title: Effects of total hemoglobin and hemoglobin S concentration on cerebral blood flow during transfusion therapy to prevent stroke in sickle cell disease.
abstract: BACKGROUND
  The standard treatment of stroke in sickle cell disease is chronic transfusion to maintain the fraction of abnormal hemoglobin (hemoglobin S [HbS]) below 20%. Risks associated with such transfusion can be reduced by allowing higher HbS levels, but the physiological consequences of this modification are unknown. Cerebral blood flow is elevated in sickle cell disease proportionate to the degree of anemia and is reduced by transfusion. We tested the effects of various HbS levels on cerebral blood flow during the course of transfusion therapy.
  
  
  METHODS
  We monitored cerebral blood flow (by the 133Xe inhalation method) in three patients whose chronic transfusion program was changed from a traditional regimen (HbS < 20%) to a moderate one, allowing HbS to rise to 45% to 50% between treatments. As expected, cerebral blood flow was higher with lower hemoglobin and higher HbS concentration. However, the HbS fraction appeared to exert a separate influence on the hyperemia, independent of total hemoglobin concentration. Furthermore, cerebral blood flow was higher during the modified regimen, despite equivalent anemia.
  
  
  CONCLUSIONS
  These results suggest caution in adapting the modified transfusion regimen. Although HbS concentrations of 50% did not cause any frank neurological sequelae, the possible consequences of the associated hyperemia over time are unknown. We conclude that larger clinical and physiological studies of moderate transfusion regimens (allowing higher concentration of HbS) are necessary before it can become standard therapy.
authors.affiliation: Department of Pediatrics, Columbia University College of Physicians and Surgeons, New York, NY.
authors.forename: A M
authors.initials: AM
authors.lastname: Hurlet-Jensen
authors.forename: I
authors.initials: I
authors.lastname: Prohovnik
authors.forename: S G
authors.initials: SG
authors.lastname: Pavlakis
authors.forename: S
authors.initials: S
authors.lastname: Piomelli
mesh_terms: D000293:Adolescent; D000328:Adult; D000755:Anemia, Sickle Cell / Q000150:complications / Q000175:diagnosis / Q000628:therapy*; D001803:Blood Transfusion; D002560:Cerebrovascular Circulation; D002561:Cerebrovascular Disorders / Q000517:prevention & control*; D005260:Female; D006400:Hematocrit; D006451:Hemoglobin, Sickle / Q000032:analysis*; D006454:Hemoglobins / Q000032:analysis*; D006801:Humans; D008279:Magnetic Resonance Imaging
chemical_list: D006451:Hemoglobin, Sickle; D006454:Hemoglobins