Airway calibre as a confounder in interpreting bronchial responsiveness in asthma.

BACKGROUND: The relation between airway responsiveness to constrictor agents and forced expiratory volume in one second (FEV1) is important when interpreting change in airway responsiveness after an intervention. The aim of the study was to analyse the relation between FEV1 as a percentage of predicted values (% predicted) and airway responsiveness between and within asthmatic subjects. METHODS: Results of non-specific bronchial challenge tests were pooled from two randomised crossover studies comparing the effect of a non-sedative antihistamine with placebo in 35 patients with moderate asthma. The design of the two studies was similar: the provocative concentration of either histamine (first study) or methacholine (second study) resulting in a 20% decrease in ventilatory capacity (PC20) was repeated at two week intervals while patients were treated with the antihistamine or placebo. The dose of inhaled corticosteroid was gradually reduced during the study. Data were analysed with PC20 as the dependent variable in a general linear model so that the influence on PC20 of inhaled corticosteroid dose, antihistamine, and choice of bronchoconstricting agent could be separated from the influence of FEV1% predicted. RESULTS: The correlation coefficient between mean PC20 and mean prechallenge FEV1 for each patient was 0.45. In the general linear model two thirds (65%) of the variation in PC20 was due to variation between subjects. One third of the within subject variation in PC20 could be explained by variation in prechallenge FEV1% predicted (a change in FEV1 of 27% predicted was associated with one doubling or halving of PC20). Treatment with the antihistamine had no influence on PC20, except when histamine was used as the bronchoconstricting agent. The dose of inhaled corticosteroid had a small but significant effect. CONCLUSIONS: The variation in a patient's PC20 over time (several months) is related to changes in FEV1% predicted. Variation in FEV1% predicted explains less of the variation in bronchial responsiveness between subjects where a patient specific factor, which is probably related to the pathogenesis of bronchial asthma, seems to dominate.     

Effect of inhaled thiorphan, a neutral endopeptidase inhibitor, on the bronchodilator response to inhaled atrial natriuretic peptide (ANP).

BACKGROUND: The hormone atrial natriuretic peptide (ANP) causes bronchodilation and partially protects against direct and indirect bronchial challenges. Both in vitro and in vivo studies have found that the protective effect of ANP against bronchoconstriction is enhanced by inhibition of the enzyme neutral endopeptidase (NEP). It was hypothesised that pretreatment with thiorphan, an NEP inhibitor, might enhance the bronchodilator response to inhaled ANP. METHODS: In a randomised double blind placebo controlled crossover study, six asthmatic patients (one woman) of mean (SD) age 47.3 (3.8) years and forced expiratory volume in one second (FEV1) 1.91 (0.42) 1, 55 (3.8)% predicted, were studied. All were shown at screening to have at least a 25% improvement in FEV1 to inhaled salbutamol. On five study visits the patients received either thiorphan 1 mg (in 2 ml) followed by ANP 5 mg or placebo (saline), or placebo (saline) followed by ANP (5 mg), placebo or salbutamol 5 mg. Spirometric parameters were measured after each inhalation and thereafter for the next two hours. RESULTS: ANP alone caused a bronchodilator response up to 15 minutes when compared with placebo or thiorphan alone with a mean (SE) change in FEV1 of 16.8 (8.1)% and 16.1 (6.8)% at 10 and 15 minutes from baseline, respectively. Prior inhalation of thiorphan prolonged the duration of the bronchodilator effect of ANP up to 60 minutes with a mean (SE) change in FEV1 of 23.1 (3.4)% at 60 minutes. There was no difference in the maximum degree of bronchodilation following the administration of ANP alone compared with the combination of thiorphan and ANP. The degree and duration of the bronchodilator response produced by ANP, or the combination of the NEP inhibitor and ANP, were less than that produced by salbutamol. CONCLUSIONS: These results confirm that, at least in part, the bronchodilator response to inhaled ANP is modulated by NEP. Analogues of ANP which are stable to NEP may have greater bronchodilator activity than ANP in the treatment of asthma.     

Effects of platelet activating factor on airway calibre, airway responsiveness, and circulating cells in asthmatic subjects.

The effects of inhaled platelet activating factor were compared with those of inhaled methacholine (control) on airway calibre, airway responsiveness to methacholine and isoprenaline, and circulating cells in eight subjects with mild, stable asthma. Platelet activating factor was given in six doses at 15 minute intervals and airway response measured as change in partial expiratory flow at 30% of vital capacity (Vp30). Platelet activating factor caused a fall in Vp30, the mean (SEM) maximum percentage fall being 28.9 (4.2) five minutes after the first dose (12 micrograms) and 50.9 (8.0) after the second dose (24 micrograms). Tachyphylaxis occurred, however, with the four subsequent doses of inhaled platelet activating factor. There was transient neutropenia after the first dose, from a mean of 3.6 (0.2) x 10(9) to 2.2 (0.5) x 10(9) neutrophils/l; this response also showed tachyphylaxis with subsequent doses. The mean PC40 (the concentration of methacholine needed to cause a 40% fall in Vp30) was unchanged one, three, and seven days after administration of platelet activating factor. There was no significant correlation between baseline PC40 methacholine and the maximal fall in Vp30 after either the first (12 micrograms) or the second dose (24 micrograms) of platelet activating factor. The control challenge with methacholine produced a degree of bronchoconstriction similar to that of platelet activating factor but was not associated with any significant change in bronchial responsiveness or in circulating cells. The bronchodilator response to inhaled isoprenaline measured three days after inhalation of platelet activating factor and of methacholine was similar after the two challenges. Thus asthmatic subjects who are hyperresponsive to methacholine show a similar bronchoconstrictor response to platelet activating factor, as has been observed in normal subjects; overall this did not cause airway hyperresponsiveness to methacholine.     

Effect of inhaled frusemide on responses of airways to bradykinin and adenosine 5'-monophosphate in asthma.

BACKGROUND--Inhaled frusemide exerts a protective effect against bronchoconstriction induced by several indirect stimuli in asthma. This effect could be caused by interference with neural pathways. The effect of inhaled frusemide on bronchoconstriction induced by inhaled bradykinin, which is thought to cause bronchoconstriction via neural mechanisms, was studied and compared with the effects of adenosine 5'-monophosphate (AMP) which probably produces its airway effects by augmenting mast cell mediator release and interfering with neural pathways. METHODS--Patients first underwent AMP and bradykinin challenges. They were then studied in a randomised, placebo controlled, double blind fashion. Ten atopic asthmatic subjects, studied on four days, were pretreated with inhaled frusemide (40 mg) or placebo for 10 minutes, five minutes before challenge with increasing concentrations of nebulised AMP or bradykinin. RESULTS--On the open visit days the provocative concentrations required to reduce forced expiratory volume in one second (FEV1) by 20% from baseline (PC20) for AMP and bradykinin were 16.23 (1.42-67.16) and 2.75 (0.81-6.6) mg/ml. There was a significant correlation between baseline AMP and bradykinin PC20 values. For AMP the geometric mean PC20 values following pretreatment with inhaled frusemide and matched placebo were 80.97 (9.97- > 400.0) and 14.86 (2.6-104.6) mg/ml respectively (95% CI 0.49 to 0.98). For bradykinin the geometric mean PC20 values following pretreatment with inhaled frusemide and matched placebo were 13.22 (2.53- > 16.0) and 2.52 (0.45-5.61) mg/ml respectively (95% CI 0.43 to 1.01). Frusemide afforded 5.45 and 5.24 fold protection against AMP and bradykinin-induced bronchoconstriction respectively. Furthermore, there was a significant correlation between protection afforded to the airways against AMP and bradykinin. CONCLUSIONS--These data suggest that inhaled frusemide affords protection against bradykinin-induced bronchoconstriction which is comparable to that against AMP, supporting a common mechanism of action for frusemide.     

Relation between the bronchial obstructive response to inhaled lipopolysaccharide and bronchial responsiveness to histamine.

BACKGROUND: Bronchoconstriction has developed after inhalation of lipopolysaccharide in a dose of 20 micrograms in asthmatic patients and of 200 micrograms in normal subjects. This study set out to determine whether the bronchial response to lipopolysaccharide was related to non-specific bronchial responsiveness and atopy. METHODS: Sixteen subjects with a fall in specific airway conductance of 40% (PD40sGaw) after inhaling up to 900 micrograms histamine inhaled 20 micrograms lipopolysaccharide (from Escherichia coli type 026:B6) a week after bronchial challenge with a control solution of saline. The bronchial response over five hours was measured as change in FEV1 and area under the FEV1-time curve. RESULTS: FEV1 fell significantly more after lipopolysaccharide than after diluent inhalation, the difference in mean (SE) FEV1 being 4.6% (5.4%); response was maximal 60 minutes after lipopolysaccharide inhalation and lasted more than five hours. Histamine PD20FEV1 and PD40sGaw correlated with the fall in FEV1 after lipopolysaccharide inhalation. There was no difference in the proportions of responders and non-responders to lipopolysaccharide who were atopic. CONCLUSION: Lipopolysaccharide induced bronchial obstruction is associated with non-specific responsiveness but not with atopy.     

Effect of regular inhaled salbutamol on airway responsiveness and airway inflammation in rhinitic non-asthmatic subjects

BACKGROUND: Regular, inhaled beta 2 agonists may increase airway responsiveness in asthmatic subjects. The mechanism is not known but may be via an increase in airway inflammation. A study was undertaken to examine the effect of regular inhaled salbutamol on airway responsiveness to methacholine and hypertonic saline, on the maximal response plateau to methacholine, and on inflammatory cells in induced sputum in rhinitic non-asthmatic subjects. METHODS: Thirty subjects with a baseline maximal response plateau of > 15% fall in forced expiratory volume in one second (FEV1) entered a randomised, placebo controlled, parallel trial consisting of two weeks run in, four weeks of treatment, and two weeks washout. Methacholine challenges were performed at the beginning of the run in period, before treatment, after treatment, and after washout. Hypertonic saline challenges were performed before and after treatment and induced sputum samples were collected for differential cell counting. RESULTS: There was no change in airway responsiveness, maximal response plateau to methacholine, or in induced sputum eosinophils or mast cells. The maximum fall in FEV1 after hypertonic saline increased in the salbutamol group (median change 6.0%, interquartile range (IQR) 11.0) but did not change in the placebo group (median change 1.3%, IQR 5.5). CONCLUSIONS: Regular inhaled salbutamol for four weeks increases airway responsiveness to hypertonic saline but does not alter airway responsiveness to methacholine or cells in induced sputum in non-asthmatic individuals with rhinitis. The relevance of these findings to asthmatic subjects has not been established.


     

Effect of allergen challenge on airway responsiveness to histamine and sodium metabisulphite in mild asthma.

BACKGROUND: Airway responsiveness to histamine and methacholine, direct smooth muscle spasmogens, is increased following inhalation of allergen. Although the aetiology of this phenomenon is unclear, increased cellular or neural activity may be involved since allergen also induces increases in airway responsiveness to the mast cell stimulus adenosine-5'-monophosphate (AMP) and the neural stimulus bradykinin. METHODS: To explore this further, the airway responsiveness to sodium metabisulphite (MBS), an indirect neural stimulus with similar characteristics to bradykinin, was compared in 18 mild steroid-naive asthmatic subjects with the airway responsiveness to histamine before and after allergen challenge with extracts of house dust mite, grass pollen, or cat. All subjects inhaled doubling increments of histamine and MBS until the concentration provoking a 20% fall in forced expiratory volume in one second (PC20) was reached before and three hours after allergen challenge. Twelve of the subjects had additional challenges at 24 hours after the allergen. RESULTS: Following allergen challenge all subjects showed an early response and 14 also had a late asthmatic response. For histamine there was a significant increase in airway responsiveness at both three and 24 hours compared with values before the allergen (0.89 (0.25) and 1.53 (0.52) doubling dose changes, respectively). In contrast, airway responsiveness to MBS was unaltered by allergen challenge (0.29 (0.27) and -0.33 (0.28) doubling dose changes compared with pre-allergen values at three and 24 hours, respectively). CONCLUSION: These data suggest that activation of airway sensory nerves is unlikely to contribute to the increase in airway responsiveness following inhalation of allergen. The previously observed allergen induced increase in airway responsiveness to bradykinin and AMP may involve non-neural pathways.     

Effect of inhaled corticosteroids on bronchial responsiveness in patients with "corticosteroid naive" mild asthma: a meta-analysis

BACKGROUND: Inhaled corticosteroids are the most efficacious anti-inflammatory drugs in asthma. International guidelines also advocate the early introduction of inhaled corticosteroids in corticosteroid naive patients. A study was undertaken to assess the effects of inhaled corticosteroids on bronchial hyperresponsiveness in patients with corticosteroid naive asthma by conventional meta-analysis. METHODS: A Medline search of papers published between January 1966 and June 1998 was performed and 11 papers were selected in which the patients had no history of treatment with inhaled or oral corticosteroids. Bronchial responsiveness to bronchoconstricting agents was considered as the main outcome parameter. Doubling doses (DD) of histamine or methacholine were calculated. RESULTS: The total effect size of inhaled corticosteroids (average daily dose 1000 microg) versus placebo in the 11 studies was +1.16 DD (95% confidence interval (CI) +0.76 to +1.57). When only the eight short term studies (2-8 weeks) were analysed the effect size of the bronchoconstricting agent was +0.91 DD (95% CI +0.65 to +1.16). No relationship was found between the dose of inhaled corticosteroid used and the effect on bronchial responsiveness. CONCLUSION: This meta-analysis in patients with corticosteroid naive asthma indicates that, on average, high doses of inhaled corticosteroids decrease bronchial hyperresponsiveness in 2-8 weeks. It remains unclear whether there is a dose-response relationship between inhaled corticosteroids and effect on bronchial hyperresponsiveness.     

Effect of an inhaled antihistamine on exercise-induced asthma.

The ability of the H1 receptor antagonist clemastine to prevent exercise-induced asthma (EIA) has been studied in 10 adult asthmatic subjects. Exercise was performed for eight minutes on a cycle ergometer on two occasions on each of two days. The first test each day was without premedication and the second was preceded by inhalation of 0.05% clemastine or saline placebo given single blind in random order. Ventilatory function was assessed by serial measurements of peak expiratory flow rate (PEFR) and forced expiratory volume in one second (FEV1). All four tests for each patient were closely matched in terms of oxygen uptake and total ventilation which were monitored throughout exercise. The response to exercise after clemastine or placebo has been compared both directly and in terms of the degree of protection afforded against EIA compared with the initial test on the same day. Clemastine was significantly better than placebo for both PEFR and FEV1. All 10 subjects had less EIA after clemastine, which suggests an important role for histamine in its production. Other mechanisms may also be involved to a variable degree in different individuals.     

Potentiating effect of inhaled acetaldehyde on bronchial responsiveness to methacholine in asthmatic subjects.

BACKGROUND--It has recently been reported that acetaldehyde induces bronchoconstriction indirectly via histamine release. However, no study has been performed to assess whether acetaldehyde worsens bronchial responsiveness in asthmatic subjects so this hypothesis was tested. METHODS--Methacholine provocation was performed on three occasions: (1) after pretreatment with oral placebo and inhaled saline (P-S day), (2) after placebo and inhaled acetaldehyde (P-A day), and (3) after a potent histamine H1 receptor antagonist terfenadine and acetaldehyde (T-A day) in a double blind, randomised, crossover fashion. Nine asthmatic subjects inhaled 0.8 mg/ml acetaldehyde or saline for four minutes. After each inhalation a methacholine provocation test was performed. RESULTS--Methacholine concentrations producing a 20% fall in FEV1 (PC20-MCh) on the P-A day (0.48 mg/ml, 95% CI 0.21 to 1.08) and T-A day (0.41 mg/ml, 95% CI 0.22 to 0.77) were lower than those on the P-S day (0.85 mg/ml, 95% CI 0.47 to 1.54). There was no change in the PC20-MCh between the P-A and T-A days. A correlation was observed between the logarithmic values of PC20-MCh (log PC20-MCh) on the P-S day and the potentiating effect of acetaldehyde on the methacholine responsiveness [(log PC20-MCh on P-A day)-(log PC20-MCh on P-S day)] (rho = 0.82). CONCLUSIONS--Acetaldehyde induces bronchial hyperresponsiveness in patients with asthma by mechanisms other than histamine release.     

Effect of betamethasone on airway obstruction and bronchial response to salbutamol in prednisolone resistant asthma.

Twelve patients with chronic severe asthma, having previously shown an FEV1 increase of less than 20% of the predicted value with prednisolone treatment (20-60 mg daily for 10 days), took part in a double blind crossover comparison of equipotent anti-inflammatory doses of betamethasone and prednisolone. Betamethasone (8 mg) and prednisolone (40 mg) were administered daily for 10 days with a washout period of 10 days between. In this first part of the study betamethasone was administered intramuscularly and prednisolone orally. Placebo injections and tablets were used. Mean FEV1 was not significantly different before each period. There was a significant increase in FEV1 while they were taking betamethasone but not prednisolone. Individual analysis of the data showed that FEV1 increased with betamethasone in nine patients and remained stable or decreased in three. During treatment with prednisolone baseline FEV1 increased moderately in three patients (FEV1 0.3, 0.5 and 0.6 l) and remained stable or decreased in nine. There was no significant difference between the bronchodilator responses to cumulative doses of inhaled salbutamol when they were measured immediately before, on the last day of treatment with each steroid, and between steroid treatment periods. The same protocol was followed four months later in five of the 12 patients but both drugs were administered orally on this occasion. Similar results were obtained. The greater effect of betamethasone on bronchial obstruction may be due to its longer biological half life or to some unidentified property of its metabolites. The bronchial response to inhaled beta 2 agonist appears not to be influenced by either steroid in these patients.     

Effect of inhaled budesonide on bronchial reactivity to histamine, exercise, and eucapnic dry air hyperventilation in patients with asthma.

BACKGROUND: It has been suggested that inhaled corticosteroids may provide greater protection against constrictor stimuli that act indirectly such as exercise than those that act directly such as histamine. METHODS: The effects of six weeks treatment with inhaled budesonide (800 micrograms twice daily) on bronchial reactivity to histamine, exercise, and eucapnic voluntary hyperventilation of dry air were compared in a double blind, placebo controlled, non-crossover study in 40 subjects with asthma. Change in bronchial reactivity to histamine and eucapnic hyperventilation over the six weeks was measured as change in the provocative dose of histamine or dry air causing a 20% fall in FEV1 (PD20 histamine and PV20 eucapnic hyperventilation (EVH) of dry air); this was not possible for exercise because of the development of refractoriness. To enable the change in response to all three stimuli to be compared, the response (percent fall in FEV1) to a fixed dose was measured for all three challenge tests. RESULTS: After budesonide there was an increase in PD20 histamine from 0.48 to 2.81 mumol and in PV20 EVH from 364 to 639 litres, and a significant correlation between the changes in PD20 histamine and PV20 EVH (r = 0.63). The median percentage fall in FEV1 in response to eucapnic hyperventilation, exercise, and histamine was similar before budesonide (25.5%, 26.6%, and 24.5%); the reduction in the percentage fall in FEV1 with budesonide was also similar for the three challenges (18.9%, 17.5%, and 16.6%), and all differed significantly from the changes following placebo. There was a significant correlation between change in percentage fall in FEV1 after budesonide with the three stimuli (histamine v exercise: r = 0.48; histamine v eucapnic hyperventilation: r = 0.46; exercise v eucapnic hyperventilation: r = 0.63). CONCLUSION: The similar magnitude of change in bronchial reactivity to all three stimuli after budesonide and the within subject correlation obtained between these changes suggest that corticosteroids act by a common mechanism to protect against eucapnic hyperventilation, exercise, and histamine.     

Effect of inhaled prostaglandin E2 on bronchial reactivity to sodium metabisulphite and methacholine in patients with asthma.

Inhaled frusemide protects against the bronchoconstrictor response to a wide range of stimuli that cause bronchoconstriction by indirect mechanisms. One possible explanation for this protection relates to the known ability of frusemide to enhance synthesis of prostaglandin E2 (PGE2). Studies in vitro suggest that PGE2 might protect against indirectly acting bronchoconstrictor challenges rather than those that act directly on airway smooth muscle, though little is known about the effects of PGE2 in vivo. The effect of inhaled PGE2 on the bronchoconstrictor response to inhaled sodium metabisulphite (a stimulus with an indirect action) and methacholine (which acts directly on airway smooth muscle) was studied in nine patients with asthma. Subjects were studied on four days, inhaling PGE2 (100 micrograms) or placebo in a double blind fashion followed immediately by a cumulative dose challenge with sodium metabisulphite or methacholine. The response to the constrictor stimuli was measured as the provocative dose causing a 20% fall in FEV1 (PD20). There was no significant change in FEV1 after inhaled PGE2 compared with placebo, nor any significant change in the response to methacholine; the geometric mean methacholine PD20 was 0.9 mumol after PGE2 and 0.56 mumol after placebo (mean difference 0.7 (95% confidence limits--0.1, 1.5) doubling doses). PGE2, however, protected against sodium metabisulphite, the geometric mean sodium metabisulphite PD20 being 11.8 mumol after PGE2 and 1.8 mumol after placebo (mean difference 2.5 (95% CL 1.9, 3.1) doubling doses). PGE2 conferred significantly greater protection against sodium metabisulphite than methacholine (mean difference 1.8 (95% CL 0.8, 2.8) doubling doses). This suggests that PGE2, like frusemide, has an inhibitory effect on pathways relevant to the bronchoconstriction induced by sodium metabisulphite, with little or no effect on those relevant to methacholine.     

Effect of pH on bronchial response to inhaled histamine.

In order to investigate the effect of pH on bronchial responsiveness to inhaled histamine, 15 subjects with non-specific bronchial hyperreactivity performed two histamine inhalation tests, one with unbuffered, and the other with buffered histamine acid phosphate solutions. The unbuffered histamine solutions were prepared with 0.9% sterile saline and had a pH range from 4.3 to 7.3, while the buffered histamine solutions were prepared with a phosphate buffer and had a pH range of 6.5 to 7.4. The two histamine inhalation tests were similar in all other regards. The geometric mean histamine provocation concentration required to produce a 20% reduction in FEV1 (PC20) was significantly lower for the unbuffered histamine (1.33 mg/ml) than for the buffered histamine (1.67 mg/ml), p less than 0.05. The two PC20s differed by less than one doubling dilution, the range of reproducibility of the test, in 12 of the 15 subjects. The pH effect was only noted when the pH of the histamine solutions was below five (histamine concentrations from one to eight mg/ml). We conclude that the acid pH of higher concentrations of histamine acid phosphate solutions has a slight but significant enhancing effect on the bronchial responsiveness to inhaled histamine.     

Adding salmeterol to an inhaled corticosteroid: long term effects on bronchial inflammation in asthma

BACKGROUND: Addition of the long acting beta2 agonist salmeterol to inhaled corticosteroids leads to better symptomatic asthma control than increasing the dose of inhaled corticosteroids. However, little is known about the long term effects of adding salmeterol on the asthmatic inflammatory process, control of which is considered important for the long term outcome of asthma. METHODS: After a 4 week fluticasone run-in period, 54 patients with allergic asthma were randomised to receive twice daily treatment with fluticasone 250 microg with or without salmeterol 50 microg for 1 year in a double blind, parallel group design (total daily dose of fluticasone 500 microg in both treatment groups). Primary outcomes were sputum eosinophil numbers and eosinophil cationic protein concentrations. Secondary outcomes were neutrophil associated sputum parameters and a respiratory membrane permeability marker. The effects on allergen induced changes were determined before and at the end of the treatment period. RESULTS: Adding salmeterol to fluticasone resulted in improved peak expiratory flow, symptom scores, rescue medication usage, and bronchial hyperresponsiveness (p < 0.05 for all). There was no sustained effect on sputum cell differential counts and cytokine concentrations during the treatment period or on changes induced by allergen challenge at the end of treatment (p > 0.05). However, adding salmeterol significantly reduced sputum ratios of alpha2-macroglobulin and albumin during the treatment period (p = 0.001). CONCLUSIONS: The addition of salmeterol to fluticasone produces no sustained effect on allergen induced cellular bronchial inflammation but leads to a significant improvement in size selectivity of plasma protein permeation across the respiratory membrane. This may contribute to the improved clinical outcome seen in patients with allergic asthma when a long acting beta2 agonist is combined with inhaled corticosteroids.     

Effect of prednisone and beclomethasone dipropionate on airway responsiveness in asthma: a comparative study.

To examine the effect of corticosteroids on bronchial hyperresponsiveness, a randomised, double dummy, single blind crossover study was performed in 18 subjects with chronic asthma, comparing the effect of three weeks' treatment with inhaled beclomethasone dipropionate, 1200 micrograms daily, and oral prednisone 12.5 mg daily. The 12 week study began with a three week run in period of baseline treatment, which was continued unchanged throughout the study, and the two treatment periods were separated by a three week washout period. Patients kept daily Airflometer readings and attended the laboratory every three weeks for spirometry and a histamine inhalation test for determining the provocative dose of histamine causing a 20% fall in FEV1 (PD20). The mean FEV1 at the start was 1.9 litres (56% predicted). There was no significant change in PD20 with prednisone treatment, the mean PD20 being 0.56 and 0.59 mumol before and after treatment. There was, however, a significant improvement in PD20 with beclomethasone dipropionate treatment, the geometric mean PD20 being 0.38 and 1.01 mumol before and after treatment (p less than 0.001). There was a small but significant improvement in mean FEV1 after beclomethasone dipropionate treatment--from 1.9 to 2.2 litres--but no change after prednisone. Both medications produced significant and similar improvements in morning and evening Airflometer readings, post-bronchodilator improvement, and diurnal variation. Thus at doses that had similar beneficial effects on lung function beclomethasone dipropionate caused a significant improvement in bronchial hyperresponsiveness whereas prednisone caused no change. The superior topical anti-inflammatory effect of beclomethasone dipropionate may account for the different effects on bronchial hyperresponsiveness.     

Bronchial responsiveness to inhaled histamine and isoprenaline in patients with airway obstruction

In order to examine the hypothesis that bronchial reactivity to non-specific constrictor stimuli is influenced by the resting tone of the bronchial smooth muscle, the airway responses to inhaled histamine solution and inhaled isoprenaline were measured in 19 patients with airway obstruction. There was a significant positive correlation between the size of the constrictor response to histamine and the dilator response to isoprenaline (r = +0.83; p less than 0.01) as measured by changes in specific airway conductance. Patients with asthma showed greater bronchial reactivity to both histamine and isoprenaline than those with chronic bronchitis, although some patients had changes intermediate between the two extremes.     

Evaluation of bronchial responsiveness to exercise in children as an objective measure of asthma in epidemiological surveys.

BACKGROUND: Exercise has been proposed as a useful challenge test for the measurement of bronchial responsiveness in community surveys of the prevalence of childhood asthma. This study aimed to develop a standardised exercise challenge in which the sensitivity to detect asthma was increased by inhalation of dry air. METHODS: Sixty four children aged 12-13 years who had reported wheeze in the past 12 months and 70 control subjects were invited to participate in an exercise challenge at school. Subjects performed eight minutes of cycle exercise while breathing dry air at a workload calculated to produce a minute ventilation of 60% maximum voluntary ventilation during the final three minutes. A fall in forced expiratory volume in one second (FEV1) of 10% or more from baseline was considered a positive test. Data on recent asthma symptoms, asthma morbidity, and use of medication were collected by parent completed questionnaires in those subjects who reported wheeze in the past 12 months. Repeatability of the exercise test was determined in a further 13 children with known asthma. RESULTS: Fifty five children (88%) who reported wheeze in the previous 12 months and 54 control subjects (77%) were studied. Nine subjects in whom baseline FEV1 was less than 75% predicted did not perform the exercise test. Technically unsatisfactory tests were obtained in five subjects. Twenty six (57%) subjects who reported wheeze and three controls (6%) had a positive exercise test, giving a sensitivity of 57% (26 of 46) and specificity of 94% (47 of 50). Estimates of the repeatability of the exercise test showed a mean difference in percentage fall in FEV1 for patients with asthma of 3.08% (95% limits of agreement -7.76% to 13.92%). CONCLUSIONS: Despite attempts to maximise the stimulus to bronchoconstriction in this exercise challenge test, its sensitivity and specificity were not improved in comparison with previous epidemiological studies of the prevalence of asthma.     

Effect of inhaled formyl-methionyl-leucyl-phenylalanine on airway function.

Formyl-methionyl-leucyl-phenylalanine (FMLP), a synthetic, acylated tripeptide analogous to bacterial chemotactic factors, has been shown to cause bronchoconstriction in guinea pig, rabbit, and human airways in vitro. To determine whether FMLP causes bronchoconstriction in man in vivo, a preliminary study was undertaken in which five non-smokers (mean age 35 years, FEV1 94% (SEM 5%) predicted) and five smokers (mean age 34 years, FEV1 93% (6%) predicted) inhaled aerosols of FMLP. None of the subjects showed airway hyperresponsiveness to histamine (the provocative concentrations of histamine causing a fall of greater than or equal to 20% in FEV1 (PC20) were over 8 mg/ml). FMLP dissolved in 50% dimethylsulphoxide and 50% saline in concentrations of 0, 0.06, 0.12, 0.25, 0.5, 1.0, 2.0, and 4.0 mg/ml was administered to the subjects by means of a French-Rosenthal dosimeter, FEV1 being recorded after inhalation of each concentration. Dose dependent falls in FEV1 occurred in five non-smokers (geometric mean 1.76, 95% confidence limits 0.87-3.53 mg/ml) and three smokers (0.23, 0.07-0.78 mg/ml), with two smokers not responding by 20% to the highest concentration of FMLP. On a separate day the FMLP dose-response curves were repeated after nebulisation of 500 micrograms of ipratropium bromide. The PC20 FMLP in the responders more than doubled. In six additional normal subjects a histamine inhalation test was performed before and four and 24 hours after inhalation of FMLP. All subjects remained unresponsive to histamine. These results show that FMLP is a potent bronchoconstrictor in some non-asthmatic individuals in vivo and this may be important in bronchoconstriction related to infection in patients with chronic obstructive lung disease.     

Bronchial responsiveness to histamine: relationship to diurnal variation of peak flow rate, improvement after bronchodilator, and airway calibre

Features of asthma include increases in both bronchial responsiveness and variability of airflow rates. We examined the relationship between bronchial responsiveness to histamine and the variation of peak expiratory flow rate (PFR) during the day and in response to salbutamol (200 μg), and the initial FEV₁ at the time of the histamine test and FEV₁ response to salbutamol. Bronchial responsiveness to histamine was expressed as the provocation concentration causing a fall in FEV₁ of 20% (PC₂₀). PC₂₀ ranged between 13·9 and 130 mg/ml in nonasthmatic subjects, between 10·5 and 59·9 mg/ml in five asymptomatic asthmatics, and between 0·03 and 20·8 mg/ml in 27 asthmatics with symptoms controlled by medication. The lower the PC₂₀ (the greater the bronchial responsiveness) the lower the morning PFR (r = 0·79), the greater the increase in PFR after salbutamol (morning r = −0·75, evening r = −0·80), and the greater the difference between the highest and lowest PFR each day (r = −0·81). Measurements of PFR were abnormal, compared with those in nonasthmatic subjects, in all subjects with a PC₂₀ less than 2 mg/ml—that is, moderate or severe increase in nonspecific bronchial responsiveness—and in none with a PC₂₀ greater than 21 mg/ml—that is, normal responsiveness; five of nine asthmatics with controlled symptoms had abnormal PFR measurements when PC₂₀ was between 2 and 21 mg/ml—that is, mild hyperresponsiveness. In contrast, FEV₁ at the time of the histamine test was greater than 80% predicted in all subjects with a PC₂₀ greater than 2 mg/ml and was not less than this in 10 of 18 subjects with a PC₂₀ less than 2 mg/ml. When improvement in FEV₁ was 20% or more after salbutamol, the PC₂₀ was usually moderately or severely increased (less than 0·4 mg/ml). The results identify a close relationship between nonspecific bronchial responsiveness to histamine and the variability in flow rates which occurs spontaneously and after bronchodilator. In addition, they raise the possibility that increased airflow obstruction in asthma may be a consequence of increased responsiveness.