RUNDELL, K. W., R. L. WILBER, L. SZMEDRA, D. M. JENKINSON, L. B. MAYERS, and J. IM. Exercise-induced asthma screening of elite athletes: field versus laboratory exercise challenge. Med. Sci. Sports Exerc., Vol. 32, No. 2, pp. 309–316, 2000.
Purpose: The purpose of this study was to compare a laboratory based exercise challenge (LBC) to a field based exercise challenge (FBC) for pulmonary function test (PFT) exercise-induced asthma (EIA) screening of elite athletes.
Methods: Twenty-three elite cold weather athletes (14 men, 9 women) PFT positive for EIA (FBC screened) served as subjects. Twenty-three gender and sport matched controls (nonasthmatics) were randomly selected to establish PFT reference values for normal elite athletes. Before FBC, athletes completed a medical history questionnaire for EIA symptoms. FBC evaluations consisted of baseline spirometry, actual or simulated competition, and 5, 10, and 15 min postexercise spirometry. PFT positive athletes were evaluated in the laboratory using an exercise challenge simulating race intensity (ambient conditions: 21°C, 60% relative humidity). PFT procedures were identical to FBC.
Results: 91% of PFT positive and 48% of PFT normal athletes reported at least one symptom of EIA, with postrace cough most frequent. Baseline spirometry was the same for PFT positives and normal controls. Lower limit reference range (MN - 2 SD) of FEV1 for controls suggests that postexercise decrements of greater than ∼−7% indicate abnormal airway response in this population. Exercise time duration did not effect bronchial reactivity; 78% of FBC PFT positives were PFT normal post-LBC. Conclusion: Self-reported symptoms by elite athletes are not reliable in identifying EIA. Reference range criterion for FEV1 decrement in the elite athlete postexercise contrasts current recommended guidelines. Moreover, a large number of false negatives may occur in this population if EIA screening is performed with inadequate exercise and environmental stress.
The prevalence of exercise-induced asthma (EIA) among elite athletes has been found to be higher for cold weather athletes than for warm weather athletes. The prevalence of EIA reported for elite Finnish runners (9%) (14), the 1984 United States Summer Olympic Team (11%) (35), and the 1996 U.S. Summer Olympic Team (20%) (37) is similar to the general population (12–15%) (27,28). In contrast, 30–35% of figure skaters had postexercise pulmonary function deficits consistent with EIA (20,24), and the reported incidence of EIA in Scandinavian cross-country skiers has ranged from 14% (11) to 55% (17). We have recently observed a 23% prevalence of EIA (defined as a >10% postexercise decrement in FEV1) among 1998 Winter Olympic athletes from seven different sports (38).
Exercise at high ventilation rates in a cold, dry ambient environment has been implicated in the observed high incidence of EIA among cold weather athletes (4,6,8,10,12,23,30,31,38). The precise mechanism responsible for initiating this reaction is not well understood, but it is clear that airway cooling and/or airway drying exacerbates the condition. Other factors that may influence bronchial hyperresponsiveness include chronic exposure to poorly ventilated wax rooms in Nordic sport and exposure to high NO2 concentrations (approaching 3000 ppb) in ice arenas (18). Asthmatics experience significant increases in airway resistance with short-term NO2 exposures of 500 ppb and nonasthmatics react to 1000 ppb (7). This exposure may affect hockey players, figure skaters, and speed skaters who spend several hours a day training and competing at high ventilation rates in this environment. Whatever the precise perturbation is, the winter sport athlete is at significantly higher risk for developing EIA than the warm weather athlete.
Diagnosis and treatment of EIA by the physician is frequently based on self-reported symptoms (chest tightness, dyspnea out of proportion to the exercise intensity, coughing, wheezing, and/or excess sputum) without pulmonary function testing (11,19). While studying U.S. National Team cold weather athletes, we found that 45% pulmonary function test normal athletes (N = 87) reported symptoms and 61% of 41 pulmonary function test positive athletes (N = 41) also reported symptoms (26). The lack of statistical significance between these two groups implies that the diagnosis of EIA based on history alone is unreliable within the elite athlete population and that appropriate pulmonary function testing should accompany self-reported symptoms for accurate diagnosis.
However, pulmonary function testing of elite cold weather athletes is challenging. In some cases, athletes who are clearly symptomatic postexercise and/or exhibit performance decrements in cold conditions demonstrate normal postexercise FEV1 when exercise challenged, even in a cold environment (34). Additionally, the exercise capacity of the elite athlete may be underestimated by the clinician so that the diagnostic exercise challenge may lack the appropriate intensity or cold environment to initiate bronchoconstriction. General guidelines for EIA pulmonary function testing include an exercise challenge in ambient laboratory conditions of 6–8 min duration at an intensity of ∼85% of predicted peak heart rate (2,5,9,16,19). Personal communication with asthmatic athletes suggests that, in many cases, symptoms do not appear unless the exercise intensity approaches race pace (90–100% HRmax) and the ambient air temperature is “cold.” We believe that the exercise challenge for evaluating elite athletes for EIA should be sport and environment specific at a competitive effort intensity. We hypothesized that a “field-based” sport/intensity specific exercise challenge in a cold environment would be a more valid assessment of EIA in the elite cold weather athlete than the traditional laboratory based exercise challenge.