title: Blood viscosity and its relationship to iron deficiency, symptoms, and exercise capacity in adults with cyanotic congenital heart disease.
abstract: OBJECTIVE
  This study sought to determine the relationship between blood viscosity and iron deficiency and their impact on symptoms and exercise function in adults with cyanotic congenital heart disease.
  
  
  BACKGROUND
  Iron deficiency is believed to raise whole blood viscosity in cyanotic congenital heart disease, although available data are inconsistent.
  
  
  METHODS
  Thirty-nine cyanotic adults were prospectively assessed for iron deficiency (transferrin saturation < or =5%), hyperviscosity symptoms, and exercise capacity. Same-day measurement of whole blood viscosity and hematocrit (Hct) adjusted viscosity (cells resuspended in autologous plasma to Hct of 45%) was performed at shear rates ranging from 0.277 s(-1) to 128.5 s(-1).
  
  
  RESULTS
  Viscosity did not differ between patients with iron deficiency (n = 14) and those without (n = 25). Whole blood viscosity correlated with Hct (r = 0.63, p < 0.001 at low shear and r = 0.84, p < 0.001 at high shear) but not with red blood cell size or iron indices. Hyperviscosity symptoms were independent of iron indices but directly correlated with increased Hct-adjusted viscosity (r = 0.41, p = 0.01). Exercise capacity did not differ in iron-deficient patients. However, peak oxygen consumption was higher in those with Hct > or = 65% (12.6 +/- 3.4 ml/kg/m2 vs. 9.8 +/- 2.6 ml/kg/m2, mean +/- SD, p = 0.036) despite higher whole blood viscosity in these same individuals (p < 0.01 for all shear rates).
  
  
  CONCLUSIONS
  Iron deficiency is common in cyanotic adults but does not alter viscosity. Hyperviscosity symptoms are associated with a higher Hct-adjusted viscosity independent of cell size or iron stores. Higher Hct is associated with better exercise capacity. Further work to understand the origin of hyperviscosity symptoms is warranted.
authors.affiliation: Adult Congenital Heart Centre, Royal Brompton Hospital and National Heart and Lung Institute, Imperial College School of Medicine, London, England. brobergc@ohsu.edu
authors.forename: Craig S
authors.initials: CS
authors.lastname: Broberg
authors.forename: Bridget E
authors.initials: BE
authors.lastname: Bax
authors.forename: Darlington O
authors.initials: DO
authors.lastname: Okonko
authors.forename: Michael W
authors.initials: MW
authors.lastname: Rampling
authors.forename: Stephanie
authors.initials: S
authors.lastname: Bayne
authors.forename: Carl
authors.initials: C
authors.lastname: Harries
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Davidson
authors.forename: Anselm
authors.initials: A
authors.lastname: Uebing
authors.forename: Arif Anis
authors.initials: AA
authors.lastname: Khan
authors.forename: Swee
authors.initials: S
authors.lastname: Thein
authors.forename: J Simon R
authors.initials: JS
authors.lastname: Gibbs
authors.forename: John
authors.initials: J
authors.lastname: Burman
authors.forename: Michael A
authors.initials: MA
authors.lastname: Gatzoulis
mesh_terms: D000328:Adult; D018798:Anemia, Iron-Deficiency / Q000097:blood* / Q000503:physiopathology; D001809:Blood Viscosity; D004903:Erythrocyte Aggregation; D004906:Erythrocyte Count; D004909:Erythrocyte Indices; D005080:Exercise Test; D017079:Exercise Tolerance; D005260:Female; D006330:Heart Defects, Congenital / Q000097:blood* / Q000503:physiopathology; D006400:Hematocrit; D006801:Humans; D007501:Iron / Q000097:blood; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D011446:Prospective Studies
chemical_list: D007501:Iron