Full text of DOI:10.1002/clc.4960250610

Clin. Cardiol. 25, 291–294 (2002)
Short- and Long-Term Changes of Flow-Mediated Vasodilation in Patients
under Statin Therapy
MATTHIAS FRICK, M.D., HANNES F. ALBER, M.D., HEIKE HÜGEL, SEVERIN P. SCHWARZACHER, M.D., OTMAR PACHINGER, M.D.,
FRANZ WEIDINGER, M.D.
Division of Cardiology, Department of Medicine, University of Innsbruck, Innsbruck, Austria
tion in response to lipid-lowering therapy or other therapeutic
interventions in long-term studies.
Summary
Background: Flow-mediated vasodilation (FMD) of the
brachial artery (BA) has been shown to improve in response
to lipid-lowering therapy and other therapeutic interventions,
usually within 1 to 2 months. Whether FMD remains im-
proved under therapy in the longer term is unknown.
Hypothesis: The aim of this study was to examine the short-
and long-term changes of FMD under statin therapy.
Key words: flow-mediated vasodilation, statins, brachial
artery, ultrasound
Introduction
Methods: Flow-mediated vasodilation and nitroglycerin-
mediated vasodilation (NMD) of the BA were measured with
high-resolution ultrasound (13 MHz) at baseline and at 4 and
10 months in 18 consecutively recruited patients with coro-
nary artery disease (CAD), in whom statin therapy was newly
established.
Results: The decrease of total plasma cholesterol levels
after 4 and 10 months of statin therapy (243 ± 31 vs. 186 ± 30
vs. 191 ± 40 mg/dl; p < 0.001) was accompanied by an increase
in FMD from 4.4 ± 3.8% at baseline to 9.6 ± 2.7% at 4 months
and to 9.5 ± 2.6% at 10 months (p < 0.001). Nitroglycerin-me-
diated vasodilation showed a trend toward improvement after 4
months (14.6 ± 7.5 vs. 19.1 ± 3.6 vs. 19.4 ± 5.6%; NS). The
FMD/NMD ratio also rose significantly after 4 months and re-
mained improved after 10 months of statin therapy (0.31 ± 0.25
vs. 0.52 ± 0.16 vs. 0.50 ± 0.14; p < 0.01).
Endothelial dysfunction occurs at an early stage of athero-
sclerosis1, 2 and is closely associated with most cardiovascular
risk factors.3 Therefore, the clinical assessment of endothelial
function has become of major interest in the past years.4, 5 The
measurement of flow-mediated vasodilation (FMD) of the
brachial artery (BA) with high-resolution ultrasound is com-
pletely noninvasive and has been tested in patients with cardio-
vascular risk factors6, 7 and coronary artery disease (CAD).8, 9
Flow-mediated vasodilation has shown good correlation with
coronary endothelial function10 and with the extent of CAD as
assessed by angiography.9
However, its value in long-term studies of endothelial func-
tion remains unclear. Most studies have reported a short-term
(within 1–2 months) improvement of FMD following statin
therapy11–13 or other therapeutic interventions.14, 15 Whether
FMD shows sustained improvement over a longer period of
time, which is a prerequisite for the use of FMD as a follow-up
parameter, has not been studied.
Conclusion: Statin therapy is associated with sustained im-
provement of endothelial function up to 10 months. These data
support the utility of FMD for the assessment of vascular func-
Therefore, the aim of this study was to examine the course
of FMD in patients with newly established statin therapy over
10 months.
Methods
Patients
Address for reprints:
Dr. Franz Weidinger
Cardiology Division, Department of Medicine
Anichstrasse 35
A-6020 Innsbruck, Austria
e-mail: F.Weidinger@uibk.ac.at
Written informed consent was obtained from all patients.
The study group consisted of 18 consecutive patients (mean
age 49 ± 8 years; range 37–67 years) with elevated plasma
cholesterol levels, in whom coronary angiography was per-
formed for the evaluation of chest pain. Patients with conges-
Received: July 5, 2001
Accepted with revision: November 2, 2001

292
Clin. Cardiol. Vol. 25, June 2002
tive heart failure or valvular heart disease were excluded from
the study. Coronary artery disease was defined as visually esti-
mated percent diameter stenosis ≥30% in one or more major
vessels. Statin therapy was begun in accordance with National
Cholesterol Education Program (NCEP) guidelines.16 Nine
patients received atorvastatin, five patients pravastatin, and
four patients simvastatin. Coronary risk factors were defined
as previously reported.4, 9 Investigations were undertaken in
accordance with the Declaration of Helsinki.
The spontaneous course (repeatability) was assessed by
comparing FMD values of two visits (4 months study interval)
in 17 patients with CAD or risk factors (Table I), whose medi-
cation was left unchanged 3 months before the first visit and
during the 4-month interval.
Statistics
Data are expressed as mean ± standard deviation (SD). Nor-
mal distribution of variables was tested using the Kolmo-
gorov-Smirnov test with Lilliefors correction. Analysis of
variance (ANOVA) followed by the Scheffé-test was used for
comparison of variables among the three visits. Interobserver
variability was expressed as mean difference of FMD and lin-
ear regression analysis was calculated. Differences were con-
sidered statistically significant at p < 0.05.
Study Protocol
On the day after angiography, patients underwent assess-
ment of FMD by high-resolution ultrasound (13 MHz Sequoia
C 256, Acuson [Siemens], Mountain View, Calif.) and plasma
lipid levels were measured. Measurements of FMD and plas-
ma lipid were repeated after 4 months in all patients and after
10 months in 16 patients. Two patients withdrew before com-
pletion of the study.
Results
Assessment of Vasodilation
Characteristics of patients are shown in Table I. Total and
low-density lipoprotein (LDL) cholesterol decreased signifi-
cantly after 4 months and remained stable after 10 months of
statin therapy (Table II). High-density lipoprotein (HDL)
cholesterol and triglycerides did not change over the entire
study period (Table II).
Flow-mediated vasodilation improved from 4.4 ± 3.8 to
9.5 ± 2.7% after 4 months and to 9.5 ± 2.6% after 10 months
of statin therapy (p < 0.001) (Fig. 1A), whereas resting diame-
ters did not change (4.3 ± 0.8 vs. 4.1 ± 0.5 vs. 4.1 ± 0.5 mm;
Changes of vessel diameter after reactive hyperemia (endo-
thelium-dependent vasodilation) and after sublingual nitro-
glycerin application (endothelium-independent vasodilation)
were measured according to previously described methods.4, 9
The ultrasound examination was performed between noon and
2 P.M. by an observer blinded to the patient’s diagnosis and
drug treatment. All vasoactive drugs were withdrawn 18–24 h
before examination. Patients were instructed not to smoke and
to remain fasting prior to the ultrasound examination.
The right BA was scanned longitudinally above the antecu-
bital fossa. After optimizing the transducer position as well as
depth and gain settings, images were stored electrocardio-
gram (ECG)-triggered to the peak of the T wave on the hard
disk. Scans were taken at rest after lying for at least 10 min and
the mean of three measurements was defined as resting diam-
eter. After suprasystolic compression at 260 mmHg for 4.5
min of the right upper arm, the cuff was deflated and serial
posthyperemia BA images were again stored on the hard disk.
The mean of three maximum diameters within 120 s after
compression formed the posthyperemia diameter. After sub-
lingual application of 0.8 mg nitroglycerin, the mean of the
three maximum diameters within the following 10 min was
calculated. In addition, the FMD/NMD ratio was calculated to
evaluate the endothelium-dependent dilation (FMD) in rela-
tion to the maximum dilation of the BA as assessed by nitro-
glycerin application.
TABLE I Baseline characteristics of patients
Statin patients
Control patients
Patients
Age (range)
n = 18
49.3 ± 7.6
(37–67)
2.4 ± 0.8
(0–4)
n = 17
52.1 ± 10.5
(36–68)
1.2 ± 0.9
(0-–2)
7 (41.2)
2 (11.8)
9 (52.9)
2 (11.8)
7 (41.2)
1 (5.9)
2 (11.8)
177.6 ± 36.7
(119–233)
94.2 ± 29.5
(62–143)
26.2 ± 3.3
(20.8–31.5)
Number of risk factors
CAD (%)
Myocardial infarction (%)
Hypertension (%)
18 (100)
7 (38.9)
7 (38.9)
11 (61.1)
18 (100)
1 (5.6)
6 (33.3)
243 ± 31
(200–298)
163 ± 22
(120–189)
27 ± 3
Smoking (%)
Hypercholesterolemia (%)
Diabetes mellitus (%)
Positive family history (%)
Total cholesterol (mg/dl)
Assessment of Variability and Repeatability
LDL cholesterol (mg/dl)
BMI (kg/m2)
Interobserver variability was assessed using two methods.
First, 136 vessel diameters from 11 patients were measured
offline by two observers from images stored on the hard disk.
In addition, variability of FMD of these 11 patients was calcu-
lated. Second, scans were taken by two observers separately in
the same patients (n = 12).
(20–30)
Abbreviations: CAD = coronary artery disease, BMI = body mass in-
dex, LDL = low-density lipoprotein.

M. Frick et al.: Long-term changes of FMD
293
TABLE II Changes of plasma lipid levels and body mass index
Discussion
After 4
months
After 10
months
In this study we found that FMD showed sustained im-
provement in patients under statin therapy over the course
of 10 months. To the best of our knowledge, this is the first
study documenting a long-term improvement in peripheral
endothelial function under statin therapy beyond 6 months. In
addition, analysis of the spontaneous course (repeatability)
revealed that the mean FMD difference in patients with un-
changed medication was below the improvement seen in pa-
tients under statin therapy.
Previous studies have revealed that statin therapy may im-
prove endothelial function after a very short treatment period.
For example, Vogel et al. observed an increase of FMD in pa-
tients with total cholesterol levels between 175 and 215 mg/dl
after 2 weeks of simvastatin therapy.11 Another study of mi-
crovascular endothelial function in the forearm showed an
improvement of vascular function under simvastatin therapy
after 1 month.12
In our study, FMD increased after 4 months of statin thera-
py and remained improved over a period of 10 months. The
demonstration of sustained improvement of FMD under
statin therapy is a prerequisite for the use of this noninvasive
test as a follow-up parameter in long-term studies, because in
most FMD studies the observation period was limited to 1–3
months. Furthermore, spontaneous variations of FMD may
result from its susceptibility to current influences such as
smoking,17 high-fat meals,18 or daytime of examination,19 all
of which are potential limitations for the use of this method as
a follow-up test. These influences can be minimized under
standardized conditions as shown in this study.
Besides reducing cholesterol levels, Laufs et al. have
demonstrated another possible mechanism leading to an im-
provement of endothelial function by statins.20 They have
shown that statins can enhance the stability of endothelial ni-
tric oxide synthase mRNA and thereby increase the generation
of nitric oxide (NO).20 The strong trend toward improvement
of NMD seen in our study suggests a possible role of statins
also in the modulation of smooth muscle cell function. Indeed,
Baseline
p Value
Total cholesterol 243 ± 31
LDL cholesterol 163 ± 22
186 ± 32
105 ± 29
45 ± 11
191 ± 40
111 ± 35
47 ± 15
181 ± 87
26 ± 3
< 0.001
< 0.001
NS
NS
NS
HDL cholesterol
Triglycerides
BMI (kg/m2)
42 ± 11
242 ± 134 193 ± 78
27 ± 3 26 ± 3
Plasma lipid levels are given in mg/dl.
Abbreviations: HDL = high-density lipoprotein, NS = not significant.
Other abbreviations as in Table I.
NS). Improvement of FMD > 3% was seen in 10 patients at 4
months follow-up and < 3% in 5 patients. One patient showed
a slight decrease. At 10 months follow-up, additional improve-
ment of FMD (> 3%) was seen in three patients, and in two pa-
tients FMD decreased by <3%. Eleven patients remained vir-
tually the same (Fig. 2).
Nitroglycerin-mediated vasodilation increased nonsignifi-
cantly from 14.6 ± 7.5 to 19.1 ± 3.6% after 4 months and to 19.4
± 5.6% after 10 months (p = 0.08) (Fig. 1B). In addition, the
FMD/NMD ratio showed an improvement after 4 months
(0.52 ± 0.16 vs. 0.31 ± 0.25 at baseline) and remained increased
after 10 months of statin therapy (0.50 ± 0.14, p< 0.01).
The mean difference in measurements of the BA diameter
from images (n = 136) stored on the hard disk between two
observers was 0.04 ± 0.04 mm (r = 0.99; p < 0.001). The inter-
observer variability of calculated FMD showed a mean differ-
ence of 0.5 ± 0.5% (r = 0.99; p < 0.001). In addition, variabili-
ty of resting diameters in 12 patients, which were measured
online consecutively by two observers, was 0.06 ± 0.04 mm
(r = 0.98; p < 0.001).
The spontaneous course (repeatability) of FMD in patients
whose medication was left unchanged revealed a mean differ-
ence of 3.1 ± 2.5% FMD and similar group mean values (8.3
± 3.7 vs. 8.8 ± 3.2%; NS) between measurements at baseline
and at 4 months.
20
15
10
5
NS
*
14
12
10
8
6
4
25
20
*
15
10
5
2
0
0
Baseline 4-Months 10-Months
follow-up follow-up
Baseline 4-Months 10-Months
follow-up follow-up
0
(A)
(B)
ꢀ5
FIG. 1 (A) Long-term course of flow-mediated vasodilation (FMD);
FMD increased significantly after 4 months of statin therapy and re-
mained sustained improved after 10 months. (B) Long-term course of
nitroglycerin-mediated vasodilation (NMD). Although there was a
clear trend toward improvement, the difference did not yield signifi-
cance. NS = not significant. * p < 0.001.
Baseline
4-Months
follow-up
10-Months
follow-up
FIG. 2 Line graph showing the long-term course of flow-mediated
vasodilation (FMD) in individual patients. Nearly all patients con-
sistently showed an increase in FMD over time.

294
Clin. Cardiol. Vol. 25, June 2002
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One major concern with FMD testing has been interindivid-
ual variation as well as considerable variability of measure-
ments. Our results show that with higher frequency ultrasound
(13 MHz) the interobserver variability of both single-vessel
diameter measurements and FMD is very low (0.5%) and
compares favorably with an earlier study using 7.5 MHz.4 The
spontaneous course (repeatability) showed a mean difference
in FMD of 3%, which is slightly higher than that in previous
studies.4, 9 This is likely related to the longer study interval, to
different risk factor profile of patients, and to changes in
lifestyle and dietary habits, which have been undertaken dur-
ing the course of the study.
This study did not include a placebo-control group because
of ethical considerations. However, it was our aim to focus on
methodological aspects rather than on the efficacy of statin
therapy in improving endothelial function in a randomized
fashion. The nonsignificant improvement of NMD as well as
the additional myogenic and metabolic factors, which may be
involved in the stimulus for reactive hyperemia and conse-
quently FMD, may suggest that the statin effect is not specific
for endothelial function. Nevertheless, Joannides et al. have
shown that the NO inhibitor L-NMMA almost completely
blocked the posthyperemic large artery vasodilation, suggest-
ing NO to be the most important factor responsible for FMD.22
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Conclusion
Flow-mediated vasodilation shows sustained improvement
under statin therapy over the course of 10 months and a stable
spontaneous course in patients with unchanged medication
over a 4-month period. These results support the utility of
FMD testing in long-term treatment trials.
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