Intravascular Ultrasonic Characteristics and Vasoreactivity of the Pulmonary Vasculature in Children With Pulmonary Hypertension 11This work was supported in part by grants from the March of Dimes Birth Defects Foundation, White Plains, New York; the Bugher Physician-Scientist Training Program, the Children’s Hospital Research Institute, Denver, Colorado; the American Heart Association Established Investigator Award, Dallas, Texas; and Grant M0100069 of the General Clinical Research Centers Program, National Centers for Research Resources, National Instututes of Health, Bethesda, Maryland.