Cross refractoriness between sodium metabisulphite and exercise induced asthma

Allergen inhalation challenge, refractoriness and the effects of ibuprofen

Background

Bronchoprovocation challenges use direct or indirect acting stimuli to induce airflow obstruction. Indirect stimuli either non-allergic/non-IgE mediated (e.g. exercise, mannitol) or allergic/IgE mediated (i.e. allergen) trigger mast cells to release bronchoconstricting mediators (e.g. cysteinyl leukotrienes, histamine). Performing repeat challenges within a short timeframe (e.g. 3 h) with non-allergic indirect stimuli results in a diminished, refractory response to the second challenge that is inhibited by non-steroidal anti-inflammatory medications. Cross refractoriness occurs between indirect stimuli. It follows that repeat bronchoprovocation with allergen might exhibit refractoriness that might be altered by ibuprofen. We assessed the response to a second allergen challenge performed 24 h after an initial allergen challenge to determine if the response is refractory. If refractoriness developed, the study aimed to determine whether a single dose of ibuprofen would alter the refractory response to the second allergen challenge. In the absence of a refractory response, the study design allowed for the assessment of the effect of ibuprofen on allergen challenge outcomes, including indices of airway inflammation.

Methods

Thirteen mild atopic asthmatics were enrolled in a randomized, double-blind, placebo controlled, cross-over study. Ibuprofen (400 mg) or placebo was administered 1 h prior to the first of two allergen challenges, performed 24 h apart. Blood and sputum eosinophils, airway responsiveness to methacholine and levels of fractional exhaled nitric oxide were assessed before and 7 h after each allergen challenge. All data were log transformed and differences in geometric means were analyzed by paired t-tests.

Results

After placebo, early asthmatic responses for the two challenges were not significantly different (p = 0.82). A single 400 mg dose of ibuprofen decreased both the early (p = 0.03; n = 12) and late asthmatic responses (p = 0.03; n = 3).

Conclusion

Allergen challenges conducted 24 h apart do not exhibit refractoriness. Single dose ibuprofen inhibits early and late asthmatic responses to allergen bronchoprovocation. Ibuprofen should be withheld for at least 24 h prior to investigations utilizing allergen bronchoprovocation.

Trial registration clinicaltrials.gov #NCT02327234

Refractoriness to exercise challenge: a review of the mechanisms old and new

This article discusses the available literature on refractoriness in exercise-induced bronchoconstriction, namely, a decrease in airway responsiveness with repeated exercise challenges. The mechanisms of this naturally occurring protective feature is unknown. Reviewing previous studies together with findings in more recent studies, the authors propose desensitization of the G protein-coupled cysteinyl leukotriene receptor1 as the mechanism of refractoriness and that this desensitization occurs as a result of interplay between leukotrienes and prostaglandins.

Airway refractoriness to inhaled mannitol after repeated challenge

Exercise and inhaled mannitol are thought to cause bronchoconstriction through a similar mechanism in asthma. The response to exercise becomes refractory with repeated challenges. This study aimed to investigate whether repeated challenge with mannitol induces refractoriness, as with exercise. Forty-one children with asthma underwent two consecutive dose-response mannitol challenges (Phase 1); the second challenge proceeded after recovery (FEV(1) : 95% or more of baseline value) from the first. The response to mannitol was expressed as a provocative dose causing a 15% fall in FEV(1) (PD(15) ) and the response-dose ratio (RDR) (% fall in FEV(1) /cumulative dose). In 18 subjects who were deemed to have mannitol refractoriness in Phase 1, a mannitol challenge was performed before and after a methacholine challenge (Phase 2). In Phase 1, the time taken for the FEV(1) to recover after the first mannitol challenge ranged from 20 to 100 min with a median of 50 min. In the 23 subjects with a measurable mannitol PD(15) in both challenges, the geometric mean (95%CI) PD(15) in the second challenge (163 mg [114-232]) was significantly higher than that in the first challenge (66 mg [50-88], P < 0.001). The geometric mean (95%CI) RDR decreased from the value of 0.083%/mg (0.055-0.125) in the first challenge to 0.029%/mg (0.017-0.048) in the second challenge (P < 0.001). In Phase 2, prior challenge with methacholine or mannitol did not significantly alter subsequent bronchoconstriction to the opposite challenge. Repeated challenge with mannitol resulted in less bronchoconstriction when compared with the initial challenge. This refractoriness seems not to be attributable to functional loss of responsiveness or non-specific effect of prior bronchoconstriction.

Protective effect of bronchial challenge with hypertonic saline on nocturnal asthma

Inhalation of hypertonic saline (HS) causes bronchoconstriction in asthmatic subjects. Repeated inhalation of HS leads to substantially reduced bronchoconstriction, known as the refractory period. Refractoriness due to different stimuli has also been described (cross-refractoriness). Nocturnal asthma is defined as an increase in symptoms, need for medication, airway responsiveness, and/or worsening of lung function that usually occurs from 4 to 6 am. Our objective was to determine the effect of refractoriness on nocturnal asthma. The challenge test consisted of inhalations of 4.5% saline with increasing durations until a reduction of 20% in forced expiratory volume in 1 s (FEV1) (PD20HS) or total time of 15.5 min. Twelve subjects with nocturnal asthma were challenged with HS at 16:00 and 18:00 h and FEV1 was measured at 4:00 h. One to 2 weeks later, FEV1 was determined at 16:00 and 4:00 h. LogPD20HS at 18:00 h was significantly greater than logPD20HS at 16:00 h, 0.51 +/- 0.50 and 0.69 +/- 0.60 mg, respectively (P = 0.0033). When subjects underwent two HS challenges in the afternoon, mean (+/- SD) FEV1 reduction was 206 +/- 414 mL or 9.81 +/- 17.42%. On the control day (without challenge in the afternoon) FEV1 reduction was 523 +/- 308 mL or 22.75 +/- 15.40% (P = 0.021). Baseline FEV1 values did not differ significantly between the control and study days, 2.48 +/- 0.62 and 2.36 +/- 0.46 L, respectively. The refractory period following HS challenges reduces the nocturnal worsening of asthma. This new concept may provide beneficial applications to asthmatic patients.

Effects of diurnal variation and prolonged refractoriness on repeated measurements of airways responsiveness to methacholine

BACKGROUND

A number of studies have suggested that diurnal variation in airways responsiveness underlies the circadian rhythm of ventilatory function in asthma. Measurements of airways responsiveness are therefore often performed at standardised times in order to avoid this possible effect, but this is not practical for epidemiological studies. Refractoriness to methacholine has also been reported and this, too, could confound the results of methacholine tests repeated over short intervals. This investigation was carried out to evaluate the possible magnitude of diurnal variation and refractoriness in repeated measures of airways responsiveness to methacholine.

METHODS

To investigate diurnal variation in airways responsiveness, 24 asthmatic subjects aged 18-45 underwent five methacholine tests over three days which were not necessarily consecutive: day 1 at 08:00 hours; day 2 at 08:00 hours, 14:00 hours, 20:00 hours; day 3 at 20:00 hours. To investigate refractoriness a retrospective analysis was undertaken of all paired methacholine tests performed in individuals within our unit between 1984 and 1990 where there had been no intervention likely to affect the results.

RESULTS

The first investigation revealed no diurnal change in airways responsiveness although there was a change in FEV1. Mean PD20 did, however, increase 1.57 fold from 08:00 hours on day 1 to 08:00 hours on day 2 for subjects studied on consecutive days. The second investigation confirmed that a test interval of up to 24 hours (but not of 48 or more hours) was associated with a refractory index (PD20 test 2/PD20 test 1) of > 1.

CONCLUSIONS

No diurnal variation in airways responsiveness was detected for measurements made between 08:00 hours and 20:00 hours, but an interval between successive tests of up to 24 hours was associated with refractoriness. Diurnal variation is not likely to exert an important confounding effect on methacholine tests carried out between 08:00 hours and 20:00 hours, but confounding could result from refractoriness if tests are repeated at intervals up to 24 hours.

Bronchoprotective role for endogenous prostaglandin E2

The possibility that impaired production of bronchoprotective factors contributes to the pathogenesis of asthma cannot be excluded. Prostaglandin E2 (PGE2) could be such a factor. It is a dominant cyclo-oxygenase product of airway epithelium and smooth muscle; it has inhibitory effects on inflammatory cells and pathways involved in bronchoconstriction at concentrations known to occur in the airway; inhalation of PGE2 has considerable bronchoprotective effects in patients with asthma; and manoeuvres that increase or decrease endogenous production of PGE2 have beneficial and deleterious effects on airway function.