1. VA Greater Los Angeles Healthcare SystemCardiology SectionDavid Geffen UCLA School of MedicineUCLA Medical Center Department of Pulmonary Critical CareLos AngelesCAUSA
2. Department of MedicineThe University of Alabama at BirminghamBirminghamALUSA
3. United Therapeutics CorporationResearch Triangle ParkNCUSA
4. Insight & MeasurementLLCDurhamNCUSA