Asthma diagnosis and treatmentThe bronchoprotective effect of inhaling methacholine by using total lung capacity inspirations has a marked influence on the interpretation of the test result
Section snippets
Deep inhalations and bronchoprotection
Maximal lung inflation, as achieved by taking deep inhalations, to total lung capacity (TLC) has long been known to be both a bronchodilator4 and a bronchoprotector.5, 6 The bronchoprotective effect in healthy subjects is quite potent, and it has been hypothesized that its loss might be one of the fundamental mechanisms underlying the development of asthma.6 Some have stated that bronchoprotection does not occur in asthma.5 However, significant bronchoprotection does occur in some subjects with
Methacholine methods
There are many published methods for the performance of methacholine challenges. Recently, the American Thoracic Society (ATS) published methods for 2 of the commonly used techniques: the 2-minute tidal breathing method and the 5-breath dosimeter method.3 The methodology outlined is identical for both methods, with the exception of the methods of aerosol generation and inhalation. The 2-minute tidal breathing method12 was modified from an earlier Dutch 30-second tidal breathing method.13
Methods comparisons
Before the publication of the methacholine comparison study noted above,19 we undertook a larger study to compare the 2 ATS methods in subjects with asthma. The major rationale behind this undertaking was to confirm whether the 2 methods did indeed produce identical results when there was at least some theoretical reason to suspect the possibility of nonidentity. We expected that if the 2 methods were not identical, the differences should be uniform across the range of airway responsiveness.
Our
The problem
This issue raises a major concern in the interpretation of methacholine challenge test results. The 2 methods as outlined by the ATS do not produce equivalent results. The lack of equivalency, however, is not uniform throughout the range of AHR but is limited to subjects with borderline-to-mild AHR, precisely the range in which most positive diagnostic methacholine challenge results will fall. In our opinion the dosimeter method as performed by using standard (ATS) criteria produces an
Recommendation
We would make a strong recommendation that diagnostic methacholine challenges should be done with an inhalation method that does not involve TLC inhalations. The tidal breathing method is easy, inexpensive, and reproducible and excellent for untrained subjects. A modified dosimeter method with sub-TLC inhalations21 would also suffice.
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Bronchoprovocation Testing in Asthma: An Update
2018, Immunology and Allergy Clinics of North AmericaBronchoprotective effect of deep inspirations in cough variant asthma: A distinguishing feature in the spectrum of airway disease?
2018, Respiratory Physiology and NeurobiologyGuidelines for methacholine provocation testing
2018, Revue des Maladies RespiratoiresTraumatic Spinal Cord Injury: Pulmonary Physiologic Principles and Management
2018, Clinics in Chest MedicineCitation Excerpt :Responders to histamine demonstrated reduction in surrogate spirometric indices of airway size and airway size relative to lung size.80 Similar to the bronchodilator studies, one explanation for these findings would be preexisting airway narrowing, in that findings of a further small reduction in airway caliber induced by a bronchoconstrictive agent would produce a large increase in resistance, because airway resistance is inversely proportional to the fourth power of the radius.81 Support came from further studies demonstrating the ability of: (1) pretreatment with ipratropium bromide to attenuate hyperresponsiveness to ultrasonically nebulized distilled water; (2) pretreatment with baclofen and oxybutynin chloride, both with anticholinergic properties, to inhibit methacholine hyperresponsiveness; and (3) pretreatment with metaproterenol to attenuate methacholine and histamine-induced hyperresonsiveness.76,79,82,83
Disclosure of potential conflict of interest: D. Cockcroft is on the advisory board of Methapharm, Merck, AstraZeneca, and Novartis; has received grants from Methapharm, IVAX, BI, Topigen, Merck, and AstraZeneca; and is on the speakers' bureau for Merck, GlaxoSmithKline, and AstraZeneca. B. E. Davis has declared that she has no conflict of interest.