Measurement of eNO will be obtained prior to measurement of pre-EVH spirometry. Exhaled NO will be measured employing a technique modified after Silkoff et al (1997) and following American Thoracic Society guidelines for eNO assessment (American Thoracic Society, 1999). In brief, this technique utilizes a resistive device that provides a constant low expiratory flow rate and ensures vellum closure. The combination of vellum closure and low flow rates, specifically 50 ml/s, assures accurate measurement of specific pulmonary derived eNO, while excluding potential contamination by nasal and paranasal sinuses NO (which can be a large source of eNO). Nitric oxide concentrations will be measured using a rapid-response chemiluminescent analyzer (NIOX™ System, Aerocrine, Sweden), which has a response time of < 700 ms for 10-90% full scale. The Food and Drug Administration has approved this device for clinical application in asthma management. The measurement circuit will consist of a mouthpiece-filter connected to a resistor/flow meter and collection bag. The participant will inhale to total lung capacity (TLC), insert the mouthpiece, and then immediately exhale slowly. During expiration, the participant will attempt to maintain a target flow of 50 ml/sec. The target period of exhalation time will be 10 seconds. However, for participants that are not able to perform the 10 second exhalation, the time requirements may be decreased to 6 seconds. Dietary history by recall for the 4-6 hours prior to testing will be obtained to screen for dietary sources of NO.