 1. The hemodynamics of PH in SCD reflect a spectrum of abnormalities. Approximately 40-50 of PH in SCD patients have hemodynamics similar to other forms of PAH; a mean pulmonary arterial pressure 25 mmHg, normal left-sided filling pressures PCWP or left ventricular end diastolic pressure 15 mmHg and an elevated PVR 1, 3. But at least 50 of PH in SCD patients have at least some degree of PVH usually due to diastolic dysfunction of the left ventricle 7. How an elevated PVR is defined in PH of SCD is controversial. While typically in other forms of PAH, it is defined as 3 Wood units or 240 dynes.seccm5, this is reflective of a normal PVR of 120-160 dynes.seccm5. In SCD, the anemia-induced elevations in cardiac output observed in these patients produce a baseline PVR of 60-100 dynes.seccm5 suggesting that a PVR of 160 dynes.seccm5 or 2 Wood units may be a more appropriate value 8. 