Inspiratory Stridor in Elite Athletes*

Inspiratory Stridor in Elite Athletes* Kenneth W. Rundell, PhD; and Barry A. Spiering, MS

Study objectives: Diagnosis and medical intervention for exercise-induced bronchospasm (EIB) are often based on self-reported symptoms, without spirometric confirmation. Inspiratory stridor (IS), a symptom of vocal cord dysfunction (VCD), is frequently mistaken for EIB wheeze. Athletes with exercise IS that spontaneously resolves on activity cessation are suspect for VCD and may not have EIB. This study estimated IS prevalence in elite athletes and determined its relationship to EIB. Subjects/methods: Three hundred seventy athletes (174 female and 196 male subjects) provided a medical history, and underwent spirometry before and after exercise challenge. Exercise challenges were conducted in cold, dry ambient conditions. EIB positive (EIB ⴙ) was defined as a > 10% postexercise fall in FEV1. Athletes were monitored for IS during exercise; 78.4% of the athletes in this study (n ⴝ 290) were tested on multiple occasions. Results: EIB was identified in 30% of 370 athletes tested (58 female and 53 male subjects). IS was observed in 5.1% (18 female and 1 male subjects) during exercise and spontaneously resolved in these subjects within 5 min after exercise cessation. Ten IS-positive (IS ⴙ) athletes (52.6%) were EIB ⴙ, and 8 of these athletes had a previous EIB diagnosis; however, ␤2-agonist treatment resolved IS in only 2 subjects. Eight of nine IS ⴙ/EIB-negative (EIB ⴚ) athletes had a previous EIB diagnosis; seven subjects received ␤2-agonist treatment with no IS resolution. Resting spirometric measurements did not distinguish IS, but postexercise mid-flow (FEF50/FIF50) ratio > 1.5 was more frequent (33%, p < 0.05) among IS ⴙ athletes. The FEF50/FIF50 ratio was higher for IS ⴙ/EIB ⴙ athletes than for IS ⴚ/EIB ⴙ athletes (1.97 ⴞ 1.69 vs 0.81 ⴞ 0.39, p < 0.05). The postexercise fall in FVC was greater (p < 0.05) for IS ⴙ/EIB ⴚ athletes (9.2 ⴞ 5.0%) than for IS-negative (IS ⴚ) /EIB ⴚ athletes (5.3 ⴞ 4.3%). No difference in postexercise FEV1 was identified between IS ⴙ and IS ⴚ athletes (within EIB ⴙ or EIB ⴚ groups). Conclusions: Five percent of athletes were IS ⴙ, with EIB comorbidity observed in 53% of these subjects. Misdiagnosis of IS as EIB is common. The lack of a ␤2-agonist response in combination with postexercise serial spirometry can be useful in excluding solitary IS and confirming EIB diagnosis. (CHEST 2003; 123:468 – 474) Key words: asthma; ␤2-agonist; bronchial provocation; exercise-induced bronchospasm; spirometry; sport; vocal cord dysfunction Abbreviations: EIB ⫽ exercise-induced bronchospasm; EIB ⫺ ⫽ exercise-induced bronchospasm negative; EIB ⫹ ⫽ exercise-induced bronchospasm positive; FEF25–75% ⫽ forced expiratory flow between 25% and 75% of FVC; FEF50 ⫽ forced expiratory flow at 50% of FVC; FEF50/FIF50 ⫽ postexercise mid-flow; FIF50 ⫽ forced inspiratory flow at 50% of FVC; IS ⫽ inspiratory stridor; IS ⫺ ⫽ inspiratory stridor negative; IS ⫹ ⫽ inspiratroy stridor positive; PEF ⫽ peak expiratory flow; PFT ⫽ pulmonary function test; VCD ⫽ vocal cord dysfunction

stridor (IS) is a condition characterized I nspiratory by high-pitched inspiratory noise that is often mistaken for the wheeze of asthma.1– 8 It typically occurs during exercise and spontaneously resolves *From the United States Olympic Committee, Lake Placid, NY. This study was supported by the United States Olympic Committee. The views, opinions, and findings contained in this report are those of the authors and should not be construed as an official United States Olympic Committee position. Manuscript received April 4, 2002; revision accepted June 11, 2002. Correspondence to: Kenneth W. Rundell, PhD, Human Performance Laboratory, Marywood University, 2300 Adams Ave, Scranton, PA 18509-1598; e-mail: [email protected] 468

within 5 min after exercise stops. The presence of IS is highly associated with vocal cord dysfunction (VCD), the paradoxical closure of the vocal cords during inspiration, or less commonly, during exhalation as well.9 Adduction of the vocal cords during inspiration at high exercise ventilation rates produces a pronounced and often loud stridor.1,5,7,9 –11 Although IS is frequently mistaken for exerciseinduced bronchospasm (EIB) because of the similar wheeze, numerous differences exist between the conditions.11 IS predominates during inhalation and originates in the neck region; the asthmatic wheeze occurs primarily during exhalation and is more chest than neck dominated.5,12 A sense of chest tightness is Clinical Investigations

characteristic of asthma and EIB,12–14 while a feeling of throat tightness predominates in IS.1,9,10 Additionally, patients with asthma or EIB are especially susceptible to nighttime symptoms, but no circadian pattern exists for IS.11 IS usually begins soon after exercise starts and resolves within 5 min of exercise cessation; however, it is highly variable and often difficult to reproduce.1,9,11 EIB, however, may require 5 to 10 min of exercise while breathing dry air to initiate a response, and symptoms peak between 5 min and 20 min after exercise stops.12–14 EIB is also highly reproducible with a variety of surrogate challenges.11,12 IS is not typically provoked by surrogate challenges such as eucapnic hyperventilation, hypertonic saline solution, or methacholine.11 Spirometry objectively defines EIB, while the efficacy of spirometry in diagnosing IS is questionable.9,10 Abnormal spirometric findings with IS may be variable and only present when the patient is symptomatic.2,3,6,8,9,11,15 Laryngoscopy during IS is necessary for visual observation of vocal cord closure to confirm a diagnosis of VCD. In addition, EIB most often responds to B2-agonist treatment while IS does not.1,3,9,11 Besides VCD, exertional IS may be caused by foreign body aspiration, poor-performance psychogenic stridor, infectious croup, laryngomalacia, subglottic stenosis, and exercise-induced anaphylaxis1; however, these are less common and can be eliminated by careful screening during the diagnosis. Interestingly, IS is frequently associated with psychologically stressful events such as competitions.1,7,9,11,16 –18 The prevalence of IS or of VCD (diagnosed by laryngoscopy) in athletes is largely unknown. An estimated 2 to 3% of the general and athlete populations are afflicted; the majority of cases reported are in adolescent female subjects.19,20 Subjects from these studies were typically patients referred with difficult-to-treat exertional asthma or EIB, which occurs comorbid with IS in 14 to 56% of reported cases.9,10 To our knowledge, only one study of VCD in elite athletes exists. In that report, VCD was identified in seven athletes who were referred for exercise-induced asthma.11 The diagnostic tools in that study were qualitative observation of pronounced IS during exercise, the lack of ␤2-agonist resolution of IS, and a normal provocation response, although three diagnoses were confirmed with laryngoscopy.11 The purpose of this study was to identify the prevalence of IS among elite athletes. We hypothesized the following: (1) IS occurs more often in the athlete population than in the general population, perhaps because of the high level of competition stress, and (2) IS is often misdiagnosed as EIB in the athlete population. www.chestjournal.org

Materials and Methods Subjects All subjects (n ⫽ 370) were developmental or elite athletes between the ages of 16 years and 37 years who volunteered to undergo routine evaluation for asthma and/or EIB at the US Olympic Training Center in Lake Placid, NY. No significant difference in study group gender proportion existed (174 female and 196 male subjects). Of the 370 athletes, 169 trained and competed outdoors and 201 trained and competed indoors. The vast majority of the subjects (n ⫽ 318) competed in winter sports, 49 others trained outdoors (running and cross-country skiing) during the winter months, and 3 subjects rarely trained in cold, dry ambient conditions. Subject sports included the following: biathlon (n ⫽ 51), bobsled (n ⫽ 1), canoe/kayak (n ⫽ 49), crosscountry skiing (n ⫽ 45), luge (n ⫽ 3), Nordic combined (n ⫽ 18), badminton (n ⫽ 2), figure skating (n ⫽ 79), ice hockey (n ⫽ 77), rhythmic gymnastics (n ⫽ 1), speed skating (n ⫽ 42), and other (n ⫽ 2). Medical History Query and Symptoms Prior to testing, subjects provided written informed consent. Subjects were queried on medical history of allergy and respiratory illness, previous asthma or EIB diagnoses, and respiratory symptoms during or after exercise; queries included events that evoke an airway response. Symptoms queried were cough, wheeze (during inspiration and/or exhalation), chest tightness, throat tightness, dyspnea, and mucus formation. IS During and after the exercise challenge, investigators noted all overt symptoms presented by the athletes, particularly, the occurrence of IS during and shortly after (within 5 min) exercise cessation. When wheeze or IS was detected by investigators, auscultation of the larynx and chest was performed to determine the origin of the sound. The audible IS during exercise that quickly resolves within 5 min of exercise cessation is a defining feature of VCD; the asthma or EIB wheeze is typically on exhalation and becomes more severe 5 to 20 min after exercise.2– 6,9,11,15,18 Exercise Challenge Actual competition, simulated competition, or a 7- to 8-min free run was used as the exercise challenge for EIB provocation. Competitions included Olympic Trials, World Team Trials, World Cup Competition, and US National Championships. Time duration for the sport-specific exercise challenge was dependent on event duration and ranged from approximately 2 min for speed skaters to 1 h for cross-country skiers and biathletes. However, ⬎ 78% of the athletes (n ⫽ 290) in this study were tested two or more times, with a field challenge and a 7- to 8-min free run (badminton, biathlon, bobsled, canoe/kayak, crosscountry skiing, luge, Nordic combined, and triathlon) or highintensity cycle ergometry (ice hockey, speed skating, rhythmic gymnastics). Temperature (⫺ 20 to ⫹ 4°C) and relative humidity (⬍ 40%) were not controlled during the exercise challenge, but conditions were cold and dry, and generally representative of the environmental challenge faced by these athletes during training or competition. Exercise intensity for all trials was at competition pace and above the ventilatory threshold. Previous work has validated this procedure and effectiveness of these time durations in provoking EIB.13,14,21–24 CHEST / 123 / 2 / FEBRUARY, 2003

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Pulmonary Function Test Procedures Standard pulmonary function tests (PFTs) were performed before and after an exercise challenge using a calibrated, computerized, 10-L, rolling dry-seal spirometer (Model 2130; SensorMedics; Yorba Linda, CA) or a calibrated, computerized, pneumotachograph spirometer (Jaeger Masterscope PC; Jaeger; Hoechberg, Germany). Spirometers were previously cross-validated and provided statistically identical measurement valves. Prior to exercise, baseline spirometry was performed to obtain three consistent trials. The spirometric maneuver involved the following: (1) three normal tidal volume breaths, (2) maximal inhalation, (3) forced maximal exhalation, and (4) maximal inhalation. The best of three trials used for analysis was selected on FVC and FEV1. After baseline spirometry, the athletes completed the exercise challenge, followed by PFT maneuvers, at 5 min, 10 min, and 15 min after exercise.13,14,21 Data Analysis The following PFT measures were analyzed: FVC, FEV1, forced expiratory flow between 25% and 75% of FVC (FEF25–75%), forced expiratory flow at 50% of FVC (FEF50), forced inspiratory flow at 50% FVC (FIF50), and peak expiratory flow (PEF). Predicted values for resting lung functions (FVC, FEV1, FEF25–75%, FEF50, FIF50, and PEF) were calculated.25 Postexercise falls in pulmonary function were determined by subtracting each postexercise PFT value from best of three preexercise baseline values and divided by baseline values. Falls ⱖ 10% in FEV1 were considered as EIB positive (EIB ⫹); subjects who did not meet this cut-off were grouped as normal (EIB negative [EIB ⫺]).13,14,21 Single sample ␹2 tests were used to determine differences in proportions. Unpaired t tests were employed to determine differences in pulmonary function measurements between EIB ⫹ and EIB ⫺ athletes and between inspiratory stridor-positive (IS ⫹)/EIB ⫹ athletes and IS ⫹/EIB⫺ athletes. Analysis of variance with the Tukey post hoc analysis was used to determine differences in the postexercise mid-flow (FEF50/ FIF50) ratio, FVC, and FEV1 for IS and EIB status. An ␣ of 0.05 was considered significant for all statistical comparisons.

Results Thirty percent (n ⫽ 111; 58 female and 53 male subjects) of the 370 athletes were identified as EIB ⫹ by a ⱖ 10% postexercise fall in FEV1 (Table 1). The 111 EIB ⫹ athletes demonstrated postexercise falls in FEV1 of 18.6 ⫾ 10.0% (mean ⫾ SD), compared to 3.1 ⫾ 4.6% for the 259 EIB ⫺ athletes.

Table 2—PFT Data From IS ⴙ Athletes Following Exercise Variables IS ⫹/EIB ⫹ (n ⫽ 10) Mean SD IS ⫹/EIB ⫺ (n ⫽ 8) Mean SD

FVC

FEV1

FEF25–75%

PEF

⫺ 13.2 7.6

⫺ 19.4 7.0

⫺ 30.7 24.0

⫺ 19.67 9.99

⫺ 9.2 5.0

⫺ 4.9* 2.6

⫺ 7.9* 6.1

1.2* 16.9

*Significantly different from IS ⫹/EIB ⫹ values (p ⬍ 0.05).

Approximately 5% of the 370 athletes (n ⫽ 19; 18 female and 1 male subjects) demonstrated IS during and/or immediately after exercise; 53% of the 19 IS ⫹ athletes (n ⫽ 10) presented comorbid EIB. The 19.4 ⫾ 7.0% postexercise fall in FEV1 for the IS ⫹/EIB ⫹ group was not different than the fall in FEV1 for inspiratory stridor-negative (IS ⫺)/EIB ⫹ athletes (18.5 ⫾ 10.2%). The proportion of IS ⫹ athletes with EIB was not different than the proportion of IS ⫹ athletes who did not have EIB (Table 2). IS was comorbid with EIB in 2.7% of all athletes evaluated and with 9% of the EIB ⫹ population. The prevalence of IS among EIB ⫺ athletes was 3.5%. Eight of the 10 IS ⫹/EIB ⫹ athletes had a previous diagnosis of EIB or asthma by a physician. Preexercise prophylaxis with a ␤2-agonist failed to resolve IS in six of these eight athletes. Eight of nine IS ⫹/EIB ⫺ athletes also had a previous physician diagnoses of EIB or asthma; seven subjects were treated with a ␤2-agonist without successful resolution of IS. Table 3 presents gender and IS/EIB distributions for outdoor and indoor athletes. There were significantly fewer outdoor athletes (n ⫽ 169) than indoor athletes (n ⫽ 201) [p ⬍ 0.05], and the proportion of female subjects was significantly less for outdoor athletes (40%) than for indoor athletes (53%) [p ⬍ 0.05]. IS was identified in 8.3% of outdoor athletes (13 female and 1 male subjects) and 2.5% of indoor athletes (5 female subjects) [p ⬍ 0.05; Fig 1], despite a significantly greater number of indoor female athletes than outdoor female athletes. EIB

Table 1—EIB Status Following Exercise (n ⴝ 370)* Status EIB ⫹ (n ⫽ 111) Mean SD EIB ⫺ (n ⫽ 259) Mean SD

FVC

FEV1

FEF25–75%

⫺ 12.3 8.7

⫺ 18.6 10.0

⫺ 26.1 21.2

5.3† 4.4

⫺ 3.1† 4.6

⫺ 2.1† 11.5

PEF ⫺ 21.2 16.6 ⫺ 6.4† 11.2

*Data are presented as the percentage of postexercise fall. †Significant difference between EIB ⫹ and EIB ⫺ (p ⬍ 0.05). 470

Table 3—Gender and IS/EIB Distribution Among the Entire Cohort of Athletes (n ⴝ 370) Subjects

Outdoor Athletes (n ⫽ 169)

Indoor Athletes (n ⫽ 201)

Female IS ⫹ IS ⫹/EIB ⫹

68 14* 8*

106† 5† 2†

*Indicates one male subject in the group. †Significantly different than corresponding outdoor category. Clinical Investigations

Figure 1. Frequency of IS among the total study population (n ⫽ 370), the outdoor athletes (n ⫽ 169), and the indoor athletes (n ⫽ 201). The occurrence of IS was significantly more frequent among outdoor athletes than indoor athletes. *p ⬍ 0.05.

was comorbid with 8 of 14 IS ⫹ outdoor athletes and only 2 of 5 IS ⫹ indoor athletes (p ⬍ 0.05). Resting PFT data from 19 randomly selected gender-matched and EIB-matched control subjects was compared to the 19 IS ⫹ athletes. None of the resting PFT measurements distinguished IS ⫹ athletes from IS ⫺ control athletes (Table 4). FEF50/ FIF50 ratios for IS ⫹ and control subjects are presented in Figure 2. No difference was identified between IS ⫹ and control FEF50/FIF50 ratios for either preexercise (1.13 ⫾ 1.13 vs 0.86 ⫾ 0.37) or postexercise (1.51 ⫾ 1.53 vs 0.94 ⫾ 0.36) measurements. However, the proportion of a postexercise FEF50/FIF50 ratio ⬎ 1.5 was significantly greater for IS ⫹ than for control athletes (33% and 0%, respectively; p ⬍ 0.05). A significant difference was found between postexercise IS ⫹/EIB ⫹ and IS ⫺/EIB ⫹ FEF50/FIF50 ratios (1.97 ⫾ 1.69 vs 0.81 ⫾ 0.39; p ⬍ 0.05), but not between postexercise IS ⫹/EIB ⫺ and IS ⫺/EIB ⫺ FEF50/FIF50 ratios (1.00 ⫾ 0.302 vs 1.06 ⫾ 0.30).

Figure 2. FEF50/FIF50 ratios for IS ⫹ subjects (n ⫽ 19) and randomly selected matched control subjects (n ⫽ 19) before (Pre) and after (Post) exercise (Exer). No difference was noted for FEF50/FIF50 ratios between IS ⫹ and control subjects together (total subjects). When grouped according to EIB status, postexercise FEF50/FIF50 ratios were significantly greater for IS ⫹/EIB ⫹ athletes (*p ⬍ 0.05). Data are presented as the mean ⫾ SEM.

Figure 3 depicts postexercise falls in FVC and FEV1 for IS ⫹ and IS ⫺ athletes. The fall in FVC was significantly less for IS ⫺/EIB ⫺ athletes (5.3 ⫾ 4.3%) than for IS ⫹/EIB ⫺ athletes (9.2 ⫾ 5.0%), IS ⫹/ EIB ⫹ athletes (13.2 ⫾ 2.68%), and IS ⫺/EIB ⫹ athletes (12.3 ⫾ 0.87%) [p ⬍ 0.05]. FEV1 was significantly different between EIB ⫺ and EIB ⫹ athletes (p ⬍ 0.05) but not different between IS ⫹ and

Table 4 —Resting PFT Data from Gender- and EIBMatched Control Athletes Compared to IS ⴙ Athletes Variables Control subjects Mean SD % predicted Mean SD IS ⫹ subjects Mean SD % predicted Mean SD

FVC

FEV1

4.56 0.57

3.80 0.44

119.2 11.8 4.37 0.58 115.2 9.0

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115.0 15.6 3.84 0.59 116.8 11.52

FEF25–75% 4.04 1.05 100.7 29.4 4.32 0.91 107.2 18.6

FEF50

PEF

3.74 1.91

7.46 1.23

88.7 56.2 4.74 0.59 108.3 11.1

103.7 18.2 7.46 1.57 104.2 18.7

Figure 3. Postexercise falls in FVC and FEV1 for IS ⫹ and IS ⫺ athletes grouped according to EIB status (IS ⫹/EIB ⫺ [n ⫽ 9], IS ⫺/EIB ⫺ [n ⫽ 250], IS ⫹/EIB ⫹ [n ⫽ 10], IS ⫺/EIB ⫹ [n ⫽ 101]), presented as mean ⫾ SEM. FEV1 was significantly different between EIB ⫺ and EIB ⫹ athletes (†p ⬍ 0.05) but not between IS ⫹ and IS ⫺ within EIB status. The postexercise fall in FVC for IS ⫺/EIB ⫺ was significantly less than FVC for all other groups. *p ⬍ 0.05. CHEST / 123 / 2 / FEBRUARY, 2003

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IS ⫺ groups. No other postexercise pulmonary function distinguished IS ⫹ from IS ⫺.

Discussion The purpose of this study was to report the prevalence of IS in elite athletes. To our knowledge, this report is the first to provide a comprehensive estimate of IS for an athlete population. Overall prevalence of IS in our cohort of developmental and elite athletes was 5.1%; the 8.3% prevalence in the outdoor athlete group was significantly higher than the 2.5% observed in the indoor athlete group (p ⬍ 0.05). The prevalence of IS in the athlete population and within the outdoor subpopulation was higher than the 2.5% estimate for the general population.1 Although we did not directly view the athletes’ vocal cords by laryngoscopy while they were symptomatic, we believe that our careful observation and examination (including auscultation of the larynx of symptomatic athletes) during and immediately after exercise accurately identified IS and that we were able to distinguish IS from EIB-generated wheeze. Multiple tests were obtained on 78.4% of the 370 subjects (n ⫽ 290) in this study. Adding support to our findings, 18 of the 19 IS ⫹ athletes (9 of 9 IS ⫹/EIB ⫺ subjects and 9 of 10 IS ⫹/EIB ⫹ subjects) had been tested numerous times. The audible IS during exercise in our subjects that quickly resolved when exercise stopped is a defining clinical feature of VCD and is valuable for diagnosis.2– 6,9,11,15,18 We concur that direct observation of vocal cord adduction by laryngoscopy is the “gold standard” for diagnosis of VCD. However, since this procedure is most effective while the patient is symptomatic, laryngoscopy may not always be practical.9 –11 Furthermore, laryngoscopy has been found to be diagnostic in only 60% of the symptomatic patients examined.9 The inconsistent occurrence of IS and the fact that VCD often appears only in high-stress situations (eg, competition) makes successful laryngoscopy difficult at best, and only confirms a suspected diagnosis.11 An important finding of this study, although not novel, was that IS is often misdiagnosed as EIB. In our study, eight of nine athletes who presented IS but were EIB ⫺ had previously received a diagnosis of asthma or EIB by a family physician. The absence of a bronchodilator response by 7 IS ⫹/EIB ⫺ athletes and 8 of 10 IS ⫹/EIB ⫹ athletes is consistent with a diagnosis of extrathoracic airway obstruction. This lack of symptomatic relief from a ␤2-agonist has been suggested to be an important discriminator between asthma and VCD.9,11 The 30% prevalence of EIB in our study population was representative of EIB in the elite athlete popula472

tion. Others have reported a 20 to 50% prevalence, depending on the sport evaluated.13,14,21–24,26 –28 Fiftythree percent of our IS ⫹ athletes had comorbid EIB; this was 2.7% of the 370 athletes screened and 9% of the 111 athletes identified as EIB ⫹. This number is consistent with a study by Newman et al,9 who reported 56% of 95 laryngoscopically confirmed patients with VCD also had asthma. In an earlier study, Newman and Dubster15 found that 30% of patients referred for asthma also had VCD. A report by Wamboldt et al29 found that 12 of 84 adolescents (14%) referred for asthma had comorbid VCD. This is not different than our finding of 9% IS/EIB comorbidity. It has been stated that “there is no sport-specific predilection for VCD”1; however, to our knowledge, only one report of VCD in elite athletes has been published.11 The seven athletes in that study participated in boxing, racquetball, cross-country skiing, track, figure skating, swimming, and basketball. Our study cohort included 169 outdoor and 201 indoor athletes, of whom the vast majority trained and competed in cold, dry ambient conditions. The frequency of EIB (28% and 31% for outdoor and indoor athletes, respectively) was not different between the groups. Since IS appears to be a greater problem for female than for male subjects,1,2,9,15,19 and there were significantly more female subjects in the indoor group than the outdoor group (53% vs 40%), we expected to find a higher prevalence of IS among the indoor athletes. However, IS was significantly more prevalent among the outdoor athletes; of 19 IS ⫹ athletes, 14 were from the outdoor group and 5 were from the indoor group (p ⬍ 0.05). This contradictory finding suggests that environmental stimuli may affect the occurrence of IS. Moreover, comorbidity with EIB was significantly greater with the outdoor group (8 of 14 subjects vs 2 of 5 subjects, p ⬍ 0.05). This suggests a relationship may exist between exercising in cold, dry ambient air and extrathoracic airway sensitivity manifested as IS. Whether repeated cold-air hyperpnea sensitizes the upper airways and results in IS is unknown. Several studies have described abnormal inspiratory flow volume loops during periods of IS symptoms2,3,6 –11,15; however, making a diagnosis of VCD based solely on PFT results is tenuous. The sensitivity of the flow volume loop has been described as low.9 –11 Most of these studies identify normal or variable resting PFT results and flattened or truncated inspiratory loops while the patient was symptomatic. McFadden and Zawadski11 found PFT results to be normal at rest, variable when symptomatic, and normal within 1 min of symptom resolution in VCD-diagnosed elite athletes. Newman et al9 observed truncation of the inspiratory loop in 17% of VCD and VCD/asthmatic patients, even while paClinical Investigations

tients were asymptomatic. Morris et al10 found that inspiratory truncation was not different between VCD ⫹ and VCD ⫺ patients (20% and 13%, respectively). We found no distinguishing resting PFT measurements between IS ⫹ and control subjects, and did not see obvious inspiratory truncation. Although Newman et al9 found that patients with VCD had statistically greater FEF50/FIF50 ratios, even at rest, we observed measurable signs of inspiratory abnormalities only in the postexercise spirograms of IS ⫹/EIB ⫹ athletes. Christopher et al8 stated that during episodes, all individuals with VCD demonstrated inspiratory limits that can be distinguished from normal patients by an elevated FEF50/ FIF50 ratio ⬎ 2. Elevated FEF50/FIF50 ratios ⬎ 1.5 were found in 33% of IS ⫹ subjects, while control subjects had no FEF50/FIF50 ratios ⬎ 1.5. When IS ⫹ and control subjects were categorized according to EIB status, the EIB ⫺ group showed no differences in FEF50/FIF50 ratios, either before or after postexercise. However, IS ⫹/EIB ⫹ subjects had significantly higher FEF50/FIF50 ratios than control subjects after exercise (but not before exercise). Interestingly, spirometry revealed a large postexercise fall in FVC without a concomitant fall in FEV1 in the IS ⫹/EIB ⫺ population. Others7,10 reported a decrease in FVC when patients were symptomatic; this response has been attributed to a decrease in inspiratory volume and not increased peripheral airways obstruction. Although our data demonstrated a significantly greater postexercise fall in FVC for IS ⫹/EIB ⫺ athletes than for IS ⫺ /EIB ⫺ athletes, postexercise falls in FVC for the EIB ⫹ groups were not different between IS ⫹ and IS ⫺ athletes. In our study, we found that 5% of an elite athlete population demonstrated IS during exercise that resolved quickly on cessation of activity. Moreover, the prevalence was significantly higher among outdoor female competitors than their indoor counterparts. Although we did not perform laryngoscopy to directly view vocal cord closure, the IS documented in this study and the inability of a ␤2-agonist to resolve stridor is highly suggestive of VCD. In addition, a postexercise FEF50/ FIF50 ratio ⬎ 1.5 in IS ⫹/EIB ⫹ athletes and the significant postexercise fall in FVC in IS ⫹/EIB ⫺ athletes is consistent with a decrease in inspiratory volume due to extrathoracic obstruction. We suggest that spirometry can be useful for diagnosis of VCD in athletes when combined with audible symptoms, history, and laryngoscopy. ACKNOWLEDGMENTS: The authors thank Lester B. Mayers, MD, and Dan A. Judelson and Meredith H. Wilson for technical assistance. We also acknowledge the athletes and coaching staff for their support and assistance. www.chestjournal.org

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Clinical Investigations