EVH and Spirometric Testing All subjects will undergo baseline assessment of lung function using the KoKo Legend Portable Spirometer. The subjects will then undergo eucapnic voluntary hyperventilation testing. EVH testing will require the subject to hyperventilate dry air containing 5% carbon dioxide at room temperature for six minutes at a target ventilation of 30 times the subject's forced expiratory volume in one second (FEV1). The EVH test will be considered positive if a fall in FEV1 of 10% or more from baseline is recorded after a 6 minute period of hyperpnea. To overcome the problem of any post-test respiratory muscle fatigue, the FEV1 will be recorded at least three minutes after challenge and then repeated at three-minute intervals through 21 minutes.