Deep inspirations have been shown to decrease the sensitivity of airways to narrowing (airway reactivity) after inhalation of agents that induce constriction of the bronchi in healthy adults. This response is absent in adult asthmatics; however, there is data demonstrating that use of continuous positive airway pressure (CPAP) for short periods of time may decrease airway reactivity in adult asthmatics. This suggests that although deep inspirations may not result in decreased airway reactivity, sustained lung inflation may lead to changes in asthmatic airway smooth muscle structure that lead to a decrease in airway reactivity. The purpose of our study is to determine whether short and long term use of CPAP in children and adults leads to decreased airway reactivity. If airway reactivity is decreased with CPAP, this may provide a novel therapeutic strategy for patients with asthma.