Interpretation of the results of methacholine inhalation challenge tests

Repeatability of methacholine challenges in 2- to 4-year-old children with asthma, using a new technique for quantitative delivery of aerosol

To determine the repeatability of bronchial responsiveness in awake young children, two methacholine challenge tests were performed on separate days in 16 children with stable asthma (mean age, 3 3/4 years). Methacholine was administered using a new method for quantitative delivery of aerosol that eliminates the effect of dilution of the aerosol by entrainment of air and enables quantitative delivery of aerosol according to body weight. Respiratory function was monitored by measurement of respiratory resistance by the interrupter technique (Rint), respiratory resistance and reactance at 5 Hz (Rrs5, Xrs5) by the impulse oscillation technique, transcutaneous measurements of oxygen (PtcO2), and specific airway resistance (sRaw). Repeatability was evaluated by determining the provocative dose that caused a defined percentage of change relative to baseline (PD%: Rint PD30, Rrs5 PD30, Xrs5 PD80, PtcO2 PD10, and sRaw PD80. Repeatability was estimated from the difference between the PD% obtained at the time of the two tests. Using the numeric value of these differences, the repeatability of Xrs5 PD60, PtcO2 PD10, and sRaw PD50 was [mean (SD)]: [0.8 (0.5)] [0.5 (0.4)] and [0.7 (0.6)] doubling doses, respectively. Rint PD30 and Rrs5 PD30 proved to be less reproducible: [1.2 (1)] and [1.6 (0.9)] doubling doses, respectively. The new method of aerosol delivery offers a means of standardizing the bronchoconstrictor stimulus, and the results show that estimates of bronchial responsiveness in young children can be obtained reproducibly within one doubling dose of methacholine.

Sensitivity and maximal response to methacholine in perennial and seasonal allergic rhinitis

BACKGROUND

Airway hyperresponsiveness to pharmacological agonists is a common feature in subjects with allergic rhinitis.

OBJECTIVE

The aim of this study was to investigate differences in threshold value and shape of the concentration-response curves to methacholine between subjects with perennial allergic rhinitis and subjects with seasonal rhinitis.

METHODS

We studied a sample of 72 non-asthmatic patients with allergic rhinitis. They were subdivided into two groups: subjects with only seasonal symptoms and skin sensitization to grass and/or Parietaria pollen allergens (seasonal group, n = 38), and subjects with perennial symptoms and skin sensitization to house dust mite, alone or with other allergens (perennial group, n = 34). They were challenged with methacholine (up to 200 mg/mliter), and concentration-response curves were characterized by the threshold value (PC20 = provocative concentration of methacholine required to produce a 20% fall in FEV1) and maximal response plateau, if possible. The measurements in the seasonal group were done within the pollen season.

RESULTS

The geometric mean methacholine PC20 for subjects of the perennial group was 6.9 mg/mliter, compared with 23.4 mg/mliter in subjects of the seasonal group (P < 0.01). A plateau response was detected in 16 subjects of the perennial group and in 28 subjects of the seasonal group (P < 0.05). Moreover, the level of plateau was higher in subjects of the perennial group when compared with subjects of the seasonal group (23.8 +/- 2.0% vs 19.2 +/- 1.6%, P < 0.05).

CONCLUSION

In subjects with allergic rhinitis, sensitization to perennial allergens is associated not only with lower methacholine threshold values, but also with lower prevalence and higher level of plateau than sensitization to pollen allergens.

Longitudinal measurement of airway hyperresponsiveness in selected subjects with persisting pulmonary symptoms

The relationship between airway hyperresponsiveness and pulmonary symptoms was examined longitudinally in 52 subjects. Subjects were part of a larger study, the Natural History of Asthma, and had repeated measures of airway hyperresponsiveness using methacholine. Atopy was determined using skin tests and serum IgE levels. The subjects completed a standardized respiratory questionnaire. Each subject reported respiratory and pulmonary symptoms at either their initial or follow-up visit. The subjects did not, however, have a physician-confirmed diagnosis of asthma. Subjects were divided into groups according to the current status of their respiratory symptoms. The four groups included subjects who were initially normal but developed respiratory symptoms at follow-up; subjects who had symptoms at all visits; subjects with respiratory symptoms at their initial visit but who had no symptoms at follow-up; and subjects who had respiratory symptoms prior to their initial visit and who did not have a recurrence during follow-up. There was no statistical difference in airway hyperresponsiveness, IgE, or skin test scores at the initial visits. Subjects who had airway responsiveness were significantly more atopic than subjects who did not have airway responsiveness. Subjects were classified as "consistently positive," "variable," or "consistently negative" responders according to the pattern of methacholine-induced airway hyperresponsiveness. Overall, among the four groups, 33% were consistently positive at all visits, 43% were variable, and 22% were consistently negative. Airway hyperresponsiveness was statistically associated with atopy, but not necessarily associated with questionnaire-based respiratory symptomatology. These factors need to be considered in epidemiological studies of asthma utilizing respiratory questionnaires.

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.

Effect of inhaled amiloride on the bronchial response to methacholine and cold air hyperventilation challenges

Inhaled amiloride has been recently demonstrated to have an effect on the decline of pulmonary function in patients with cystic fibrosis. Other diuretics have been demonstrated to provide protection against bronchoconstriction in asthmatic subjects. We report on the effect of inhaled amiloride on cold air hyperventilation challenge (CAHC) and methacholine challenge in asthmatics. We studied nine subjects with mild-moderate asthma in a double-blind, placebo-controlled, crossover study. Our results showed amiloride did not significantly protect against the bronchoconstriction induced by CAHC. Inhaled amiloride did not affect FEV1 in the hour after inhalation, and there was no significant difference between placebo or amiloride on the dose of methacholine causing a 20 percent fall in FEV1. Inhaled amiloride appears not to have a profile of action as previously seen with inhaled furosemide.

Methacholine inhalation challenge in children with idiopathic chest pain

Bronchial reactivity to inhaled methacholine (MCH) was evaluated in 32 patients with 'idiopathic' chest pain. Each pain was recurrent in nature. The incidence of cases with a provocative concentration causing a 20% fall in the forced expiratory volume in 1 sec (PC20) of 10 mg/ml or less was 62.5% (20 cases), while it was only 11.1% (three cases) in 27 healthy controls. Seventeen patients had no personal history of allergic diseases, elevated serum IgE level or positive house dust mite-specific IgE antibody. Among these 17, eight (47.1%) had a PC20 of 10 mg/ml or less, the incidence of which was also higher than that of the healthy controls. During the challenge, eight patients complained of chest pain similar to that experienced before. The present results indicate that bronchial hyper-reactivity is an important cause of 'idiopathic' chest pain. Patients with unexplained chest pain should be considered for inhalation challenge.

Angiotensin-converting enzyme inhibitors in patients with bronchial responsiveness and asthma

Twenty-one subjects with known bronchial hyperreactivity were prospectively randomized in double-blind fashion to receive one of two angiotensin-converting enzyme inhibitors (ACE-I), enalapril or spirapril, for three weeks. Spirometry and methacholine provocation were performed prior to, during, and following ACE-I usage. Three of 21 subjects developed a nonproductive cough. However, only one subject wheezed slightly. Spirometry and bronchial reactivity (PD20) were unchanged throughout the study.

Longitudinal changes in bronchial hyperresponsiveness in asthmatic and previously asthmatic children

To determine if nonspecific bronchial hyperresponsiveness is present to the same degree in previously asthmatic children compared with currently asthmatic children, a longitudinal study was conducted. On the basis of a standardized respiratory questionnaire, 139 children from asthmatic families, between the ages of 6 and 21 years, were identified. Subjects had skin tests, a serum IgE level, and a methacholine challenge test. IgE and skin tests demonstrated atopy in both the previously and currently asthmatic children, which persisted over time. Bronchial hyperresponsiveness within the asthmatic children was not significantly different between visits. Previously asthmatic children did have significantly decreased airway hyperresponsiveness over time. Age did not affect the results of the bronchial hyperresponsiveness in the currently asthmatic children. Currently asthmatic children, however, were significantly more atopic when compared with previously asthmatic children at their initial evaluation. Currently asthmatic children were also more bronchial responsive and remained so over time. Bronchial hyperresponsiveness is persistent in children with current asthma symptoms.

Indices of nonspecific bronchial responsiveness in a pediatric population

A cross-sectional survey of the prevalence of asthma and bronchial hyperreactivity among schoolchildren (7 to 11 years old) was carried out in three areas of the Latium region (Central Italy). Out of 1,777 children tested with methacholine challenge (MCT), 15.1 percent had a 20 percent fall in FEV1 after a provocative concentration (PC20FEV1) of 4 mg/ml of methacholine or less; 69.7 percent had a PC20FEV1 less than 64.0 mg/ml, whereas 50.3 percent were nonresponders. Two continuous measures of bronchial responsiveness, the slope (percentage of change in FEV1 per mg/ml of methacholine) and the area under the dose response curve, were calculated in order to avoid the loss of information in nonresponders. Applying a receiver operating characteristic (ROC) curve analysis, the three estimators did not show any statistically significant difference in their overall performance in detecting asthma (ROC areas: PC20FEV1 = 0.683, slope = 0.681, area = 0.702 or asthma-like symptoms. The log transformation of slope, having a unimodal and slightly skewed shape, is an appealing continuous measure of bronchial responsiveness useful for epidemiologic studies. The final choice of an appropriate estimator of the concentration-response curve to methacholine, however, depends upon both the statistical tests or the modelling procedures to be used and clarification of the prognostic value of different indices of bronchial responsiveness.

Effect of PAF-acether inhalation on nonspecific bronchial reactivity and adrenergic response in normal and asthmatic subjects

Bronchial hyperreactivity, although recognized as a hallmark of asthma, is not totally understood. Mast cell-derived mediators, including histamine, have been shown to cause immediate bronchoconstriction, but until recently, no single mediator has been shown to induce prolonged changes in airway reactivity. Recent reports indicate PAF-acether (PAF) can induce increased nonspecific bronchial reactivity in normal subjects but not in asthmatics. We sought to elucidate the role of PAF in airway hyperreactivity by comparing the effect of inhaled PAF on methacholine and isoproterenol airway responsiveness in six nonasthmatic and six asthmatic subjects. Neither nonspecific airway reactivity nor isoproterenol responsiveness was changed following PAF inhalation in the nonasthmatic subjects in the six days following PAF. Asthmatics had increased airway responsiveness to methacholine at two hours post-PAF, which did not persist. Responsiveness to isoproterenol did not change in the asthmatic subjects. Additional evaluation of the role of PAF in causing changes in airway reactivity is warranted.

Association of MS Pi phenotype with airway hyperresponsiveness

Asthmatic families (AFs) and normal families (NFs) were studied to determine the relationship between bronchial hyperresponsiveness and alpha 1-antitrypsin protease inhibitor phenotype. We studied IgE levels, skin test scores, and methacholine sensitivity. In both the AF and NF groups, the subjects with the MS phenotype had significantly greater methacholine-induced bronchial hyperresponsiveness sensitivity than the MM and MZ subjects. These findings suggest that the S allele may be associated with bronchial hyperresponsiveness.

Effect of inhaled furosemide on the bronchial response to methacholine and cold-air hyperventilation challenges

Inhaled furosemide has been recently demonstrated to inhibit the bronchoconstrictive effects of exercise, ultrasonically nebulized distilled water, and antigen challenge. The presumed mechanism of action of these challenges is through mast cell degranulation. We report on the effect of inhaled furosemide on cold-air hyperventilation challenge (CAHC) and methacholine challenge. We studied 10 subjects with mild to moderate asthma in a double-blind, placebo-controlled, crossover study. Inhaled furosemide did not affect FEV1 in the hour after inhalation, and there was no significant difference between placebo or furosemide on the dose of methacholine causing a 20% fall in FEV1. Our results demonstrated inhaled furosemide significantly attenuated the bronchoconstrictive effect at 6 and 9 minutes after CAHC (p less than 0.05 and 0.029, respectively) when furosemide was compared to placebo and approached significance at 12 and 15 minutes after CAHC (p = 0.052 and 0.56, respectively). Inhaled furosemide attenuates CAHC but does not effect methacholine-induced bronchoconstriction.

Effect of platelet-activating factor inhalation on nonspecific bronchial reactivity in man

Bronchial hyperactivity is a recognized hallmark of asthma, characterized by an exaggerated bronchial response to numerous mediators, including histamine. It is also well recognized that bronchial hyperresponsiveness is increased following allergen exposure, although no particular mediator has been shown to induce this response. The recent observation that PAF can induce increased nonspecific bronchial reactivity in normal subjects emphasizes its importance as an inflammatory mediator. In this report we sought to further elucidate the role of PAF in airway hyperreactivity by comparing the effect of PAF on methacholine-induced airway responsiveness in six non-asthmatic subjects. Nonspecific airway responsiveness was not significantly increased following PAF inhalation at 6 hours nor was it increased at 1, 2, 7, or 14 days. Further elucidation of the potential role of PAF in explaining changes in airway reactivity is necessary.

Clinical expression of bronchial hyperreactivity in children

Airway hyperreactivity is a consistent finding in most children with asthma and is responsible for many clinical manifestations of asthma. BH in children has been elicited by bronchial challenge with methacholine and histamine, cold air (isocapnic hyperventilation), and exercise. Pharmacologic agents employed in therapy of childhood asthma, which may modulate both the late asthmatic reaction and bronchial hyperreactivity, include cromolyn sodium, glucocorticoids, and possibly ketotifen. Beta adrenergic agonists, though effectively blocking the early asthmatic response, had no effect on the late response and did not alter bronchial hyperreactivity. Theophylline, in both children and adults, and enprophylline (not yet studied in children) may modify both the early and late responses, but do not appear to have an effect on bronchial hyperreactivity. New drugs that may have potential value in reducing bronchial hyperreactivity include calcium channel blockers and PAF antagonists.