Methacholine challenge testing: comparison of the two American Thoracic Society-recommended methods

Development of an AI Model for Predicting Methacholine Bronchial Provocation Test Results Using Spirometry

Background/Objectives: The methacholine bronchial provocation test (MBPT) is a diagnostic test frequently used to evaluate airway hyper-reactivity. MBPT is essential for diagnosing asthma; however, it can be time-consuming and resource-intensive. This study aimed to develop an artificial intelligence (AI) model to predict the MBPT results using forced expiratory volume in one second (FEV1) and bronchodilator test measurements from spirometry. Methods: a dataset of spirometry measurements, including Pre- and Post-bronchodilator FEV1, was used to train and validate the model. Results: Among the evaluated models, the multilayer perceptron (MLP) achieved the highest area under the curve (AUC) of 0.701 (95% CI: 0.676-0.725), accuracy of 0.758, and an F1-score of 0.853. Logistic regression (LR) and a support vector machine (SVM) demonstrated comparable performance with AUC values of 0.688, while random forest (RF) and extreme gradient boost (XGBoost) achieved slightly lower AUC values of 0.669 and 0.672, respectively. Feature importance analysis of the MLP model identified key contributing features, including Pre-FEF25-75 (%), Pre-FVC (L), Post FEV1/FVC, Change-FEV1 (L), and Change-FEF25-75 (%), providing insight into the interpretability and clinical applicability of the model. Conclusions: These results highlight the potential of the model to utilize readily available spirometry data, particularly FEV1 and bronchodilator responses, to accurately predict MBPT results. Our findings suggest that AI-based prediction can improve asthma diagnostic workflows by minimizing the reliance on MBPT and enabling faster and more accessible assessments.

Bronchoprovocation Testing in Asthma: An Update

Bronchial hyperresponsiveness (BHR) is defined as a heightened bronchoconstrictive response to airway stimuli. It complements the cardinal features in asthma, such as variable or reversible airflow limitation and airway inflammation. Although BHR is considered a pathophysiologic hallmark of asthma, it should be acknowledged that this property of the airway is dynamic, because its severity and even presence can vary over time with disease activity, triggers or specific exposure, and with treatment. In addition, it is important to recognize that there is a component that is not reflective of a specific disease entity.

Direct bronchoprovocation test methods: history 1945-2018

INTRODUCTION

Bronchoprovocation inhalation challenge tests with direct acting stimuli (e.g. methacholine) are widely used clinically to aid in the diagnosis of asthma. Areas covered: The history of direct challenges with histamine and muscarinic agonists is reviewed. This began with parenteral administration of stimuli with responses monitored clinically and by VC, progressing to inhalation dose-response challenges monitored by FEV₁ and FEV₁/VC ratio, both (the challenge method and the technology to measure FEV₁) developed by Robert Tiffeneau in the mid-1940s. Careful standardization of methods has become appreciated albeit after-the-fact. Recent guidelines recommend standardizing the methacholine PD₂₀ at 400 μg above which a methacholine challenge is considered negative.

CONCLUSIONS

The methacholine inhalation test is highly sensitive for a diagnosis of current asthma when symptoms under evaluation are clinically current and when methacholine is inhaled without deep inhalations. Under these circumstances, a methacholine PD₂₀ > 400 μg excludes current asthma with reasonable certainty. PD₂₀ values >25 μg and ≤400 μg will have a variable specificity and positive predictive value for asthma which increases the lower the PD₂₀ and the higher the pre-test probability for a diagnosis of asthma. A PD₂₀ ≤25 μg has high specificity and low sensitivity for asthma.

Methacholine challenge test: Comparison of tidal breathing and dosimeter methods in children

INTRODUCTION

Methacholine Challenge Test (MCT) is used to confirm, assess the severity and/or rule out asthma. Two MCT methods are described as equivalent by the American Thoracic Society (ATS), the tidal breathing and the dosimeter methods. However, the majority of adult studies suggest that individuals with asthma do not react at the same PC₂₀ between the two methods. Additionally, the nebulizers used are no longer available and studies suggest current nebulizers are not equivalent to these. Our study investigates the difference in positive MCT tests between three methods in a pediatric population.

METHODS

A retrospective, chart review of all MCT performed with spirometry at the Montreal Children's Hospital from January 2006 to March 2016. A comparison of the percentage positive MCT tests with three methods, tidal breathing, APS dosimeter and dose adjusted DA-dosimeter, was performed at different cutoff points up to 8 mg/mL.

RESULTS

A total of 747 subjects performed the tidal breathing method, 920 subjects the APS dosimeter method, and 200 subjects the DA-dosimeter method. At a PC₂₀ cutoff ≤4 mg/mL, the percentage positive MCT was significantly higher using the tidal breathing method (76.3%) compared to the APS dosimeter (45.1%) and DA-dosimeter (65%) methods (P < 0.0001).

CONCLUSION

The choice of nebulizer and technique significantly impacts the rate of positivity when using MCT to diagnose and assess asthma. Lack of direct comparison of techniques within the same individuals and clinical assessment should be addressed in future studies to standardize MCT methodology in children.

Realising the potential of various inhaled airway challenge agents through improved delivery to the lungs

Inhaled airway challenges provoke bronchoconstriction in susceptible subjects and are a pivotal tool in the diagnosis and monitoring of obstructive lung diseases, both in the clinic and in the development of new respiratory medicines. This article reviews the main challenge agents that are in use today (methacholine, mannitol, adenosine, allergens, endotoxin) and emphasises the importance of controlling how these agents are administered. There is a danger that the optimal value of these challenge agents may not be realised due to suboptimal inhaled delivery; thus considerations for effective and reproducible challenge delivery are provided. This article seeks to increase awareness of the importance of precise delivery of inhaled agents used to challenge the airways for diagnosis and research, and is intended as a stepping stone towards much-needed standardisation and harmonisation in the administration of inhaled airway challenge agents.

Airway hyperresponsiveness in chronic obstructive pulmonary disease: A marker of asthma-chronic obstructive pulmonary disease overlap syndrome?

BACKGROUND

The impact of airway hyperreactivity (AHR) on respiratory mortality and systemic inflammation among patients with chronic obstructive pulmonary disease (COPD) is largely unknown. We used data from 2 large studies to determine the relationship between AHR and FEV₁ decline, respiratory mortality, and systemic inflammation.

OBJECTIVES

We sought to determine the relationship of AHR with FEV₁ decline, respiratory mortality, and systemic inflammatory burden in patients with COPD in the Lung Health Study (LHS) and the Groningen Leiden Universities Corticosteroids in Obstructive Lung Disease (GLUCOLD) study.

METHODS

The LHS enrolled current smokers with mild-to-moderate COPD (n = 5887), and the GLUCOLD study enrolled former and current smokers with moderate-to-severe COPD (n = 51). For the primary analysis, we defined AHR by a methacholine provocation concentration of 4 mg/mL or less, which led to a 20% reduction in FEV₁ (PC₂₀).

RESULTS

The primary outcomes were FEV₁ decline, respiratory mortality, and biomarkers of systemic inflammation. Approximately 24% of LHS participants had AHR. Compared with patients without AHR, patients with AHR had a 2-fold increased risk of respiratory mortality (hazard ratio, 2.38; 95% CI, 1.38-4.11; P = .002) and experienced an accelerated FEV₁ decline by 13.2 mL/y in the LHS (P = .007) and by 12.4 mL/y in the much smaller GLUCOLD study (P = .079). Patients with AHR had generally reduced burden of systemic inflammatory biomarkers than did those without AHR.

CONCLUSIONS

AHR is common in patients with mild-to-moderate COPD, affecting 1 in 4 patients and identifies a distinct subset of patients who have increased risk of disease progression and mortality. AHR may represent a spectrum of the asthma-COPD overlap phenotype that urgently requires disease modification.

Adenosine dry powder inhalation for bronchial challenge testing, part 1: inhaler and formulation development and in vitro performance testing

Dry powder administration of adenosine by use of an effective inhaler may be an interesting alternative to nebulisation of adenosine 5'-monophosphate in bronchial challenge testing, because of a shorter administration time and more consistent delivered fine particle dose over the entire dose range. In this study, we tested various powder formulations and classifier based dispersion principles and investigated the in vitro performance of the most promising formulation/classifier combination in a new test inhaler system. Spray-dried formulations of either pure adenosine (100%) or adenosine and lactose as diluent (1% and 10% adenosine) were prepared to cover the entire expected dose range for adenosine (0.01-20mg). All three powders, in all 12 suggested doses, dispersed well with the newly developed test inhaler with a multiple air jet classifier disperser, into aerosols with an average volume median diameter of 3.1μm (3.0-3.3μm). For eleven out of 12 dose steps, the fine particle fractions<5μm as percent of the loaded dose varied within the range of 67-80% (mean: 74%). The new test concept allows for more consistent aerosol delivery over the entire dose range with narrower size distributions than nebulisation and thus may improve adenosine administration in bronchial challenge testing.

Bronchoprovocation testing in asthma

This article covers the relationships between BHR and airway inflammation. Recent evidence suggests that various commonly used bronchoprovocation challenges (BPCs) differ in their potential to serve as inflammatory biomarkers. The response to direct stimuli depends on the smooth muscle's response to the chemical, whereas in indirect challenges, the reaction is caused by the smooth muscle's responsiveness to the mediators induced by the stimuli. The information obtained from studies with BPC has provided insights into the pathogenesis and pathophysiology of asthma, and the relationships between airway inflammation and bronchial hyper-responsiveness.

Poor asthma control and exposure to traffic pollutants and obesity in older adults

BACKGROUND

Environmental and host predictors of asthma control in older asthmatic patients (>65 years old) are poorly understood.

OBJECTIVE

To examine the effects of residential exposure to traffic exhaust and other environmental and host predictors on asthma control in older adults.

METHODS

One hundred four asthmatic patients 65 years of age or older from allergy and pulmonary clinics in greater Cincinnati, Ohio, completed the validated Asthma Control Questionnaire (ACQ), pulmonary function testing, and skin prick testing to 10 common aeroallergens. Patients had a physician's diagnosis of asthma, had significant reversibility in forced expiratory volume in 1 second or a positive methacholine challenge test result, and did not have chronic obstructive pulmonary disease. The mean daily residential exposure to elemental carbon attributable to traffic (ECAT) was estimated using a land-use regression model. Regression models were used to evaluate associations among independent variables, ACQ scores, and the number of asthma exacerbations, defined as acute worsening of asthma symptoms requiring prednisone use, in the past year.

RESULTS

In the adjusted model, mean daily residential exposure to ECAT greater than 0.39 μg/m(3) was significantly associated with poorer asthma control based on ACQ scores (adjusted β = 2.85; 95% confidence interval [CI], 0.58-5.12; P = .02). High ECAT levels were also significantly associated with increased risk of asthma exacerbations (adjusted odds ratio, 3.24; 95% CI, 1.01-10.37; P = .05). A significant association was found between higher body mass index and worse ACQ scores (adjusted β = 1.15; 95% CI, 0.53-1.76; P < .001). Atopic patients (skin prick test positive) had significantly better ACQ scores than nonatopic patients (adjusted β = -0.39; 95% CI, -0.67 to -0.11; P < .01).

CONCLUSION

Higher mean daily residential exposure to traffic exhaust, obesity, and nonatopic status are associated with poorer asthma control among older asthmatic patients.

Methacholine challenge test: diagnostic characteristics in asthmatic patients receiving controller medications

BACKGROUND

The methacholine challenge test (MCT) is commonly used to assess airway hyperresponsiveness, but the diagnostic characteristics have not been well studied in asthmatic patients receiving controller medications after the use of high-potency inhaled corticosteroids became common.

OBJECTIVES

We investigated the ability of the MCT to differentiate participants with a physician's diagnosis of asthma from nonasthmatic participants.

METHODS

We conducted a cohort-control study in asthmatic participants (n= 126) who were receiving regular controller medications and nonasthmatic control participants (n= 93) to evaluate the sensitivity and specificity of the MCT.

RESULTS

The overall sensitivity was 77% and the specificity was 96% with a threshold PC(20) (the provocative concentration of methacholine that results in a 20% drop in FEV(1)) of 8 mg/mL. The sensitivity was significantly lower in white than in African American participants (69% vs 95%, P= .015) and higher in atopic compared with nonatopic (82% vs 52%, P= .005). Increasing the PC(20) threshold from 8 to 16 mg/mL did not noticeably improve the performance characteristics of the test. African American race, presence of atopy, and lower percent predicted FEV(1) were associated with a positive test result.

CONCLUSIONS

The utility of the MCT to rule out a diagnosis of asthma depends on racial and atopic characteristics. Clinicians should take into account the reduced sensitivity of the MCT in white and nonatopic asthmatic patients when using this test for the diagnosis of asthma.

An algorithmic approach to chronic dyspnea

QUESTION

The objective of the study was to prospectively evaluate an algorithmic approach to the cause(s) of chronic dyspnea. MATERIALS/PATIENTS/METHODS: Prospective observational study. The study group consisted of 123 patients with a chief complaint of dyspnea of unknown cause present for >8 weeks. Dyspnea severity scores were documented at entry and after therapy. Patients underwent an algorithmic approach to dyspnea. Therapy could be instituted at any time that data supported a treatable diagnosis. Whenever possible, accuracy of diagnosis was confirmed with an improvement in dyspnea after therapy. Tests required, spectrum and frequency of diagnoses, and the values of individual tests were determined.

RESULTS

Cause(s) was(were) diagnosed in 122/123 patients (99%); 97 patients had one diagnosis and 25 two diagnoses. Fifty-three percent of diagnoses were respiratory and 47% were non-respiratory. Following therapy, dyspnea improved in 63% of patients.

CONCLUSIONS

The prospective algorithmic approach led to diagnoses in 99% of cases. A third of patients were diagnosed with each tier of the algorithm, thus minimizing the need for invasive testing. Specific diagnoses led to improvement in dyspnea in the majority of cases. Based on the results of this study, the algorithm can be revised to further minimize unnecessary tests without loss of diagnostic accuracy.

The effect of challenge method on methacholine-induced changes in sensitivity and air trapping

BACKGROUND

The methacholine challenge test performed with the tidal breathing method induces a greater fall in FEV(1) than the dosimeter method; however, the effect of the challenge method on methacholine-induced fall in FVC has not been investigated.

OBJECTIVE

To determine the influence of the challenge method on methacholine-induced changes in FEV(1) and FVC.

METHODS

Airway responsiveness to methacholine was determined by dosimeter method and tidal breathing method in 37 subjects with suspected asthma. The dosimeter was modified to deliver an identical volume to that obtained with the tidal breathing method and the same nebulizer model was used for the two challenges. The response was expressed by the provocative concentration of methacholine causing a 20% fall in FEV(1) (PC(20)) and by the percent fall in FVC at the PC(20) value relative to FVC after saline inhalation.

RESULTS

The PC(20) values obtained with the tidal breathing method and the dosimeter method were similar, with geometric mean values of 3.15 (95%CI, 1.85-5.34 mg/mL) and 2.51 (1.37-4.61 mg/mL, P = 0.092), respectively. The percent fall in FVC at the PC(20) value obtained with the dosimeter was significantly greater than that obtained with the tidal breathing method, with mean values of 11.8 (95%CI, 10.0-13.5%) and 9.4 (95%CI, 8.1-10.8, P = 0.002), respectively.

CONCLUSIONS

Differences in methacholine PC(20) values obtained with the two challenge methods recommended in guidelines may be overcome by introducing some technical modifications in the dosimeter method. However, the technical factors that affect methacholine sensitivity and air trapping are at least partially different.

Public facility workers' immunological characteristics involved with development of respiratory allergic diseases in Korea

We evaluated the immuno-pulmonary status of employees working at public facilities to determine whether they are at greater risk of developing respiratory allergies. Fifty-two employees from child daycare centers, elderly nursing homes, subway stations, and hypermarkets, and 17 office workers were recruited. All were subjected to a skin prick test (SPT) for 25 aeroallergens and the methacholine bronchial challenge test. Various immunological parameters, including plasma IgE and IgG4 levels, hematology parameters, and in vitro cytokine production from peripheral T cells, were assessed. Forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1) were also determined. Of the facility employees, 54% responded to the SPT, and house dust mite induced positive skin reactions most frequently. Compared to the SPT-negative facility employees and the office workers, the SPT-positive facility employees had upregulated plasma IgE levels and eosinophil frequency in their peripheral blood. Their peripheral T cells also showed elevated IL-4 production relative to IFNgamma production. Four public facility employees who reacted to the methacholine challenge test had elevated eosinophil frequencies, increased plasma IgE levels, and lowered FEV1/FVC values. This study suggests that workers at public facilities could show greater risk towards the development of respiratory allergic diseases.

Methacholine challenge--comparison of an ATS protocol to a new rapid single concentration technique

Bronchial methacholine challenge is well established in asthma diagnostics and research. ATS guidelines propose a five step standard dosimeter (SDM) protocol with incremental concentrations of methacholine to calculate the concentration causing a 20% drop in FEV(1) in an individual (PC(20)FEV(1)). In contrast, the aerosol provocation system (APS) by Viasys automatically determines the administered dose of methacholine by measuring the effective nebulisation time and referring it to drug concentration and nebuliser power. Therefore, it offers a feasible and less time-consuming provocation procedure by applying incremental doses (PD(20)) of methacholine using a single concentration (16mg/mL methacholine, APS-SC). In this study we compared these two methods in 52 young adults (25+/-5.8 years). Following a screening visit, subjects were randomly assigned to undergo either SDM or APS-SC followed by the other method within 1 week. A close correlation between concentration and dosage causing a 20% fall of FEV(1) was found (r=0.69, p<0.001). Using the ATS categorisation of bronchial responsiveness we interpreted the results of the APS-SC method as follows: PD(20) methacholine<0.3mg as "moderate to severe BHR", 0.3 - 0.6mg as "mild BHR", 0.6 - 1.0mg as "borderline BHR", and>1.0mg as "normal bronchial response". We conclude that the five-step APS-SC is a suitable method, providing reliable results. In clinical practice the APS-SC is a timesaving procedure and less prone to errors since only one dilution of methacholine is necessary compared to the SDM.

Exercise-induced asthma may be associated with diminished sweat secretion rates in humans

BACKGROUND

Muscarinic receptor agonists increase water secretion from the acinar cells of respiratory, sweat, salivary, and lacrimal glands. Mice lacking the gene for aqueous water channel aquaporin (Aqp) 5 exhibit methacholine-induced bronchiolar hyperreactivity when compared to normal mice. Individuals with asthma also have enhanced airway responsiveness to methacholine and diminished airway hydration. Because Aqp5 in humans is also expressed in respiratory, sweat, salivary, and lacrimal glands, we hypothesized that those individuals with exercise-induced asthma and excessive bronchiolar reactivity should also have decreased muscarinic receptor-dependent sweat, salivary, and tear gland secretions.

METHODS

Healthy, athletic subjects who are suspected of having exercise-induced bronchospasm were recruited, and FEV(1) values were determined following provocative airway challenges with methacholine. Measurements of pilocarpine-induced sweat secretion were taken in 56 volunteers, and some additional subjects also had timed collections of saliva and tear production.

RESULTS

Subjects manifesting excessive airway reactivity demonstrated by exaggerated methacholine-induced reductions in FEV(1) also had diminished values for pilocarpine-induced sweat secretion (n = 56; r = - 0.59; p < 0.0001). The rate of pilocarpine-stimulated sweat secretion in our subjects correlated highly with salivary flow rate (r = 0.69; p < 0.0001) and tearing rate (r = 0.86; p < 0.001).

CONCLUSION

Hyperhidrosis, sialorrhea, and excessive tearing are traits that may indicate a phenotype that predicts resistance to hyperactive airway diseases such as exercise-induced asthma in humans.

Differences in the response to methacholine between the tidal breathing and dosimeter methods: influence of the dose of bronchoconstrictor agent delivered to the mouth

BACKGROUND

It has been postulated that differences in provocative concentration of methacholine causing a 20% fall in FEV1 (PC20) values between the dosimeter method and tidal breathing method might be due to differences in the dose of agonist delivered to the mouth. The aim of the present study was to determine the influence of the dose of aerosol delivered to the mouth on differences in the response obtained with each challenge method.

METHODS

This study measured airway responsiveness to methacholine by dosimeter method and tidal breathing method in 27 subjects with suspected asthma. The dosimeter was modified to deliver an identical volume to that obtained with the tidal breathing method. Concentration-response curves were characterized by the PC20.

RESULTS

The dosimeter method PC20 was significantly higher than the tidal breathing method PC20, with geometric mean values of 4.03 (95% confidence interval [CI], 1.86 to 8.78 mg/mL) and 2.19 (95% CI, 1.32 to 3.64 mg/mL; p = 0.04), respectively. The mean difference in the PC20 value detected with each method was similar in subjects with tidal breathing method PC20 values > or = 2 mg/mL (0.77 doubling concentrations) and in those with PC20 values < 2 mg/mL (0.96 doubling concentrations; p = 0.83).

CONCLUSIONS

The tidal breathing method produces PC20 values significantly lower than a modified dosimeter method, which delivers the same volume of aerosol. These results suggest that the discordant PC20 values obtained with the two methods are not due to differences in the dose of agonist delivered to the mouth.

Exercise-induced asthma, respiratory and allergic disorders in elite athletes: epidemiology, mechanisms and diagnosis: part I of the report from the Joint Task Force of the European Respiratory Society (ERS) and the European Academy of Allergy and Clinical Immunology (EAACI) in cooperation with GA2LEN

AIMS

To analyze the changes in the prevalence of asthma, bronchial hyperresponsiveness (BHR) and allergies in elite athletes over the past years, to review the specific pathogenetic features of these conditions and to make recommendations for their diagnosis.

METHODS

The Task Force reviewed present literature by searching Medline up to November 2006 for relevant papers by the search words: asthma, bronchial responsiveness, EIB, athletes and sports. Sign criteria were used to assess level of evidence and grades of recommendation.

RESULTS

The problems of sports-related asthma and allergy are outlined. Epidemiological evidence for an increased prevalence of asthma and BHR among competitive athletes, especially in endurance sports, is provided. The mechanisms for development of asthma and bronchial hyperresponsiveness in athletes are outlined. Criteria are given for the diagnosis of asthma and exercise induced asthma in the athlete.

CONCLUSIONS

The prevalence of asthma and bronchial hyperresponsiveness is markedly increased in athletes, especially within endurance sports. Environmental factors often contribute. Recommendations for the diagnosis of asthma in athletes are outlined.

The effect of challenge method on sensitivity and reactivity to adenosine 5'-monophosphate in subjects with suspected asthma

BACKGROUND

The following two methods of inhalation challenge have been used to determine the airway responsiveness: the tidal-breathing method; and the dosimeter method. The objective of the study was to determine the influence of the challenge method on the response to adenosine 5'-monophosphate (AMP).

METHODS

This study measured airway responsiveness to AMP by dosimeter and tidal-breathing methods in 25 subjects with suspected asthma. The two AMP challenges were conducted in random order, on separate days, at the same time of day, at intervals of 1 to 5 days. Concentration-response curves were characterized by the provocative concentration of a substance causing a 20% fall in FEV1 (PC20) and slope.

RESULTS

The dosimeter PC20 values were significantly higher than the tidal-breathing PC20 values, with geometric mean (95% confidence interval [CI]) values of 50.35 mg/mL (95% CI, 19.50 to 129.72 mg/mL) and 28.97 mg/mL (95% CI, 11.99 to 69.98 mg/mL; p = 0.02), respectively. The mean difference in the PC20 values obtained with each method was 0.80 doubling concentrations (95% CI, 0.16 to 1.44 doubling concentrations). The mean values for the slope were 17.0%/log mg/mL (95% CI, 12.5 to 21.5 mg/mL) with the tidal breathing method and 13.8%/log mg/mL (95% CI, 9.0 to 18.7 mg/mL; p = 0.03) with the dosimeter.

CONCLUSIONS

The tidal-breathing method produces AMP PC20 values that are significantly lower than the dosimeter method and slope values that are significantly higher than the dosimeter method. These data suggest that the results obtained with each method of testing may not be comparable.

Effect of challenge method on sensitivity, reactivity, and maximal response to methacholine

BACKGROUND

Recent data suggest that the tidal breathing method may produce methacholine provocation concentration that caused a decrease in forced expiratory volume in 1 second of 20% (PC20) values significantly lower than the dosimeter method; however, the effect of the challenge method on the shape of the concentration-response curve has not been investigated.

OBJECTIVE

To determine the effect of the challenge method on sensitivity, reactivity, and maximal response to methacholine.

METHODS

We measured airway responsiveness to methacholine using dosimeter and tidal breathing methods in 30 individuals with suspected asthma. Concentration-response curves were characterized by their PC20 (sensitivity), slope (reactivity), and, if possible, level of plateau.

RESULTS

Dosimeter PC20 values were significantly higher than tidal breathing values (geometric mean, 8.9 and 5.2 mg/mL, respectively); the mean difference in PC20 values obtained using each method was 0.78 doubling concentrations (P = .01). The mean slopes were 22.7%/log mg/mL using the tidal breathing method and 24.9%/log mg/mL using the dosimeter method; the mean difference in the slopes obtained using each method was -2.17%/log mg/mL (P = .18). In 10 individuals who showed a plateau with the 2 methacholine challenge tests, the mean level of plateau was 19.8% using the tidal breathing method and 19.5% using the dosimeter method; the mean difference in the plateau values obtained with each method was 0.3% (P = .87).

CONCLUSIONS

Although the tidal breathing method produces methacholine PC20 values significantly lower than the dosimeter method, both methods provide similar values for slope and level of plateau. These results suggest that the technical factors that affect methacholine sensitivity and the shape of the curve are different.

Difference between dosimeter and tidal breathing methacholine challenge: contributions of dose and deep inspiration bronchoprotection

BACKGROUND

Two bronchoprovocation methods are widely used. Compared to the tidal breathing method, the dosimeter method delivers approximately half the dose and involves five deep inhalations. Both the lower dose and the bronchoprotective deep inhalations contribute to the lesser airway response of the dosimeter.

OBJECTIVE

To determine the relative role of dose and deep inspiration in the difference between the two methods.

METHODS

Subjects with asthma (n = 24) underwent three methacholine challenges: a dosimeter challenge, a 2-min tidal breathing challenge (twice the dose), and a modified 2-min tidal breathing challenge (twice the dose plus five deep inhalations).

RESULTS

The dosimeter method produced a nonsignificantly lower response than the modified tidal breathing method (p = 0.14). Both deep inhalation methods produced significantly less response than did the standard tidal breathing method (p = 0.011). In the 12 subjects with the most mild airway hyperresponsiveness (AHR), the differences between the deep inhalation method and the tidal breathing method were greater (p = 0.007). By contrast, deep inhalations produced no effect in the 12 subjects with greater AHR; the two tidal breathing methods produced identical results, while the dosimeter produced less response than either (p = 0.033). Six current asthmatics with mild airway responsiveness (tidal breathing method) had negative dosimeter methacholine challenge results.

CONCLUSIONS

In subjects with moderate airway responsiveness, the difference between the methods is due to the difference in dose, whereas in subjects with mild AHR, deep inhalations had a large effect overwhelming the dose effect and producing false-negative methacholine challenge results in 25% of the subjects.

Bronchial hyperresponsiveness in irritable bowel syndrome

Extraintestinal symptoms are often found in patients with irritable bowel syndrome (IBS). Recent studies suggest that IBS is associated with bronchial hyperresponsiveness. But it is still arguable that the bronchial hyperresponsiveness is associated with IBS patients. The purpose of this study is to investigate the possible relationship between IBS and bronchial hyperresponsiveness. Forty-two patients with IBS and 42 control subjects were included in this study. All patients underwent pulmonary function, methacholine challenge, and skin prick tests. There was no statistical difference between the two groups with respect to percentage of all pulmonary function test parameters, including FEV(1)%, FCV%, FVC/FEV(1), and FEF(25 - 75)%. Only two persons in the alternating-type IBS patient group and one person in the control group tested positive in the methacholine provocation test. But all PC(20) values were above 16 mg/ml. These results do not demonstrate a relationship between bronchial hyperresponsiveness and IBS. However, a relationship might exist in a subpopulation of IBS patients.

Methacholine challenge: comparison of two methods

BACKGROUND

Guidelines for the 2-min tidal-breathing and the five-breath dosimeter methods for methacholine challenge have recently been published by the American Thoracic Society (ATS). Although subjects are exposed to twice as much aerosol at any given concentration during the tidal-breathing method compared to the dosimeter method, they were thought to give equivalent results.

OBJECTIVE

To compare the 2-min tidal-breathing and the five-breath dosimeter methacholine challenges.

SETTING

Tertiary care university-based bronchoprovocation laboratory.

PATIENTS

Forty subjects with currently symptomatic asthma.

INTERVENTIONS

The two methacholine tests were done in random order on separate days at the same time of day at 1- to 7-day intervals.

RESULTS

The dosimeter provocation concentration of methacholine causing a 20% fall in FEV(1) (PC(20)) was almost twice that of the tidal-breathing PC(20): 2.4 mg/mL vs 1.3 mg/mL (paired t test, p < 0.00005). The difference was greater in those with mild airway hyperresponsiveness (AHR) [PC(20) > 1.0 mg/mL; 3.2-fold] compared to those with moderate AHR (PC(20) < 1.0 mg/mL; 1.6-fold) [p = 0.04]. Three subjects with mild asthma and mild AHR (tidal-breathing PC(20), 1.9 to 4.3 mg/mL) had a nonmeasurable PC(20) (> 32 mg/mL) with the dosimeter.

CONCLUSIONS

The tidal-breathing method, which exposes the subject to twice as much aerosol at each concentration, produced approximately twice the response. The total lung capacity maneuvers with breathhold during the dosimeter method may inhibit the response in some patients with asthma.