SYMPATHETIC-NERVE DISCHARGE IN NORMAL-PREGNANCY AND PREGNANCY-INDUCEDHYPERTENSION

Background Microneurographic assessment of processed bursts that repre sent multi-unit nerve discharge has suggested that sympathetic hyperac tivity occurs in pregnancy induced hypertension and preeclampsia in co mparison with normal pregnancy. Objective To examine the differences b etween peripheral sympathetic outputs in pregnancy-induced hypertensio n and normal pregnancy by directly measuring single impulses of neural discharge. Design We compared the sympathetic neural discharge at res t and its reflex responses in subjects with pregnancy-induced hyperten sion and normal pregnancy and re-examined their progress at least 6 we eks post partum. The patients with pregnancy-induced hypertension were hospital in-patients for whom the diagnosis could be strictly defined and the normally pregnant women were recruited to match the former. M ethods Standard microneurography was performed to quantify single impu lses of action potentials, together with the processed multi-unit burs ts from fibres innervating the leg muscles. We measured neural dischar ge with vascular vasoconstrictive properties, heart rate and finger ar terial blood pressure at rest and their responses to standard isometri c hand-grip exercise and cold pressor tests. Results As expected, pati ents with pregnancy-induced hypertension (n = 13) had higher levels of finger arterial blood pressure than did women with normal pregnancies (n = 11). The number of single impulses of action potentials (per min and per 100 cardiac beats) in resting patients with pregnancy-induced hypertension was more than three times greater than that in resting w omen with normal pregnancies, and the number of multi-unit bursts was twofold greater. After delivery of their child, sympathetic activity a nd heart rate in nine patients decreased, but finger arterial blood pr essure decreased in patients with pregnancy-induced hypertension only. Conclusions From results of cross-sectional and longitudinal studies, pregnancy-induced hypertension is associated with a greater resting s ympathetic output than that of women with normal pregnancies. Follow-u p data after parturition suggest that this hyperactivity is not the on ly cause of hypertension. (C) 1998 Lippincott-Raven Publishers.