ORIGINAL

Niger J Paed 2012; 39 (3):105 - 109

Ekure EN

Onifade E

Esezobor C I

Banwo, T

Systolic blood pressure of Nigerian

children with sickle cell disease

DOI:http://dx.doi.org/10.4314/njp.v39i3.3

Accepted: 16th January 2012

Results: One hundred and twenty

three children with SCD and 62

apparently healthy controls were

studied; 62% were females. The

mean age of the children with SCD

was 8.93±3.91years (range 1-17

years) and was similar to the

Abstract: Background: Blood pres-

sure readings of adult Nigerians

with sickle cell disease (SCD) are

reported to be lower than that of the

general population but similar

studies in children are unavailable.

Objectives: To determine the sys-

tolic blood pressure (SBP) of chil-

dren with SCD and compare it with

that of healthy controls. Also, to

correlate the SBP of children with

SCD with age, gender, height and

weight.

(

)

Esezobor C I

Ekure EN

Department of Paediatrics,

College of Medicine,

University of Lagos,

PMB 12003,

Lagos State, Nigeria.

Email: esezobor@gmail.com

Tel: +2348058440582

controls. SBP was similar in both

groups of children (90.9±12.7 ver-

sus 92.2±15.2 mmHg; p=0.53) and

increased with age. In 91 (74%)

children with SCD the SBP was

th

below the 50 centile for the

Onifade E,

general population. Multiple linear

regressions involving sex, age,

height and weight found no

independent factor to be a signifi-

cant predictor of the SBP in

Department of Paediatrics,

South Tees Foundation

NHS Trust, Friarage Hospital,

Bulamoor Road, Northallerton,

DL6 1JG, UK

Methods: Children with SCD were

recruited from the Paediatric Hae-

matology Clinic of the Lagos Uni-

versity Teaching Hospital. Data

collected included bio-demographic

details, social classification, height

and weight measurements and pre-

sent clinical status. SBP was meas-

children with SCD.

Conclusion: The SBP of children

with SCD is similar to that of age

and sex-matched controls. The sex,

age, weight and height did not

significantly predict SBP in

Banwo, T

Alder Hey Children’s Hospital,

Alder Hey Children’s NHS

Foundation Trust, Liverpool, UK

u r e d u s i n g

a

D o p p l e r

®

(VASCUTRACK 120 ) and a mer-

cury sphygmomanometer. Similar

data were obtained from age and

sex matched apparently healthy

children.

multiple linear regression.

Introduction

for this phenomenon is uncertain with₄₅various suggested

hypotheses including anthropometry.

Blood pressure (BP) in childhood is a predictor of adult

BP with evidence that childhood hypertension can track

into adulthood. More importantly, hypertension in

childhood is usually secondary and may be prevented or

amenable to cure. Despite these, BP checks are not

performed routinely in children.

Similar studies in Nigerian children are as yet unavail-

able thus prompting us to determine the systolic blood

pressure (SBP) of children with SCD. Also, we aimed to

determine the linear relationship between SBP and gen-

der, age, height and weight.

1

Hypertension is known to be more prevalent among

people of the black race, who also frequently carry the

2

sickle cell gene. Sickle cell disease (SCD) is associated

with high morbidity from recurrent episodes of vaso-

occlusive and anaemic crises. Mortality most times

occurs during acute crises and may be secondary to

various organ failures including the kidneys. Kidney

disorders are often associated with hypertension. Adult

Nigerians with sickle cell disease have however been

shown to have low BP when compared with individuals

Patients and Methods

Children with documentary evidence of SCD were

recruited from the weekly Paediatric Haematology

Clinic of Lagos University Teaching Hospital (LUTH).

Only children with SCD in steady state were enrolled;

excluded were children with fever or ongoing

3

with normal haemoglobin genotype. The exact reason

vaso-occlusive crisis, those needing hospitalization or

1

06

7

discharged from hospital admission in the past two

weeks. Age and sex matched controls were recruited

from the nursery, primary and secondary schools of the

University of Lagos. For children under the nursery

school age, controls were enrolled from the Well Baby

Clinic of LUTH. Any child found on physical examina-

tion to have one or more of the following were also

excluded: frontal bossing, gnathopathy, jaundice,

marked pallor and hepatosplenomegaly. The study par-

ticipants were enrolled on a consecutive basis. Ethical

clearance for the study was obtained from the Health

Research and Ethics Committee of LUTH. Permission

was obtained from the authorities of the schools. The

parent/guardian of each children provided written in-

formed consent. The study lasted 6 months.

High Blood Pressure Education Program. Linear

associations between SBP and weight and height were

quantified using Pearson’s correlation. Sex and other

independent factors found on bivariate analysis to have

significant correlation with SBP were simultaneously

entered into an equation to predict the mean SBP. A Ρ

value less than 0.05 was considered statistically

significant.

Results

One hundred and eighty five children aged one year to

1

7 years were enrolled for the study; 123 were children

Data Collection

with SCD. The mean (SD) age of the children with

sickle cell disease was 8.93±3.91years and was similar

to the mean age of the 62 apparently healthy controls. Of

the children with SCD, 6 (4.9%) had haemoglobin SC

(HbSC). In each group females make up 62% of the

population. The children with SCD were significantly

shorter (126.7cm versus 134.2cm) and weighed less

(25.1kg versus 31.6kg) than age and sex-matched

controls (Table 1).

Data collected from every child included relevant bio-

demographic data, weight and height. Height was meas-

ured using a wall-mounted stadiometer with the child

standing barefoot, legs together and looking straight

ahead. For subjects under two years length was meas-

ured using an infantometer. Subjects were weighed

barefoot, wearing only light clothing or underwear, us-

®

ing a Seca scale. The social status of each child was

derived using the classification proposed by Olusanya et

al which utilizes the mother’s education and the fa-

Table 1: Demographics of patients included in study

6

Variables

Cases, n

Controls, n

p value

1.00

ther’s occupation. After being seated for about five min-

utes, two SBP readings were taken at about 10 minutes

interval for each child. A Doppler (VASCUTRACK 120

by Seward) and a mercury sphygmomanometer (Welch

Allyn, Skaneateles Falls, NY) were used for this pur-

pose. While in the sitting position, a cuff with an inflat-

able bladder width of at least 40% of the child’s mid

upper arm circumference that covered at least 80% of

Age years),

1

6

1

-5

25

58

40

13

29

20

-10

1-17

Sex

7

the upper arm length was applied around the right arm.

Male

Female

59

64

30

32

0.957

0.10

Measurements were done in the sitting position. After

cuff placement, transmission gel was placed on the

probe of the Doppler which was used to locate the point

of loudest blood flow of the radial artery. With the probe

of the Doppler secured over this point, the sphygmoma-

nometer cuff was inflated until the blood flow was no

longer heard and then deflated slowly until the initial

burst of sound was heard from the audio-amplified Dop-

pler probe; the mercury level of the sphygmomanometer

at the point of the initial burst of sound when deflating

the cuff was taken as the SBP. This point corresponds

with the first korotkoff sound heard when using a stetho-

scope. The average of the two readings was taken as the

SBP of the child.

Social class

Upper

Middle

Lower

Mean weight 25.1 (8.9)

SD) kg

Mean height 126.7 (19.4)

SD) cm

15

72

36

15

33

14

31.6 (12.8)

*

0.00

0.02

(

*

134.2 (21.2)

(

*

Standard deviation

The mean SBP in the group of children with SCD was

0.9±12.7mmHG and was similar to that of the healthy

controls (92.2±15.2mmHG) (Figure 1). The SBP was

9

Data Management

th

below the 50 , between the 50-95 and ≥95 centile for

age, sex and height in 91 (74%), 29 (23.6%) and 3

(2.4%) children with SCD respectively. There was a

gradual increase in the SBP with increasing age in both

children with SCD and healthy controls (Figure 2).

All data were entered into a proforma, crosschecked for

errors, and analyzed using the SPSS statistical package

version 17.0. Continuous variables were reported as

means and standard deviation and analyzed by student’s

t test. Categorical variables were analyzed using chi-

square or Fischer’s exact tests where applicable. The

SBP of each child with SCD was compared with that of

the general population as published by the National

1

07

Fig 1: Box Plot comparing the systolic blood of children

with sickle cell disease and healthy controls

Table 3: Multiple linear regression model of mean SBP

simultaneously accounting for sex, age, weight and

height in children with SCD

Unstandardized

coefficient

1.25

Standardized

Independent

variables

coefficient P value

Sex

0.050

0.23

0.51

0.25

Age

0.74

Height

Weight

2

0.03

0.47

0.05

0.33

0.84

0.11

R =0.33, P value=0.00

t= -0.63, df=183, P=0.53

Fig 2: Line graph showing the systolic BP in healthy

control and children with sickle cell disease at different

ages

Discussion

The majority of the children with SCD in the present

study had SBP below the 50th centile for the general

population. Lower BP h₈a₉s been documented in children

4

and adults with SCD. The reasons for lower BP in

SCD population are unclear but have been partly

attributed to the phenomenon of increased renal tubular

sodium and wat₅er excretion thus promoting lower arte-

4

rial pressures. Other reports however attribute the

lower BP to a lower weight and i₃n₁c₀r₁e₁ased vasodilation

in adults and children with SCD.

With increasing

age especially after adolescence, kidney function may

deteriorate relatively faster in persons with SCD

resulting in hypertension. Indeed two of the three

children with elevated BP in the present study were in

their adolescence. However the SBP documented in our

study represents the mean of two SBP readings taken 10

minutes apar₂t and thus may be transient or due to white

Age category (years)

1

Bivariate correlations in the sickle cell population

coat effect. The relatively lower BP in the population

revealed significant positive linear relationship between

SBP and age, weight and height (Table 2). In a multiple

linear regression model involving the above mentioned

factors, the model only accounted for 33% of the SBP

and no variable was a significant predictor of SBP

with SCD implies that BP values that are considered

normal or mild hypertension in healthy individuals may

represent significant risk factor for mo₄rbidity and

mortality in the population with SCD.

(

Table 3).

In the present study, although the value of SBP in chil-

dren with SCD was lower than that of the controls, this

was not significant. This result is in contrast with some

Table 2: Univariate correlation between mean systolic

BP and age, weight and height in children with sickle

cell disease

reports where participants with SCD₉₁h₁ad lower SBP

4

compared to their AA counterparts.

These studies

were however conducted predominantly in adolescent

and adult populations. A study involving children with

SCD docu₁m₃ ented similar results as ours.Adams- Camp-

bell et al found that SBP did not differ between the

groups of children with sickle cell anaemia, sickle cell

trait and normal haemoglobin despite significantly lower

diastolic BP (DBP) among the children with SCD. This

was irrespective of the significant difference in weight

between the two groups in both studies. The results of

our study and that of Adam-Campbell suggest that lower

body weight may not be the only reason for low₄er BP in

Independent

Factors

Correlation P value

Coefficient

Age

0.56

0.57

0.00

Weight

Height

1

children with SCD. A recently published study involv-

ing Nigerian adults found comparable SBP between the

group with SCD and the controls despite lower DBP in

the adults with SCD, and together with the report of

1

08

1

3

16 17

Adam-Campbell may imply differential effects of SCD

on SBP and DBP. The lower DBP in the group with

SCD despite similar SBP may be also due to the com-

mon absence of the fifth korotkoff s₁o₅ und in the persons

with hyperdynamic states like SCD.

korotkoff sounds are not always present in children,

especially₅in children with hyperdynamic states like

1

anaemia.

In both the children with SCD and the controls, SBP

increased with increasing age. This increase with age

may also reflect increases in weight and height which

have also been reported to₇correlate positively with BP

in the general population. As expected, height and

weight bore significant positive linear relationship with

SBP on bivariate analysis. However, none of these

Conclusion

There is no significant difference in the SBP of children

with SCD compared to age and sex matched controls.

Age, sex, height and weight were not significant

predictors of SBP on multiple linear regressions.

factors remained a significant predictor of SBP in

multiple linear regressions, suggesting the effects of

some unexplored factors on the SBP. Indeed the model

of age, sex, height and weight could only predict about a

third of the change in SBP. This observation is in con-

trast to the finding of Homi et al which showed that the

difference in BP between adolescents with SCD a₁n₀d

normal control was due to differences in body weight.

Conflict of interest: None

Funding source: None

Acknowledgement

A limitation of our study was the inability to perform

haemoglobin electrophoresis in the participants used as

controls. The reluctance of parents and school authori-

ties to permit bloodletting in an apparently healthy child

weighed against performing haemoglobin electrophore-

sis in the controls. This introduces the small probability

that some of our controls may have sickle cell disease,

although, the two to three percentage prevalence of SCD

in the general population and our rigorous exclusion

criteria make this a remote possibility. Another limita-

tion was measuring only SBP. However DBP is more

prone to errors than the SBP because the fourth and fifth

Dr. F.E.A. Lesi and Dr E.O. Temiye are acknowledged for

assistance in data analysis and earlier phase of study conceptu-

alization respectively.

References

6

7

.

Olusanya O, Okpere E, Ezimokhai

11. Rodgers GP, Walker EC, Podgor

MJ. Is "relative" hypertension a

risk factor for vaso-occlusive com-

plications in sickle cell disease?

Am J Med Sci 1993;305(3):150-6.

12. De la Sierra A, Segura J, Banegas

JR, Gorostidi M, de la Cruz JJ,

Armario P, et al. Clinical features

of 8295 patients with resistant

hypertension classified on the basis

of ambulatory blood pressure

monitoring. Hypertension 2011;57

(5):898-902.

13. Adams-Campbell LL, Nwankwo

MU, Ukoli FA, Biu T. The sickle

gene: a marker for blood pressure?

J Natl Med Assoc 1993;85(5):385-

7.

14. Oguanobi NI, Onwubere BJ, Ibeg-

bulam OG, Ike SO, Anisiuba BC,

Ejim EC, et al. Arterial blood pres-

sure in adult Nigerians with sickle

cell anemia. J Cardiol 2010;56

1

.

Lauer RM, Clarke WR. Childhood

risk factors for high adult blood

pressure: the Muscatine Study.

Pediatrics 1989;84(4):633-41.

Cooper R, Rotimi C. Hypertension

in blacks. Am J Hypertens 1997;10

M. The importance of social class

in voluntary fertility control in a

developing country. W Afr Med J.

1

985;4:205-12.

2

3

.

The fourth report on the diagnosis,

evaluation, and treatment of high

blood pressure in children and

adolescents. Pediatrics 2004;114(2

Suppl 4th Report):555-76.

Johnson CS, Giorgio AJ. Arterial

blood pressure in adults with sickle

cell disease. Arch Intern Med

(7 Pt 1):804-12.

Aderibigbe A, Omotoso AB, Awo-

busuyi JO, Akande TM. Arterial

blood pressure in adult Nigerian

sickle cell anaemia patients. West

Afr J Med 1999;18(2):114-8.

Pegelow CH, Colangelo L,

Steinberg M, Wright EC, Smith J,

Phillips G, et al. Natural history of

blood pressure in sickle cell dis-

ease: risks for stroke and death

associated with relative hyperten-

sion in sickle cell anemia. Am J

Med 1997;102(2):171-7.

8

9

1

4

5

.

1

981;141(7):891-3.

. De Jong PE, Landman H, van Eps

LW. Blood pressure in sickle cell

disease. Arch Intern Med 1982;142

(6):1239-40.

0. Homi J, Homi-Levee L, Gentles S,

Thomas P, Serjeant G. Adolescent

blood pressure in a cohort study of

sickle cell disease. Arch Intern

Med 1993;153(10):1233-6.

Grell GA, Alleyne GA, Serjeant

GR. Blood pressure in adults with

homozygous sickle cell disease.

Lancet 1981;2(8256):1166.

(3):326-31.

1

09

1

5. Beevers G, Lip GY, O'Brien E.

ABC of hypertension: Blood pres-

sure measurement. Part II-

conventional sphygmomanometry:

technique of auscultatory blood

pressure measurement. BMJ

16. Sinaiko AR, Gomez-Marin O,

Prineas RJ. Diastolic fourth and

fifth phase blood pressure in 10-15

-year-old children. The Children

and Adolescent Blood Pressure

Program. Am J Epidemiol

17. O'Sullivan J, Allen J, Murray A. A

clinical study of the Korotkoff

phases of blood pressure in chil-

dren. J Hum Hypertens 2001;15

(3):197-201.

2

001;322(7293):1043-7.

1990;132(4):647-55.