Increased Sympathetic Activity Present in Early Hypertensive Pregnancy is Not Lowered by Plasma Volume Expansion

Abstract

Objective: To evaluate whether sympathetic activity is increased in early-onset hypertensive pregnancy and whether this can be influenced by management with plasma volume expansion. Methods: The study group consisted of 74 subjects, of which 37 had early-onset hypertensive disorders of pregnancy (preeclampsia or gestational hypertension with fetal growth restriction), who were included at 24 to 34 weeks in a randomized controlled trial of management with (n = 18) or without (n = 19) plasma volume expansion. Heart rate and blood pressure variabilities, LF/HF ratio for heart rate, baroreflex sensitivity, and phase difference at low frequency (LF≈0.1 Hz) were calculated by spectral analysis from continuous heart rate and blood pressure recordings of the finger pulse wave (Portapres™, TNO). Measurements were performed at inclusion, after 20 to 40 hours and after 65 to 100 hours. The control group consisted of 29 women with a normal pregnancy and 8 women who had late-onset preeclampsia after 34 weeks. Controls were measured at 32 weeks. All controls had a normal blood pressures at that time. Results: LF variability of heart rate and blood pressure were significantly higher and baroreflex sensitivity was significantly lower in early-onset patients compared with normal controls. A significant trend towards higher LF variability of blood pressure and lower baroreflex sensitivity was found from normal controls to late-onset controls to early-onset patients. Parameters of sympathetic activity were not influenced by plasma volume expansion. Conclusion: Sympathetic activity was increased in early-onset hypertensive pregnancy. However, this was not affected by management with plasma volume expansion, suggesting that hypovolaemia in preeclampsia is a secondary phenomenon.

Keywords:

• Pregnancy induced hypertension
• Preeclampsia
• Spectral analysis
• Sympathetic activity
• Plasma volume expansion