Which of the following indicates a positive response in an exercise challenge test for bronchospasm?

A significant drop in FEV1 post-exercise indicates a positive response in an exercise challenge test for bronchospasm. In this context, FEV1 refers to the Forced Expiratory Volume in one second, which is a critical measurement in assessing lung function and detecting airway obstruction. During an exercise challenge, individuals who are susceptible to bronchospasm may exhibit a decline in this measurement due to the constriction of their airways in response to physical activity.

This decline is a clear indication that the patient's airways are reactive, characteristic of conditions such as asthma. When the airways constrict, it becomes more difficult to exhale air, thereby reducing the FEV1 value following exercise. This response can help clinicians determine if the patient is experiencing exercise-induced bronchoconstriction, which is important for proper diagnosis and management of respiratory conditions.

The other options are not indicative of bronchospasm in this context. A decrease in heart rate during exercise is not typically associated with bronchospasm, and an increase in tidal volume would suggest improved ventilation rather than airway constriction. Similarly, no change in respiratory rate does not provide information about airway reactivity, as bronchospasm would likely increase the respiratory rate due to difficulty breathing.