Department of Perinatal and Maternal Medicine,
National Defense Medical College,
Saitama, Japan
To the Editor:
Cockell and Poston (April 1997)1 reported
that flow-mediated vasodilation is enhanced in pregnant women but
reduced in preeclampsia. They assessed the vasodilation using biopsies
of small arteries. Therefore, their assessment was not in vivo but in
vitro study. We assessed flow-mediated vasodilation in pregnant women
noninvasively. Noninvasive assessment of flow-mediated vasodilation in
nonpregnant subjects was first reported by Celermajer et
al,2 who measured the brachial artery with
high-resolution ultrasound (7.5-MHz transducer). We previously reported
that with a 30-MHz transducer it is possible to detect
endothelial dysfunction more accurately by measuring
the radial artery.3
We examined 60 Japanese women including 20 nonpregnant normotensive
healthy women (28.7±5.0 years old), 18 normal pregnant women
(31.3±5.0 years old, 35.8±3.1 weeks of pregnancy), and 22 pregnant
women with preeclampsia (29.8±3.8 years old, 36.0±3.3 weeks of
pregnancy). The diagnosis of preeclampsia was made according to the
criteria of the Committee on Terminology of the American Collage of
Obstetricians and Gynecologists.4 All 60 subjects
were nonsmokers.
Images of the radial artery in 60 women were obtained longitudinally
with a 30-MHz mechanical linear probe and an SSD-550 system (Aloka,
Tokyo, Japan). In each study, we confirmed the clear visualization of
the three layers of the vessel wall, including the "m" lines (the
interface between media and adventitia) in both near and far walls.
When the clear visualization of these layers was confirmed, the probe
was fixed with a steel flexible arm. Adequate scans were obtained in
all cases. A cuff of 140 mm in width placed on the upper arm was
inflated to 30 mm Hg above the systolic pressure for 5
minutes. The radial artery diameter was measured before inflation
(baseline) and after deflation of the cuff. Imaging of the artery was
performed for 6 minutes after cuff deflation. The radial artery
diameter was defined as the distance from the near side of the "m"
line in the near wall to the near side of the "m" line in the far
wall. Measurements were taken within 1 minute before cuff inflation
(baseline) and 30, 60, 90, 120, 180, 240, 300, and 360 seconds after
cuff deflation at end diastole. Flow-mediated vasodilation
was determined by calculating the change in the radial artery diameter
(percent increase for the baseline diameters). Student's t
test was used for statistical analysis, and a value of
P<.01 was considered significant.
Baseline radial artery diameters in nonpregnant women, normal pregnant
women, and preeclamptic women were 2.26±0.42, 2.41±0.38, and
2.22±0.35 mm, respectively. No significant differences were seen
among these groups. Maximum dilation was obtained 1 minute after cuff
deflation. The percent increases of radial artery diameter during
reactive hyperemia in nonpregnant women, normal pregnant women,
and preeclamptic women were 11.8±3.6%, 18.9±3.4%, and 7.9±3.0%,
respectively. In normal pregnant women, vasodilation was significantly
greater than that in nonpregnant women (P<.001).
Vasodilation in preeclamptic women was significantly less than that in
normal pregnant women (P<.001) or nonpregnant women
(P<.001).
Our results indicate that peripheral vascular
endothelial function in pregnant women was improved,
but in preeclamptic women endothelial function was
impaired. Our conclusions were in accordance with the findings of
Cockell and Poston. Using our method, we can asses the
endothelial function in pregnant women noninvasively.
Because Cockell and Poston used biopsies obtained at cesarean section,
their assessment was limited to subjects at or near term, but our
method is applicable to subjects even in early pregnancy. Further work
is in progress to evaluate the usefulness of our method as a predictor
of preeclampsia.
References
1.
Cockell AP, Poston L. Flow-mediated vasodilation
is enhanced in normal pregnancy but reduced in preeclampsia.
Hypertension. 1997;30:247–251.
2.
Celermajer DS, Sorensen KE, Gooch VM, Spiegelhalter DJ, Miller
OI, Sullivan ID, Lloyd DJ, Deanfield JE. Non-invasive detection of
endothelial dysfunction in children and adults at risk
of atherosclerosis. Lancet. 1992;340:1111–1115.[Medline]
[Order article via Infotrieve]
3.
Kobayashi H, Yoshida A, Kobayashi M, Nakao S. Non-invasive
detection of endothelial dysfunction with 30 MHz
transducer. Lancet. 1996;347:1336–1337.
4.
American College of Obstetricians and Gynecologists.
Hypertension in Pregnancy. Technical Bulletin No. 219.
Washington, DC: ACOG; 1996.
Fetal Health Research Group,
Division of Obstetrics and Gynaecology,
St Thomas' Hospital,
London, UK
We read with interest the letter of Yoshida et al describing a
study of the reactive hyperemic response in radial arteries of
nonpregnant and pregnant women and of patients with preeclampsia. Using
ultrasonography, the authors have shown blunted dilatation after cuff
inflation on the upper arm in women with preeclampsia when compared
with findings in normal pregnant women. These data would appear to
confirm our in vitro findings described in
Hypertension,1 in which we showed
blunted endothelium-dependent, nitric oxide–mediated
dilatation to shear stress in small arteries obtained during caesarean
section from women with preeclampsia. However, some degree of caution
should be applied when ascribing endothelium dependence
to the abnormal dilatory response in the radial arteries, since
vasodilation induced by hyperemia of the upper arm will
undoubtedly lead to endothelium-independent elements of
relaxation unrelated to increased flow per se2 in
the lower arm. Previous studies have circumvented this problem by
applying the cuff to the lower arm, thus evoking an increase in shear
stress in the upper arm but precluding any influence of locally acting
metabolites.3 Nonetheless, Yoshida et al have
shown clearly that vasodilator responses are significantly increased in
pregnant women compared with nonpregnant and are blunted in women with
preeclampsia. Together with our observations in resistance-sized
arteries in vitro, these data add further strength to the hypothesis
that impairment of vasodilatory responses may contribute to elevation
of the blood pressure in women with preeclampsia.
References
1.
Cockell AP, Poston L. Flow-mediated vasodilation is
enhanced in normal pregnancy but reduced in preeclampsia.
Hypertension. 1997;30:247–251.
2.
Meredith IT, Currie KE, Roddy MA, Ganz P, Creager MA.
Postischemic vasodilation in human forearm is dependent on
endothelium-derived nitric oxide. Am J
Physiol. 1996;270:H1435–H1440.
3.
Celermajer DS, Adams MR, Clarkson P, Robinson J, McCredie
R, Donald A, Deanfield JE. Passive smoking and impaired
endothelium-dependent arterial dilatation
in healthy young subjects. N Engl J Med. 1996;334:150–154.
© 1998 American Heart Association, Inc.
Letters to the Editor
Noninvasive Assessment of Flow-Mediated Vasodilation With 30-MHz Transducer in Pregnant Women
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