Effects of blood pressure on orbital and middle cerebral artery resistances in healthy pregnant women and women with preeclampsia

OBJECTIVE: The object of the study was to test the hypothesis that preeclampsia leads to an abnormal vascular response to increasing blood pressure in cerebral vessels by analyzing the relationship between mean arterial pressure and resistance index in the central retinal, ophthalmic, and middle cerebral arteries in women with normal pregnancies and women with preeclampsia. STUDY DESIGN: Transcranial and color flow Doppler ultrasonographic studies were used to determine systolic, diastolic, and mean velocities and the resistance indexes in the central retinal, ophthalmic, and middle cerebral arteries in 24 women with normal pregnancies and 18 women with preeclampsia. In each group the relationship between the mean arterial pressure and the resistance index was determined for each artery by means of linear regression analysis. The Pearson correlation coefficients for each mean arterial pressure versus resistance index relationship were compared between the groups. In a separate analysis middle cerebral artery data obtained from 79 women with preeclampsia (with and without headache) were compared with data from the normal pregnancy group and analyzed in terms of the relationship between mean arterial pressure and resistance index. RESULTS: The resistance index in women with normal pregnancies decreased with increasing mean arterial pressure in all 3 Vessels studied (ophthalmic artery r= -0.33, central retinal artery r= -0.43, middle cerebral artery r= -0.30). In the women with preeclampsia, however, as mean arterial pressure increased the resistance index increased in the orbital Vessels and decreased in the middle cerebral artery (ophthalmic artery r = 0.54, central retinal artery r= 0.65, middle cerebral artery r= -0.25). The correlation coefficients in the women with preeclampsia were significantly different from those in the women with normal pregnancies for the ophthalmic and central retinal arteries (P =.001) but not for the middle cerebral artery (P =.8). Within-group analysis in the patients with normal pregnancies showed no differences between the correlation coefficients of the studied vessels. In the women with preeclampsia the ophthalmic artery (P=.02) and the central retinal artery (P=.005) were significantly different from the middle cerebral artery but not from each other. Women with preeclampsia who had headache had a different correlation coefficient for the middle cerebral artery than did those without headache (r= -0.34 versus r= 0.23; P <.001). The correlation coefficient for the middle cerebral artery for women with preeclampsia without headache was not significantly different from the central retinal artery and ophthalmic artery correlation coefficients in the general preeclampsia group. CONCLUSIONS: Women with preeclampsia demonstrate a different relationship between blood pressure and resistance index in the ophthalmic and central retinal arteries than do women with normal pregnancies. In the middle cerebral artery, however, preeclampsia does not appear to affect the resistance index response to increasing mean arterial pressure in women with headache. In women with preeclampsia without headache the relationship seen in the ophthalmic artery and central retinal artery is preserved in the middle cerebral artery. This may indicate a failure in the autoregulatory capacity of the middle cerebral artery in the presence of headache. Alternatively the resistance index response in the ophthalmic artery and central retinal artery may represent small-caliber vessel vasospasm that is not present in the middle cerebral artery in women with preeclampsia who have headache.