CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 8, September 2012
458
AFRICA
involved the pairs of: FBPR and SBPR, AVE
1-3
and AVE
2-4
,
and
AVE
1-5
and AVE
2-6
.
Differences in the distribution of compared
BP readings under the JNC-7 model for the mixed sub-population
and a modified JNC-7 classification model for the hypertensive
sub-population were respectively tested for significance using
the Chi-square test.
Fisher’s exact test was used in evaluating the statistical
significance of the differences in the distribution of compared
readings under the
<
140/90
mmHg and
≥
140/90
mmHg groups.
Correlation between the compared variables was evaluated using
Pearson’s correlation. For all statistical tests, a
p
-
value
<
0.05
was
considered statistically significant.
Results
Blood pressure measurements were conducted on 186 consenting
adults. Of these, 170 participants (91.4%) had complete sets of
the six readings required for data analysis. This was taken as the
final study population. This final study sample comprised BP
readings from 87 males and 83 females (M:F
=
1.05:1),
with age
range 18–86 years (46.7
±
13.9).
Patients who had been previously diagnosed as having
systemic hypertension comprised 35.9% (
n
=
61)
of the final
sample. All had received prescription(s) for antihypertensive
medications during previous clinic visits. Females comprised
59% (
n
=
36)
of the hypertensive sub-population and 43% (47 of
109)
of the remaining mixed sub-population (
p
=
0.06,
Fisher’s
exact test). Patients comprising the hypertensive sub-population
were older than those in the mixed sub-population [24–86
years (51.3
±
12.2)
vs 18–74 years (44.1
±
14.2);
p
=
0.0009,
independent
t
-
test].
Table 1 shows the descriptive statistics for the BP variables
that were compared in this study. These were presented as
range of values (mean
±
standard deviation). Within each of
the groups in Table 1, the independent
t
-
test found statistically
non-significant differences (in respective systolic and diastolic
component comparison) between the means of the first and
second BP readings, as well as the means of the averages of three
readings, and the averages of five readings (
p
>
0.05
for all).
For the single, triple and quintuple measurement models
respectively, systolic/diastolic readings, which included the
FBPR, were higher than those that excluded the first reading in
64.2%/58.7%; 78%/68.8%; 82.6%/78.9%
of readings among the
mixed population. Similarly, corresponding proportions among
the hypertensive population were 67.2%/70.5%; 82%/78.7%;
82%/85.2%
of the systolic/diastolic readings.
Differences between the sub-populations in the relative
proportion of FBPR-included readings which were higher than
FBPR-excluded readings were statistically insignificant for both
systolic and diastolic comparisons (Chi-square test,
p
>
0.05
for
all). In both sub-populations, it was observed than the tendency
to have higher systolic/diastolic readings with the inclusion of
FBPR was amplified in the triple and quintuple measurement
models.
Conversely, in each of the three measurement models,
readings excluding FBPR were greater than those including
FBPR in 27.5%/35.8% (single), 9.2%/8.3% (triple), 4.6%/6.4%
(
quintuple) of the systolic/diastolic readings among the mixed
population. Corresponding findings among the hypertensive
sub-population were 26.2%/23%; 14.8%/9.8% and 13.1%/6.6%.
Similarly, differences between the sub-populations in the
relative proportion of FBPR-excluded readings which were higher
than FBPR-included readings were statistically insignificant
for both systolic and diastolic comparisons (Chi-square test,
p
>
0.05
for all). It was also observed than the tendency to
have higher systolic/diastolic readings with the exclusion of
FBPR was reduced in the triple and quintuple models in both
sub-populations.
Table 2 shows the differences (expressed as absolute values)
between the compared readings. Readings including FBPR were
found to be equal to those excluding FBPR in 8.3–12.8%/5.5–
22.9%
and 6.6–13.1%/6.6–11.5% of systolic/diastolic readings
among the mixed and hypertensive sub-populations, respectively.
Differences between the proportions of equal readings in
the sub-populations were not statistically significant (
p
>
0.05
for all). Clinically significant differences (
≥
5
mmHg)
were observed between compared systolic/diastolic readings in
18.3–56.9%/0.9–26.6%
and 26.2–65.6%/1.6–47.5% of readings
among the mixed and hypertensive sub-populations respectively.
The proportion of clinically significant differences
between readings including FBPR and those excluding FBPR
reduced greatly in the average measurement models. For each
TABLE 1. BLOOD PRESSUREVARIABLES INVOLVED
IN THE COMPARATIVEANALYSES
Vari-
ables
Final study
population
n
=
170 (
mmHg)
Hypertensive
sub-population
n
=
61 (
mmHg)
Mixed
sub-population
n
=
109 (
mmHg)
SYS-1 93–244 (146
±
32.4) 112–244 (164.9
±
32.2) 93–228 (135.5
±
27.4)
DIA-1 44–143 (86.3
±
17.3) 44–143 (95.4
±
15.4) 55–136 (81.2
±
16.2)
SYS-2 87–250 (141.8
±
31.1) 105–250 (159.7
±
31.8) 87–225 (131.8
±
25.8)
DIA-2 51–143 (83.9
±
16.4) 60–143 (92.6
±
14.3) 51–129 (79.1
±
15.5)
SYS
1-3
90–248 (141.9
±
31.1) 109–249 (160.3
±
31.4) 90–223 (131.6
±
25.9)
DIA
1-3
52–143 (84.1
±
16.6) 59–143 (93.1
±
14.5) 52–130 (79.1
±
15.7)
SYS
2-4
88–250 (138.4
±
30.4) 100–250 (156
±
31.2) 88–220 (128.6
±
25.2)
DIA
2-4
49–143 (82.3
±
16.3) 54–143 (90.6
±
14.3)
49–128 (77.7
±
15.6)
SYS
1-5
89–249 (139.1
±
30.4) 103–249 (156.9
±
30.9) 89–219 (129.2
±
25.2)
DIA
1-5
49–143 (82.5
±
16.3) 55–143 (91.1
±
14.3) 50–128 (77.7
±
15.4)
SYS
2-6
87–250 (136.5
±
29.8) 103–250 (153.9
±
30.6) 87–220 (126.8
±
24.5)
DIA
2-6
49–142 (81.5
±
16.6) 53–142 (90.1
±
14.7) 49–126 (76.6
±
15.7)
TABLE 2. DIFFERENCES BETWEEN COMPARED READINGS
Differences
Range
(
mean
±
SD*)
(
mmHg)
0
mmHg
n
(%)
<
5
mmHg
n
(%)
≥
5
mmHg
n
(%)
Mixed sub-population
SYS-1 – SYS-2 0–31 (6.9
±
5.9)
9 (8.3)
47 (43.1) 62 (56.9)
SYS
1-3
–
SYS
2-4
0–11 (3.4
±
2.7) 14 (12.8) 77 (70.6) 32 (29.4)
SYS
1-5
–
SYS
2-6
0-11 (2.5
±
2.0) 14 (12.8) 89 (81.7) 20 (18.3)
DIA-1 – DIA-2 0–16 (3.8
±
3.1) 6 (5.5)
80 (73.4) 29 (26.6)
DIA
1-3
–
DIA
2-4
0–6 (1.6
±
1.4) 25 (22.9) 105 (96.3) 4 (3.7)
DIA
1-5
–
DIA
2-6
0–21 (1.6
±
2.1) 15 (13.8) 108 (99.1) 1 (0.9)
Hypertensive sub-population
SYS-1 – SYS-2 0–30 (9
±
7.5)
4 (6.6)
21 (34.4) 40 (65.6)
SYS
1-3
–
SYS
2-4
0–20 (5
±
3.8)
2 (3.3)
31 (50.8) 30 (49.2)
SYS
1-5
–
SYS
2-6
0–11 (3.3
±
2.5) 8 (13.1) 45 (73.8) 16 (26.2)
DIA-1 – DIA-2 0–24 (5.1
±
4.5)
4 (6.6)
32 (52.5) 29 (47.5)
DIA
1-3
–
DIA
2-4
0–34 (3
±
4.4)
7 (11.5) 54 (88.5) 7 (11.5)
DIA
1-5
–
DIA
2-6
0–19 (1.9
±
3.4)
5 (8.2)
60 (98.4)
1 (1.6)
