亞裔與白人幼童其血壓心跳及BMI並無不同,但亞裔之LF/HF較白人高;不論族裔,女孩子的LF/HF較男孩子高
Differences in heart
rate variability between Asian and Caucasian children living in the same
Canadian community
Katharine E. Reed,
Darren E.R. Warburton, Crystal L. Whitney, and
Heather A. McKay
Abstract: Heart rate variability (HRV) is
an umbrella term for a variety of measures that assess autonomic influence on
the heart. Reduced beat-to-beat variability is found in individuals with a variety
of cardiac abnormalities. A reduced HRV positively correlates with obesity,
poor aerobic fitness, and increasing age. Racial (black–white) differences are apparent
in adults and adolescents. We aimed to evaluate (i) Asian–Caucasian differences
in HRV and (ii)
differences in HRV between girls and boys. Sixty-two children (30 male (15
Caucasian, 15 Asian) and 32 female (15 Caucasian,
17 Asians)) with a mean age of
10.3 ± 0.6 y underwent 5 min resting HRV recording, fitness testing (Leger’s
shuttle), and self-assessed maturity.
Outcome HRV measures were a ratio of low to high frequency power (LF:HF), standard deviation of R–R intervals (SDRR) and root
mean square of successive R–R intervals (RMSSD). Data were compared between
groups using analysis of covariance (ANCOVA). There were no race or sex
differences for time domain variables, mean R–R, body mass index, or blood
pressure. Compared with Caucasian children, Asian children displayed a higher
adjusted (fitness, R–R interval) LF:HF ratio (72.9 ±
59.4 vs. 120.6 ± 85.3, p < 0.05). Girls demonstrated
a higher adjusted LF:HF power
than boys (117.2 ± 85.1 vs. 76.6 ± 62.4, p = < 0.05). In conclusion, Asian and
Caucasian children display
different frequency domain components of heart rate variability.
Key words: autonomic nervous system,
sympathetic, vagal, race, aerobic fitness, sex.
Résumé : La
variabilité de la fréquence cardiaque (HRV) est un terme général qui englobe
une série de mesures afin
d’évaluer
l’influence autonome du coeur. Chez les individus présentant une anomalie
cardiaque, on observe une moins
grande
variation de battement à battement. Une HRV moindre est corrélée positivement
avec l’obésité, une piètre
condition
physique et le vieillissement. On observe des différences raciales (Noirs–Blancs)
chez des adultes et des adolescents.
Nous
voulons analyser (i) les différences de
de
et 32
filles (15 Caucasiennes et 17 Asiatiques), âge : 10,3 ± 0,6 ans, participent à
une évaluation de
5 min au
repos, au test de Léger (course-navette sur
retenues sont
le ratio de la puissance de basse fréquence sur la puissance de haute fréquence
(LF:HF), l’écart type des
intervalles
R–R (SDNN) et la valeur quadratique moyenne d’intervalles R–R successifs
(RMSSD). On analyse les différences
au moyen
d’une analyse de covariance. On n’observe aucune différence entre les races et
les genres dans les résultats
suivants :
variables à réponse temporelle, R–R moyen, IMC et pression sanguine.
Comparativement aux enfants
caucasiens,
les Asiatiques présentent un meilleur ratio LF:HF ajusté (condition physique,
intervalle R–R) : 72,9 ± 59,4
vs. 120,6
± 85,3, p < 0,05. Les filles présentent une
plus grande puissance LF:HF ajustée : 117,2 ± 85,1 vs. 76,6 ±
62,4, p = <
0,05. En conclusion, les composantes de la variabilité de la fréquence
cardiaque des enfants caucasiens et
asiatiques
n’ont pas la même réponse temporelle.
Mots clés
: système nerveux autonome, sympathique, vagal, race, puissance aérobie,
sexe.
[Traduit
par
Appl. Physiol.
Nutr. Metab. 31: 1–6 (2006) doi:10.1139/H05-015
© 2006 NRC Canada
1
Pagination not
final/Pagination non finale
Received 8
January 2005. Accepted 18 July 2005. Published on the NRC
Research Press Web site at http://apnm.nrc.ca on 23 March
2006.
K.E. Reed,
D.E.R. Warburton, and C.L. Whitney. School of Human Kinetics,
H.A. McKay.1 Department of Orthopaedics / Family Practice, University of British
Columbia, 5th Floor, Research Pavilion, 828
1Corresponding author (e-mail:
mckayh@interchange.ubc.ca).
Introduction
Heart rate variability (HRV)
measured by power spectral
analysis provides a quantitative marker
of autonomic nervous
system influence on heart rate and
has been shown to
reflect cardiovascular health. In
adults, impaired variability
has been reported following
myocardial infarction
(Sosnowski
et al. 2002), in chronic heart failure, and in left
ventricular
dysfunction (Nolan et al. 1992). In young children,
reduced HRV values are associated with
atrial septal
defects (Finley et al. 1989) and
increased likelihood of sudden
infant
death syndrome (Edner et al. 2002). An unfavourable
autonomic profile balance (manifesting
as reduced beatto-
beat variability) reflects a
predominately sympathetic influence
on control of heart rate and is
positively correlated
with general obesity (Martini et
al. 2001; Nagai et al. 2004;
Gutin et al. 2000), high visceral
fat deposition (Gao et al.
1996), lower aerobic fitness (Gregoire et al. 1996; Aubert et
al. 2001), male gender (Sinnreich et al. 1998), and increasing
age (Umetani
et al. 1998); (Reardon and Malik 1996).
Racial (black–white)
differences in HRV have been previously
studied in adults, with blacks having
a lower sympathetic
drive than age-matched whites (Guzzetti et al. 2000)
(Liao et al. 1995). There are only limited data in young
children
and none that compare Asians and
Caucasians. Previous
data concerning race differences in
youth have been
equivocal. Whilst one investigation
found that black adolescents
display less favourable
HRV measures (i.e., a greater
sympathetic contribution to total power)
than age-matched
whites (Faulkner et al. 2003),
another found reduced sympathetic
activity in blacks (Urbina
et al. 1998). Heart rate variability
has been explored exclusively in
Asian populations in
adults and children, but has not been
compared with other
races. Results from independent
studies of Asian (Kikuchi et
al. 2003;
Kazuma et al. 2002; Nagai et al. 2004) or Caucasian
children
(Faulkner et al. 2003; Mandigout et al. 2002)
suggest there may be racial
differences in time and frequency
domains of HRV, with Asian children
living in
displaying a lower HRV than Caucasian
children living in
western societies.
than 2 million Canadians reporting
an Asian origin (Statistics
Canada 2004). There have,
however, been no comparisons
between Asian and Caucasian children
living in the
same North American community.
The effect of male or female
gender on HRV is well documented
in adults, with the majority of
researchers reporting
that women, at least until late
middle age, demonstrated a
higher vagal
influence on heart rate control than men
(Gregoire
et al. 1996; Liao et al. 1995; Antelmi et al. 2004).
However, the influence of sex
appears to be modulated by
age (Umetani
et al. 1998) and studies that have examined
sex differences in children have
found that girls have lower
variability than boys (Umetani
et al. 1998; Faulkner et al.
2003). These
studies, which involved 24 h HRV monitoring,
showed lower time domain values in
girls aged 14–16 y and
1–20 y,
respectively. To our knowledge, no studies have used
5 min
recording to examine sex differences.
Thus, our primary objective was
to determine whether
differences in HRV existed between
Asian–Canadian (AC)
and Caucasian–Canadian (CC)
children living in the same
community. Our second objective was to
explore differences
in HRV between prepubertal girls and boys using a 5 min
recording.
We hypothesize that compared with
CC children, AC children
will have lower levels of the time
domain variables
(standard
deviation of R–R intervals (SDRR) and root mean
square of successive R–R intervals,
(RMSSD)) accompanied
by greater sympathetic
predominance, evidenced by a higher
LF:HF
in the frequency domain variables. We also hypothesize
that girls will demonstrate altered
HRV profiles, specifically
lower variability, compared with
age-matched boys using
5 min recordings similar to
those derived from 24 h recordings.
Materials and methods
Participants
Sixty-six Asian and Caucasian
children from grades 4 and
5 were randomly selected from a
larger cohort of participants
in a school-based exercise
intervention (Action
Schools!,
B.C., N = 514). Parents of the children
completed
a health history questionnaire
on the child’s behalf. Children
with cardiovascular disease were
deemed ineligible to participate
in the intervention; thus, no
further children were excluded
from the present study. Children
were classified as
Caucasian, Asian, East Indian,
or Other based on the birthplace
of both parents. Children were
classified as “Asian” if
both parents, or all 4
grandparents, were born in
parents or all 4 grandparents were born
in
(i.e., Africa or
The
Board approved the
investigation and all participants and
their legal guardians provided
written consent.
Measurements
Short-term, 5 min resting HRV
was taken using Polar
S810 Heart
Rate Monitors (Polar Electro,
measurement error attenuates the
correlation observed between
variables, we attempted to control
potentially confounding
variables by (i) instructing children not to
consume
a caffeinated beverage for at
least 2 h before HRV measurement,
(ii) taking all
measurements before lunch break activity,
and (iii) making all recordings on school premises.
Children lay supine on a padded
mat in a quiet, softly lit
room. Recording began immediately
and lasted for 6 min.
Digitally coded R–R interval
length was input into Polar
software (Polar Electro) using an
infrared transmitter to display
a tachogram
on screen. After the first minute of data
was discarded, R–R intervals were
automatically filtered
using median- and
moving-average-based filtered methods.
Acquisition and filtering of
R–R data using Polar software
has been previously described (Jurca et al. 2004). Data (R–R
intervals) were then exported as text to
HRV Analysis Software
(Biomedical
Signal Analysis,
R–R series were transformed to
the frequency domain via
fast Fourier transformation.
Spectral power was determined,
in accordance with the Task Force
of the European Society
of Cardiology and the North
American Society of Pacing
Electrophysiology (Task Force
1996), as very low frequency
(VLF; 0.01–0.04 Hz), low
frequency (LF; 0.04–0.15 Hz), or
high frequency (HF; 0.15–0.5 Hz).
LF:HF was chosen as the
© 2006 NRC Canada
2 Appl. Physiol. Nutr. Metab. Vol. 31, 2006
primary measure of interest, as it
provides information regarding
relative
vagal or sympathetic predominance (Pagani
et al.
1986). Values for
HF and LF are given as normalized
units (nu).
For HF, normalized units are calculated as
HF / (total power – VLF) × 100
where HF is measured in ms2. For LF,
normalized units are
calculated as
LF / (total power – VLF) × 100
where LF is measured in ms2.
Secondary variables of interest
were the global time domain
measure, the standard deviation
of normalized R–R intervals
(measured in milliseconds
(ms); SDRR), and the root mean
squared of successive R–R
intervals (also measured in ms; RMSSD),
which is thought
to represent vagal
activity.
Height in bare feet was
measured to the nearest
Weight, in light indoor
clothing, was measured using an
electronic scale (SECA,
by ±
made. The average of 2 values or
the median of 3 values was
used for analysis. Body mass index
(BMI) was calculated as
kg/m2. Aerobic fitness was
determined via Leger’s
shuttle run (Leger et al. 1988). Children
begin running
at
minute. Children continued running
until they were unable
to maintain the required pace at
a given level. This maximal
test was developed for children and
estimates aerobic capacity
from running speed and duration.
Blood pressure was
measured in duplicate on the left arm
after 5–10 min quiet
rest using an automated
sphygmomanometer (VSM
were within 5 mmHg for systolic
blood pressure, the
lowest value was recorded. If the
difference exceeded 5 mmHg
then a third measurement was taken.
Children self-assessed
their physical maturity using line
drawings and descriptions
of pubic hair (boys and girls)
and breast stage (girls) based
on Tanner staging (Tanner 1955).
Stage 1 represents prepuberty,
stage 2 represents early puberty,
stage 3 represents
middle puberty, stage 4 late
represents puberty, and stage 5
is considered post pubertal.
Statistical procedures
HRV measures that were skewed (Kolmogorov–Smirnov
Z, p < 0.05) were transformed (natural
logarithm (ln)) to
normalize the distribution. In these
cases, statistical comparisons
were based on the ln scales. Analysis of covariance
(ANCOVA) was used to evaluate
race and sex differences in
HRV. Owing to their established
relationship with HRV, we
controlled for aerobic fitness (Leger’s
mean resting heart rate by
including them as covariates in
the analysis. Statistical
significance was set at alpha level p <
0.05. All statistical analyses
were performed using SPSS
version 12.0 for Windows (SPSS Inc.,
Results
Sixty-two children (
and 17 girls; 30 CC children
comprising 15 boys and 15
girls) aged 9–11 years were included
in the analysis. Data
from 4 children were excluded owing
to excessive movement
during recording. Descriptive
characteristics (means ±
SD) of the participants by sex
and race are provided
(Table 1). All children reported to be in
Tanner stage 1 or 2.
There were no racial
differences for age, BMI, heart rate,
or blood pressure. CC children
ran a significantly greater
number of
11.3 and 19.9 ± 5.7,
respectively, p = 0.006).
There were no sex differences
for age, BMI, aerobic fitness,
heart rate, or blood pressure.
Heart rate variability
measurements
Group means (non-adjusted) for
raw and log-transformed
data by race and sex are provided
(Table 2). There were no
race or sex differences for total
power, SDRR intervals, or
RMSSD.
There was a difference in LF:HF between AC and CC
children (F = 5.8, p = 0.01), with AC children having a
higher LF:HF than CC children (Table
3). Analysis by sex
showed a higher LF:HF ratio (F = 4.3, p = 0.04) in girls than
in boys (Table 3). Within-sex
differences showed that AC
children had higher (NS) LF:HF than CC
children (93.9 ±
16.6 and
59.2 ± 16.5, F = 2.1, p = 0.17 for AC and CC boys,
respectively; 144.5 ± 20.7 and 86.2 ± 22.1,
F = 3.5, p = 0.71
for AC and CC girls,
respectively).
Discussion
Comparison between Asian and
Caucasian children
This was the first
investigation to examine differences in
HRV between Caucasian and Asian
children living in the
same Canadian community. AC
children had higher LF:HF
when compared with CC children of
the same age. A lower
© 2006 NRC Canada
Reed 3
Pagination not
final/Pagination non finale
Asians Caucasians Boys Girls
n 32 30 30 32
Age (y) 10.3 (0.6) 10.5 (0.6)
10.2 (0.6) 10.5 (0.6)
BMI (kg/m2) 18.6 (3.5) 18.6
(2.6) 18.8 (2.9) 18.4 (3.2)
No of.
SBP (mmHg) 102.2 (9.1) 105.7
(10.5) 103.9 (8.1) 103.6 (11.2)
DBP (mmHg) 65.1 (7.5) 65.5
(8.2) 66.6 (6.8) 64.1 (8.5)
Heart rate (b/min) 81.1 (12.1)
76.9 (10.1) 77.9 (12.1) 80.0 (10.1)
Note: Values are means (± SD). BMI,
body mass index; DBP, diastolic blood pressure; SBP, systolic blood
pressure; b/min, beats per minute).
*Race difference at a
significance level of p < 0.05.
Table 1. Descriptive characteristics of
participants by sex and race.
LF:HF
is indicative, although not definitive, of a higher
sympathetic and (or) lower vagal influence on heart rate.
However, this finding of a
differential influence on heart
rate according to race is further
supported by the higher
(NS) values for RMSSD seen in
CC children. This time domain
measure is strongly influenced by vagal modulation of
the SA node. Additionally, when
measured in the supine position,
as in the present study, global
measure of HRV such
as SDNN are modulated primarily
by the activity of the
vagus. Although the differences in SDNN and
RMSSD between
AC and CC children failed to
reach statistical significance
here, both measures are clearly
higher in the latter
group.
Our findings support previous
work that highlights a racial
difference in adults and adolescents in
HRV (Liao et al.
1995;
Faulkner et al. 2003); (Urbina et al. 1998). Investigations
that compared African–American with
Caucasian–
American adolescents have been
equivocal. While one study
revealed that 15-year-old
African–American males generally
had less favourable
HRV outcome measures (greater sympathetic
modulation of heart rate) (Faulkner et
al. 2003), a similar
study (Urbina
et al. 1998), reported that 13- to 17-yearold
African–American male youth had
less sympathetic tone
and greater short-term
variability. Racial differences in HRV
were evident at rest and during
cardiovascular stress tests
such as the Valsalva
manoeuvre (Urbina et al.
1998). Similar
comparisons have not been previously made
in younger age
groups or, until now, between Asian
and Caucasians.
Comparison between girls and
boys
In this cohort, boys had a
greater contribution of highfrequency
power to total power than girls.
Boys and girls
scored similarly on aerobic fitness
tests, but girls had an elevated
LF:HF
power ratio compared with boys. These results
support previously reported sex
differences (Faulkner et al.
2003) (Silvetti
et al. 2001) wherein girls, aged 15 y and 1–
20 y, respectively,
demonstrated a lower HRV than boys.
Both of these investigations
found that time domain variables
(namely
SDRR and the standard deviation of normal R–R
intervals for 5 min segments, SDANN)
were higher in boys.
In the same investigation,
however, Silvetti and colleagues
(Silvetti
et al. 2001) reported no sex differences for
RMSSD. Conversely, the present study
found that differences
in HRV measures were significant
when measured in
the frequency domain (LF:HF).
Differences were also evident
in the time domain variable
measures (SDRR and
RMSSD), but these failed to
reach statistical significance.
Previously, it has not been
shown that sex differences in
HRV were observed with
short-term (5 min) recordings. The
discrepancies between the findings of this
study, and those
of other studies i.e., no
difference in time domain, only in
frequency domain variables, is likely
because of the duration
of the recording. Frequency
domain methods should be preferred
to the time domain methods when
short-term recordings
are investigated (Task Force
1996).
The relationships between
physical activity and indices of
spectral power parallel those reported
in adults (i.e., more
active individuals typically
demonstrate greater vagal predominance)
(Gregoire et al. 1996). Aerobic training is believed
to improve the electrical
stability of the myocardium,
with regular exercise improving the
cardiac autonomic profile
(Melanson and Freedson 2001). Nagai and colleagues
(Nagai et al. 2004) conducted a
cross-sectional investigation
and separated 96 girls and boys
into 4 groups; lean physically
active, lean sedentary, obese
physically active, and
obese sedentary. Lean active
children had significantly better
HRV parameters compared with
the other group. However,
physical activity also appeared to
contribute to enhanced autonomic
nervous system activity in both lean
and obese children.
In the present investigation,
differences in heart rate
variability between girls and boys, and
between AC and CC
children persisted after adjusting for
physical fitness.
Although a substantial
proportion of the variance in HRV
can be accounted for by factors
such as age, sex, BMI, physical
activity, and fitness, the Framingham
Heart Study and
the Kibbutzim Family study found
that up to 34% of the
variance was accounted for by genetic
factors (Singh et al.
1999; Sinnreich et al. 1999). Although sex differences in
© 2006 NRC Canada
4 Appl. Physiol. Nutr. Metab. Vol. 31, 2006
Asian Caucasian Boys Girls
LF 48.78 (16.62) 37.57 (14.81)
38.71 (14.81) 47.62 (17.41)
Ln 3.82 (0.38)* 3.54 (0.40)* 3.57
(0.41)† 3.79 (0.39)†
HF 51.22 (16.62) 62.53 (14.83)
61.25 (14.81) 52.33 (17.39)
Ln 3.87 (0.35)* 4.10 (0.28)* 4.07
(0.28)† 3.89 (0.36)†
LF:HF
120.57 (85.31) 72.92 (59.42) 76.57 (62.4) 117.19 (85.12)
Ln 4.54 (0.73)* 4.05 (0.67)* 4.11
(0.68)† 4.51 (0.74)†
RMSSD 55.11 (34.45) 75.50
(54.77) 65.18 (38.21) 64.12 (53.17)
Ln 3.83 (0.59) 4.06 (0.72) 4.03
(0.56) 3.87 (0.76)
SDRR 56.41 (27.37) 64.92
(38.02) 60.17 (30.01) 60.81 (35.91)
Ln 3.89 (0.59) 4.01 (0.62) 3.94
(0.63) 3.94 (0.59)
TP 559 (660) 626 (824) 624
(855) 558 (735)
Ln 5.66 (1.27) 5.58 (1.41) 5.64
(1.41) 5.61 (1.27)
Note: Statistical significance refers
to log transformed and raw units data in each case. HF, high frequency
power; LF, low frequency power;
RMSSD, root mean squared of successive R–R intervals; SDRR, standard
deviation of R–R intervals; TP, total
power; Ln, log-transformed value).
*Race difference at p < 0.05.
†Sex difference at p < 0.05.
Table 2. Group (race and sex) mean (± SD) of raw and
log-transformed heart rate variability
data (non-adjusted).
adult HRV measures are well
documented, race differences
and sex differences in children
have not been well investigated.
We acknowledge some limitations
in the study. Although
we controlled for aerobic
fitness, we were unable to match
children on physical activity. Second,
we performed a crosssectional
comparison of sex and race. Analysis of
heart rate
variability in children is a complex
issue, and the evolving
nature of the autonomic nervous
system as maturation occurs
adds further difficulty.
Longitudinal investigations of
HRV are necessary to determine whether
time and frequency
domain measures show similar age-,
race-, and sex-related
patterns over time.
Conclusions
There is a paucity of
literature describing HRV in young
children and none that compared Asian
to Caucasian children.
We demonstrated that AC
children aged 9–11 y had
significantly elevated LF:HF power compared
with CC children
living in the same community. These
findings support
previous investigations suggesting
black–white differences
in heart rate variability in
children, but introduce new findings
regarding altered variability profiles
between Asian and
Caucasian
children. Although this difference is unlikely to
result in adverse health implications
during childhood, racial
norms for HRV measures should be
determined and considered
during clinical examinations and
experimental investigation.
Further studies to establish
racial norms may be
warranted.
Acknowledgements
We acknowledge support from the
Ministry of Health
Planning, B.C., the
Research,
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© 2006 NRC Canada
Reed 5
Pagination not
final/Pagination non finale
Group Adjusted log LF:HF
Asians 4.52 (0.12)*
Caucasians 4.07 (0.13)*
Males 4.11 (0.13)†
Females 4.48 (0.12)†
*Race difference at p < 0.05.
†Sex difference at p < 0.05.
Table 3. Adjusted (aerobic fitness and heart
rate) means of log-transformed low
: high frequency
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Summary
1997, Vol. 14, No. 6, Pages 597-606