CLINICAL RESEARCH
Blood Viscosity and its Relationship to Iron Deficiency, Symptoms, and Exercise Capacity in Adults With Cyanotic Congenital Heart Disease
Craig S. Broberg, MD*,*,
Bridget E. Bax, PhD||,
Darlington O. Okonko, BSc, MRCP ,
Michael W. Rampling, MD¶,
Stephanie Bayne, BS ,
Carl Harries, BS*,
Simon J. Davidson, BS ,
Anselm Uebing, MD*,
Arif Anis Khan, MD*,
Swee Thein, MD#,
J. Simon R. Gibbs, MD*,*,
John Burman, MD and
Michael A. Gatzoulis, MD, PhD*
* Adult Congenital Heart Centre
Department of Cardiac Medicine
Department of Exercise Physiology
Department of Haematology, Royal Brompton Hospital and National Heart and Lung Institute, Imperial College School of Medicine
|| Child Health, Department of Clinical Developmental Sciences, St. George's Hospital, University of London
¶ Division of Biomedical Sciences, Department of Physiology and Biophysics, Imperial College School of Medicine
# Department of Haematological Medicine, King's College London Medical School, King's College Hospital
** Hammersmith Hospital, London, England
Manuscript received December 8, 2005;
revised manuscript received February 24, 2006,
accepted March 16, 2006.
* Reprint requests and correspondence: Dr. Craig S. Broberg, UHN 62, Division of Cardiology, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239 (Email: brobergc{at}ohsu.edu).
Portions of this data were presented orally at the American College of Cardiology Scientific Sessions, March 2005, in Orlando, Florida.
OBJECTIVES: 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 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 s1 to 128.5 s1.
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 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.
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Abbreviations and Acronyms
| | Hb = hemoglobin | | Hct = hematocrit | | MCH = mean corpuscular hemoglobin | | MCHC = mean corpuscular hemoglobin concentration | | MCV = mean corpuscular volume | | RBC = red blood cell | | Tsat = transferrin saturation | | VO2 = oxygen consumption | | VSD = ventricular septal defect |
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