Blood viscosity and its relationship to iron deficiency, symptoms, and exercise capacity in adults with cyanotic congenital heart disease.
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.
Broberg
Craig S
CS
Adult Congenital Heart Centre, Royal Brompton Hospital and National Heart and Lung Institute, Imperial College School of Medicine, London, England. brobergc@ohsu.edu
Bax
Bridget E
BE
Okonko
Darlington O
DO
Rampling
Michael W
MW
Bayne
Stephanie
S
Harries
Carl
C
Davidson
Simon J
SJ
Uebing
Anselm
A
Khan
Arif Anis
AA
Thein
Swee
S
Gibbs
J Simon R
JS
Burman
John
J
Gatzoulis
Michael A
MA
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
D007501:Iron