Indirect challenge tests: Airway hyperresponsiveness in asthma: its measurement and clinical significance

Stress-induced respiratory pattern changes in asthma

OBJECTIVES

To build upon prior research on stress-related breathing pattern changes in asthma. Previous research has considered a limited set of respiratory parameters and has remained equivocal. Emotions and stress are known to change the respiratory pattern. In asthma, certain breathing patterns have adverse effects on the airways and lead to symptom exacerbation.

METHODS

We studied respiration during resting conditions and an acute psychosocial stressor (a free speech and mental arithmetic task) in participants with asthma (n = 20) and healthy controls (n = 19). The respiratory pattern was recorded with respiratory inductance plethysmography. Partial pressure of end-tidal carbon dioxide (PCO(2)) was measured with capnometry before and after stress.

RESULTS

The overall minute ventilation was higher in asthma (mean [standard deviation] = 9.0 [4.0] L versus 6.8 [4.1] L, p < .05), but levels of the PCO(2) were comparable (34.6 [3.5] mm Hg versus 35.0 [3.7] mm Hg, p = .667) to healthy controls during prestress and poststress phases. Participants with asthma also showed a significant lengthening of inspiration, expiration, and the total respiratory cycle during stress compared with healthy controls (p < .05). During stress tasks, all participants showed marked increases in tidal volume, inspiratory flow, minute ventilation, tidal volume instability, ribcage contribution to tidal volume, and ribcage-abdominal asynchrony. A significant increase in tidal volume instability and a tendency toward lengthening of expiration and the total respiratory cycle were observed in quiet-sitting periods at prestress to poststress in asthma.

CONCLUSIONS

Expiratory lengthening and variable tidal volumes are characteristic for individuals with asthma during psychosocial stress. The function and possible association of these changes with symptom exacerbations require further study.

Cough in asthma

Asthma is one of the most common causes of chronic cough, and cough may be the sole or predominant symptom of asthma. The mechanisms of cough in asthma are complex and presumbably multi-factorial. In particular, the pathophysiologic basis of cough variant versus classic asthma is poorly understood. Recent research utilizing various inhalation challenge tests suggests that preservation of the bronchodilating and bronchoprotective effects of deep inspirations is a distinguishing feature of cough variant asthma. This review outlines the tussive agents used in cough research (including tussive and direct, indirect and combined bronchoconstrictive stimuli), their mechanisms of action, the receptors involved in eliciting cough, and characteristic responses in classic asthma and cough variant asthma.

Adenosine 5'-monophosphate challenge elicits a more peripheral airway response than methacholine challenge

Adenosine 5'-monophosphate (AMP) and methacholine are commonly used to assess airway hyperreactivity. However, it is not fully known whether the site of airway constriction primarily involved during challenges with either agent is similar. Using a ventilation distribution test, we investigated whether the constriction induced by each agent involves the lung periphery in a similar fashion. Ventilation distribution was evaluated by the phase III slope (S) of the single-breath washout, using gases with different diffusivities like helium (He) and hexafluorosulfur (SF(6)). A greater postchallenge increase in S(He) reflects alterations at the level of terminal and respiratory bronchioles, while a greater increase in S(SF6) reflects alterations in alveolar ducts, increases to an equal extent reflecting alterations in more proximal airways where gas transport is still convective for both gases. S(SF6) and S(He) were measured in 15 asthma patients before and after airway challenges (20% forced expired volume in 1-s fall) with AMP and methacholine. S(He) increased to a greater extent than S(SF6) after AMP challenge (5.7 vs. 3.7%/l; P = 0.002), with both slopes increasing to an equal extent after methacholine challenge (3.1%/l; P = 0.959). The larger increase in S(He) following AMP challenge suggests distal ventilation impairment up to the level of terminal and respiratory bronchioles. With methacholine, the similar increases in S(He) and S(SF6) suggest a less distal impairment. AMP, therefore, seems to affect more extensively the very peripheral airways, whereas methacholine seems to have an effect on less distal airways.

Mannitol as an indirect bronchoprovocation test for the 21st century

OBJECTIVES

To review mannitol challenge data and advocate the approval of this testing modality in the United States.

DATA SOURCES

A literature review was performed using the MEDLINE database for English-language articles published between January 1, 1993, and July 31, 2009, using the following keywords: mannitol bronchoprovocation test, inhaled mannitol, inhaled mannitol and asthma, and inhaled mannitol and exercise-induced asthma.

STUDY SELECTION

Trials were selected that established the effect of mannitol as a bronchoprovocation challenge, explored mannitol's mechanism of action, and compared mannitol to other accepted bronchoprovocation challenges.

RESULTS

Mannitol has demonstrated the ability to detect airway hyperreactivity in individuals. The mechanism of action is through the release of mast cell mediators. The sensitivity and specificity compare well with other indirect challenge testing methods.

CONCLUSION

Mannitol is a polyol sugar that can be converted to a powdered form and encapsulated. Once encapsulated it can be inhaled and causes narrowing of the airways in susceptible individuals. Mannitol likely triggers the release of inflammatory and/or bronchospasm mediators, causing the smooth muscle of the airway to contract and resulting in airway narrowing. The magnitude of decrease in forced expiratory volume in 1 second and the dose of mannitol needed to provoke the airway response provide a readily measurable and clinically useful assessment of airway hyperreactivity. Mannitol challenge is an accepted testing method in Australia, Europe, and Korea. Acceptance of the mannitol challenge in the United States would complement existing methods for assessing bronchial hyperreactivity and likely improve patient care.

Introduction: Airway hyperresponsiveness in asthma: its measurement and clinical significance

This supplement to CHEST, titled "Airway Hyperresponsiveness in Asthma: Its Measurement and Clinical Significance," resulted from a symposium that brought together experts from Canada, the United States, and Australia to discuss the progress in the understanding of measurements of airway hyperresponsiveness. There was an additional focus on the indirect measurement of airway inflammation and its interaction with airway hyperresponsiveness, as well as the role of measuring airway inflammation in the management of asthma.