Subjects will be excluded if they had prior cardiac/pulmonary disease or surgeries (other than asthma for the acute exacerbation group), significant musculoskeletal abnormalities (such as scoliosis) that might compromise baseline pulmonary function testing, a history of smoking tobacco or marijuana, and prematurity (birth at less than 37 weeks gestation. In addition, those with an allergy to ultrasound gel will be excluded from participation.