Hemodilution Reduces Clinic and Ambulatory Blood Pressure in Polycythemic Patients

Abstract

Abstract-Limited information is available for humans on whether blood viscosity affects total peripheral resistance and, hence, blood pressure. Our study was aimed at assessing the effects of acute changes in blood viscosity on both clinic and 24-hour ambulatory blood pressure (BP) values. In 22 normotensive and hypertensive patients with polycythemia, clinic and 24-hour ambulatory BPs were measured before and 7 to 10 days after isovolumic hemodilution; this was performed through the withdrawal of 400 to 700 mL of blood, with concomitant infusion of an equivalent volume of saline-albumin solution. Hematocrit, plasma renin activity, plasma endothelin-1, right atrial diameter (echocardiography), and blood viscosity were measured under both conditions. Plasma renin activity and right atrial diameter were used as indirect markers of blood volume changes. Plasma endothelin-1 was used to obtain information on a vasomotor substance possibly stimulated by our intervention, which could counteract vasomotor effects. Isovolumic hemodilution reduced hematocrit from 0.53Ϯ0.05 to 0.49Ϯ0.05 (PϽ.01). Plasma renin activity, plasma endothelin-1 and right atrial diameter were unchanged. Clinic blood pressure was reduced by hemodilution (systolic, 144.3Ϯ5.4 to 136.0Ϯ3.9 mm Hg[meanϮSEM]; diastolic, 87.0Ϯ2.8 to 82.1Ϯ2.6 mm Hg, PϽ.05 for both) and a reduction was observed also for 24-hour average ABP (systolic, 133.6Ϯ2.9 to 129.5Ϯ2.7 mm Hg; diastolic, 80.0Ϯ2.0 to 77.3Ϯ1.7 mm Hg, PϽ.05 for both). The reduction was consistent in hypertensive patients (nϭ12), whereas in normotensive patients (nϭ10) it was small and not significant. Both clinic and 24-hour average heart rates were unaffected by the hemodilution. Thus, in polycythemia, reduction in blood viscosity without changing blood volume causes a significant fall in both clinic and 24-hour ambulatory BPs; this is particularly true when, as can often happen, blood pressure is elevated. This emphasizes the importance this variable may have in the determination of blood pressure and the potential therapeutic value of its correction when altered. (Hypertension. 1998;31:848-853.)Key Words: blood viscosity Ⅲ hemodilution Ⅲ blood pressure monitoring, ambulatory Ⅲ hemorheology B P is determined by cardiac output and peripheral vascular resistance. The latter depends to a large degree on the caliber and length of arterioles. It also depends, however, on blood viscosity, with which it bears a linear relationship over a wide range of values. 1Although studied extensively in animals, 2-5 the effects of blood viscosity on human BP have received only limited attention except for (1) the epidemiological evidence that there is a relationship between hematocrit and BP levels in both normotensive and hypertensive subjects 6 -15 and (2) the clinical evidence of an increased prevalence of hypertension in subjects with secondary eritrocytosis and polycythemia. 16,17 In particular, no information is available on the BP effects of interventions that reduce blood viscosity (ie, whether this maneuver induces...

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