Cardiopulmonary Exercise Testing in the Evaluation of Patients with Occupational Asthma and Reactive Airways Dysfunction Syndrome

Background: Cardiopulmonary exercise testing (CPET) is a well recognized tool for the functional assessment of patients with cardiovascular and pulmonary disorders. The exercise response of asthmatics has been well characterized but the exercise response of patients with occupational asthma is less well understood. In this report we describe the clinical utility of CPET by characterizing the cardiovascular and pulmonary responses to exercise in patients with occupational asthma (OA) and a closely related entity, reactive airways dysfunction syndrome (RADS). Methods: We evaluated clinical and cardiopulmonary exercise data (mean±SD) from patients with OA (n = 22, age = 40.1±8.9 years, 14 males) and RADS (n = 23, age = 37.7±9.7 years, 18 males) who exhibited comparable pulmonary function. Oxygen uptake, CO₂ output, ventilatory parameters, cardiac hemodynamics, O₂ delivery, 12 lead EKG, systemic BP, and O₂ saturation were monitored at rest and during cycle ergometer exercise. Results: Compared with the RADS group, OA patients demonstrated higher resting dead-space ventilation (41±8 vs 35 ± 9%, p = 0.04), reduced exercise capacity (94±32 vs 122 ± 47 W, p = 0.01), higher respiratory quotients at 50 W (0.98 ± 0.14 vs 0.91 ± 0.08, p = 0.04), decreased power output past attainment of the anaerobic threshold (28.1 ± 17.1 vs 44.7 ± 15.1 W, p = 0.002) and a strong tendency for lower anaerobic thresholds (53 ± 9 vs 60 ± 14% pred VO₂max,p = 0.06). Conclusion: In the 2 groups with occupational bronchial hyperreactivity, each with mild disease severity, OA patients exhibited greater decrements in cardiovascular conditioning when compared with the RADS group, perhaps because of the more prolonged, chronic respiratory insult experienced by the OA group. These data indicate that CPET in patients with work-related bronchial hyperreactivity is of significant utility in the impairment evaluation process.