FACTORS AFFECTING EXERCISE INDUCED BRONCHOSPASM

哮喘是导致人体功能受限的第二大原因

Asthma is the second leading cause of functional limitation in the under 45-year-old age group. The acute exacerbation of symptomes by physical exertion to which these patients are susceptible can be further exacerbated by a cold and/or dry environment. There is compelling evidence that the mechanism for bronchoconstriction is loss of heat from the airways with consequent cooling of the respiratory tract. During exercise, however, both asthnatics and normal subjects demonstrate an increased expiratory flow which is most likely due to both bronchodilation and increased elastic recoil of the lung. It would appear, therefore, that the mechanism responsible for this increase in airflow serves as a competetive mechanism to exercise-induced bronchospasm (EIB). Swim training decreases overall asthma disability scores and use of medicine but does not diminish EIB severity. Run training appears to accomplish these benefits and also to reduce EIB. We hypothesize that the difference between these two forms of training is a difference in adaptive respiration stimulus. Running results in an increase in threshold to airway cooling due to an adaptive process in the respiratory tract from repeated bouts of hyperpnea under a broad range of climatic conditions. The warm, humid swimming pool environment would not provide a sifficiently adaptive stimulus. The aim of this project is to asses the roles in EIB of physical fitness and/or airway adaptation to cooling via swim and run training plus eucapnic hyperpnea in a three-way crossover design.