CARDIOVASCULAR JOURNAL OF AFRICA • Vol 22, No 1, January/February 2011
AFRICA
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workers accompanied the African participants, who were intro-
duced to the setup. Each subject received a ‘participant sheet’,
which guided him/her through the different research stations
where the various measurements were done.
During the course of the morning, basic health, demographic
and lifestyle questionnaires were completed. Participants were
requested to indicate their income per month according to the
codes in the questionnaire and they also had to specify the
duration of smoking (in years) or use of tobacco products. A
fasting blood sample was taken by a registered nurse from the
antebrachial vein using sterile winged infusion sets and syringes,
and anthropometric measurements were taken in a private room.
Blood pressure (BP) and pulse-wave velocity (PWV) measure-
ments were also taken in a private bedroom.
When all questionnaires were completed and all cardiovascu-
lar measurements taken, each participant received breakfast as
well as a small financial compensation. In the event of a subject
being identified with any abnormalities (such as hypertension or
diabetes), the subject was referred to his/her local clinic, hospital
or physician. Each subject received a short report containing his/
her health information.
Height, body mass, waist circumference (WC) and hip
circumference of each subject were taken according to standard
procedures.
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The circumferences were measured in triplicate.
Maximum height was measured to the nearest 0.1 cm using the
Invicta Stadiometer (IP 1465, UK). Weight was measured to the
nearest 0.1 kg using a digital scale (Precision Health Scale, A
& D Co, Japan). A flexible metallic measuring tape was used
to measure the circumferences, taken with the subjects stand-
ing upright, with the face directed towards the observer and
the shoulders relaxed. The WC was measured at the thinnest
visible point (below the last rib) of the trunk of the body. The
hip circumference was measured at the broadest point over the
gluteal muscles. Body mass index (BMI) was determined with
the formula: body mass/body height
2
.
After a 10-minute rest in the sitting position, BP (systolic and
diastolic) and HR were measured using the OMRON HEM-757
apparatus, with the BP cuff on the left upper arm. The appropri-
ate cuff sizes were used for obese subjects. Two measurements
were taken, with a five-minute rest interval.
PWV (both carotid-radialis and carotid-dorsalis pedis) was
measured using the Complior SP apparatus. The following two
distances were measured on the left side of each subject: carotid-
radialis (from the suprasternal notch to the radial artery in the
wrist) and carotid-dorsalis pedis (from the suprasternal notch to
the dorsalis pedis artery in the foot). The subtraction method was
used, i.e. the distance from the carotid artery to the suprasternal
notch was subtracted from the measurement to the dorsalis pedis
or the radialis.
Cardiovascular parameters were monitored, making use
of the Finometer
™
device (FMS, Finapres Medical Systems,
Amsterdam, Netherlands). This entailed a five-minute continu-
ous recording of each subject’s cardiovascular parameters under
resting, yet awake conditions. After the first two minutes the
upper arm pressure was calibrated with the finger pressure for
each individual subject (i.e. return-to-flow systolic calibration).
The last two minutes of each recording were used to calculate the
average of the cardiovascular variables, namely stroke volume
(SV), cardiac output (CO), total peripheral resistance (TPR) and
Windkessel arterial compliance (Cwk).
Biochemical analyses
Plasma and serum samples were prepared using standard
methods and stored at –80°C until analysis. High-sensitivity
C-reactive protein (hs-CRP) and serum lipids were determined
on a Konelab 20i (Labsystems Clinical Laboratory Division,
Vantaa, Finland) clinical chemistry analyser. Cotinine analyses
were performed using the IMMULITE 2000 nicotine metabolite
assay (Siemens Medical Solutions Diagnostics Ltd, Los Angeles,
CA, USA) and a solid-phase competitive chemiluminescent
immunoassay (Catalog Number L2KNM6). HIV status was
determined immediately after blood sampling with a rapid test,
according to the protocol of the National Department of Health of
South Africa. Serum was used for testing with the First Response
test and was repeated with the Pareeshak test for confirmation.
Statistical analysis
All statistical analyses were performed using Statistica version 8
(Statsoft, Inc, Tulsa, OK, 2007). Statistical results are presented
as means, standard errors and 95% confidence intervals (CI).
Variables that were not normally distributed were logarithmically
transformed, namely TG and hs-CRP. An independent
t
-test and
analysis of covariance (ANCOVA) were performed to compare
the variables between the two ethnic groups and to determine
significant differences. Self-reported smokers were included in
the smoking group for statistical analyses.
Similar tests were performed to compare the variables
between smokers and non-smokers within each ethnic group,
and also while adjusting for age, gender, BMI and WC. Mean
arterial pressure (MAP) was included as an adjustment variable
while comparing PWV data. The Chi-square test was used to
determine significant differences between categorical variables.
We performed correlations and partial correlations between
smoking and cardiometabolic values within each ethnic group.
Complete datasets were not available for all participants during
the statistical analysis, hence small discrepancies in participant
numbers in the tables.
Results
The characteristics of the African and Caucasian subject groups
are compared in Table 1. Most variables differed significantly
between the two groups (
p
≤
0.001). The African group had a
higher proportion of smokers, whereas height, weight, BMI and
WC levels were significantly higher in the Caucasians. Africans
showed a more detrimental cardiovascular profile.
Caucasians had significantly lower hs-CRP values than the
Africans, who presented a more favourable lipid profile than the
Caucasians. Cotinine levels were significantly higher in Africans
compared to their Caucasian counterparts, which was expected,
due to higher numbers of reported smokers among the Africans.
The results also revealed significant differences in socio-econom-
ic status (SES), in that the majority ofAfrican subjects were living
on low incomes. A total of 90% of Africans earned less than
R1 000 per month. By contrast, the majority of the Caucasian
group (65.6%) was living on more than R5 000 per month.
Table 2 compares the African smokers and non-smokers.
Smokers were older than non-smokers and had significantly
lower weight, BMI and WC than non-smokers. Smokers showed
significantly higher PWV, TG and cotinine levels than in non-
smokers. CO was significantly higher in smokers than non-
