exercise challenge test has only a supplementary role in the detection of clinical asthma in population samples.

The effects of airway hyperresponsiveness, wheezing, and atopy on longitudinal pulmonary function in children: a 6-year follow-up study

We examined growth of spirometric lung function in 696 children of European ancestry who were followed from ages 9 to 15 years and stratified according to their degree of responsiveness to methacholine inhalation challenge, atopic status, and respiratory symptoms. Subjects were participants in the longitudinal Multidisciplinary Health and Development Study in Dunedin, New Zealand. Forced expired volume in 1 second (FEV1), and vital capacity (VC) were measured at 9, 11, 13, and 15 years of age, concurrently with assessment of airway responsiveness determined by the concentration of methacholine causing a 20% fall in FEV1 (PC20 FEV1). Atopic status was assessed at age 13 by skin-prick testing to 11 allergens. In children demonstrating airway hyperresponsiveness, FEV1 increased with age at a slower rate, and the FEV1/VC ratio had a faster rate of decline through childhood, compared to non-responsive children. Subjects with positive skin tests to house dust mite and cat dander also had lower mean FEV1/VC ratios than the control group. Any reported wheezing was associated with slower growth of FEV1 and VC in males. We conclude that in New Zealand children with airway responsiveness and/or atopy to house dust mite or cat growth of spirometric lung function is impaired.

Effect of dietary sodium on the severity of bronchial asthma

BACKGROUND

A high sodium intake has been found to increase bronchial reactivity in men with asthma. The effects of change in sodium intake on peak flow rate have not been determined.

METHODS

The effect of changing dietary salt intake for two weeks on the severity of asthma as measured by peak expiratory flow (PEF) was studied in 17 patients with mild asthma in an open randomised crossover trial. PEF measurements were made by the patients in their own homes. Patients were placed on three levels of dietary sodium intake: normal, low, and high. Sodium intake was assessed by 24 hour urine collection.

RESULTS

The mean (SD) urine sodium was 147 (45), 84 (32), and 201 (73) mmol/24 hours in the normal, low, and high sodium intake periods respectively. There were no significant differences in PEF or PEF amplitude (highest--lowest PEF), an index of asthma lability, between the three dietary salt periods. CONCLUSION A low and high dietary salt intake for two weeks has no effect on peak expiratory flow in patients with mild asthma.

Profile of bronchial responsiveness in children with respiratory symptoms

A postal questionnaire inquiring into the presence of respiratory symptoms was sent to 3698 children aged 7 and 8 years. Those reporting either cough or wheeze were randomised, and a sample invited to attend for skin testing. A total of 192 symptomatic children, half of whom were atopic and half non-atopic, were randomly selected to enter the study. All children performed and recorded best of three peak expiratory flow measurements twice a day and completed a 10 point respiratory symptom score card each day for one year. They also recorded all treatment taken and made a note of relevant life events. Each child was seen monthly for general assessment and for measurement of nonspecific bronchial responsiveness to methacholine. Of the 192 children, 183 successfully completed the study. For six subjects 11 measurements of the provocation dose required to cause a 20% fall in forced expiratory volume in one second (PD20) were available for analysis and on the remaining 177, greater than or equal to 12 measurements. The prevalence and degree of bronchial hyper-responsiveness (PD20 less than 6.4 mumol) and its relationship to atopy was examined by comparing the percentage of members of each symptom group demonstrating bronchial hyper-responsiveness and the number of occasions on which they did so, and by comparison of minimum and median PD20 values. The range of bronchial responsiveness shown during the study period by each child was expressed as doubling doses of methacholine and compared between symptom groups. Atopy and wheeze were both independently associated with an increased prevalence and greater degree of bronchial hyper-responsiveness when compared with non-atopy and cough respectively, all differences being significant a the 0.001 level.. Thirty three per cent of subjects demonstrated a rnge of methacholine responsiveness of >4 and 13.4% of >6 doubling doses during one year.

Physiologic and nonphysiologic determinants of aerobic fitness in mild to moderate asthma

We studied 27 patients (seven male, 20 female) with stable mild-to-moderate asthma to measure their level of physical fitness and to determine if a relationship existed between aerobic fitness and the degree of airway reactivity, expiratory flow rates, or the amount of habitual leisure-time physical activity. Nonspecific bronchial hyperreactivity (NSBHR) was quantified by methacholine inhalation challenge. On a separate day, exercise capacity was evaluated with incremental exercise testing to exhaustion after bronchodilator pretreatment. The level of physical activity was assessed with a validated written questionnaire. FEV, was 78 +/- 13% predicted prebronchodilator and 92 +/- 14% predicted postbronchodilator. The mean provoking concentration of methacholine that caused a 20% decrease in FEV1 (PC20) was 1.14 +/- 1.38 mg/ml and ranged from 0.019 to 5.71 mg/ml. There was no correlation between PC20 and prebronchodilator FEV1 r = 0.37, p greater than 0.05). Mean maximal oxygen uptake (VO2max) was not significantly different from predicted normal values (36.9 +/- 10.8 versus 38.5 +/- 5.3, p = 0.32). Mean maximal O2pulse (maximal heart rate/VO2max), anaerobic threshold, and dyspnea index were within normal limits. There was no relationship between VO2max and FEV1 when expressed as percentages of predicted values (r = 0.08, p = 0.71) or between VO2max and PC20 (r = 0.23, p = 0.25). There was, however, a significant relationship between VO2max and the level of habitual leisure-time activity (F = 3.64, p less than 0.05). Results from the exercise questionnaire suggested that asthmatics perceive their disease as a limiting factor to improved aerobic fitness and that they lack adequate knowledge about asthma and exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of cysteinyl-leukotriene receptor antagonist ICI 204.219 on allergen-induced bronchoconstriction and airway hyperreactivity in atopic subjects

The effects of a highly selective leukotriene D4 receptor antagonist, ICI 204.219, on allergen-induced bronchoconstriction and changes in airway reactivity were evaluated in a double-blind, placebo-controlled, crossover trial. Ten atopic subjects were selected for the study on the basis of an immediate fall in forced expiratory volume in 1 s (FEV1) of at least 15% and a least a doubling dose fall in their PC20-histamine (the concentration of histamine needed to reduce FEV1 by 20%) after antigen challenge. Baseline PC20-histamine was determined before the ingestion of a single oral 40 mg dose of ICI 204.219 or matched placebo. 2 h later subjects were challenged with aerosolised allergen; FEV1 was measured for the next 6 h then PC20-histamine was remeasured. Two subjects did not complete the study for reasons not related to the trial medication. ICI 204.219 significantly attenuated the early and late phase bronchoconstriction to inhaled allergen (mean treatment difference in area under the FEV1-time curves 2529 [95% Cl 1085-3972] delta %FEV1.min; p less than 0.005: and 3537 [528-6545] delta %FEV1.min; p less than 0.03) and suppressed the allergen-induced increase in non-specific bronchial reactivity (mean treatment difference 1.03 [0.34-1.71] doubling dilutions of histamine; p less than 0.01). These findings suggest that ICI 204.219 may be a disease-modifying agent in asthma. Further studies are under way to evaluate its clinical efficacy.