Abstract
Healthy subjects show wide interindividual variation in their
heart rate behavior, but the factors affecting heart rate dynamics
are not well known. This research was undertaken to evaluate heart
rate variability (HRV) and baroreflex sensitivity (BRS) in a large
random sample of subjects without evidence of heart disease, and
to estimate the relation of heart rate behavior to age, sex and
cardiovascular risk factors.
Short-term HRV was analyzed from 15-minute periods of standardized
recording in supine and upright positions using time and frequency
domain measures, and BRS was calculated using the Valsalva maneuver
in an original randomly selected population of 600 hypertensive
and 600 control middle-aged subjects. In addition, HRV was analyzed
from the same segments using new measures based on fractals and
complexity (chaos theory) of R - R interval dynamics in
the same random population, and from 24-hour period in 114 healthy
subjects aged from 1 to 82 years.
Large interindividual variation was observed in the measures
of HRV and BRS in middle-aged subjects; coefficient of variation
(CV) of the standard deviation of R - R intervals (SDNN)
39% (54 ± 21 ms) and CV of BRS 49% (9.9 ± 4.9
ms/mmHg). In healthy middle-aged men, SDNN was weakly related
to age (r = -0.19, p < 0.01),
HDL cholesterol (0.19, p < 0.01), serum
insulin (-0.23, p < 0.001) and triglyceride
(-0.25, p < 0.001) levels.
In women, SDNN was only related to insulin levels (r = -0.23,
p < 0.001). BRS was related to systolic
blood pressure (r = -0.31 and -0.30,
in men and women respectively, p < 0.001
for both) and blood glucose (r = -0.25,
p < 0.01) and serum insulin levels (r = -0.34,
p < 0.001) in women. Lesser intersubject
variation was observed in the non-linear measures of HRV; CV 14% of
short-term scaling exponent (a1), a measure of fractal-like correlation
properties of HRV, (1.21 ± 0.17) and
CV 12% of approximate entropy, a measure of complexity,
(1.13 ± 0.14). Neither a1 or ApEn was
related to any risk factors. Women had lower overall short-term
HRV (p < 0.01) and BRS (p < 0.001),
but a higher spectral high-frequency component of HRV, higher ApEn
and lower a1 (p < 0.001 for all) compared
to men. The impairment in overall HRV was confined to the hypertensive
subjects with metabolic features of the insulin resistance syndrome
(IRS, n = 69), but the BRS and spectral
high-frequency component were also impaired in hypertensive subjects
without IRS compared to normotensive subjects. The 24-hour cardiac
interbeat interval dynamics changed markedly from childhood to
old age. Children showed similar complexity and fractal correlation
properties of R - R intervals as young adults. Healthy aging
resulted in R - R interval dynamics with higher regularity
and predictability and altered fractal scaling.
The traditional measures of HRV and BRS are weakly related
to many cardiovascular risk factors in subjects without heart disease,
but the interindividual variation of HRV and BRS is only partly
explained by these factors, suggesting a genetic background of
the intersubject variation in cardiovascular autonomic regulation.
The new dynamical measures of HRV show less interindividual variation
than the conventional measures of HRV in healthy subjects and are
not related to cardiovascular risk variables, suggesting that these
dynamical measures quantify the "intrinsic" capacity of a healthy
cardiovascular control system without the significant influence
of life-style, metabolic or demographic variables. However, there
are sex and age-related differences also in the fractal and complexity
measures of heart rate behavior.
| Identifer | oai:union.ndltd.org:oulo.fi/oai:oulu.fi:isbn951-42-5227-6 |
| Date | 15 April 1999 |
| Creators | Pikkujämsä, S. (Sirkku) |
| Publisher | University of Oulu |
| Source Sets | University of Oulu |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/publishedVersion |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess, © University of Oulu, 1999 |
| Relation | info:eu-repo/semantics/altIdentifier/pissn/0355-3221, info:eu-repo/semantics/altIdentifier/eissn/1796-2234 |
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