Implications of sino-aortic baroreceptor reflex dysfunction in severe preeclampsia.

Loss of sino-aortic baroreceptor reflex sensitivity has been associated with various forms of hypertension. Baroreflexive dysfunction antedates elevation of blood pressure (BP) in some forms of hypertension, and may play a role in their pathogenesis. We studied baroreflex function in seven women with severe preeclampsia being treated with intravenous hydralazine. As indices of baroreflex sensitivity and hemodynamic competence, we measured the reflexive elevations in heart rate (HR) (delta HR/delta BP) and cardiac index (CI) (delta CI/delta BP) in response to hydralazine-induced falls in blood pressure. The change in cardiac index per unit change in systemic vascular resistance index (SVRI) (delta CI/delta SVRI) served as an additional measure of hemodynamic competence. The results indicated that a higher baseline blood pressure was associated with a dramatic reduction in baroreflex sensitivity (delta HR/delta BP) and baroreflex control of blood pressure (delta CI/delta BP and delta CI/delta SVRI). In patients with higher baseline blood pressures, the severe impairment of baroreflex function eliminated the normal circulatory buffer against vasodilator-induced hypotension. Abrupt and profound reductions in blood pressure and the development of fetal distress in response to hydralazine occurred in the patients with higher initial blood pressures. In addition, the present results suggest that phenomena such as the blood pressure lability and increased responsiveness to angiotensin that characterize preeclampsia are, at least in part, reflections of baroreflex dysfunction.