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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 27, No 5, September/October 2016
AFRICA
317
and metatarsal joint region) according to the manufacturer’s
instructions. Body fat and percentage of body fat were used to
indicate overall obesity.
Blood pressure was measured with an automatic
sphygmomanometer (OMRON
®
, Model HEM-742 IntelliSense
INT, China) in the sitting position in a comfortable room and
after bladder emptying. The cuff size was chosen according to
the circumference of the child’s arm and the manufacturer’s
recommendation. Three measurements were taken on the left
arm at two-minute intervals after a five- to 10-minute resting
period. The forearm was supported on a flat surface at nearly
120° with the arm.
Resting systolic (SBP) and diastolic blood pressure (DBP)
and heart rate (HR) were determined as the arithmetic mean of
the last two measures. Pulse pressure (PP) was calculated as the
difference between SBP and DBP. The mean arterial pressure
(MAP) was calculated from the formula [SBP
+
(2
×
DBP)]/3.
The blood pressure percentile was determined using available
software
(https://www.bcm.edu/bodycomplab/), which accounts
for the gender, height and age of each child.
Blood pressure was classified according to the WHO criteria.
23
Briefly, it was considered normal if the SBP and DBP were
below the 90th percentile. If SBP or DBP were above the 95th
percentile (P95), the child was included in the category of ‘high
BP’. If the SBP or DBP was intermediary between the extremes
(
>
P90
<
P95), the child was classified as ‘borderline BP’.
Statistical analysis
Continuous variables are expressed as mean ± standard deviation
when normally distributed or as median and interquartile
range when the normal distribution model was not accepted
(Kolmogorov–Smirnov test). Comparison of two means
was done with the Student’s
t
-test for normal variables, and
comparison of two medians was performed with the Wilkinson
test. The comparison of proportions of categorical variables in
two or more groups was performed using the chi-squared test.
Comparison of means in three or more groups was performed
by one-way ANOVA followed by the
post hoc
Tukey’s test. The
degree of association between continuous variables was obtained
with Pearson’s correlation coefficient (
r
).
A multivariate analysis (stepwise forward procedure) was
used to indicate independent predictors of systolic and diastolic
blood pressure. Gender, birth weight, age, height, body weight,
body mass index, absolute and relative fat mass and lean mass
(all with
p
<
0.05 in bivariate analysis) were included in the model
as predictors. Co-linearity variables were automatically excluded
from the model. Statistical analyses were performed using SPSS
for Windows, version 20.0. The significance level for all tests was
set at
p
<
5%.
Results
Table 1 shows the main clinical characteristics of the sample,
divided by gender. There was a predominance of girls (61.1%)
and, as expected, children of black race (95.5%). Only nine
children showed intermediate skin colour, suggesting a mixed
ancestry of black and white. The boys had an overall birth
weight higher than that of the girls, and a low birth weight (
<
2
500 g) was reported in only 15 children.
It can be observed (Table 1) that most of the anthropometric
and biochemical variables were similar in pre-pubertal boys
and girls, with the exception of HR, which was higher in
girls, and WHR, which was higher in boys. According to BMI
classification, excessive body weight was found in 17.7% of the
sample (95% CI
=
12.4–23.0%), with 7.1% being overweight
and 10.6% obese. Eleven children were underweight and the
remaining 152 (76.7%) children were of normal weight.
Table 2 shows the anthropometric, haemodynamic and
biochemical variables according to BMI classification. Age across
the four groups was similar (
p
>
0.05). As expected, the current
body weight of the overweight and obese groups was higher
than that of the normal group. The current weight was 61%
higher in the obese group than in the normal group. Interestingly,
birth weight was also higher in the groups with excessive fat
mass. As expected, other anthropometric variables related to fat
accumulation were also different between the normal BMI group
and the groups with excessive fat accumulation. The obese group
showed 2.56 times more fat mass than the normal BMI group.
While all biochemical variables were unaffected along BMI
categories, except for triglycerides, which showed higher values
in the obese group, a different pattern was observed in relation to
blood pressure. An obvious gradient of increasing SBP and DBP
values was observed from the underweight group to the obese
group. SBP was statistically higher in the obese group compared
with the underweight, normal and overweight groups, while the
DBP was significantly different between the obese groups and
the normal and underweight groups.
Significant differences among other variables are shown in
Table 2. Comparisons were performed between the normal-
Table 1. Physical and clinical characteristics of pre-pubertal
schoolchildren in Luanda in 2012
Variables
Boys (
n
=
77) Girls (
n
=
121) All (
n
=
198)
p-v
alue
Age (years)
9.43 ± 1.03 9.21 ± 1.12 9.29 ± 1.41 0.18
Birth weight (kg)
3.29 ± 0.56 3.12 ± 0.58 3.19 ± 0.58 0.05
Current weight (kg)
33.08 ± 9.06 33.07 ± 10.2 33.07 ± 9.72 0.99
Height (cm)
136.7 ± 8.05 137.8 ± 9.75 137.4 ± 9.12 0.44
BMI (kg/m
2
)
17.70 ± 4.0 17.19 ± 3.61 17.39 ± 3.76 0.36
WC (cm)
59.58 ± 8.94 58.38 ± 9.25 58.85 ± 9.13 0.37
HC (cm)
71.82 ± 9.71 71.95 ± 10.4 71.9 ± 10.12 0.93
WHR
0.82 ± 0.04 0.81 ± 0.04 0.81 ± 0.03 0.008
Fat mass (kg)
6.36 ± 3.97 6.85 ± 4.14 6.66 ± 4.07 0.41
SBP (mmHg)
104.7 ± 8.9 103.8 ± 8.1 104.1 ± 4.2
0.46
DBP (mmHg)
62.6 ± 7.8
63.6 ± 6.3
63.2 ± 0.4
0.33
HR (bpm)
80.1 ± 9.5
84.7 ± 10.2 82.9 ± 13.4 0.002
Glycaemia (mg/dl)
87.4 ± 15.3 86.5 ± 14.4 86.8 ± 15.5 0.69
(mmol/l)
4.85 ± 0.85 4.80 ± 0.80 4.82 ± 0.86
TC (mg/dl)
170.9 ± 36.8 172.5 ± 34.4 171.8 ± 34.1 0.75
(mmol/l)
4.43 ± 0.95 4.47 ± 0.89 4.45 ± 0.88
Triglycerides (mg/dl)
66.3 ± 31.9 63.5 ± 29.4 64.6 ± 4.0
0.54
(mmol/l)
0.75 ± 0.36 0.72 ± 0.33 0.73 ± 0.05
LDL-C (mg/dl)
102.1 ± 33.2 101.4 ± 33.2 101.7 ± 22.6 0.89
(mmol/l)
2.64 ± 0.86 2.63 ± 0.86 2.63 ± 0.59
HDL-C (mg/dl)
56.8 ± 13.1 59.5 ± 12.3 58.5 ± 9.1
0.13
(mmol/l)
1.47 ± 0.34 1.54 ± 0.32 1.52 ± 0.24
LDL-C/HDL-C
1.9 ± 0.8
1.8 ± 0.7
1.8 ± 0.3
0.28
Data presented as mean ± standard deviation, BMI; body mass index, WC,
waist circumference; HC, hip circumference; WHR, waist/hip ratio, SBP;
systolic blood pressure; DBP; diastolic blood pressure, HR; heart rate, TC, total
cholesterol; LDL-C; low-density lipoprotein cholesterol, HDL-C; high-density
lipoprotein cholesterol.