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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 32, No 3, May/June 2021
AFRICA
135
Vessel widths were calculated by measuring the six largest
arterioles and six largest venules coursing through a zone
between 0.5 and one disc diameter from the optic disc margin.
Estimates are summarised as CRAE and CRVE, representing the
average diameter (
µ
m) of the arterioles and venules, respectively.
28
Standard procedure was to calculate the CRAE and CRVE values
from the optic disc-centred image of the right eye. The left eye
was used only when gradable right eye images were not obtained.
The retinal arteriolar–venular ratio (AVR) was calculated
separately, which serves as a dimensionless measurement
independent of the optical properties of the eye and camera.
Additionally, fundus images were analysed by an independent
retinal grading expert blinded to the participants’ demographic,
medical and other study results.
The presence or absence of the following parameters, all
associated with possible underlying cardiometabolic disorders,
were assessed qualitatively in a binary fashion: retinal tortuosity,
cotton wool spots, retinal haemorrhage, telangiectasia and
micro-aneurysms. The presence of any cotton wool spots,
retinal haemorrhage, teleangiectatic vessels or micro-aneurysms
were counted as positive for each parameter, whereas retinal
tortuosity was determined according to a pictorial grading scale,
as previously published.
29
Statistical analysis
All data were statistically analysed with Statistica
TM
version 13.3
(TIBCO Software Inc, CA, USA). Continuous variables with
normal distributions are expressed as mean (standard deviation)
or mean [95% confidence interval (CI)], and non-parametric
data as median (interquartile range). Independent
t
-tests and
Mann–Whitney
U
-tests (with continuity correction) were used to
compare parametric and non-parametric continuous variables,
respectively, among male and female groups, and the Fisher exact
(two-tailed) test to compare categorical variables. Correlations
between continuous cardiometabolic variables and vascular
variables (FMD%, CRAE, CRVE and AVR) were evaluated
by Pearson’s correlation coefficient (non-parametric data were
normalised by logarithmic transformation where indicated).
The relationship between categorical cardiovascular risk factor
variables (expressed as ‘yes’ or ‘no’) and vascular variables was
evaluated by analysis of co-variance (ANCOVA) after adjusting
for age and/or gender where indicated. Statistical significance
was set at
p
<
0.05 for all statistical models.
Results
The study enrolled 66 participants (55% female) with a mean age
of 35.4 (10.6) years. Continuous demographic, anthropometric,
biochemical and vascular data for the whole cohort are depicted
in Table 1, in which additional comparisons are made between
the male and female subsets. Mean WHR, median BMI and
median waist circumference values for the whole cohort fell well
within the normal range. In the male subset in particular, BMI
and waist circumference values were in the lower margins of the
normal range, and male participants had significantly smaller
BMI and WHR values compared to females.
Concerning biochemical variables, female participants had
significantly higher triglyceride levels compared to males. For
males, baseline brachial artery diameter values were higher, and
FMD% values were lower compared to females. Additionally,
38.2% of females and 62.9% of males presented with an FMD%
lower than the sample median (
p
=
0.05). Mean retinal vessel
diameters were trending higher for CRVE in males, while there
were no differences noted for CRAE or AVR.
In a separate set of retinal assessments, qualitative fundus
grading and analyses of retinal vessel geometric characteristics
showed that retinal tortuosity was present in approximately
18% of the participants, and was predominantly detected in the
retinal arterioles. Furthermore, a single micro-aneurysm was
identified in one participant, while no cotton wool spots, retinal
haemorrhage or telangiectasia were observed in this cohort.
The prevalence of cardiovascular risk factors is shown in Fig.
1. Of the whole cohort, 86.4% of participants indicated that
they were current smokers, and 31.8% presented with systolic
hypertension, with 40.7% of males being hypertensive. Diastolic
hypertension was identified in 23.8% of the study population
and in 29.6% of the male subset. Of the female subset, 36.1%
were considered overweight or obese and 30.6% presented with
central obesity. Reduced HDL-C levels were found in 28.8% of
the whole cohort and in 38.9% of females, compared to 16.7%
of males.
As expected, an inverse correlation was observed between
baseline brachial artery diameter and FMD% (Pearson’s
correlation coefficient,
r
: –0.33;
p
=
0.009), and a strong
positive correlation was noted between the retinal blood vessel
equivalents, CRAE and CRVE (Pearson’s correlation coefficient,
r
: 0.5;
p
<
0.001).
The correlations between cardiometabolic and vascular
(FMD%, CRAE and CRVE) variables in the whole cohort are
shown in Table 2. The results indicate that waist circumference
showed a positive correlation with FMD%, although there was
no correlation with WHR. Both systolic and diastolic blood
Table 1. Population characteristics
Variables
Whole cohort
(n
=
66)
Females
(n
=
36)
Males
(n
=
30)
p
-value
(F:M)
Age (years)
35.4 (10.6)
34.1 (10.6)
36.9 (10.5)
0.29
WHR
0.8 (0.05)
0.8 (0.05)
0.8 (0.04)
0.01
BMI (kg/m
2
)
22.1 (19.3–24.7) 23.4 (19.8–27.2) 20.7 (18.8–23.9)
0.03
WC (cm)
75.5 (69–81) 76 (70.5–80.25)
74 (68–81)
0.49
SBP (mmHg)
129.9 (16.9)
127.8 (16.2)
132.9 (17.7)
0.24
DBP (mmHg)
79.6 (14.1)
78.1 (13.9)
81.5 (14.3)
0.33
Total C (mmol/l)
3.8 (3.3–4.4)
4 (3.2–4.7)
3.7 (3.3–4.3)
0.54
HDL-C (mmol/l)
1.25 (1–1.5)
1.3 (1–1.6)
1.2 (1–1.4)
0.38
LDL-C (mmol/l)
2.1 (1.7–2.6)
2.2 (1.7–2.6)
1.9 (1.5–2.6)
0.17
TG (mmol/l)
0.8 (0.6–1)
0.8 (0.6–1)
0.9 (0.7–1.2)
0.04
Fasting glucose
(mmol/l)
4.5 (4.2–4.9) 4.45 (4.05–4.7) 4.5 (4.3–4.9)
0.21
HbA
1c
(%)
5.4 (0.5)
5.4 (0.5)
5.5 (0.4)
0.27
CRAE (
µ
m)
156.2 (14.5)
155.3 (12.9)
157.2 (16.4)
0.61
CRVE (
µ
m)
250.3 (21)
247.4 (18.6)
253.6 (23.5)
0.07
AVR
0.6 (0.06)
0.6 (0.06)
0.6 (0.05)
0.53
Baseline brachial
artery diameter (mm)
3.5 (0.6)
3.2 (0.5)
3.9 (0.5)
<
0.001
FMD (%)
9.6 (6.7–14.1) 11.4 (7.7–15.8) 8.6 (3.4 – 12.5)
0.06
Parametric data are expressed as mean (standard deviation) and non-parametric
data as median (interquartile range).
WHR, waist-to-hip ratio; BMI, body mass index; WC, waist circumference; SMP,
systolic blood pressure; DBP, diastolic blood pressure; Total C, total cholesterol;
HDL-C, high-density lipoprotein cholesterol; LDL-C, low-density lipoprotein
cholesterol; TG, triglycerides; HbA
1c
, glycated haemoglobin; CRAE, central retinal
arteriolar equivalent; CRVE, central retinal venular equivalent; AVR, retinal arteri-
ole-to-venule ratio; FMD, flow-mediated dilatation; F:M, female vs male.