Bioassay of salmeterol in children using methacholine challenge with impulse oscillometry.

BACKGROUND: Bronchoprovocation with methacholine (MC) is the most sensitive method of determining bioequivalence of inhaled bronchodilators. FEV1 is used to determine the endpoint, but many children cannot perform spirometry reproducibly. The purpose of this study was to determine whether MC, using impulse oscillometry (IOS) as the endpoint, can differentiate between two doses of salmeterol (SM). METHODS: This was a single-blind, randomized study of 10 subjects with mild stable asthma, ages 4-11 years. None were taking a long-acting ß-agonist but most were on low-dose inhaled corticosteroid. On one study day, MC was performed 1 hr after one inhalation from each of two separate Advair 100/50 Diskus (100 µg salmeterol treatment). On a second day, MC was performed after one inhalation from Advair Diskus and one inhalation from Flovent Diskus 100 (50 µg salmeterol treatment). The provocative concentration of methacholine causing a 40% increase in total airway resistance (PC40 R5 ) was calculated. RESULTS: The reduction in R5 (bronchodilator effect) was 15.5% and 18.4% for 50 and 100 µg, respectively (NS). After MC (bronchoprotective effect), the geometric mean (95%CI) PC40 R5 (mg/ml) was 2.4 (1.3-4.4) during screening, 22.9 (8.5-61.6) after 50 µg SM and 47.0 (25.2-87.8) after 100 µg SM (P = 0.051 for 50 vs. 100 using a linear mixed effects model). No adverse effects were observed. CONCLUSIONS: MC with IOS endpoint will be a useful method for determining bioequivalence of a generic inhaler in children. Seventy-two subjects will be required to achieve 80% power to assess bioequivalence of SM. Pediatr Pulmonol. 2016;51:570-575. © 2015 Wiley Periodicals, Inc.

Discovery of novel quaternary ammonium derivatives of (3R)-quinuclidinyl amides as potent and long acting muscarinic antagonists.

Novel quaternary ammonium derivatives of (3R)-quinuclidinyl amides have been identified as potent M3 muscarinic antagonists with a long duration of action in an in vivo model of bronchoconstriction. The synthesis, structure-activity relationships and biological evaluation of this series of compounds are reported.

Airway responsiveness depends on the diffusion rate of methacholine across the airway wall.

During methacholine challenge tests of airway responsiveness, it is invariably assumed that the administered dose of agonist is accurately reflected in the dose that eventually reaches the airway smooth muscle (ASM). However, agonist must traverse a variety of tissue obstacles to reach the ASM, during which the agonist is subjected to both enzymatic breakdown and removal by the bronchial and pulmonary circulations. This raises the possibility that a significant fraction of the deposited agonist may never actually make it to the ASM. To understand the nature of this effect, we measured the time course of changes in airway resistance elicited by various durations of methacholine aerosol in mice. We fit to these data a computational model of a dynamically contracting airway responding to agonist that diffuses through an airway compartment, thereby obtaining rate constants that reflect the diffusive barrier to methacholine. We found that these barriers can contribute significantly to the time course of airway narrowing, raising the important possibility that alterations in the diffusive barrier presented by the airway wall may play a role in pathologically altered airway responsiveness.

Asma en la infancia, ¿se corresponden las respuestas con las preguntas? / Childhood asthma: do the answers coincide with the questions?

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On the functional consequences of bronchial basement membrane thickening.

Reticular basement membrane (RBM) thickness and airway responses to inhaled methacholine (MCh) were studied in perennial allergic asthma (n = 11), perennial allergic rhinitis (n = 8), seasonal allergic rhinitis (n = 5), and chronic obstructive pulmonary disease (COPD, n = 9). RBM was significantly thicker in asthma (10.1 +/- 3.7 microm) and perennial rhinitis (11.2 +/- 4.2 microm) than in seasonal rhinitis (4.7 +/- 0.7 microm) and COPD (5.2 +/- 0.7 microm). The dose (geometric mean) of MCh causing a 20% decrease of 1-s forced expiratory volume (FEV(1)) was significantly higher in perennial rhinitis (1,073 microg) than in asthma (106 microg). In COPD, the slope of the linear regression of all values of forced vital capacity plotted against FEV(1) during the challenge was higher, and the intercept less, than in other groups, suggesting enhanced airway closure. In asthma, RBM thickness was positively correlated (r = 0.77) with the dose (geometric mean) of MCh causing a 20% decrease of FEV(1) and negatively correlated (r = -0.73) with the forced vital capacity vs. FEV(1) slope. We conclude that 1) RBM thickening is not unique to bronchial asthma, and 2) when present, it may protect against airway narrowing and air trapping. These findings support the opinion that RBM thickening represents an additional load on airway smooth muscle.

Comparisons of peak diurnal expiratory flow variation, postbronchodilator FEV(1) responses, and methacholine inhalation challenges in the evaluation of suspected asthma.

STUDY OBJECTIVES: The validity of peak expiratory flow variation (PEFvar) as defined by National Heart, Lung, and Blood Institute (NHLBI) guidelines as a diagnostic tool for suspected asthma or its comparative value to methacholine inhalation challenge (MIC) or postbronchodilator (BD) FEV(1) responses has not been formally assessed. We prospectively analyzed the correlation of 28 different PEFvar indexes (including 4 NHLBI-compatible indexes) with MIC and pre-BD and post-BD FEV(1) responses in suspected asthmatic subjects with normal findings on lung examination, chest radiography, and baseline spirometry. DESIGN: Participants were asked to record peak expiratory flow four times daily for 2 to 3 weeks, followed by an MIC. During a minimum 6-month follow-up period, a clinical diagnosis of asthma was made or ruled out based on testing results and response to antiasthma therapy. SETTING: Medical school-affiliated subspecialty private practice of allergy, asthma, and immunology. PARTICIPANTS: One hundred twenty-one suspected asthmatic patients with normal findings on lung examination, chest radiography, and baseline spirometry. MEASUREMENTS AND RESULTS: Fifty-seven subjects completed both the peak flow diary and the MIC and were accepted for statistical analysis. There were no statistically significant correlations between any peak expiratory flow index and MIC. Among the three diagnostic tools evaluated, MIC had the highest sensitivity (85.71%). All the PEFvar indexes and post-BD responses had low sensitivity and high false-negative rates. CONCLUSIONS: PEFvar and post-BD FEV(1) responses are poor substitutes for MIC in the assessment of patients with suspected asthma with normal findings on lung examination, chest radiography, and spirometry. Our findings warrant a reconsideration of the NHLBI guidelines recommendation of the utility of PEFvar as a diagnostic tool for asthma in clinical practice.

Kinetics of respiratory system elastance after airway challenge in dogs.

We compared the time courses of lung mechanical changes with intravenous (iv) injection vs. aerosol administration of histamine, methacholine, and ACh in dogs. We interpret these results in terms of a spring-and-dashpot model of airway smooth muscle receiving activation via a tissue compartment when agonist is delivered by the iv route and through an additional airway wall compartment when it is delivered by the aerosol route. The model accurately accounts for the principal features of the respiratory system elastance response curves. It also accounts for the differences between iv and aerosol responses, supporting the notion that agonist delivered by aerosol has to traverse a longer pathway to the airway smooth muscle than does agonist delivered iv. The time constants representing diffusive exchange of agonist between compartments were not significantly different for the three agonists, suggesting that the three agonists shared a common principal means of clearance, which was presumably blood flow.

Human tracheobronchial deposition and effect of a cholinergic aerosol inhaled by extremely slow inhalations.

Ten subjects inhaled the same amounts of cholinergic aerosol of a mass median diameter (MMD) of 7.7 microns in a normal provocation test and in a test with extremely slow inhalations (ESI). This new technique using ESI and large droplets/particles gives a high degree of deposition in small ciliated airways which cannot be obtained by using small particles. The purpose was to compare measured effects with calculated doses of the aerosol in large and small ciliated airways. The effect on large airways was measured by airway resistance (R(aw)), and the effect on small airways was measured by the phase III slope of single breath nitrogen test (N2-delta). Mouth and throat deposition was calculated from human experimental data, and deposition of the cholinergic aerosol into large and small airways was calculated, using a computerized lung model. The study showed that the extremely slow inhalation caused a larger effect on R(aw) and tendency to a larger effect on N2-delta compared to the effect in the normal provocation. Deposited dose in the large airways, in percent of inhaled dose, was calculated to be 25-33% for normal inhalation and 20-24% for ESI. Calculated deposited dose in the small airways (bronchioles; generations 12-16) was 1.8-3.4% for normal inhalation and 18-25% for ESI. For large airways a stronger effect was induced by ESI, perhaps by the more uniform distribution of particles within each generation, compared to normal inhalations when particles deposit near the bifurcations. Concerning the small airways, N2-delta did not differ significantly between normal and ESI provocations, indicating that they did not react much on cholinergic exposure. We believe that our approach using ESI for small airway deposition of a nebulized aerosol can be of value for estimating the effects of various substances on large and small airways.

Peptidoleukotriene (PLT) release and absorption from the airways of the isolated perfused guinea pig lung following chemical and antigenic challenge.

PURPOSE: To study the release and absorption of peptidoleukotrienes (PLTs) from the airways of the guinea pig lung following calcium ionophore A23187 (CI), benzalkonium chloride (BAC), ethylene diamine tetra-acetic acid (EDTA) or ovalbumin (OA) challenge. METHODS: PLT C4/D4/E4 were quantified in the perfusate of the isolated perfused guinea pig lung (IPGPL) following intratracheal administration of CI, BAC, EDTA or OA in different doses. The formation and airway-to-perfusate transfer kinetics of PLTs were analyzed by fitting mean data for cumulative PLT in perfusate vs. time to an A-->B-->C first-order release and transfer model, with dose-dependent transfer rate constants. RESULTS: CI induced apparent first order release of PLTs with a t1/2 approximately equal to 1.2 minutes. The amount of PLT released was CI dose-dependent, as was the airway-to-perfusate transfer rate constant. These reached maxima of 0.254 microgram and 0.0557 min.-1, respectively, around a CI dose of 100 micrograms. In OA-sensitized IPGPL preparations, OA induced a similar dose-dependent release of PLTs, although the rates of PLT release were much greater and more variable than those seen with CI. In OA sensitized IPGPL preparations, at an OA dose of 1000 micrograms, the maximum amount of PLT released was 0.289 micrograms and the maximal airway-to-perfusate transfer rate constant was 0.0229 min-1. BAC and EDTA failed to induce quantifiable PLT release from the airways. CONCLUSIONS: Rapid release of the inflammatory mediators, PLT C4/D4/E4, could be induced in the unsensitized IPGPL by CI, and in the sensitized IPGPL by OA. Transfer into perfusate occurred in both cases with dose-dependent t1/2 ranging from 12.4 through 57.8 minutes.