Ambulatory Blood Pressure Recordings in Children and Adolescents

(1)

An increased recognition of the prevalence and

significance of essential hypertension (HTN) in

youths has occurred in the last two decades with the

Ambulatory

Blood

Pressure

Recordings

in

Children

and

Adolescents

Gregory A. Harshfield, PhD*; Bruce S. Alpert, MD*; Derrick A. Pulliam, BS*;

Grant W. Somes, PhD; and Dawn K. Wilson, PhD*

ABSTRACT. Objective. To provide reference data for

ambulatory blood pressure monitoring (ABPM) and to

determine the influence of age, sex, and race on these values.

Methods. ABPM was performed on 300 healthy,

nor-motensive boys and girls between the ages of 10 and 18

years, including 160 boys and 140 girls, of whom 149

were white and 151 were black. Mean systolic blood

pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) while awake and during sleep were calculated for black and white boys and girls aged 10 to 12 years, 13 to 15 years, and 16 to 18 years.

Results. Boys compared with girls 10 to 12 years of

age had higher mean (±SD) SBP (115 ± 9 vs 112 ± 9 mm

Hg P < .01) and DBP (67 ± 7 vs 65 ± 5 mm Hg P < .01)

while awake. Boys compared to girls 13 to 15 years of age had higher SBP while awake (116 ± 11 vs 112 ± 8mm Hg P < .01). Boys compared with girls 16 to 18 years of age had higher SBP while awake (125 ± 12 vs 111 ± 9mm Hg P < .01) and during sleep (116 ± 11 vs 106 ± 9 mm Hg).

Comparisons within sex showed similar changes with

age for boys and girls. Blacks compared with whites 13 to 15 years of age had higher SBP during sleep (109 ± 11 vs 105 ± 10 mm Hg P < .01), and blacks compared with

whites 16 to 18 years of age had higher DBP during sleep (66 ± 7 vs 58 ± 6 mm Hg P < .01). Comparisons across age

groups within race showed that blacks 16 to 18 years of age had higher SBP during sleep than blacks 10 to 12

years of age (109 ± 11 vs 104 ± 10 mm Hg), and higher

DBP during sleep (66 ± 7 mm Hg P < .01) than blacks 10

to 12 years of age (61 ± 7 mm Hg P < .01) and 13 to 15

years of age (61 ± 8; P < .01 mm Hg). The changes with

age were not significant for white subjects.

Conclusion. These results provide age-specific refer-ence data for ABPM in youths. These values differ by sex

(boys more than girls) and race (Blacks more than

Whites). Pediatrics 1994;94:180-184; hypertension, ambu-latory blood pressure, sex differences, ethnic differences.

ABBREVIATIONS. ABPM, ambulatory blood pressure

monitor-ing; HTN, essential hypertension; BP, blood pressure; SBP, systolic

blood pressure; DBP, diastolic blood pressure; HR, heart rate;

bpm, beats per minute.

publication of the First and Second Task Force

Re-ports on Blood Pressure Control in Children.”2 These

reports provided much needed guidelines for

evalu-ating blood pressure (BP) and diagnosing HTN in

youths. These reports also provided reference values

for age- and sex-specific casual BP for children and

adolescents. The authors stressed the importance of

obtaining casual BP under standardized conditions

to control for the potential confounding effects of

such factors as posture and anxiety.

Ambulatory blood pressure monitoring (ABPM)

provides an alternative to casual BP measurements

for evaluating BP and diagnosing HTN. With ABPM,

physicians are able to identify “hypertensives” in

whom BP is elevated only in the physician’s office, a condition referred to as “white coat” hypertension.3

Estimates of the prevalence of white coat

hyperten-sion in the adult population range from 26 to 68%,

depending on the criteria used. ABPM also provides

a better index of BP load than casual BP,6 as

evi-denced by superior relationships with measures of

BP-induced target organ damage to the eyes,7 heart,8 arteries9 and kidneys.10’11 Furthermore, retrospective

studies have shown that ABPM predicts morbid

car-diovascular events better than traditional casual BP

measurements.12’13

Initially, the lack of reference data on normal

in-dividuals limited the use and acceptance of ABPM.

These data are now available for adults with the

publication of numerous large studie&4’8 and a

meta-analysis of 23 studies.19 However, there is a

paucity of studies that have used ABPM on youths.

Therefore, the purpose of this report is threefold. First, the relationships between casual BP and

mea-surements obtained from ABPM in youths are

de-scribed. Second, reference values of awake and

asleep BP and heart rate (HR) obtained by ABPM on

a large sample of healthy children and adolescents are provided. Third, the influence of age, sex, and body size on these measurements is described.

From the *Department of Pediatrics, University of Tennessee, Memphis, TN; the Dept of Epidemiology, University of Tennessee, Memphis, TN; and the §Dept of Medicine, Medical College of Virginia.

Received for publication Jan 7, 1993; accepted Dec 23, 1993.

Reprint requests to (G.A.H.) University of Tennessee, Memphis, 848 Adams Ave. Memphis, TN 38103.

METHODS

Written informed parental consent was obtained before testing.

The subjects were 300 healthy, normotensive children and

adoles-cents recruited for a study on cardiovascular risk factors in youth.

Recruitment was performed through advertisements in the

(2)

Health status was evaluated based on medical history and either parental or self-report to rule out the presence of

cardiovas-cular abnormalities. The demographic characteristics and casual

measurements of the subjects are provided in Table I.Casual BP and HR measurements were obtained with a Dinamap BP monitor (Model 1846SX, Critikon, Tampa, FL). Dinamap BP readings were initially checked on each subject against those obtained by a technician using a mercury column and stethoscope to insure the accuracy of the measurements (within ±4 mm Hg). Subjects not meeting these criteria were not included in the study. The casual measurements were the average of 10 readings, with 30-second intervals of rest between measurements. The readings were taken with a cuff of appropriate siz& in the seated position after 5 minutes of sitting quietly.

Ambulatory Blood Pressure Monitoring

ABPM was performed on 208 subjects with the Spacelabs 5200

(Spacelabs Inc, Redlands, WA) as described2#{176} and on 92 subjects with the Accutracker II (Suntech, Salem, NC) with a similar pro-tocol. The Spacelabs 5200 recorder used the oscillometric tech-nique to measure systolic blood pressure (SBP) and fifth phase diastolic blood pressure (DBP). The Accutracker II used the ascul-tatory technique to measure SBP and fifth phase DBP. Briefly, the subject was seated and the ambulatory BP recorder applied and calibrated by a technician using a mercury column and stetho-scope to insure the accuracy of the measurements (within ±4 mm Hg for both SBP and DBP). Subjects not meeting these criteria

were not included in the study. The functioning of the recorder

was demonstrated to the subject and the details of the protocol were described. The subject was instructed to relax his/her arm during a BP determination, and to provide diary information for determining sleep periods. The subject was then instructed to resume his/her normal daily activities and to return the following day to remove the recorder. The Spacelabs recorder was set to take a reading at 20-minute intervals between the hours of 06:00 and 24:00 and 60-minute intervals between the hours of 24:00 and

06:00. The Accutracker was set to take a reading at 20-minute

intervals throughout the entire recording. A successful recording was one in which <25% of the readings during the recording were considered artifacts,2#{176} and the subjects had data for at least 20 hours of the day. A total of 84% of the subjects attempted met the criteria for acceptable calibrations and recordings.

Data Analyses

Comparison of subject characteristics were performed by ttests and x analyses with Statview II (Abacus Concepts Inc, Berkeley, CA), as was the calculation of correlation coefficients. The average

BP while awake and during sleep was calculated for each subject.

Comparisons by race and sex were performed by analysis of variance using SuperANOVA (Abacus Concepts Inc, Berkeley,

CA). The subjects were then divided into three age groups for

further analyses, 10 to 12 years of age, 13 to 15 years of age, and 16

to 18 years of age. Two factor analysis of variance was used to test for interactions between age groups and both sex and race. Post

hoc comparisons were performed by the Fisher Protected Least

Sq uares Difference test.

RESULTS

Casual measurements are provided in Table I. For the group as a whole, boys were taller than girls (163

± 13 vs 157 ± 10 cm; P < .001) and had higher casual

SBP (110 ± 12 vs 103 ± 11 mm Hg; P < .01). Girls had faster casual HR (81 ± I I vs 75 ± 12 beats per minute (bpm); P < .001). Black compared with white subjects were older (13.2 ± 1.8 vs 12.4 ± 2.0 years; P < .03), taller (166 ± 9 vs 157 ± 12 cm; P < .001), had higher casual DBP (64 ± 12 vs 60 ± 9 mm Hg; P < .003), and lower casual HR (76 ± I I vs 80 ± 12 bpm; P < .002). Casual and Ambulatory Blood Pressure

Casual SBP was correlated with SBP while awake

(r = 0.4; P < .0001) and during sleep (r = 0.3; P <

.0001). In addition, casual DBP was correlated with DBP while awake (r = 0.31; P < .0001) and during sleep (r = 0.21; P < .001).

Ambulatory Systolic Blood Pressure

The values of SBP while awake and during sleep

by sex, race, and age group are presented in Table 2.

Overall, SBP while awake was higher for boys

com-pared with girls (117 ± 11 vs 112 ± 9 mm Hg; P <

.001), as was SBP during sleep (109 ± 11 vs 105 ± 10

mm Hg; P < .01). Black and white children had

similar SBP while awake and during sleep. The three

age groups had similar SBP while awake. However,

the 10 to 12 year age group had lower SBP during

sleep than the 16 to 18 year age group (106 ± 10 vs

110 ± 11 mm Hg; P < .05).

The age group-by-sex interactions were significant for SBP while awake (P < .0008) and during sleep

(P < .02). Comparisons between boys and girls

within age groups showed that boys 10 to 12 years of

age had higher SBP while awake than girls 10 to 12

years of age (P < .01). Boys compared with girls 13 to

15 years of age had higher SBP while awake (P < .01).

Boys compared with girls 16 to 18 years of age had

TABLE 1. Sex, Race, a

Mean (± nd Age*

SD) for Ca sual Measure ments o f Systolic B lood Press ure, Diast olic Blood Pressure, H eart Rat e, and Bed y Size by

Age, y Boys Girls

Black White Black White

10-12 13-15 16-18 10-12 13-15 16-18 10-12 13-15 16-18 10-12 13-15 16-18

Sample, n 21 29 20 50 30 10 24 20 37 31 23 5

Height, 160±10 168±9 170±10 153±12 166±11 168±16 152±12 162±10162±5 150±9 161±9 157±6

cm

Weight,kg 59±19 66±19 63±15 49±12 62±16 62±25 48±14 54±15 59±13 45±13 55±15 54±15

Systolic 107 ± 12 114 ± 13 119 ± 12 105 ± 10 110 ± 10 112 ± 8 103 ± 12 103 ± 13 101 ± 8 104 ± 11 106 ± 9 96 ± 6

blood pressure, mm Hg

Diastolic 64±10 65±14 66±14 60±9 62±9 63±9 61±10 61±10 66±14 55±7 64±7 62±8

blood pressure, mm Hg

Heartrate, 78±8 72±9 67±8 81±12 74±10 67±11 82±13 79±12 76±9 86±11 80±8 80±8

bpm

* Significant differences described in text.

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TABLE 2. Mean (±SD) Systolic Blood Pressure (SBP) While Awake and Asleep as a Function of Sex, Race, an d Age*

Age Group,

Awake SBP (mm Hg)

Boys Girls

Total Black White Total

Black White

10-12 115 ± 9 115 ± 10 115 ± 10 111 ± 8 112 ± 9 112 ± 9 13-15 116±10 116±11 116±11 112±9 112±8 112±8 16-18 125±13 126±13 125±13 112±8 106±9 111±9

Asleep SBP (mm Hg)

Black

Boys

White

Girls

10-12 105±10 110±11 107±11 102±9 107±8 105±9 13-15 111 ± 10 106 ± 10 108 ± 10 107 ± 12 104 ± 11 105 ± 12

16-18 118±8 113±15 117±11 107±8 97±6 106±9

*Significant differences described in text.

higher SBP while awake (P < .01) and during sleep

(P < .01). The age group-by-race interaction was sig-nificant for SBP during sleep (P < .03). Comparisons across race showed that blacks 13 to 15 years of age had higher SBP during sleep than whites in the same

group (P < .01). Comparisons across age groups

within race showed that blacks 16 to 18 years of age

had higher SBP during sleep than blacks 10 to 12

years of age (P < .01).

Ambulatory Diastolic Blood Pressure

The values for DBP while awake and during sleep

by sex, race, and age group are presented in Table 3.

Overall, DBP while awake and during sleep were

similar for boys and girls. DBP while awake was

similar for black and white subjects. However, black

subjects had higher DBP during sleep than white

subjects (66 ± 7 vs 58 ± 6 mm Hg; P < .01). Subjects

16 to 18 years of age had higher DBP while awake

(69 ± 5 mm Hg) than either subjects 10 to 12 years of age (65 ± 7 mm Hg; P < .05) or 13 to 15 years of age (65 ± 7 mm Hg; P < .05). In addition, subjects 16 to 18

years of age had higher DBP during sleep (64 ± 7

mm Hg) than either subjects 10 to 12 years of age

(60 ± 7 mm Hg; P < .05) or 13 to 15 years of age (60 ± 8 mm Hg; P < .05).

The age group-by-race interaction was significant for DBP during sleep (P < .01). Blacks 16 to 18 years

of age had higher DBP during sleep than whites in

the same age group (P < .01). Comparisons across

age groups within race showed that blacks 16 to 18

years of age had higher DBP during sleep than blacks 10 to 12 years of age (P < .01) or 13 to 15 years of age

(P < .01).

Ambulatory Heart Rate

The values of HR while awake and during sleep by

sex, race, and age group are presented in Table 4.

Overall, HR was faster for girls compared with boys both while awake (88 ± 8 vs 84 ± I I bpm; P < .0002) and during sleep (77 ± 13 vs 72 ± 12 bpm; P < .0006). In addition, the HR while awake for the 10 to 12 year

age group (89 ± 9 bpm) was faster than for both the

13 to 15 year age group (84 ± 10 bpm; P < .05) and the 16 to 18 year age group (85 ± 10 bpm; P < .05).

The age group-by-sex interactions were significant for HR while awake (P < .02) and during sleep (P <

.05).

Comparisons between boys and girls within age

groups showed that 13 to 15-year-old girls had faster awake HR than boys in the same age group (P < .01). In addition, girls 16 to 18 years of age had faster awake HR (P < .01) and asleep HR (P < .01) than boys

TABLE 3. Mean (±SD) Diastolic Blood Pressure (DBP) While Awake and Asleep as a Function of Sex, Race, and Age8

Age Group, y

Awake DBP (mm Hg)

Boys Girls.

Black White Total Black White Total

10-12 68±7 67±7 67±7 64±5 64±6 65±5

13-15 66±6 64±6 65±6 64±6 66±8 66±7

16-18 69±6 69±4 69±5 70±6 67±3 70±6

Asleep DBP (mm Hg)

Black

Boys

White

Girls

10-12 62±9 60±7 61±8 59±4 60±7 60±6

13-15 63±9 59±7 61±8 59±7 60±9 60±8

16-18 65±7 58±7 63±7 66±7 57±6 65±8

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TABLE 4. Age*

Mean (±SD) Heart Rate (HR) While Awake and Asleep as a Function of Sex, Race, and

Age Group,

y

Awake HR (beats per minute)

Boys Girls.

Black White

10-12 86±11 89±10 88±11 90±7 88±8 89±8

13-15 83±10 80±9 82±9 87±9 88±10 87±10

16-18 78±10 80±11 78±10 89±8 85±7 89±8

Asleep HR (beats per minute)

Black

Boys White

Girls

10-12 71±12 76±14 75±13 79±11 77±9 78±10

13-15 73±11 70±11 72±11 75±17 74±16 74±16

16-18 68±11 70±14 79±10 82±11 70±7 80±12

*Significant differences described in text.

16 to 18 years of age. Comparisons within sex

showed that boys 10 to 12 years of age had faster

awake HR than boys 13 to 15 years of age (P < .01) and 16 to 18 years of age (P < .01).

Body Size and Ambulatory Blood Pressure

Height was positively correlated with SBP while

awake (r = 0.21; P < .001) and during sleep (r = 0.18;

P < .001), and negatively correlated with HR while awake (r = -0.25; P < .001) and during sleep (r =

0.17; P < .01). Weight was positively correlated with

SBP while awake (r = 0.33; P < .001), DBP while

awake (r = 0.26; P < .001), SBP during sleep (r = 0.29;

P < .001) and DBP during sleep (r = 0.17; P < .001). In

addition, weight was negatively correlated with HR

while awake (-0.14; P < .02). Blood Pressure Recording Unit

The subjects were divided into groups based on

the BP recording unit which was used to collect the

data. The subjects who wore the Spacelabs 5200

rel-ative to the Accutracker II had higher levels of DBP while awake (68 ± 6 vs 63 ± 7 mm Hg; P < .01) and during sleep (64 ± 7 vs 56 ± 7 mm Hg; P < .01). In addition, these subjects had higher SBP during sleep (108 ± 10 vs 105 ± 12 mm Hg; P < .03). However, these subjects were also older (13.5 ± 2.5 vs 12.7 ± 2.0 years; P < .01). The differences in the BP while

awake and during sleep were no longer apparent

following an adjustment for age. DISCUSSION

ABPM is a valuable tool for assessing and treating

HTN in adults.2’ However, ABPM has not been used

routinely in pediatric populations for at least three reasons?- First, the early recorders were too

cumber-some for use on children and adolescents. The

newer generation of recorders are considerably

smaller, lighter, and quieter.24’25 From the experi-ences in this study, most children above the age of 10 years have little difficulty wearing them. Second, the

early recorders were very sensitive to arm

move-ment?- A child would forget to relax his/her arm

during a BP determination. This resulted in a large

number of artifactual readings. The newer

genera-tion of recorders have improved transducers and

algorithms for determining BP.24 The result has been a reduction in the number of artifactual readings to

10 to 15%, which are levels comparable with those

found in studies in adults.24 Third, reference data has not been available based on values derived from a large number of healthy, normotensive children and

adoles-cents. This study provides these reference data.

Factors known to contribute to differences in

ca-sual BP in youths were also associated with

differ-ences in ABPM measurements)’2 The Second Task

Force on Blood Pressure Control in Children empha-sized the importance of age and sex, providing sep-arate norms for boys and girls as a function of age. Similar relationships were found for healthy, normo-tensive adults.26’27 Boys had higher awake and asleep SBP than girls of comparable age. In addition, 10 to

12-year-old boys had higher awake DBP. The

pat-terns of BP across age groups were similar for boys and girls, although not identical. Only a few studies

in adults examined the influence of sex on AMBP

measurements. These studies were summarized by

Staessen et a119 in a meta-analysis. They determined differences reported in eight studies, adjusting for differences in sample sizes. The 24-hour BP was 6/4

mm Hg higher in men compared with women.

Black adults have higher casual BP than white

adults.28’29 However, the question of racial

differ-ences in casual BP in children and adolescents has

yet to be established. A recent meta-analysis by

Alpert and Fox#{176}identified 17 studies with racial comparisons of subjects aged 13 to 18 years of age. Of these, nine reported higher SBP for white compared

with black boys, and three reported higher SBP for

black compared with white boys. Five studies

re-ported higher SBP for white compared with black

girls, and seven reported higher SBP for black

com-pared to white girls. In the current study using

ABPM, black subjects in the older age groups had

higher BP during sleep than white subjects of

com-parable age. Furthermore, the level of BP during

sleep in black but not white subjects increased with age. The racial differences in BP during sleep in this

study is consistent with previous studies by this group20’31 and others32’3 in both youths and adults.

(5)

In this study with ABPM, the levels of SBP and

DBP during the day in both boys and girls were

higher, and those during the night were lower, than those for casual BP provided by the Task Force. This is probably due to an increased activity level during

ABPM

determinations during the day and a

de-creased activity level during the night.

SUMMARY AND CONCLUSIONS

This study demonstrates the feasibility of ABPM in

a pediatric population using the new generation of

BP recorders. In addition, the results of this study provide reference values for ABPM in children based on a large sample of healthy, normotensive children and adolescents.

Using ABPM on every child with possible HTN is

not recommended. However, this technique is

ap-propriate in some circumstances. For example, the

comparison of ABPM from a patient with suspected

HTN with data from normals provided by studies

such as this can determine if that child has HTN or

“white coat” HTN. In addition, ABPM can help to

identify youths with abnormal variations of BP that

may predispose them to the early development of

BP-induced target organ damage. For example,

dif-ferences between casual BP and ABPM

measure-ments may help to explain the findings of

BP-in-duced target organ changes in some youths before

the development of clinicaly hypertension, including left ventricular hypertrophy’35 and early atheroscie-rosis.’ It is possible that these individuals were

ex-posed to a greater BP load over the course of a

normal day than was reflected by casual BP.

The values of BP and HR presented in this study

may not be strictly considered norms because they

were not obtained from a true random sample of the

population. However, this is by far the largest data-set reported to date on this age group.

ACKNOWLEDGMENTS

This research was supported by National Institutes of Health Grants HL-35788, HL-42645, and GCRC M01-RROO2I.

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Pediatrics

Wilson

Gregory A. Harshfield, Bruce S. Alpert, Derrick A. Pulliam, Grant W. Somes and Dawn K.