Ma. Belfort et al., Effects of blood pressure on orbital and middle cerebral artery resistances in healthy pregnant women and women with preeclampsia, AM J OBST G, 180(3), 1999, pp. 601-607
OBJECTIVE: The object of the study was to test the hypothesis that preeclam
psia leads to an abnormal vascular response to increasing blood pressure in
cerebral vessels by analyzing the relationship between mean arterial press
ure and resistance index in the central retinal, ophthalmic, and middle cer
ebral 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 res
istance indexes in the central retinal, ophthalmic, and middle cerebral art
eries in 24 women with normal pregnancies and 18 women with preeclampsia. I
n each group the relationship between the mean arterial pressure and the re
sistance index was determined for each artery by means of linear regression
analysis. The Pearson correlation coefficients for each mean arterial pres
sure 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 betwee
n mean arterial pressure and resistance index.
RESULTS: The resistance index in women with normal pregnancies decreased wi
th increasing mean arterial pressure in all 3 Vessels studied (ophthalmic a
rtery 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 decreas
ed in the middle cerebral artery (ophthalmic artery r = 0.54, central retin
al artery r= 0.65, middle cerebral artery r= -0.25). The correlation coeffi
cients in the women with preeclampsia were significantly different from tho
se in the women with normal pregnancies for the ophthalmic and central reti
nal arteries (P =.001) but not for the middle cerebral artery (P =.8). With
in-group analysis in the patients with normal pregnancies showed no differe
nces between the correlation coefficients of the studied vessels. In the wo
men with preeclampsia the ophthalmic artery (P=.02) and the central retinal
artery (P=.005) were significantly different from the middle cerebral arte
ry but not from each other. Women with preeclampsia who had headache had a
different correlation coefficient for the middle cerebral artery than did t
hose without headache (r= -0.34 versus r= 0.23; P <.001). The correlation c
oefficient for the middle cerebral artery for women with preeclampsia witho
ut 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 b
etween blood pressure and resistance index in the ophthalmic and central re
tinal arteries than do women with normal pregnancies. In the middle cerebra
l artery, however, preeclampsia does not appear to affect the resistance in
dex response to increasing mean arterial pressure in women with headache. I
n women with preeclampsia without headache the relationship seen in the oph
thalmic artery and central retinal artery is preserved in the middle cerebr
al artery. This may indicate a failure in the autoregulatory capacity of th
e middle cerebral artery in the presence of headache. Alternatively the res
istance index response in the ophthalmic artery and central retinal artery
may represent small-caliber vessel vasospasm that is not present in the mid
dle cerebral artery in women with preeclampsia who have headache.