Effect of deep inspiration on airway caliber in children with asthma

The lower respiratory airway wall in children in health and disease

Alone or in association with other lung or thorax component disorders, the airway wall (AWW) remains one of the most frequently involved elements in paediatric lung diseases. A myriad of AWW disorders will present with similar symptomatology. It is thus important for the clinician to reappraise the normal development and structure of the AWW to better understand the underlying disease patterns. We herein provide an overview of the structure of the AWW and a description of its development from the fetal period to adulthood. We also detail the most common AWW changes observed in several acute and chronic respiratory disorders as well as after cigarette smoke or chronic pollution exposure. We then describe the relationship between the AWW structure and lung function. In addition, we present the different ways of investigating the AWW structure, from biopsies and histological analyses to the most recent noninvasive airway (AW) imaging techniques. Understanding the pathophysiological processes involved in an individual patient will lead to the judicious choice of nonspecific or specific personalised treatments, in order to prevent irreversible AW damage.

Use of specific airway resistance to assess bronchodilator response in children

BACKGROUND AND OBJECTIVE

Changes in specific airway resistance (ΔsRaw) after bronchodilation, as measured by plethysmography and FEV(1) , are frequently considered to be interchangeable indices of airway obstruction. However, the baseline relationship between these two indices is weak, and the value of ΔsRaw that best predicts FEV(1) reversibility in children has yet to be determined. The aim of this study was (i) to establish the sRaw cut-off value that best distinguishes between positive and negative bronchodilator responses, as measured by FEV(1) reversibility; (ii) to determine whether the discrepancy between ΔsRaw and ΔFEV(1) might be explained by independent correlations between ΔFEV(1) and both ΔsRaw (mainly airway obstruction) and ΔFVC (airway closure); and (iii) to assess the effect of height and age on the relationship between ΔsRaw and ΔFEV(1) .

METHODS

A retrospective study was performed in 481 children (median age 10.5years, range 6.1-17.6) with actual or suspected asthma, for whom sRaw and spirometry data were obtained at baseline and after administration of a bronchodilator.

RESULTS

The sRaw cut-off value that best predicted FEV(1) reversibility was a 42% decrease from baseline (P=0.0001, area under the curve 0.70, sensitivity 55%, specificity 77%) and was independent of height and age. Changes in FEV(1) were significantly but independently related to ΔsRaw and ΔFVC (index of air trapping) (r=0.40, P<0.0001 and r=0.39, P<0.0001, respectively).

CONCLUSIONS

A 42% decrease in sRaw predicted FEV(1) reversibility reasonably well, whereas a smaller decrease in sRaw failed to detect approximately one out of two positive responses detected by FEV(1) , with no influence of height or age.

Effects of exercise training and montelukast in children with mild asthma

PURPOSE

Data from the general population suggest that habitual exercise decreases bronchial responsiveness, but the possible role of exercise in asthmatics is undefined. The leukotriene receptor antagonist montelukast decreases bronchial responsiveness and exercise-induced symptoms in asthmatic children. This randomized study in children with mild asthma evaluated the combined effects of aerobic training for 12 wk and montelukast or placebo on bronchial responsiveness (BHR) to methacholine, exercise-induced bronchoconstriction (EIB), inflammatory markers in exhaled breath condensate (EBC), and asthma exacerbations.

METHODS

Fifty children (mean age +/- SD: 10.2 +/- 2.4 yr) with mild stable asthma were randomly assigned to placebo (N = 25) or montelukast (N = 25). Before and after training, we assessed BHR and EIB and markers of airway inflammation-that is, exhaled nitric oxide (eNO), pH, and cysteinyl-leukotriene concentration-in EBC.

RESULTS

Training increased maximal workload and peak minute ventilation. After training, the methacholine dose causing a 20% fall in FEV1 (PD20) increased in both groups. A decreased slope of FEV1 decline at increasing methacholine dose was found only in montelukast-treated children. EIB prevalence halved after training in both groups (EIB + children, placebo group: 10 pretraining, 4 posttraining; EIB + children, montelukast group: 8 pretraining, 5 posttraining; P < 0.05 by chi on all children). Resting eNO was unaffected, whereas the pH of EBC decreased after training in both groups. Cysteinyl-leukotriene concentrations were low in most children at both times. During training, montelukast-treated children showed fewer asthma exacerbations compared with the same period of the previous year.

CONCLUSIONS

In children with mild stable asthma, exercise training decreased bronchial responsiveness to methacholine. Montelukast also decreased bronchial reactivity (FEV1 slope) and protected against exacerbations, suggesting a beneficial synergistic action of these two interventions in mild asthma.

Post-exercise airway narrowing in healthy primary school children

Changes in lung function after exercise in healthy primary school children have mostly been described in field studies. More complete description and insight into relevant mechanisms may be provided in lung function laboratory. The aim was to describe airway caliber and response to deep inhalation (DI) after exercise in healthy primary school children. Respiratory resistance (Rrs) by the forced oscillation technique and spirometry were measured before and after exercise in 50 healthy primary school children. The Rrs response to DI was assessed in 31 subjects, assuming a significantly larger decrease in Rrs after exercise would attest relief of exercise-induced airway smooth muscle contraction. Measurements were taken before, 5 min (E5) and 15 min (E15) after exercise. Significantly larger Rrs and lower forced expiratory volume in 0.5 s were observed at E5 versus baseline or E15 (p < 0.05). DI induced significant decrease in Rrs (p = 0.01) that was not different between E5 and baseline. Healthy primary school children exhibit changes in Rrs and spirometry after exercise indicating small but significant airway narrowing. The response to DI similar at baseline and E5 suggests airway narrowing from hyperemia in the bronchial wall rather than airway smooth muscle constriction.

Impulse oscillometry is sensitive to bronchoconstriction after eucapnic voluntary hyperventilation or exercise

Airway responses were compared following 6-minute eucapnic voluntary hyperventilation and 6-minute exercise challenges by examining resting and post-challenge impulse oscillometry and spirometry variables. Twenty-two physically active individuals with probable exercise-induced bronchoconstriction took part in this study. Impulse oscillometry and spirometry were performed at baseline and for 20 minutes post-challenge at 5-minute intervals. High correlation was found between the two measures of change in airway function for both methods of challenge. Impulse oscillometry detected a difference in degree of response to the challenges, whereas spirometry indicated no difference, suggesting that impulse oscillometry is a more sensitive measure of change in airway function.

[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.

Deep inspiration-induced changes in lung volume decrease with severity of asthma

We have previously reported that the magnitude of deep inspiration (DI)-induced bronchodilation is only slightly reduced in mild asthmatics, compared to healthy subjects. The aim of this study was to evaluate whether increased severity of asthma is associated with impairment in the ability of DI to induce changes in lung volume. Thirty-six consecutive asthmatics recruited from the Pulmonary and the Allergy Outpatient Clinics of the Institute of Respiratory Diseases of the University of Palermo were divided into 3 groups: Intermittent (I), Mild Persistent (MP) and Moderate-Severe (MS), based on GINA guidelines. Single dose methacholine (Mch) bronchoprovocations were performed in the absence of DI, to induce at least 15% reduction in inspiratory vital capacity (IVC) from baseline. The post-Mch IVC was followed by 4 consecutive DI and by another IVC, to determine the bronchodilatory effect of DI. The bronchodilatory effect of DI was found to significantly decrease with increasing severity of asthma (I: 68+/-5.4%, MP: 45+/-7.2%, MS: 4+/-15.6%; ANOVA: P<0.0001). Bronchodilation by DI, but not FEV(1) or FEV(1)/FVC, was also inversely correlated to symptom scores (r=-0.42, P=0.01) and to weekly salbutamol usage (r=-0.47, P=0.004). These observations provide support to the hypothesis that the attenuation of the bronchodilatory effect of DI contributes to the severity of the clinical manifestations of asthma.

Airway Narrowing Measured by Spirometry and Impulse Oscillometry Following Room Temperature and Cold Temperature Exercise

STUDY OBJECTIVE

The efficacy of using impulse oscillometry (IOS) as an indirect measure of airflow obstruction compared to spirometry after exercise challenges in the evaluation of exercise-induced bronchoconstriction (EIB) has not been fully appreciated. The objective was to compare airway responses following room temperature and cold temperature exercise challenges, and to compare whether IOS variables relate to spirometry variables.

DESIGN

Spirometry and IOS were performed at baseline and for 20 min after challenge at 5-min intervals.

SETTING

Two 6-min exercise challenges, inhaling either room temperature (22.0 degrees C) or cold temperature (- 1 degrees C) dry medical-grade bottled air. At least 48 h was observed between these randomly assigned challenges.

PARTICIPANTS

Twenty-two physically active individuals (12 women and 10 men) with probable EIB.

INTERVENTIONS

Subjects performed 6 min of stationary cycle ergometry while breathing either cold or room temperature medical-grade dry bottled air. Subjects were instructed to exercise at the highest intensity sustainable for the duration of the challenge. Heart rate and kilojoules of work performed were documented to verify exercise intensity.

MEASUREMENTS AND RESULTS

Strong correlations were observed within testing modalities for post-room temperature and post-cold temperature exercise spirometry and IOS values. Spirometry revealed no differences in postexercise peak falls in lung function between conditions; however, IOS identified significant differences in respiratory resistance (p < 0.05), with room temperature-inspired air being more potent than cold temperature-inspired air.

CONCLUSIONS

Correlations were found between spirometric and IOS measures of change in airway function for both exercise challenges, indicating close equivalency of the methods. The challenges appeared to elicit the EIB response by a similar mechanism of water loss, and cold temperature did not have an additive effect. IOS detected a difference in degree of response between the temperatures, whereas spirometry indicated no difference, suggesting that IOS is a more sensitive measure of change in airway function.

Length oscillation induces force potentiation in infant guinea pig airway smooth muscle

Deep inspiration counteracts bronchospasm in normal subjects but triggers further bronchoconstriction in hyperresponsive airways. Although the exact mechanisms for this contrary response by normal and hyperresponsive airways are unclear, it has been suggested that the phenomenon is related to changes in force-generating ability of airway smooth muscle after mechanical oscillation. It is known that healthy immature airways of both humans and animals exhibit hyperresponsiveness. We hypothesize that the profile of active force generation after mechanical oscillation changes with maturation and that this change contributes to the expression of airway hyperresponsiveness in juveniles. We examined the effect of an acute sinusoidal length oscillation on the force-generating ability of tracheal smooth muscle from 1 wk, 3 wk, and 2- to 3-mo-old guinea pigs. We found that the length oscillation produced 15-20% initial reduction in active force equally in all age groups. This was followed by a force recovery profile that displayed striking maturation-specific features. Unique to tracheal strips from 1-wk-old animals, active force potentiated beyond the maximal force generated before oscillation. We also found that actin polymerization was required in force recovery and that prostanoids contributed to the maturation-specific force potentiation in immature airway smooth muscle. Our results suggest a potentiated mechanosensitive contractile property of hyperresponsive airway smooth muscle. This can account for further bronchoconstriction triggered by deep inspiration in hyperresponsive airways.