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Chief of the Pulmonary and Critical Care Medicine Service, Walter Reed Army Medical Center.
Correspondence to: COL Arn H. Eliasson, MC, USA, FCCP, US Army, Pulmonary and Critical Care Medicine Service, Walter Reed Army Medical Center, Washington, DC 20307-5001
In this issue of CHEST, (see page 649) Mannix and colleagues report their findings from bronchoprovocation testing in a group of competitive figure skaters. This report raises issues that deserve further comment.
First, the study illustrates important difficulties with bronchoprovocation testing. The authors identified 16 of 29 skaters (55%) who could be provoked by either on-ice exercise or eucapnic voluntary hyperventilation (EVH).1 Only five of those with a positive response were provoked by both tests, and one skater with known asthma failed to be provoked by either test. Furthermore, EVH was shown to be a more potent stimulus of bronchospasm than on-ice exercise. This finding raises the question of what to do about those skaters who respond to EVH but who do not respond with pulmonary function test (PFT) changes to the stimulus of immediate importance, their skating routine. It would be improper to label these skaters as having exercise-induced asthma or to treat these asymptomatic skaters. How can this disparate information be interpreted?
What we need is an uncomplicated test that distinguishes patients who have asthma from those whose symptoms are due to other causes. Such a test does not exist. None of the currently available modes of bronchoprovocation reliably identifies all clinically verified asthmatics. In addition, all bronchoprovocation tests will at times be falsely positive in normal people.2 Asthma is a clinical syndrome with characteristic signs and symptoms and the hallmark of airway hyperreactivity.3 The problem arises in accurately demonstrating airway hyperreactivity with bronchoprovocation. Clearly it is a worthwhile endeavor to clarify these issues with further study. It would be enormously useful to have an inexpensive, safe, and accessible test that is both sensitive and specific for asthma. The test would be especially useful if it did not require a high degree of cooperation or effort from the study subject, as is currently the case with the necessary PFT maneuvers prechallenge and postchallenge. Such a test would find immediate utility in the clinical evaluation of dyspnea, cough, and chest discomfort. The test would also be extremely valuable in disability evaluations and for induction evaluations in the military.4 ,5 ,6 By all means, research in bronchoprovocation methods should be encouraged.
A second issue brought to attention by the paper by Mannix and colleagues is the implication it has for the pathophysiology of airway hyperreactivity. One theory uses the rationale that airway cooling and rewarming is the underlying mechanism for airway hyperreactivity.7 This theory is appealing because of both the common observation that asthma worsens with cold weather and the high prevalence of airway reactivity in athletes engaged in winter sports.8 ,9 But, why did Mannix and colleagues find that on-ice skating is less effective as a bronchoprovocation tool than hyperventilation of ambient temperature dry gas? Perhaps exercise with release of catecholamines blunts the response to bronchoprovocation. Or perhaps it is airway drying rather than airway cooling and rewarming that is the important stimulus. As airway drying occurs, water from endobronchial cells shifts and may cause intracellular osmotic changes that provoke the bronchospastic response.10 This theory is bolstered by evidence that osmotically active agents such as mannitol11 and sodium chloride12 ,13 can provoke bronchospasm while inhaled furosemide can blunt responses.14 ,15 Furthermore, an elegant study by Argyros and colleagues16 demonstrated that varying levels of water loss and not heat flux correlated with the degree of bronchospastic response. When it comes to bronchoprovocation in pulmonary disease, one should not say, "cool your jets." Rather, the expression should be, "dry up and blow away!"
Footnotes
The views expressed herein are those of the author and do not purport to reflect the views of the US Army or the Department of Defense.
References
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