The Journal of Pediatrics
Volume 137, Issue 1 , Pages 6-8, July 2000

Does heart rate variability explain increased blood pressure in adolescents?☆☆☆

Division of Pediatric Cardiology, New York Medical College, Valhalla, NY 10595

Article Outline

Abbreviations:  HRV , Heart rate variablility

 

See related article, p.63.

Tanaka et al have performed elegant investigations of blood pressure and heart rate control in large numbers of healthy Swedish and Japanese children.1, 2, 3, 4, 5, 6 Because the autonomic nervous system regulates moment-to-moment heart rate and blood pressure changes, past and present research has employed techniques to explore autonomic circulatory control. Autonomic nervous system dysfunction may relate to orthostatic intolerance, hypertension, heart failure, and other disease states.7 Various tests of autonomic activity have been applied, including pharmacologic challenge, but these tests may be difficult to implement or to interpret in children. Thus Tanaka and other investigators8, 9 have used spectral power analysis (frequency analysis) of beat-to-beat heart rate and blood pressure measurements to assess the variation at different frequencies corresponding to different putative physiologic control mechanisms. Often these techniques are subsumed under the aegis of heart rate variability. On the one hand, HRV offers the potential for rapid noninvasive determination of autonomic nervous system activity in humans.5, 6, 7, 8 On the other hand, HRV must be carefully interpreted in context because measurements are greatly influenced by experimental conditions, respirations, and other biologic signals. Nonetheless, HRV techniques offer a relatively simple and painless window on autonomic control and have been extensively used.

In this issue of The Journal, Tanaka et al9 examine data from healthy children using a correlative, multivariate approach to investigate the relation between autonomic activity and hypertension in children. They use a cross-sectional design to study healthy schoolchildren segregated between 2 groups by age: preadolescents (6-12 years old) and adolescents (13-16 years old). Although Tanner staging was not performed, it may be that age, and perhaps size, are the most relevant independent variables regarding changes in autonomic control. These studies took advantage of a unique opportunity to study pediatric patients within their usual daily school environment and away from the more artificial environment of the research laboratory or doctor’s office. Measurements were made with subjects supine and in a standing position, but the most salient results pertain to measurements made during supine rest. Beat-to-beat R-R intervals were measured by continuous electrocardiography, and beat-to-beat arterial blood pressure was measured by finger plethysmography. Continuous respiratory data were also collected. Power spectral analysis was performed. For illustrative purposes, I have depicted representative tachograms, which are sequences of R-R intervals and systolic blood pressure for each heart beat, and their respective power spectra (Figure).

  • View full-size image.

  • Figure. Representative R-R interval and systolic blood pressure tachograms (left panels) and their respective power spectra (right panels) . Low-frequency power (LFP) and high-frequency power (HFP) peaks are shown. High-frequency power corresponds to respiratory sinus arrhythmia. Low-frequency power reflects sympathetic vasomotion (BP spectra) and corresponding R-R changes mediated by the baroreflex. BP, Blood pressure.

Low-frequency spectral power, believed to reflect primarily sympathetic influences, and high-frequency power, believed to reflect primarily respiratory vagal regulation of heart rate, were calculated. The ratio of low-frequency to highfrequency power was used as an overall measure of sympathovagal balance.6, 7, 10, 11 Using multivariate analysis, Tanaka et al9 determined relations between blood pressure and the modulation of autonomic tone, assessed by HRV techniques. HRV does not measure absolute autonomic tone. Implicit in its use is that it assesses “modulation” of actual autonomic tone and also that such modulation relates closely to actual neurologic activity. The results of this study demonstrate not only the expected increase in blood pressure with age but also more interesting features. High-frequency power was generally lower in adolescents than in preadolescents, reflecting a transition from parasympathetic to sympathetic dominance; preadolescents had a more prominent sinus arrhythmia, in contrast to data from infants and much younger children12 and data from adult patients showing decreased vagal tone.13 Thus parasympathetic activity must have a maximum during preadolescence. There was significant correlation between resting arterial pressure and sympathovagal balance during adolescence but not preadolescence. This was due primarily to decreased high-frequency power (ie, vagal tone) but represents relative dominance of sympathetic activity in those with the highest blood pressures. These data are important because they suggest a potential prognostic use for HRV measurements. Also, if we agree that HRV mirrors autonomic activity, the data suggest a relation between autonomic activity and blood pressure. Previous data in adults with hypertension have shown a similar relationship between HRV and blood pressure compared with their normotensive contemporaries.14, 15 The present data may also indicate that healthy preadolescents are as yet tabula rasa , a clean slate, in which early intervention could affect future hypertensive disease consistent with the statement by Tanaka et al that “autonomic function plays an important role in the normal development of increasing blood pressure after the pubertal period.”9

The data should be interpreted cautiously from a patient population viewpoint. They were obtained from a particular group of children and may not be completely generalizable. Standing was used as the orthostatic stimulus, which is arguably the most physiologic orthostatic stimulus, although rapid standing as practiced here may not be “typical” standing. Moreover, it may prove difficult to replicate the standing methods in a group of American youngsters who seldom remain motionless. Finally, the data are not longitudinal and therefore do not provide evidence for persistence of the blood pressure–sympatho-excitation relation in teenagers with time or determine whether HRV truly predicts future important hypertension in individual patients.

HRV techniques must also be interpreted cautiously. Although they are in general use as research tools for assessing cardiac autonomic activity, it remains unclear just what information is contained in HRV data and to what degree they truly represent autonomic activity.7, 16, 17, 18, 19 Current HRV techniques require a steady state of autonomic activation, and the signal itself must be “stationary” in a statistical sense.

HRV techniques have been used since the 1980s after the pioneering work of Axelrod et al.11 When combined with spectral analysis, characteristic patterns of heart rate variation emerged. HRV was predominantly contained within several overlapping “bands” representing different sources of heart rate variation: the “easiest” to interpret was the high-frequency power band between 0.2 and 0.5 Hz. Cross-spectral analysis has confirmed covariation with respiration, and so the high-frequency power may be properly said to reflect respiratory sinus arrhythmia. Vagal blockade with atropine does indeed eliminate the high-frequency band completely. However, respiratory sinus arrhythmia can contribute to pressure fluctuations and vice versa, suggesting that under some circumstances the high-frequency peak contains sympathetic information.17 Ultra-low and very-low frequencies below .04 Hz may represent slow oscillations in thermoregulation and circadian rhythm but are incompletely studied and require long sequences of heart beats during which it is difficult to assume the steady state. Low-frequency power from 0.04 to 0.15 Hz was first observed by Mayer20 as oscillations in small blood vessels (“Mayer waves”), which vary directly with sympathetic excitation and cause a proportionate variation in systolic blood pressure. The appearance of bands at similar frequency in R-R intervals suggested that sympathoexcitation could be estimated. However, other data have shown potential dissociation between blood pressure and R-R interval,18 particularly if respiration is incorrectly discounted.19 The relation between blood pressure and R-R interval may reflect the function of the heart rate–controlling arm of the arterial baroreflex, which is affected in large part by vagal activity. Sympathetic vascular variation is then “transferred” into R-R variation through this efferent vagal arm of the baroreflex.21 Thus there are both sympathetic and parasympathetic contributions to low-frequency power. Interpretation of the ratio of low- to high-frequency power as an index of sympathovagal “balance” requires the utmost caution because it combines all the insecurities of low-frequency and high-frequency power.16 It is always safest, as done in the study by Tanaka et al,9 to measure R-R interval, blood pressure, and respiratory variation as covariates.

With these caveats in mind, results of the study by Tanaka et al9 remain valuable contributions because the data are obtained from healthy children in whom unusual effects on the low- and high-frequency bands are unlikely to occur. Also, the principal results are obtained with patients supine when data are statistically stationary. The results indicate a correspondence between sympatho-excitation and elevated blood pressure in adolescents. A final note of caution: although HRV techniques may provide a seemingly low-effort approach to assessing cardiovascular autonomic function in hypertension, hypotension, and other circulatory disease states, the techniques are not [yet] for general use but rather still remain within the domain of research requiring interpretation within the context of the overall circulatory state.

Back to Article Outline

References 

  1. Tanaka H, Thulesius O, Yamaguchi H, Mino M, Konishi K. Continuous non-invasive finger blood pressure monitoring in children. Acta Paediatr. 1994;83:646–652
  2. Tanaka H, Thulesius O, Borres M, Yamaguchi H, Mino M. Blood pressure responses in Japanese and Swedish children in the supine and standing position. Eur Heart J. 1994;15:1011–1019
  3. Tanaka H, Thulesius O, Borres M, Yamaguchi H, Mino M. Circulatory responses in children with unexplained syncope evaluated by continuous non-invasive finger blood pressure monitoring. Acta Pediatr. 1994;83:754–761
  4. Tanaka H, Yamaguchi H, Matushima R, Tamai H. Instantaneous orthostatic hypotension in children and adolescents: a new entity of orthostatic intolerance. Pediatr Res. 1999;46:691–696
  5. Tanaka H, Yamaguchi H, Tamai H, Mino M, Konishi K, Thulesius O. Haemodynamic changes during vasodepressor syncope in children and autonomic function. Clin Physiol. 1997;17:121–133
  6. Tanaka H, Tamai H. Recent advances in autonomic function tests of the cardiovascular system in children. Med Principles Pract. 1998;7:157–171
  7. Task Force of the European Society of Cardiology and the North American society of Pacing and Electrophysiology. Heart rate variability standards of measurement, physiological interpretation and clinical use. Circulation. 1996;93:1043–1065
  8. Stewart JM, Erb M, Sorbera C. Heart rate variability and the outcome of head-up tilt in syncopal children. Pediatr Res. 1996;40:702–709
  9. Tanaka H, Borres M, Thulesius O, Tamai H, Ericson MO, Linblad L-E. Blood pressure and cardiovascular autonomic function in healthy children and adolescents. J Pediatr. 2000;137:63–67
  10. Pagani M, Lombardi F, Guzzeti S, Rimoldi O, Furlan R, Pizzinelli P, et al.  Power spectral analysis of heart rate and arterial pressure variabilities as a marker of sympatho-vagal interaction in man and conscious dog. Circ Res. 1986;59:178–193
  11. Akselrod S, Gordon D, Ubel FA, Shannon DC, Barger AC, Cohen RJ. Power spectrum analysis of heart rate fluctuation: a quantitative probe of beat-to-beat cardiovascular control. Science. 1981;213:220–222
  12. Finley JP, Nugent ST. Heart rate variability in infants, children and young adults. J Auton Nerv Syst. 1995;51:103–108
  13. Lipsitz LA, Mietus J, Moody GB, Goldberger AL. Spectral characteristics of heart rate variability before and during postural tilt. Relations to aging and risk of syncope. Circulation. 1990;81:1803–1810
  14. Guzzetti S, Dasai S, Pesis M, Casati R, Masu AM, et al.  Altered pattern of circadian neural control of heart period in mild hypertension. J Hypertens. 1991;9:831–838
  15. Langewitz W, Ruddel H, Schachinger H. Reduced parasympathetic cardiac control in patients with hypertension at rest and under mental stress. Am Heart J. 1994;127:122–128
  16. Eckberg DL. Sympathovagal balance, a critical appraisal. Circulation. 1997;96:3224–3232
  17. Taylor JA, Eckberg DL. Fundamental relations between short-term RR interval and arterial pressure oscillations in humans. Circulation. 1996;93:1527–1532
  18. Ahmed MW, Kadish AH, Parker MA, Goldberger JJ. Effect of physiologic adrenergic stimulation on heart rate variability. J Am Coll Cardiol. 1994;24:1082–1090
  19. Parati G, Saul P, Di Rienzo M, Mancia G. Spectral analysis of blood pressure and heart rate variability in evaluating cardiovascular regulation. A critical appraisal. Hypertension. 1995;25:1276–1286
  20. Mayer S. Studien zur Physiologiedes Herzens und der Blutgefasse:5. Abhandlung: Uber spontane Blutdruckschwankungen. Sber Akad Wiss, 3. Abteilung. 1876;74:281–307
  21. Baselli G, Cerutti S, Civardi S, Liberati D, Lombardi F, Malliani A, et al.  Spectral and cross spectral analysis of heart rate and arterial blood pressure variability signals. Comput Biomed Res. 1986;19:520–534

☆ Reprint requests: Julian M. Stewart, MD, PhD, Professor of Pediatrics and Physiology, Director, The Center for Pediatric Hypotension, Division of Pediatric Cardiology, Suite 618, Munger Pavilion, New York Medical College, Valhalla, NY 10595.

☆☆ J Pediatr 2000;137:6-8.

PII: S0022-3476(00)23232-0

Refers to article:

  • Blood pressure and cardiovascular autonomic function in healthy children and adolescents

    Hidetaka Tanaka, Magnus Borres, Olav Thulesius, Hiroshi Tamai, Mats O. Ericson, Lars-Erik Lindblad
    The Journal of Pediatrics July 2000 (Vol. 137, Issue 1, Pages 63-67)

The Journal of Pediatrics
Volume 137, Issue 1 , Pages 6-8, July 2000

Article Tools

* Image Usage & Resolution