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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 29, No 3, May/June 2018
148
AFRICA
10 kHz using an A/D converter, and then transferred into a
computer for real-time monitoring and signal analysis.
15
BFV spectra were measured in the relaxed seated posture for
one minute. After real-time monitoring, 30 consecutive cardiac
cycles were selected from one-minute spectra to characterise the
feature points of velocity waveform and calculate its indices. The
waveform was extracted using a threshold method and computed
using an ensemble averaging technique.
The averaged BFV waveform was used to identify velocity
feature points, as shown in Fig. 1 (right side). BFV in CCA were
characterised into five components: peak systolic (S1), second
systolic (S2), insicura between systole and diastole (I), peak
diastolic (D) and end-diastolic (d) velocities.
7
These values were
used to calculate the following velocity indices: resistive index
(RI
=
1 –
d
/S1), velocity reflection index (VRI
=
S2/S1 – 1) and
vascular elasticity index (VEI
=
1 – I/D), which were originally
used by Azhim
et al
.
16
Statistical analysis
Data are expressed as mean and standard error of mean (SEM).
The differences between VF groups as well as BP groups were
analysed by one-way ANOVA. A
p
-value less than 0.05 was
considered statistically significant. Statistical analyses were
performed using the statistical package for the social sciences
software (SPSS 21.0, USA).
Results
Table 1 represents the differences in body mass and metabolic
variables in the VF and BP groups. We found the same pattern
of differences in the three designated groups of VF and BP,
respectively. Participants who were older had higher VF and BP
levels and greater height and weight than younger participants.
BMI, WC and glucose levels were significantly greater in the higher
VF and hypertensive groups. However, there were no significant
differences for height, TC, HDL and LDL in all three BP groups.
As shown in Table 2, hypertensive subjects had higher VF
levels compared to normotensive and pre-hypertensive subjects
(
p
<
0.05). It is to be expected that SBP, DBP and mean BP were
significantly higher in the higher VF group than in other two
groups (Table 3). The most pronounced, S1 velocity, was lower
(
p
<
0.05) in the hypertensive than the normotensive group. The
D velocity was lower (
p
<
0.05) in the pre-hypertensive than the
normotensive group.
There were differences noted in the VRI between the
hypertensive and other two groups. Resistive index was
significantly lower in the hypertensive than in the normotensive
and pre-hypertensive groups. The other BFV waveforms, S2, d
and I, showed no significant differences between the BP groups.
We also found that S1, D velocities, RI and VEI indices were
significantly lower in the higher VF group (
p
<
0.05), as shown
in Table 3. By contrast, VRI was larger in the higher VF group.
Discussion
This study highlights the association between BFV changes and
high VF accumulation and the development of hypertension
in non-obese individuals. It is suggested that lowering VF level
could reduce the incidence of hypertension as an early disease-
prevention step to improve haemodynamic function.
Fat distribution has been receiving increasing attention when
evaluating the development of hypertension.
2,17
Visceral fat has
been demonstrated to have an association with hypertension,
but not other factors, including BMI, subcutaneous fat and
lower-body fat.
2
Our study extends this analysis to emphasise
the relationship between visceral hypertension and BFV of
non-obese individuals.
Similar to our study, a previous study reported that
individuals with essential hypertension suffered from significant
accumulation of VF in the abdominal region.
2
Our study also
showed that elevated VF level leads to a significant increase in
SBP, DBP and MBP (Table 3).
Significant differences in S1, D, RI, VRI and VEI were
observed between the lower VF group and the other two groups.
We found that S1 and D velocities decreased with increasing
VF. It is to be expected that VEI in the higher VF group was
significantly lower due to the significant decrease in D velocity. D
is peak diastolic velocity, which increases due to vascular elastic
Table 2. Changes in blood flow velocities and visceral fat in
normotensive, pre-hypertensive and hypertensive subjects
Variable
Normotensive Pre-hypertensive Hypertensive
p
-value
VF (level)
2.4
±
0.2
5.3
±
0.5*
8.5
±
1*
†
<
0.01
Blood flow velocities (cm/s)
d
20.6
±
0.7
20.3
±
0.7
22
±
1.4
NS
S1
100.6
±
2.2
93.9
±
3.4
79.4
±
4.6*
<
0.01
S2
54.4
±
1.9
52.6
±
2.1
60.9
±
2.2
NS
I
32
±
1.3
29.7
±
1.1
31.3
±
1.9
NS
D
44.9
±
1.1
41.0
±
1.0*
39.7
±
2.2
<
0.05
RI
0.794
±
0.008 0.776
±
0.009 0.719
±
0.016*
†
<
0.01
VRI
–0.453
±
0.021 –0.412
±
0.030 –0.215
±
0.037*
†
<
0.01
VEI
0.295
±
0.017 0.277
±
0.019 0.212
±
0.021 NS
Data are presented as mean
±
SEM. Significantly different: *
p
<
0.05 vs normo-
tensive group;
†
p
<
0.05 vs pre-hypertensive group.
NS: not significant. VF: visceral fat; d: end-diastolic velocity; S1: peak systolic
velocity; S2: second systolic velocity; I: insicura between systole and diastole; D:
peak diastolic velocity; RI; VRI: velocity reflection index; VEI: vascular elastic-
ity index.
Table 3. Effect of different levels of visceral fat on
blood pressure readings and blood flow velocities
Variable
Lower VF
Middle VF
Higher VF
p
-value
BP data (mmHg)
SBP
113.1
±
1.5
123.6
±
2.7*
134.9
±
3.2*
†
<
0.01
DBP
68.6
±
1.2
75.3
±
1.8*
87.2
±
2.6*
†
<
0.01
MBP
83.5
±
1.2
91.4
±
1.9*
103.1
±
2.7*
†
<
0.01
Blood flow velocities (cm/s)
d
20.5
±
0.7
20.5
±
1.1
20.6
±
0.8
NS
S1
99.3
±
2.2
98.6
±
4.7
80.7
±
3.2*
†
<
0.01
S2
53.5
±
1.7
54.0
±
3.1
56.9
±
1.7
NS
I
31.5
±
1.2
30.3
±
1.7
30.5
±
1.1
NS
D
44.4
±
1.0
42.1
±
1.6
38.9
±
1.2*
<
0.05
RI
0.789
±
0.008 0.786
±
0.012 0.740
±
0.011*
†
<
0.01
VRI
–0.449
±
0.021 –0.426
±
0.041 –0.278
±
0.027*
†
<
0.01
VEI
0.297
±
0.016 0.286
±
0.024 0.215
±
0.014*
<
0.05
Data are presented as mean
±
SEM. Significantly different: *
p
<
0.05 vs lower
VF group;
†
p
<
0.05 vs middle VF group.
NS: not significant, VF: visceral fat, BP: blood pressure, SBP: systolic blood
pressure; DBP: diastolic blood pressure; d: end-diastolic velocity; S1: peak
systolic velocity; S2: second systolic velocity; I: insicura between systole and
diastole; D: peak diastolic velocity; RI; VRI: velocity reflection index; VEI:
vascular elasticity index.