Mannitol as a Challenge Test to Identify Exercise-induced Bronchoconstriction in Elite Athletes

Department of Allergy, Asthma, and Clinical Immunology, Alfred Hospital and Monash University, Prahran, Victoria; Department of Respiratory Medicine, Royal Prince Alfred Hospital, Camperdown; and Department of Pharmacy, University of Sydney, Sydney, New South Wales, Australia

	ABSTRACT

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Bronchial provocation tests provide objective criteria for asthma and exercise-induced bronchoconstriction (EIB) and were recommended to justify the use of inhaled ß₂-agonists by athletes at the Winter Olympics 2002. Eucapnic voluntary hyperpnea (EVH) was one test recommended to identify EIB. Provocation with EVH requires a special dry gas mixture limiting its availability. Provocation tests with osmotic aerosols require less expensive equipment that is easily portable. We assessed the sensitivity of a challenge with mannitol to identify responsiveness to EVH in 50 elite summer sport athletes who were unselected if they had respiratory symptoms. Asthma was previously diagnosed by a doctor in 27 subjects, and 21 subjects were currently under treatment for EIB or asthma. The mean predicted FEV₁ was 103.6 ± 10.8%, FVC was 99 ± 13.3%, and mean forced expiratory flow during the middle half of the FVC was 104 ± 22.7%. A total of 25 subjects were positive to EVH challenge (mean percentage of fall in FEV₁ was 25.4 ± 15% SD), and 26 subjects had a positive mannitol challenge (geometric mean [95% confidence interval] provoking dose causing a 10% fall in forced expiratory volume in one second [PD₁₀] was 202 mg [134, 300], with 24 of the subjects positive to both challenges). Mannitol had a sensitivity of 96% and specificity of 92% to identify a positive response to EVH and, as such, could be used as an alternative to EVH to identify EIB.

　

Key Words: athletes • exercise • asthma • osmotic aerosol • hyperpnea

Exercise-induced bronchoconstriction (EIB), defined as a transient increase in airway resistance that occurs after vigorous exercise (1), is now being reported commonly in elite athletes (2). Athletes at the 2002 Olympic Games in Salt Lake City were required to provide objective evidence of asthma or EIB to justify the use of an inhaled ß₂-adrenoceptor agonist before an event (3). This requirement encourages the need for reliable tests to identify EIB in elite athletes. Although pharmacologic challenges are used to assist the diagnosis of asthma (4), they have been shown to be suboptimal for identifying EIB in population studies (5, 6). Exercise challenges, although specific for identifying EIB, have a low sensitivity in identifying EIB when performed in the laboratory in elite or well-conditioned athletes (7). Sport-specific exercise in the field is limited with respect to the standardization of both the workload and the environmental conditions of temperature and humidity (7). To overcome some of these problems, the eucapnic voluntary hyperpnea (EVH) challenge with dry air (8–10) has been used and recommended to assess EIB in elite athletes (3, 11).

Osmotic challenges with hypertonic saline (12–14) and mannitol (15) have been used as alternative surrogate tests to identify EIB in individuals with clinically recognized asthma (15). Relative to exercise and EVH, the osmotic challenges require less complex and expensive equipment. The mannitol challenge, in particular, has a potential to be used in field, clinic, and laboratory environments to identify EIB in elite athletes. Subjects with currently active asthma who are responsive to hypertonic saline are also responsive to mannitol (16). As with the hypertonic (4.5%) saline challenge (13, 17), a positive response to mannitol has been shown to identify individuals with asthma with EIB (15) and to have good repeatability (16). The role played by osmotic challenge tests in the detection of EIB in elite athletes is yet to be defined.

We have recently shown in a group of elite summer sport athletes that methacholine responsiveness does not predict responsiveness to EVH challenge (18). For the same group of athletes, taking the response to EVH challenge as the "gold standard" for identifying EIB, in this study we report the sensitivity and the specificity of an osmotic challenge using a dry powder of mannitol to identify athletes who are responsive to EVH.

	METHODS

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Subjects
Fifty elite athletes were recruited from sports medicine centers and sporting teams throughout Melbourne, Australia. The subjects were unselected if they had previous respiratory problems or a doctor diagnosis of asthma. The subjects were asked to refrain from both coffee and exercise on the day of testing and to withhold their pulmonary medications for the appropriate time.

Study Design
Each subject visited the Alfred Hospital twice; the visits were separated by more than 1 day but less than 1 week. The mannitol and EVH challenge tests were performed in random order.

Spirometry
A baseline FEV₁ was measured twice before the challenge, and where the value differed by more than 200 ml, a third measurement was taken. The values are expressed as percentage of the predicted normal (19). On completion of the challenges, 200 µg of salbutamol was administered.

Mannitol Challenge Test
The subjects performed the mannitol challenge test according to the protocol of Anderson and coworkers (16) using a single dose Inhalator (Boehringer Ingelheim, Ingelheim, Germany). The dose protocol consisted of 0 (empty capsule acting as a placebo), 5, 10, 20, 40, 80, 160, 160, and 160 mg mannitol, resulting in a maximum cumulative dose of 635 mg. The 80- and 160-mg doses were given in multiples of 40-mg capsules. Two FEV₁ maneuvers were performed 60 seconds after each dose, and the highest FEV₁ measurement was recorded. If the subject had a decrease in FEV₁ of greater than 10% in response to a dose, then the same dose was repeated. The challenge was stopped when a 20% decrease in FEV₁ was measured or when a total cumulative dose of 635 mg had been administered.

The provoking dose of mannitol required to induce a 10% and 15% fall in FEV₁ (PD₁₀ and PD₁₅) was calculated. The FEV₁ used to calculate the percentage of fall was the one recorded after the 0-mg capsule.

Eucapnic Voluntary Hyperpnea Challenge Test
The protocol used in the performance of the EVH challenge was based on that of Argyros and coworkers (20). This involves a single level of ventilation with a target of 30 x FEV₁. This target rate is equivalent to 85% of maximum voluntary ventilation, calculated as 35 x FEV₁ (21). A fall in FEV₁ of 10% or more defines an abnormal response (9). The subjects inhaled dry gas containing 4.9% CO₂, 21% O₂, and balance N₂ at room temperature, at 85% maximal voluntary ventilation (MVV) for a total duration of 6 minutes. FEV₁ was measured 1, 3, 5, 7, and 10 minutes after challenge. The ventilation was expressed in liters per minute BTPS and as a percentage of MVV. (See online supplement for additional details on the method used.)

Statistical Analysis
Data are presented as mean ± SD or as geometric mean (GM) and 95% confidence intervals (CI). Comparisons of the fall in FEV₁ between groups of subjects after the EVH and mannitol challenge tests were performed using the Wilcoxon Rank Sum test. Regression coefficients (Pearson's r_p and Spearman's r_s) were used to assess the association between responses to the mannitol and EVH challenges. A statistical package (SPSS Version 10 for Windows; SPSS Inc., Chicago, IL) was used for these calculations (22).

	RESULTS

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Subjects
All the 50 athletes recruited (15 male, 35 female; median age 21; range 16–42 years) completed the mannitol and EVH challenge tests. (See online supplement for additional details on individual results.) The FEV₁ for each subject was within normal limits (> 80% predicted normal value). The mean predicted FEV₁ was 103.6 ± 10.8%, FVC was 99 ± 13.3%, and mean forced expiratory flow during the middle half of the FVC was 104 ± 22.7%.

Asthma was previously diagnosed by a doctor in 27 subjects, and 21 subjects were currently under treatment for EIB or asthma. Of the 21 subjects on medication, all of whom were using ß₂-agonists either regularly or on an as required basis, 13 were on additional prophylactic medication—5 were using regular inhaled corticosteroids alone, 4 were only using a cromolyn before exercise (either nedocromil sodium or sodium cromoglycate), and 4 were using a combination of both.

Comparison between Mannitol and EVH Challenge Tests
Twenty-five of the subjects (50%) had a positive EVH challenge test with a mean fall in FEV₁ of 25.4 ± 15%, in contrast to 3 ± 2% in those who had a negative EVH test. The mean ventilation rate achieved by the 50 subjects was 126.8 ± 21.9 L/minute, which represented 93.8 ± 4.7% of predicted MVV.

A total of 26 of the 50 subjects recorded a 10% or more fall in FEV₁ after inhaling up to 635 mg of mannitol  . The geometric mean (95% CI) value for PD₁₀ was 202 mg (134, 300). The mean maximum percentage of fall in FEV₁ in subjects who did not achieve a 10% fall after inhaling 635 mg was 1.9 ± 2.3%. There was one subject positive to EVH (percentage of fall in FEV₁ was 11.3%) who did not achieve a 10% fall after inhalation of 635 mg of mannitol.

fig.ommitted   Figure 1. The provoking dose (mg) of mannitol required to induce a 10% fall in FEV1 (PD10 FEV1) in relation to the response to eucapnic voluntary hyperpnea in the 26 subjects who were responsive to mannitol.

 
Using the EVH challenge as the gold standard diagnostic test for EIB in this study, the mannitol challenge test PD₁₀ has a sensitivity of 96%, a specificity of 92%, a positive predictive value of 92%, and a negative predictive value of 96%.

Of the 26 subjects recording a PD₁₀ to the mannitol, 24 achieved a fall of 10% or more on the EVH challenge; the geometric mean (95% CI) PD₁₀ was 199 mg (129, 308), and the mean percentage of fall in FEV₁ was 25.9 ± 15% after the EVH challenge. In this group of 24 subjects there was a significant association (p < 0.01) between the PD₁₀ and the percentage of fall in EVH (r_p = -0.61, r_s = -0.70). The kappa coefficient relating the response to the inhaled mannitol and EVH challenge tests was 0.80, indicating a high correlation between the two challenge tests.

Twenty-one of the subjects achieved a fall in FEV₁ greater than 15%, the geometric mean (95% CI) PD₁₅ in this group being 269 mg (190, 380). Nineteen subjects achieved both a PD₁₅ to the mannitol challenge and a positive EVH challenge, the geometric mean (95% CI) PD₁₅ to the mannitol challenge was 262 mg (178, 384), and the mean fall in FEV₁ after the EVH challenge was 28.3 ± 15.4% (r_p = -0.501, r_s = -0.465).

Responses in Subjects Taking Medication for EIB and in Subjects Previously Diagnosed with Asthma by a Doctor
A total of 15 of the 21 subjects taking medication for asthma or EIB had a 10% or more fall in FEV₁ to challenge with EVH (mean fall in FEV₁ of 27.9 ± 16.3%), whereas 17 had a PD₁₀ to mannitol (GM 95% CI, PD₁₀ was 212 mg [125, 260]). Among the 29 subjects not taking any medication, 10 had a positive EVH challenge (mean fall in FEV₁ was 21.6 ± 12.4%) and 9 subjects recorded a geometric mean (95% CI) PD₁₀ to mannitol of 181 mg (86, 381).

Of the 27 subjects with a previous clinical diagnosis of asthma, 18 had a positive EVH challenge test, with a mean percentage of fall in FEV₁ of 29.6 ± 15.6%, compared with 6 ± 6.1% in the 23 subjects who had a negative EVH test. A total of 20 of the 27 subjects with a previous diagnosis of asthma recorded a geometric mean (95% CI) PD₁₀ to mannitol of 178 mg (109, 290), and 16 of these recorded a PD₁₅ of 241 mg (159, 376). Of the 23 subjects without a previous diagnosis of asthma, 6 had a PD₁₀ and 5 a PD₁₅ to mannitol, the geometric mean (95% CI) PD₁₀ to mannitol being 303 mg (148, 622) and PD₁₅ being 422 mg (228, 781).

	DISCUSSION

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To our knowledge, this study is the first to compare the response to an osmotic challenge with that to the dry air hyperpnea challenge in elite summer athletes. Using the EVH challenge as the gold standard for EIB, the mannitol PD₁₀ had a sensitivity of 96% in identifying athletes who were positive to EVH, with a specificity of 92%, a positive predictive value of 92%, and a negative predictive value of 96%.

The results demonstrate that in this group of athletes, there is a strong association between the response to a challenge with dry powder mannitol and that to the EVH challenge. Both the EVH and mannitol challenge tests were well tolerated by all subjects, and the bronchoconstriction provoked by these challenges was rapidly reversed in all subjects by the inhalation of 200 µg of salbutamol.

In this study, we chose to use the response to the EVH challenge, identified by the International Olympic Committee (IOC) as the optimal laboratory-based challenge for the identification of EIB (3), as the gold standard for the diagnosis of EIB. The protocol used in this study required the subject to perform hyperpnea by inhaling dry air containing 5% CO₂ at room temperature for 6 minutes at a ventilation equivalent to 30 x baseline FEV₁ (23, 11). For EVH, a threshold of 10% or greater change in FEV₁ has a specificity of 90% and a 15% or more change a 100% specificity for identifying athletes with active asthma (9). A change in FEV₁ of 10% or more is considered abnormal (9). The symptoms provoked by EVH are very similar to those that occur after exercise. The major advantage in using EVH over exercise to provoke bronchoconstriction is the ability of the subject to reliably achieve and sustain a ventilation that is higher than that which could be obtained after exercise. In this study, the athletes achieved a ventilation rate that was in excess of the target and was 93.8% of their predicted MVV, a value significantly higher than that normally achieved at maximal exercise (24).

In clinically recognized individuals with asthma, the airway response to an osmotic challenge with either a wet aerosol of 4.5% saline or a dry powder aerosol of mannitol compares well with the response to exercise and EVH (14, 15), and either test can be used as a surrogate for exercise to identify those with EIB (12, 13). In contrast to the protocols for testing with exercise and EVH, in which a single load stimulus is applied to obtain a single airway response, the osmotic challenges are given in progressively increasing doses, with the airway response measured after each dose. Such a progressive protocol increases the relative safety of these challenges and this, in conjunction with the portability of the equipment used, suggests that the osmotic challenges could be used at the point of need in an office-based practice.

To be consistent in comparing the airway response to mannitol with that to EVH we used the dose of mannitol required to provoke a 10% fall in FEV₁. In another study investigating clinically recognized asthmatic subjects, a 15% fall in response to mannitol was compared with a 15% fall in response to 4.5% saline (16). In that study (16), the mean maximum percentage of fall in FEV₁ in healthy subjects was 3.03 ± 1.49% after a cumulative dose of 635 mg of mannitol. A similar value (3.1% ± 2.9) was found in healthy children (25). On the basis of these published findings and the cutoff value of 10% for exercise (26) and EVH (9), we used 10% as the cutoff point for a positive response to mannitol in this group of subjects with normal lung function. The mean value for FEV₁ in this group of subjects with good lung function was 3.93 ± 0.67 L, such that a 10% fall represents a reduction of 390 ml or more. The selection of 10% for mannitol is also supported by the finding of a mean percentage of fall in FEV₁ of 1.9% ± 2.3 (SD) in those not achieving a 10% fall in FEV₁ to mannitol.

Twenty-one subjects achieved a 15% fall in FEV₁ after mannitol challenge, and the geometric mean (95% CI) PD₁₅ was 268 mg (190, 380). On the basis of previous studies, this degree of bronchial hyper-responsiveness would be considered to be consistent with a diagnosis of currently active asthma and would be expected to normalize in response to acute administration of nedocromil sodium (27) or chronic administration of inhaled steroids (28). A total of 16 of the 21 subjects had a PD₁₅ in the range of mild bronchial hyperresponsiveness (PD₁₅ > 155 mg). It is still not known whether such bronchial hyperresponsiveness would be present in these subjects in the absence of high cumulative levels of physical activity. The elevated levels of ventilation may result in airway injury, with subsequent airway inflammation occurring as a result of the inhalation of large volumes of air, allergens, and pollutants during training and competition.

We conclude that the response to mannitol is both sensitive and specific for identifying responses to EVH in elite summer sport athletes with very good lung function. Should the mannitol challenge test become more widely available, it could be used in the field or in clinics to identify elite athletes with potential for EIB.

	Acknowledgments

 
The use for mannitol described in this study is covered in the United States of America by Patent No. 5,817,028 and internationally by PCT/AU95000086. The patent is owned by the Central Sydney Area Health Service and has been licensed to Pharmaxis Pty Ltd., ACT, Australia.

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