Clinical Research Directory

Inclusion Criteria: 1. Must be between the ages of 25 and 65. 2. Must be currently smoking at least 1/2 pack/day (confirmed with cotinine level). 3. Must have pulmonary function test (PFT) results that meet the following (there will be two groups): Group 1: * Forced expiratory volume at one second (FEV1)/Forced vital capacity (FVC) \> 70% * Forced Expiratory Flow at 25-75% of predicted(FEF25-75) \> 79% of predicted * FVC greater than 80% of predicted Group 2: For subjects with mild lung impairment: * FEV1\>80% of predicted * FEV1/FVC\<0.7 4. Must be able to give informed consent for self. Exclusion Criteria: 1. Pregnant or breastfeeding females. 2. Body Mass Index (BMI) greater than 32. 3. Weight of greater than 220 pounds (100 kg). 4. Allergies to shell fish, seafood, eggs or iodine. 5. Heart disease, kidney disease or diabetes. 6. Diagnosis of asthma. 7. Usage of any medications that are known to affect the heart or lungs (contraceptives, anti-depressants, analgesics EXCEPT aspirin, antihypertensives, and medications for osteoporosis and gastrointestinal diseases will be allowed). 8. Any metal in or on the body between the nose and the abdomen. 9. Any major organ system disease (by judgment of study medical team). 10. A glomerular filtration rate of 60 cc per minute or less. For the subjects that will receive Sildenafil as part of the study, additional exclusion criteria are as follows: 1. Nitroglycerin usage or nitrates (in addition to nitroglycerin) and use of phosphodiesterase 5 (PDE5) inhibitors within the previous 7 days of the study date. 2. Prior history of hypersensitivity to Sildenafil.