Hyperfibrinogenemia and Hyperviscous Hypertensive Africans

Plasma in

H. L. Reid, Ph.D. and L. I. Ojogwu, M.R.C.P.

BENIN CITY, NIGERIA, WEST AFRICA

Abstract

Changes in plasma fibrinogen concentrations (PFC) and relative plasma viscosity (RPV) were investigated in 61 Nigerian Africans while they were being treated for essential hypertension. The association of these hemorheologic variables with blood pressure was examined. An analogous study was done on 30 normotensive controls for comparison. The hypertensive patients had, overall, a significant increase in both PFC and RPV (p < 0.001) as compared with control values. However, 44.3% of the hypertensive patients had PFC and RPV values within the defined normal limits. This indicates that in a proportion of the hypertensives, treatment notwithstanding, PFC and RPV are altered only within the physiologic limits. Comparison of PFC and RPV with the degree of hypertension (mild: diastolic blood pressure (DBP) = 90mmHg; moderate: DBP = 91-99mmHg; severe: DBP ≥ 100mmHg) showed significant stepwise increases at the moderate and severe levels as compared with the mild level of hypertension. The hyperfibrinogenemia and concomitant hyperviscous plasma observed in the present study could either play a role in the pathogenesis of the hypertension or be the consequence of the hypertension itself, at least in some patients. Introduction Essential hypertension is a frequently diagnosed condition in Nigerian Africans. It occurs almost equally among the male and female population with frequencies of 14 % and 10%, respectively.’ There are reports showing that hypertension is associated with rheologic disturbances.2-4 We showed in an earlier report that our hypertensive patients had abnormal heFrom the Departments of Physiology and Medicine, College Benin, Benin City, Nigeria, West Africa

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morheologic parameters, including red blood cell filterability, packed-cell volume, hemoglobin concentrations, and plasma fibrinogen titer.5 More recently we indicated that in hypertensive-diabetics drawn from the same population, there was an additive effect of hypertension in causing a significant elevation in both plasma fibrinogen and viscosity levels, an effect that was not evident for serum proteins and serum viscosity. 6.7 Tibblin and his colleagues were the first to show a correlation between hypertension and increased plasma viscosity.’ It is well established that the principal determinant of plasma viscosity is plasma fibrinogen concentration. Hemorheologic studies in hypertensive Africans are few. In an attempt to address this neglect we designed the present study to measure plasma fibrinogen concentration and plasma viscosity and examine their association with blood pressure in our black hypertensive population. The potential usefulness of these parameters may help us to understand the pathogenesis, and also follow the progress of treatment, of essential hypertension. Materials and Methods

subjects in this study were all Nigerians. All participants gave their informed consent. Sixty-one adults being treated for essential hypertension were recruited into the study. There were 31 men and 30 women. The sexes combined had a mean ( ± SD) age = 50.00:1: 11.21 (range twenty-nine to eighty-five) years. Duration of hypertension varied from one to fourteen years. None of the patients had a history of stroke or diabetes mellitus. Patients receiving treatment for malaria were excluded because of the likely influence of this condition on fibrinogen levels. Hypertension was defined as a diastolic blood pressure (DBP) >_ 90 mmHg (phase V). All patients were receiving antihypertensive therapy at the time of the study. They were mainly receiving a combination of a beta blocker and a diuretic or a vasodilator and a diuretic. Thirty normotensive volunteers, in apparently good health, were included in the study as controls. The group had a mean age of 45 .00 ± 8 . 21 (range twenty to fifty-five) years. Table I shows the blood pressure profile of the hypertensive patients and control individuals. The women were not taking contraceptive pills. The

Venous blood was collected with minimal venous stasis so that hemoconcentration was avoided. Five mL blood was anticoagulated with solid potassium edetic acid (K+EDTA) (2 mg/mL blood) for plasma viscosity measurements. Another 5 mL of blood was treated with 0.5 mL of a 31.0 g/L sodium citrate solution for plasma fibrinogen determination. Transparent plasma was prepared by centrifuging the blood in stoppered tubes, to prevent evaporation, for five minutes at 3000 g. The supernatant plasma was pipetted off and stored at room temperature (26-28°C). Both plasma viscosity and fibrinogen concentration were measured within three hours of venipuncture. Arterial blood pressure was measured by the standard sphygmomanometer procedure after the subjects had rested for at least one-half hour. Blood pressure readings were taken on the left upper limb while the subjects were sitting. Duplicate readings were taken and the mean value determined. The pulse pressure (PP) was calculated as the difference between the systolic blood pressure (SBP) and DBP. The mean arterial pressure (MAP) was calculated from the equation MAP = PP + DBP/3 .

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828 TABLE I Blood Pressure

Profile in Subjects and Hypertensive Patients

*p

Hyperfibrinogenemia and hyperviscous plasma in hypertensive Africans.

Changes in plasma fibrinogen concentrations (PFC) and relative plasma viscosity (RPV) were investigated in 61 Nigerian Africans while they were being ...
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