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Cerebrovascular Reactivity in Normal Pregnancy and Preeclampsia

From the Departments of Obstetrics and Gynecology and Medicine, Baylor College of Medicine, Houston, Texas; Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of Utah, Salt Lake City, Utah; and Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of Texas Medical Branch, Galveston, Texas.

Address reprint requests to: Shlomit Riskin-Mashiah, MD, 9 Hantke Street, Haifa 34606, Israel; E-mail: asriskin{at}newmail.net.

OBJECTIVE: To compare cerebrovascular reactivity in normotensive and preeclamptic pregnant women.

METHODS: Transcranial Doppler ultrasound was used to measure peak, end-diastolic, and mean velocities in the middle cerebral arteries of 45 normotensive and 36 pre-eclamptic women in the third trimester. All measurements were done in the left lateral position at baseline, during 5% carbon dioxide (CO₂) inhalation, and during an isometric hand-grip test. Blood pressure (BP), heart rate, oxygen (O₂) saturation, and end-tidal partial pressure of carbon dioxide (pCO₂) were recorded with each Doppler measurement. The mean pulsatility index (PI), resistance index (RI), and cerebral perfusion pressure at each time was compared using two-way repeated measures analysis of variance. Cerebrovascular reactivity, calculated as the percentage change in response to each maneuver, was also compared using analysis of covariance. A post hoc power analysis was performed to evaluate the primary measures of the study (middle cerebral artery PI and RI). Using alpha error of 5%, the statistical power to identify a difference in PI and RI in women with preeclampsia compared with normotensive women was 90% and 67%, respectively. The statistical power to identify a difference in PI and RI in response to the two maneuvers was 69% and 53%, respectively. Statistical significance was set at P < .05.

RESULTS: Preeclamptic women had higher baseline cerebral perfusion pressure (90.4 compared with 61.9 mmHg, P < .05) and lower PI (0.64 compared with 0.76, P < .05) and RI (0.46 compared with 0.51, P < .05) than normotensive pregnant women. In normotensive patients, both 5% CO₂ inhalation and isometric hand-grip test caused a significant decrease in PI (-9.5% and -6.1%, respectively) and RI (-6.5% and -4.2%, respectively). In contrast, in preeclamptic patients there was no change in any of the middle cerebral artery parameters in response to either maneuver.

CONCLUSION: Normotensive pregnant women had normal middle cerebral artery responses to both 5% CO₂ inhalation and isometric hand-grip test. Preeclamptic patients had elevated baseline cerebral perfusion pressure and reduced vasodilatory responses to both tests. These findings are consistent with a state of vasoconstriction in preeclamptic women that is unresponsive to stimuli that under normal circumstances result in vasodilation.

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