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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 27, No 4, July/August 2016
266
AFRICA
Discussion
As expected, we found that hypertensive black Africans
presented with reduced carotid distensibility when compared to
normotensives. In fact, we found significant differences for all
carotid wall thickness and distensibility measurements between
the hypertensives and normotensives prior to adjustments.
However, upon adjustment for cSBP, all differences disappeared.
The direct physical measures, such as IMT, CSWA and LD, were
similar between the hypertensive and normotensive groups after
adjustments for both cSBP andMAP. This similarity suggests that
the decreased carotid distensibility and increased carotid cross-
sectional wall area of five-year sustained hypertensive Africans
are, besides structural changes due to arterial degeneration,
also dependent on the distending pressure, and that functional
changes in the carotid artery may be more prominent than
structural changes in this population.
Our findings are consistent with evidence in white populations
that show increased stiffness to be due to the increased distending
pressure that accompanies hypertension, suggesting a functional
adaptation, and not only structural alterations of the arterial
wall.
25,26
In contrast to these and our findings, one study found
that the acute reduction in blood pressure by nitroglycerin does
not normalise large artery stiffness in essential hypertensives.
27
It is expected that sustained high blood pressure, as seen in
hypertension, would cause vascular damage by, for instance,
altering the collagen–elastin ratio of the arterial wall in favour of
collagen.
28,29
Indeed, after adjustment for mean arterial pressure,
the difference in carotid distensibility between the hypertensives
and normotensives remained, therefore suggesting the presence
of structural alterations. Nevertheless, in light of the significant
Table 3. Carotid characteristics of normotensive and hypertensive black
Africans, adjusted for potential confounders
Normotensive
(
n
=
241)
Hypertensive
(
n
=
351)
p
-value
Carotid characteristics after adjustment for central SBP
Distensibility
×
10
-3
, 1/kPa
3.77
±
1.98 3.95
±
2.22 0.50
Young’s elastic modulus
×
10
3
, kPa 3.04
±
1.84 2.80
±
2.05 0.34
Beta-stiffness index
8.43
±
4.21 8.02
±
4.61 0.47
Intima–media thickness, mm
0.71
±
0.14 0.73
±
0.17 0.19
Cross-sectional wall area, mm
2
15.2
±
4.96 16.2
±
5.25 0.09
Lumen diameter maximum, mm 6.30
±
0.82 6.41
±
1.04 0.34
Lumen diameter minimum, mm 5.85
±
0.94 6.02
±
0.89 0.12
Carotid characteristics after adjustment for mean arterial pressure
Distensibility
×
10
-3
, 1/kPa
4.38
±
2.45 3.35
±
2.66 0.0034
Young’s elastic modulus
×
10
3
, kPa 2.46
±
2.30 3.39
±
2.64 0.0082
Beta-stiffness index
7.13
±
4.68 9.32
±
5.20
<
0.001
Intima–media thickness, mm
0.71
±
0.14 0.73
±
0.18 0.42
Cross-sectional wall area, mm
2
15.6
±
5.57 16.0
±
6.07 0.35
Lumen diameter maximum, mm 6.30
±
0.97 6.44
±
1.07 0.32
Lumen diameter minimum, mm 5.86
±
0.97 6.06
±
0.92 0.17
Data are arithmetic means
±
SD. Data adjusted for age, gender, waist circumfer-
ence,
γ
-glutamyl transferase, tobacco and anti-hypertensive medication use.
Table 4. Carotid characteristics of normotensive, untreated and
treated hypertensive black Africans, adjusted for potential
confounders including central systolic blood pressure
Carotid characteristics
Normo-
tensive
(n
=
241)
Untreated
hyper-
tensives
(
n
=
227)
Treated
hyper-
tensives
(
n
=
124)
p
-value
Distensibility
×
10
-3
, 1/kPa
3.53
±
2.10 3.70
±
1.77 3.47
±
1.70 0.59
Young’s elastic modulus
×
10
3
, kPa 3.28
±
2.07 3.04
±
1.74 3.29
±
1.70 0.44
Beta-stiffness index
8.83
±
4.56 8.42
±
3.80 8.62
±
3.67 0.75
Intima–media thickness, mm 0.73
±
0.14 0.75
±
0.14 0.73
±
0.10 0.15
Cross-sectional wall area, mm
2
15.9
±
5.38 16.8
±
4.35 15.9
±
4.34 0.09
Lumen diameter maximum, mm 6.34
±
0.94 6.46
±
0.83 6.50
±
0.80 0.48
Lumen diameter minimum, mm 5.89
±
0.94 6.06
±
0.83 6.12
±
0.80 0.17
Data are arithmetic means
±
SD. Data adjusted for age, gender, waist circumfer-
ence,
γ
-glutamyl transferase, tobacco use and central systolic blood pressure.
Table 5. Anti-hypertensive medication use in the hypertensive group
Type of anti-hypertensive medication
Hypertensive participants
using medication
(
n
=
124)
Unspecified,
n
, total, (%)
61/124 (49.2)
Beta-blockers,
n
, total, (%)
12/124 (9.68)
Anti-adrenergics,
n
, total, (%)
2/124 (1.61)
Calcium channel blockers,
n
, total, (%)
30/124 (24.2)
Class 2 ACE inhibitors,
n
, total, (%)
49/124 (39.5)
Diuretics,
n
, total, (%)
54/124 (43.5)
n,
number of participants. Unspecified: only indicated as high blood pressure
pills or hypertension medication.
Table 6. Forward stepwise multiple regression analyses with carotid
distensibility and carotid intima–media thickness as dependent variables
Normotensive
(
n
=
241)
β
(95% CI)
p
-value
Hypertensive
(
n
=
351)
β
(95% CI)
p
-value
Distensibility (1/kPa)
Adjusted
R
2
0.27
0.37
Locality (urban)
–0.16 (–0.31– –0.01) 0.031
Age, years
–0.14 (–0.29–0.003) 0.058 –0.20 (–0.35– –0.05) 0.009
Waist circumference,
cm
0.22 (0.06–0.39)
0.007
Central SBP, mm Hg –0.44 (–0.59– –0.29)
<
0.001 –0.56 (–0.68– –0.45)
<
0.001
Heart rate, bpm –0.10 (–0.25–0.04)
0.16 –0.12 (–0.23– –0.01) 0.030
LDL-C, mmol/l
0.08 (–0.03–0.19)
0.18
HbA
1c
(%)
–0.14 (–0.26– –0.02) 0.018
CrCl, ml/min
–0.10 (–0.28–0.07)
0.24
ICAM-1, pg/ml
0.11 (–0.04–0.25)
0.16
Tobacco use (no/yes) –0.14 (–0.28–0.003) 0.058
IMT (mm)
Adjusted
R
2
0.25
0.35
Locality (urban)
–0.10 (–0.20– –0.01) 0.030
Gender (male)
0.26 (0.13–0.39)
<
0.001 0.25 (0.15–0.36)
<
0.001
Age, years
0.33 (0.21–0.46)
<
0.001 0.44 (0.34–0.54)
<
0.001
Waist circumference,
cm
0.14 (0.01–0.28)
0.033 0.08 (–0.02–0.19)
0.13
Central SBP, mm Hg
0.12 (0.02–0.22)
0.016
Heart rate, bpm –0.08 (–0.20–0.05)
0.21
LDL-C, mmol/l
0.07 (-0.05–0.19)
0.29 0.15 (0.05–0.25)
0.005
HbA
1c
(%)
0.07 (–0.03–0.18)
0.17
C-reactive protein,
pg/ml
0.16 (0.03–0.30)
0.017 0.06 (–0.04–0.16)
0.27
ICAM-1, pg/ml
0.12 (–0.01–0.24)
0.079
γ
-glutamyl
transferase, U/l
–0.08 (–0.18–0.02)
0.12
Tobacco use (no/yes)
–0.08 (–0.18–0.02)
0.11
Anti-hypertension
medications (no/yes)
–0.10 (–0.19– –0.003) 0.044
Data expressed as beta-values and 95% confidence intervals,
p
-values obtained with
forward stepwise multiple regression analyses. Included in each model: locality, age,
gender, waist circumference, heart rate, cSBP, LDL-C, HbA
1c
, C-reactive protein,
ICAM-1, creatinine clearance,
γ
-glutamyl transferase, tobacco and anti-hyperten-
sive medication use.
IMT, carotid–intima media thickness; CSWA, cross-sectional wall area; Max LD,
maximum lumen diameter; SBP, systolic blood pressure; LDL-C, low-density lipo-
protein cholesterol; HbA
1c
, glycated haemoglobin; ICAM-1, intercellular adhesion
molecule-1.