Blunted Autonomic Response to Volume Expansion in Formerly Preeclamptic Women with Low Plasma Volume

Abstract

Objective: We hypothesize that low plasma volume in normotensive formerly preeclamptic women reflects reduced venous storage capacity. To test this hypothesis, we compared circulatory and autonomic responses to acute volume loading between women with low and those with normal plasma volume. Methods: In 24 normotensive formerly preeclamptic women at least 6 months postpartum, we administered 500 mL of iso-oncotic fluid by constant intravenous infusion in 30 minutes, while recording changes in heart rate, blood pressure, cardiac output, and measuring active plasma renin and α-atrial natriuretic peptide concentrations. We estimated arterial sympathetic control, cardiac autonomic regulatory balance, and baroreflex sensitivity using spectral analysis. Intergroup and intragroup changes were analyzed nonparametrically. Results: 17 women (71%) had low plasma volume and 7 (29%) had normal plasma volume. Plasma volume expansion induced comparable changes in blood pressure, heart rate, baroreflex sensitivity, and active plasma renin concentration in low plasma volume and normal plasma volume. Cardiac output and α-atrial natriuretic peptide increased in low plasma volume but not in normal plasma volume. Volume expansion reduced sympathetic activity ( from 2.41 to 1.76 mm Hg², P = .03) in normal plasma volume but not in low plasma volume ( from 2.72 to 2.48 mm Hg², P > .05). Conclusion: The sympathoinhibitory response to volume expansion is diminished in low plasma volume, which suggests that cardiovascular reflex function is impaired. We speculate that this defect contributes to circulatory maladaptation to pregnancy, sympathetic dominance, and the development of gestational hypertensive disease.