Increase in airway responsiveness and effect of deep inhalation on airway caliber in allergen-induced asthma. Relationship to the late-phase response

[Alteration of bronchomotor tone after deep inhalation. Mechanisms and pediatric data]

There is significant alteration of airway calibre after deep inhalation (DI). An increase of airway calibre has been evidenced in children in case of mild asthmatic obstruction and after a positive response to methacholine or exercise challenge. Such an increase is blunted in the presence of a moderate to severe asthmatic airway obstruction and no bronchodilatory effect of DI has been found in infants. Bronchial hyperreactivity and airway inflammation strongly influence post-DI alterations of bronchomotor tone. Airways and lung parenchyma are interdependent but both exhibit imperfect elasticity. Hysterisis characterizes imperfect elasticity of pressure-volume relationship. The mechanical theory of relative hysteresis between airway and lung parenchyma is the main mechanism implicated in the induced changes of airway calibre. DI may influence results of lung function testing in children. The technique may be of interest to increase sensibility of routine lung function testing in children.

Allergen-induced changes in airway responsiveness are not related to indices of airway edema

BACKGROUND

The mechanisms behind airway hyperresponsiveness in asthma are unknown. Airway wall edema has been proposed as one possible culprit of this phenomenon.

OBJECTIVE

To test the hypothesis that airway edema may be the cause of allergen-induced increases in airway responsiveness in asthma, this trial aimed at determining the relationship between allergen-induced changes in airway responsiveness to inhaled methacholine and indirect indices of edema, namely peripheral airway resistance and the levels of the plasma protein fibrinogen in bronchoalveolar lavage (BAL) fluids.

METHODS

Twenty-six atopic individuals with mild asthma were subjected to bronchoscopy at baseline and 28 hours after allergen inhalation. Before each bronchoscopy, methacholine bronchoprovocation was performed. During bronchoscopy, peripheral airway resistance measurements were obtained by wedged bronchoscopy. BAL fluids were analyzed for fibrinogen, as well as for eosinophilic cationic protein. Cytology was performed, and cytokine gene expression was assessed with competitive reverse transcriptase PCR from cell pellets.

RESULTS

A significant increase in airway responsiveness to methacholine was recorded after allergen, but this did not correlate with changes in peripheral airway resistance (which was not affected) or with BAL fibrinogen (which decreased after allergen). Other BAL outcomes confirmed that airway inflammation was produced and was characterized by a T(H)2 cytokine pattern.

CONCLUSIONS

Airway responsiveness in asthma increases after exposure to allergen in the absence of increased indirect indices of edema. The role of edema in this phenomenon should therefore be tested more vigorously.

Maximal and partial expiratory flow rates in a population sample of 10- to 11-yr-old schoolchildren. Effect of volume history and relation to asthma and maternal smoking

The effect of volume history on forced expiratory flow rates has been reported to differ between patients with asthma and healthy persons, and it has been hypothesized that the peripheral airway inflammation of patients with asthma may underlie this difference. There are no published data, however, on the distribution of such volume history effects or the relation of these effects to airways disease in children. We obtained combined partial and maximal forced expiratory flow-volume curves on 1,834 children, age 10-11 yr, in eight communities in the United States and Canada. The effect of a deep inhalation on forced expiratory flow rates at low lung volumes was quantitated by the ratio of V (30) during a maximal expiratory maneuver (V (30M)) to V (30) during a partial expiratory maneuver (V (30P)). The V (30M)/V (30P) ratio was slightly higher among girls than boys (1.26 versus 1.18, p = 0.0001) indicating that a deep inhalation increased V (30) slightly more among girls than among boys. The V (30M)/V (30P) ratio was related to neither history of asthma nor to maternal smoking. In contrast, most spirometric indices from either the maximal or the partial expiratory flow-volume curve were lower in association with a history of asthma or a report of maternal smoking. The ratio of FEF(25-75)/FVC was particularly consistent as a measurement that discriminated both of these effects in boys and girls. These results suggest that the measurement of volume history effects offers no benefits for epidemiological studies of childhood respiratory disease whereas spirometric indices such as the FEF(25-75)/FVC ratio are quite sensitive to the effects of asthma and environmental tobacco smoke exposure on the airways.

New considerations about measuring airway hyperresponsiveness

Measuring airway responsiveness to inhaled bronchoconstrictor stimuli, such as methacholine or histamine, has become an important tool in the diagnosis of asthma. This is measured by patients inhaling increasing doses or concentrations of the bronchoconstrictor stimulus until a given level of bronchoconstriction is achieved. Inhaled allergens initiate processes that increase airway inflammation and enhance airway hyperresponsiveness in asthmatic subjects. Studies using inhaled allergen challenges have provided insight into how changes in airway hyperresponsiveness are regulated by induced inflammatory processes. These changes in airway hyperresponsiveness (1-2 doubling doses) have been shown to be of much smaller magnitude than those demonstrated when asthmatics with stable airway hyperresponsiveness are compared to normals (4-8 doubling doses). These allergen-induced changes would be of little relevance in subjects with normal airway responsiveness, because they would not increase the degree of airway responsiveness into the asthmatic range. They are, however, important in asthmatics who already have airway hyperresponsiveness because they are similar to changes associated with worsening asthma control. It is likely that the mechanisms responsible for the changes in airway hyperresponsiveness following experimental allergen exposure are similar to those producing transient worsening of control in asthmatics. Nevertheless, it is unlikely that the mechanisms of the transient allergen-induced airway hyperresponsiveness will explain the underlying mechanisms of the persistent airway hyperresponsiveness in asthmatic patients when compared with normal individuals.

Allergic inflammation in upper and lower airways

OBJECTIVE

The primary reason for this review is to discuss the relationship between upper and lower airways at various levels with the emphasis on common pathophysiologic mechanisms, and how treatment of the upper airways will benefit the lower airways.

DATA SOURCES

The main source of information is derived from original articles and books, with an extensive bibliography included.

STUDY SELECTION

Studies were derived almost exclusively from articles and reviews in peer-reviewed journals.

RESULTS

The prevalence of rhinitis and asthma are both increasing. Common to both the upper and lower airways are the triggers, many of the inflammatory cells and mediators, and the treatment modalities. By contrast, there are organ-specific differences in the reaction to various stimuli in the nose or lung, with each organ manifesting its own vocabulary of response.

CONCLUSIONS

There are meaningful relationships between upper and lower airways at various levels of our understanding. Differential responses to medications help us better understand pathogenic mechanisms in rhinitis and asthma. Further, treatment of the upper airways provides additional benefit to the lower airways.

Friction in airway smooth muscle: mechanism, latch, and implications in asthma

In muscle, active force and stiffness reflect numbers of actin-myosin interactions and shortening velocity reflects their turnover rates, but the molecular basis of mechanical friction is somewhat less clear. To better characterize molecular mechanisms that govern mechanical friction, we measured the rate of mechanical energy dissipation and the rate of actomyosin ATP utilization simultaneously in activated canine airway smooth muscle subjected to small periodic stretches as occur in breathing. The amplitude of the frictional stress is proportional to eta E, where E is the tissue stiffness defined by the slope of the resulting force vs. displacement loop and eta is the hysteresivity defined by the fatness of that loop. From contractile stimulus onset, the time course of frictional stress amplitude followed a biphasic pattern that tracked that of the rate of actomyosin ATP consumption. The time course of hysteresivity, however, followed a different biphasic pattern that tracked that of shortening velocity. Taken together with an analysis of mechanical energy storage and dissipation in the cross-bridge cycle, these results indicate, first, that like shortening velocity and the rate of actomyosin ATP utilization, mechanical friction in airway smooth muscle is also governed by the rate of cross-bridge cycling; second, that changes in cycling rate associated with conversion of rapidly cycling cross bridges to slowly cycling latch bridges can be assessed from changes of hysteresivity of the force vs. displacement loop; and third, that steady-state force maintenance (latch) is a low-friction contractile state. This last finding may account for the unique inability of asthmatic patients to reverse spontaneous airways obstruction with a deep inspiration.