OBSTETRICS Effects of magnesium on central arterial compliance in preeclampsia Dennie T. Rogers, MD; Maria Colon, MD; Cecilia Gambala, MD; Isabelle Wilkins, MD; Judith U. Hibbard, MD OBJECTIVE: The objective of the study was to investigate the effect of MgSO 4 infusion on central arterial compliance, using radial artery ap- planation tonometry in women with preeclampsia. STUDY DESIGN: Seventy women with preeclampsia were prospectively recruited. Radial pulse waveforms were obtained and the aortic wave- forms constructed. The arterial compliance surrogates, augmentation pressure (AP) and augmentation index (AIx-75), were derived from the aortic waveform and then compared: prior to MgSO 4 (t1), 1 hour after MgSO 4 bolus (t2), 4 hours after MgSO 4 infusion (t3), and 24 hours after MgSO 4 cessation (t4). Statistical analysis was performed using differ- ences of least squared means with Tukey Kramer adjustments. RESULTS: The AP and AIx-75 at t2-t4 were significantly lower com- pared with t1, with the greatest decrease in arterial stiffness at t3 (P  .05). CONCLUSION: In preeclampsia, MgSO 4 improved central arterial com- pliance. This effect was most exaggerated after 4 hours of infusion and remained 24 hours following MgSO 4 completion, suggesting either a sustained arterial compliance effect or resolution of the vasoconstrictive effect of preeclampsia. Key words: arterial compliance, magnesium sulfate, preeclampsia Cite this article as: Rogers DT, Colon M, Gambala C, et al. Effects of magnesium on central arterial compliance in preeclampsia. Am J Obstet Gynecol 2010;202:448.e1-8. I n normal pregnancy, arterial compli- ance adaptively increases by 30% in the first trimester and remains elevated thereafter, returning to normal levels by 8 weeks postpartum. 1 This enhancement of arterial compliance has been sug- gested to constitute part of the vascular adaptation to increased intravascular volume. 2 In pregnancies complicated by preeclampsia, this mechanism of adapta- tion is blunted and women with pre- eclampsia exhibit decreased arterial compliance. 2,3 With each heart beat, a pulse wave travels away from the heart along the ar- terial tree but is reflected back toward the heart and meets the next advancing wave. Under normal circumstances, the reflected wave reaches the aorta during diastole increasing the diastolic portion of the wave, allowing perfusion of the coronary arteries and maintenance of the mean arterial pressure. 4 However, when the arterial wall stiffness is in- creased (ie, decreased compliance), the arterial pulse wave travels more rapidly away from the heart, while the reflected wave returns more quickly. This causes early return of the wave reflection such that the diastolic portion of the wave moves into systole, produc- ing a second (late) systolic peak that is higher than the first. 5 The resultant sys- tolic augmentation of the aorta can be assessed by analyzing the radial pulse waveform with the simple noninvasive method of applanation tonometry. 6 This technique has been validated in various populations and is an accepted measurement for various central pres- sure and arterial compliance indices. 7 It has been used to quantify alterations in central arterial compliance associated with age, renal disease, diabetes, and chronic hypertension. 8-10 Preeclampsia is a disorder of vascular endothelium, and recent studies have utilized applana- tion tonometry to further characterize this condition. Pulse wave analysis in women with hy- pertensive disorders of pregnancy has consistently demonstrated the associa- tion of poor arterial compliance in preeclamptic and hypertensive gravi- das. 11-13 Yet few studies have addressed methods to improve arterial compliance during preeclampsia. 14 It has been pro- posed that magnesium sulfate (MgSO 4 ) use causes transient effects on blood pressure; 15 however, the effect of MgSO 4 on arterial compliance has not been well studied. It may be that MgSO 4 affects the central pressure and arterial stiffness, thus making its use beneficial beyond seizure prophylaxis in women with preeclampsia. The purpose of our study was to inves- tigate the effect MgSO 4 infusion has on central arterial stiffness in women with preeclampsia. We hypothesized that women with preeclampsia would have a decrease in augmentation pressure (AP) and augmentation index (AIx-75), an in- dication of improved central arterial stiffness and central blood pressure, while undergoing MgSO 4 therapy for seizure prophylaxis. MATERIALS AND METHODS This was a prospective observational study at the University of Illinois Hospi- From the Maternal-Fetal Medicine Division, Department of Obstetrics and Gynecology, University of Illinois Hospital at Chicago, Chicago, IL. Presented orally at the 30th Annual Meeting of the Society for Maternal-Fetal Medicine, Chicago, IL, Feb. 1-6, 2010. The racing flag logo above indicates that this article was rushed to press for the benefit of the scientific community. Reprints not available from the authors. 0002-9378/$36.00 © 2010 Mosby, Inc. All rights reserved. doi: 10.1016/j.ajog.2010.03.049 Research www. AJOG.org 448.e1 American Journal of Obstetrics & Gynecology MAY 2010