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(Circulation. 1996;93:1677-1684.)
© 1996 American Heart Association, Inc.

Articles

Mean Red Cell Volume as a Correlate of Blood Pressure

Dan S. Sharp, MD, PhD; J. David Curb, MD, MPH; Irwin J. Schatz, MD; Herbert J. Meiselman, ScD; Timothy C. Fisher, MD; Cecil M. Burchfiel, PhD; Beatriz L. Rodriguez, MD, PhD; Katsuhiko Yano, MD

From the Honolulu Epidemiology Research Unit (D.S.S., C.M.B.), Field Studies and Clinical Epidemiology Scientific Research Group, Epidemiology and Biometry Program, Division of Epidemiology and Clinical Applications, National Heart, Lung, and Blood Institute, Honolulu, Hawaii; Honolulu Heart Program (J.D.C., B.L.R., K.Y.), Kuakini Medical Center, Honolulu, Hawaii; Department of Medicine (J.D.C., I.J.S., B.L.R.), John A. Burns School of Medicine, University of Hawaii at Manoa (Honolulu); and Department of Physiology and Biophysics (H.J.M., T.C.F.), University of Southern California School of Medicine (Los Angeles).

Correspondence to Dr Dan S. Sharp, Honolulu Heart Program, National Heart, Lung, and Blood Institute, 347 N Kuakini St, Honolulu, HI 96817. E-mail dan@hhs.cba.hawaii.edu.

Background Clinical studies suggest that hypertensives have lower mean corpuscular volume (MCVs) than do normotensives. Epidemiological studies show no relation or higher MCVs. In the present study of elderly men (71 to 93 years of age) of the Honolulu Heart Program, elements of both findings are confirmed.

Methods and Results Three groups are identified: (1) those receiving no hypertension treatment, (2) those receiving treatment with any diuretic, and (3) those receiving treatment with nondiuretics only. MCV is lower in group 3 than in group 1 (-0.85 fL, P<.001) but the same in groups 1 and 2. Within groups 1 and 3, inverse relations of -0.22 and -0.09 mm Hg/fL (P<.05) are noted for systolic (SBP) and diastolic (DBP) blood pressures. No relations are observed in group 2. MCV and red blood cell count (RBC) are inversely correlated (r=-.45). In group 2, adjustment for RBC unmasks a direct relation between MCV and SBP (0.5 mm Hg/fL, P=.02) and DBP (0.3 mm Hg/fL, P=.02). In groups 1 and 3, relations between SBP and MCV are lost after adjustment for RBC (0.005 mm Hg/fL). For DBP, adding RBC plus an MCVxRBC interaction is significant (P<.001). DBP is 5 mm Hg greater in the highest RBC quartile than in the lowest. A +3 mm Hg difference between extreme MCV quartiles is noted only at high RBC levels.

Conclusions The relation between blood pressure and red cell measures is probably mediated by whole blood viscosity. Hematocrit is a determinant of whole blood viscosity. Viscosity affects peripheral resistance to blood flow, and peripheral resistance affects DBP. At high RBC levels, MCV may be "downregulated." This may lower whole blood viscosity and partially reduce DBP without compromising flow.

Key Words: blood pressure • blood viscosity • erythrocytes • vascular resistance

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