This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Inhaled nitric oxide (NO) is currently FDA approved in neonates including premature infants in the treatment of pulmonary hypertension. Inhaled NO delivered by the INOpulse delvery system utilizes an 880 ppm NO source cylinder and delivers a small pulse(6mL or 3mL) of drug at the begining of each patient breath, rarely produces adverse affects. Buildup of NO-O2 reaction products in tubing such as NO2, a molecule that can precipitate bronchospasm and pulmonary edema, can occur if the NO delivery system is not purged daily. The system will be purged prior to use, and inhaled levels maintained well below 1 ppm. We have administered NO at 80 ppm for 2 hours to healthy subjects (n>30) and to patients with sickle cell (n>20) without complications. During the study, NO2 level will be measured and the treatment will be stopped if it gets too high. Nitic Oxide can also cuase the production of methmoglobin (an abnormal form of hemoglobin), which could worsen the blood oxygen level. The level of methemoglobin will be checked during the study every 2 hours while the patient is receiving inhaled NO. Treatment dose will be reduced by 50% if methemoglobin level is greater that or equal to 5.0% and stopped if it is greater than or equal to 7.5%. If the inhaled NO is stopped too quickly, the patient could experience respiratory insufficiency, however, Nitric Oxide treatment will be stopped while the patient is still hospitalized and hours before discharge. Breathing Nitric Oxide gas should cause no discomfort.