Cerebrovascular reactivity in normal pregnancy and preeclampsia

Abstract

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 preeclamptic women in the third trimester. All measurements were done in the left lateral position at baseline, during 5% carbon dioxide (CO 2) inhalation, and during an isometric hand-grip test. Blood pressure (BP), heart rate, oxygen (O 2) saturation, and end-tidal partial pressure of carbon dioxide (pCO 2) 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% CO 2 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% CO 2 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.